WO2024002398A1 - Method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid, and such composite systems - Google Patents
Method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid, and such composite systems Download PDFInfo
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- WO2024002398A1 WO2024002398A1 PCT/CZ2022/050060 CZ2022050060W WO2024002398A1 WO 2024002398 A1 WO2024002398 A1 WO 2024002398A1 CZ 2022050060 W CZ2022050060 W CZ 2022050060W WO 2024002398 A1 WO2024002398 A1 WO 2024002398A1
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- Prior art keywords
- polylactic acid
- poly
- lactide
- temperature
- fabric
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- 239000004626 polylactic acid Substances 0.000 title claims abstract description 124
- 229920000747 poly(lactic acid) Polymers 0.000 title claims abstract description 123
- 239000002131 composite material Substances 0.000 title claims abstract description 80
- 238000000034 method Methods 0.000 title claims abstract description 58
- 229920001222 biopolymer Polymers 0.000 title claims abstract description 44
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 claims abstract description 87
- 239000004744 fabric Substances 0.000 claims abstract description 69
- 229920001432 poly(L-lactide) Polymers 0.000 claims abstract description 65
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 claims abstract description 49
- 239000002121 nanofiber Substances 0.000 claims abstract description 48
- 238000009987 spinning Methods 0.000 claims abstract description 39
- 229920001434 poly(D-lactide) Polymers 0.000 claims abstract description 34
- 229920000642 polymer Polymers 0.000 claims abstract description 34
- 238000002844 melting Methods 0.000 claims abstract description 31
- 230000008018 melting Effects 0.000 claims abstract description 31
- 239000011159 matrix material Substances 0.000 claims abstract description 29
- 239000000203 mixture Substances 0.000 claims abstract description 24
- -1 poly(L-lactide) Polymers 0.000 claims abstract description 19
- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 11
- 239000002904 solvent Substances 0.000 claims abstract description 7
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 5
- XVMSFILGAMDHEY-UHFFFAOYSA-N 6-(4-aminophenyl)sulfonylpyridin-3-amine Chemical compound C1=CC(N)=CC=C1S(=O)(=O)C1=CC=C(N)C=N1 XVMSFILGAMDHEY-UHFFFAOYSA-N 0.000 claims abstract 2
- 230000008021 deposition Effects 0.000 claims abstract 2
- JUJWROOIHBZHMG-UHFFFAOYSA-N Pyridine Chemical compound C1=CC=NC=C1 JUJWROOIHBZHMG-UHFFFAOYSA-N 0.000 claims description 44
- 239000000243 solution Substances 0.000 claims description 31
- 239000000463 material Substances 0.000 claims description 15
- 238000002156 mixing Methods 0.000 claims description 7
- 229910052799 carbon Inorganic materials 0.000 claims description 6
- 239000000155 melt Substances 0.000 claims description 5
- 230000005684 electric field Effects 0.000 claims description 4
- 230000007935 neutral effect Effects 0.000 claims description 3
- 229920001577 copolymer Polymers 0.000 claims 2
- 238000009738 saturating Methods 0.000 claims 2
- HPYNZHMRTTWQTB-UHFFFAOYSA-N dimethylpyridine Natural products CC1=CC=CN=C1C HPYNZHMRTTWQTB-UHFFFAOYSA-N 0.000 claims 1
- 239000011259 mixed solution Substances 0.000 claims 1
- 230000003014 reinforcing effect Effects 0.000 abstract 1
- 238000001878 scanning electron micrograph Methods 0.000 description 54
- 235000004879 dioscorea Nutrition 0.000 description 48
- 230000008569 process Effects 0.000 description 29
- UMJSCPRVCHMLSP-UHFFFAOYSA-N pyridine Natural products COC1=CC=CN=C1 UMJSCPRVCHMLSP-UHFFFAOYSA-N 0.000 description 21
- 238000001816 cooling Methods 0.000 description 15
- 238000003756 stirring Methods 0.000 description 15
- 230000016507 interphase Effects 0.000 description 13
- 238000001938 differential scanning calorimetry curve Methods 0.000 description 12
- 238000010438 heat treatment Methods 0.000 description 10
- 239000004753 textile Substances 0.000 description 9
- 238000005496 tempering Methods 0.000 description 7
- 238000005516 engineering process Methods 0.000 description 6
- 239000000835 fiber Substances 0.000 description 6
- 238000002347 injection Methods 0.000 description 6
- 239000007924 injection Substances 0.000 description 6
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 description 6
- 238000003825 pressing Methods 0.000 description 6
- 239000011877 solvent mixture Substances 0.000 description 6
- 229920001169 thermoplastic Polymers 0.000 description 6
- 229920002725 thermoplastic elastomer Polymers 0.000 description 6
- 239000004416 thermosoftening plastic Substances 0.000 description 6
- 239000002667 nucleating agent Substances 0.000 description 5
- IVWWFWFVSWOTLP-YVZVNANGSA-N (3'as,4r,7'as)-2,2,2',2'-tetramethylspiro[1,3-dioxolane-4,6'-4,7a-dihydro-3ah-[1,3]dioxolo[4,5-c]pyran]-7'-one Chemical compound C([C@@H]1OC(O[C@@H]1C1=O)(C)C)O[C@]21COC(C)(C)O2 IVWWFWFVSWOTLP-YVZVNANGSA-N 0.000 description 4
- 239000004609 Impact Modifier Substances 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 239000004014 plasticizer Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 239000004698 Polyethylene Substances 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 239000011173 biocomposite Substances 0.000 description 3
- 238000007731 hot pressing Methods 0.000 description 3
- 238000001746 injection moulding Methods 0.000 description 3
- 230000003993 interaction Effects 0.000 description 3
- 239000004310 lactic acid Substances 0.000 description 3
- 235000014655 lactic acid Nutrition 0.000 description 3
- 239000000314 lubricant Substances 0.000 description 3
- 229920000573 polyethylene Polymers 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 239000004594 Masterbatch (MB) Substances 0.000 description 2
- 208000034530 PLAA-associated neurodevelopmental disease Diseases 0.000 description 2
- 238000006065 biodegradation reaction Methods 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000009264 composting Methods 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 238000000113 differential scanning calorimetry Methods 0.000 description 2
- 238000010041 electrostatic spinning Methods 0.000 description 2
- 230000003301 hydrolyzing effect Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- PXQPEWDEAKTCGB-UHFFFAOYSA-N orotic acid Chemical compound OC(=O)C1=CC(=O)NC(=O)N1 PXQPEWDEAKTCGB-UHFFFAOYSA-N 0.000 description 2
- 239000005014 poly(hydroxyalkanoate) Substances 0.000 description 2
- 229920000903 polyhydroxyalkanoate Polymers 0.000 description 2
- 229920006381 polylactic acid film Polymers 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- HBAQYPYDRFILMT-UHFFFAOYSA-N 8-[3-(1-cyclopropylpyrazol-4-yl)-1H-pyrazolo[4,3-d]pyrimidin-5-yl]-3-methyl-3,8-diazabicyclo[3.2.1]octan-2-one Chemical class C1(CC1)N1N=CC(=C1)C1=NNC2=C1N=C(N=C2)N1C2C(N(CC1CC2)C)=O HBAQYPYDRFILMT-UHFFFAOYSA-N 0.000 description 1
- QZCLKYGREBVARF-UHFFFAOYSA-N Acetyl tributyl citrate Chemical compound CCCCOC(=O)CC(C(=O)OCCCC)(OC(C)=O)CC(=O)OCCCC QZCLKYGREBVARF-UHFFFAOYSA-N 0.000 description 1
- 239000004604 Blowing Agent Substances 0.000 description 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 1
- 229920002292 Nylon 6 Polymers 0.000 description 1
- 229920004935 Trevira® Polymers 0.000 description 1
- 239000012963 UV stabilizer Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229920003232 aliphatic polyester Polymers 0.000 description 1
- 229920006125 amorphous polymer Polymers 0.000 description 1
- 239000003963 antioxidant agent Substances 0.000 description 1
- 239000002216 antistatic agent Substances 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 229920000229 biodegradable polyester Polymers 0.000 description 1
- 239000004622 biodegradable polyester Substances 0.000 description 1
- 229920002988 biodegradable polymer Polymers 0.000 description 1
- 239000004621 biodegradable polymer Substances 0.000 description 1
- 239000012620 biological material Substances 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 150000001721 carbon Chemical group 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000007334 copolymerization reaction Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 239000000975 dye Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000012765 fibrous filler Substances 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 239000003063 flame retardant Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 230000009477 glass transition Effects 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 229920001519 homopolymer Polymers 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 238000000338 in vitro Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 229920002521 macromolecule Polymers 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002074 melt spinning Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 244000005700 microbiome Species 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- RKISUIUJZGSLEV-UHFFFAOYSA-N n-[2-(octadecanoylamino)ethyl]octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(=O)NCCNC(=O)CCCCCCCCCCCCCCCCC RKISUIUJZGSLEV-UHFFFAOYSA-N 0.000 description 1
- 239000002114 nanocomposite Substances 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 229960005010 orotic acid Drugs 0.000 description 1
- 229960004707 orotic acid monohydrate Drugs 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920002463 poly(p-dioxanone) polymer Polymers 0.000 description 1
- 239000000622 polydioxanone Substances 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 235000020004 porter Nutrition 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000036316 preload Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 229920006126 semicrystalline polymer Polymers 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 239000013501 sustainable material Substances 0.000 description 1
- 229920001059 synthetic polymer Polymers 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000009827 uniform distribution Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/0007—Electro-spinning
- D01D5/0061—Electro-spinning characterised by the electro-spinning apparatus
- D01D5/0076—Electro-spinning characterised by the electro-spinning apparatus characterised by the collecting device, e.g. drum, wheel, endless belt, plate or grid
- D01D5/0084—Coating by electro-spinning, i.e. the electro-spun fibres are not removed from the collecting device but remain integral with it, e.g. coating of prostheses
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/0007—Electro-spinning
- D01D5/0015—Electro-spinning characterised by the initial state of the material
- D01D5/003—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion
- D01D5/0038—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion the fibre formed by solvent evaporation, i.e. dry electro-spinning
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/18—Formation of filaments, threads, or the like by means of rotating spinnerets
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
- D01F6/58—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products
- D01F6/62—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polyesters
- D01F6/625—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polyesters derived from hydroxy-carboxylic acids, e.g. lactones
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F8/00—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof
- D01F8/04—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers
- D01F8/14—Conjugated, i.e. bi- or multicomponent, artificial filaments or the like; Manufacture thereof from synthetic polymers with at least one polyester as constituent
-
- D—TEXTILES; PAPER
- D02—YARNS; MECHANICAL FINISHING OF YARNS OR ROPES; WARPING OR BEAMING
- D02G—CRIMPING OR CURLING FIBRES, FILAMENTS, THREADS, OR YARNS; YARNS OR THREADS
- D02G3/00—Yarns or threads, e.g. fancy yarns; Processes or apparatus for the production thereof, not otherwise provided for
- D02G3/02—Yarns or threads characterised by the material or by the materials from which they are made
-
- D—TEXTILES; PAPER
- D03—WEAVING
- D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
- D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
- D03D15/20—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads
- D03D15/208—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads cellulose-based
- D03D15/225—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads cellulose-based artificial, e.g. viscose
-
- D—TEXTILES; PAPER
- D03—WEAVING
- D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
- D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
- D03D15/30—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the structure of the fibres or filaments
- D03D15/33—Ultrafine fibres, e.g. microfibres or nanofibres
-
- D—TEXTILES; PAPER
- D03—WEAVING
- D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
- D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
- D03D15/40—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the structure of the yarns or threads
- D03D15/47—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the structure of the yarns or threads multicomponent, e.g. blended yarns or threads
-
- D—TEXTILES; PAPER
- D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B2201/00—Cellulose-based fibres, e.g. vegetable fibres
- D10B2201/20—Cellulose-derived artificial fibres
-
- D—TEXTILES; PAPER
- D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B2331/00—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products
- D10B2331/04—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polyesters, e.g. polyethylene terephthalate [PET]
- D10B2331/041—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polyesters, e.g. polyethylene terephthalate [PET] derived from hydroxy-carboxylic acids, e.g. lactones
-
- D—TEXTILES; PAPER
- D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B2331/00—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products
- D10B2331/30—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polycondensation products not covered by indexing codes D10B2331/02 - D10B2331/14
-
- D—TEXTILES; PAPER
- D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B2401/00—Physical properties
- D10B2401/12—Physical properties biodegradable
-
- D—TEXTILES; PAPER
- D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
- D10B2505/00—Industrial
- D10B2505/02—Reinforcing materials; Prepregs
Definitions
- the invention relates to a method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid.
- the invention relates to composite systems prepared by this method.
- biodegradable polymers which are prepared from renewable raw material sources, have been the subject of ever-increasing interest.
- the advantages of these materials primarily include their effect on reducing the carbon footprint, environmental benefits resulting from their ability to biodegrade and the potential to be sustainable material systems of the future.
- biopolymers falling into this group are aliphatic polyesters, such as polyhydroxyalkanoates (PHA) and polylactic acid (PLA), which is also often called polylactide.
- PLA With intensive research into the production of second and third generation high molecular weight PLA using lignocellulose-based raw material sources and direct conversion of greenhouse gases to lactic acid using microorganisms, PLA will gain in importance.
- lactic acid contains a chiral carbon atom
- L and D there are two optical isomeric forms of lactic acid monomer, referred to as L and D, i.e. , poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA).
- L and D poly(L-lactide)
- PLLA poly(L-lactide)
- PDLA poly(D-lactide)
- an amorphous or semicrystalline polymer can be prepared at a glass transition temperature (T g ) in the range of 50 °C to 60 °C and a melting temperature (Tm) in the range of 130 °C to 180 °C.
- PLA is subject to biodegradation and, thanks to its good biocompatibility and bioresorbability, it belongs to the most widely studied polymers in clinical biomedical studies. In recent years, it has attracted interest not only as a replacement for traditional petroleum-based synthetic polymers, but also as a special polymer in various applications.
- PLA also exhibits some properties that limit its use in technical applications. These properties mainly include low impact resistance and high brittleness, which are related to the glassy state of PLA at normal room temperature.
- the low temperature resistance of PLA is mainly related to poor homonucleation of PLA and insufficient mobility of macromolecular chains during crystallization from melts. Since there is an ever-increasing interest in a long-term sustainable economy that is environmentally friendly, it is necessary to overcome the shortcomings mentioned above.
- many strategies have been implemented in the last decades to improve the utility properties of PLA. The most commonly used strategies include heterogeneous nucleation, plasticization using plasticizers, copolymerization and mixing (blending) with other polymers.
- PLA stereocomplexation Another option to improve the utility properties of PLA is stereocomplexation, which was described for the first time in 1987 by Ikada et al. [1 ],
- the formation of a PLA stereocomplex (sc-PLA) between the optical isomers poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) leads not only to an increase in mechanical properties, but also to an increase in thermal and hydrolytic resistance.
- sc-PLA melt samples by blending (mixing) PLLA/PDLA followed by an additional crystallisation step in the presence of steam or supercooled water at a temperature of 120 to 200 °C is disclosed in international application W02016172011A1 .
- Application WO2014147132A1 describes the preparation of sc-PLA by mixing solutions or melts using specific nucleating agents.
- the production of sc-PLA based samples by injection molding of PLLA/PDLA mixtures (blends) under specific temperature and pressure conditions is disclosed in international application W02008104757A1 .
- Nanofibers are obtained by a complex process of spinning the PLLA/PDLA blend from a melt, which is followed by heat treatment, washing, selective extraction, drying and hot pressing.
- the object of the invention is to provide a method of preparation of hierarchically structured self-reinforcing composite systems based on polylactic acid biopolymers and such composite systems. These systems will significantly improve the mechanical properties and temperature resistance of traditional PLA- based products, increasing their applicability in replacing fossil based polymers. Other advantages of such systems can be seen especially in the reduction of the carbon footprint and the fact that these materials can be completely based on renewable raw materials with targeted recyclability or biodegradability.
- the object of the invention is achieved by a method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid (PLA), which include nanofibers based on poly(L- lactide) (PLLA) or based on an asymmetric or symmetrical blend of poly(L-lactide) and poly(D-lactide) (PDLA).
- PLA polylactic acid
- these nanofibers are prepared by spinning a solution, preferably, for example, by the method according to WO2014094694A1 , using alternating current, where an electric field for spinning is alternately created between a spinning electrode to which alternating voltage is applied and air and/or gas ions created and/or brought into its vicinity.
- a polymer dosing device known from W02019047990A1 and/or a spinning electrode in one of the embodiments known from W02017108012A1 can be used.
- the nanofibers formed are carried in the direction of the gradient of the electric field away from the spinning electrode, forming a hollow plume (sleeve).
- This is then deposited according to the method of WO2016192697A2 on a supporting fibrous core which rotates around its own axis and/or balloons, creating a nanofibrous sheath on its surface.
- Another method of creating such a two-component linear structure is also known from WO2008149488A1 .
- the formed two-component core yam 1. contains a fibrous core 2 on which a nanofibrous sheath 3 is deposited, the nanofibrous sheath 3 being formed by a nanofibrous plume wound in a helix.
- the fibrous core 2 consists of a monofilament (see Figure 1 ) or multifilament (see Figure 2) textile yarn made from PLA biopolymer. This yam unwinds and simultaneously rotates around its own axis and/or balloons in the working space of the device in which the electrically neutral nanofibrous plume is created. Upon contact of the plume with the fibrous core 2, the plume is transformed into a flat stripe of oriented nanofibers and spirally wraps around the fibrous core 2.
- the density of the nanofibrous sheath 3 thus formed can be controlled by the rate at which the solution is dispensed onto the surface of the spinning electrode and/or by the rate at which the continuous fibrous core 2 is unwound.
- Both the fibrous core 2 and the nanofibrous sheath 3 are made from PLA biopolymer, wherein in the case of the fibrous core 2, the biopolymer usually has the same or lower melting temperature than in the case of the nanofibrous sheath 3, as will be explained below.
- the fibrous core 2 Before entering the working space and the path of the nanofibrous plume, the fibrous core 2 is preferably preheated to a desired working temperature in the range of 25 to 55 ⁇ 1 °C.
- the formed two-component core yarn 11 can, if necessary, be heat-fixed by passing through a die heated to a temperature of 55 to 100 ⁇ 1 °C and then dried in a tempering chamber located behind the working space of the device.
- the two-component core yam 1. thus formed is subsequently processed by standard textile techniques into strands, planar (2D) and spatial (3D) textile structures which can serve independently or as self-reinforcing elements of hierarchically structured biodegradable composite systems based on PLA biopolymers, or PLA copolymers, mixtures with other biopolymers, their combination, or with the addition of additives (plasticizers, nucleating agents, flame retardants, lubricants, UV stabilizers, antioxidants, dyes, antistatic agents, blowing agents, impact modifiers, etc.), fillers and/or discontinuous fiber reinforcement. As a rule, these modifications must not compromise the biodegradability of the resulting material research.
- the two-component core yarn 1. is processed into a flat (2D) textile, e.g., fabric - see Figs. 2 and 4, and deposited in a PLA- based matrix 4 - see Figs. 3 and 5. All components of this system have a melting temperature equal to or lower than the nanofibrous sheath 3 of the used two- component linear structure.
- a knitted fabric made from the two- component core yarn 1. can also be used.
- a PLA-based spinning solution is prepared by dissolving PLLA or a mixture of PLLA and PDLA in a suitable solvent system which contains dichloromethane (DCM), dimethyl sulfoxide (DMSO) and pyridine (PY).
- DCM dichloromethane
- DMSO dimethyl sulfoxide
- PY pyridine
- solutions of these polymers in DCM are preferably prepared separately, and after their mixing and homogenization, DMSO and PY are added to them.
- the polymer solution thus prepared is homogenized and then spun using one of the methods of preparation of polymer nanofibers.
- a particularly advantageous method is spinning using alternating current, during which an electrically neutral plume of nanofibers is created, which moves in the direction of the gradient of the electric field away from the spinning electrode, and at the same time is caught on a monofilament or multifilament PLA yam rotating or ballooning around its longitudinal axis, on which it creates a uniform and continuous nanofibrous sheath 3.
- a two- component yarn 1_ is prepared.
- a flat textile e.g., a fabric or knitted fabric of any type, is then prepared by a suitable textile technique and is subsequently incorporated into a PLA-based matrix 4.
- a suitable textile technique e.g., a fabric or knitted fabric of any type, is then prepared by a suitable textile technique and is subsequently incorporated into a PLA-based matrix 4.
- at least one layer of this fabric is inserted between two plates of PLA polymer or co-PLA and together with them is exposed to elevated temperature (150 to 200 °C) and pressure (150 to 250 kN).
- this semiproduct is heated for 3 to 8 minutes to a temperature of 150 to 180 °C, at which the material of the plates melts and the flat fabric is saturated with this matrix 4, and then it is heated for 15 to 80 seconds to a temperature of 160 to 200 °C, at which the textile is saturated with the matrix 4 and the entire structure is fixed.
- the core 2 and the sheath 3 of the two-component core yam 1_ do not melt, and consequently, the yam 1_ and its components retain their morphology and character.
- the result of this process is a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures, which contains at least one layer of fabric prepared from the two-component core yam 1_ based on PLA deposited in a PLA or co-PLA matrix 4.
- the textile constitutes 5 to 35 wt. % of this composite.
- these layers can be suitably oriented relative to each other, e.g., by rotating them by a suitable angle, e.g., 45 °, 90 °, or in any other way, or by combining textiles of different types.
- Fig. 1 a shows a scheme of a two-component linear structure with a monofilament yam core
- Fig. 1 b shows a scheme of a two- component linear structure with a multifilament yam core
- Fig. 2 shows a scheme of a plain weave fabric made from a two-component linear structure with a monofilament yam core
- Fig. 3 shows a scheme of a section through the hierarchically structured self-reinforcing composite system according to the invention with one fabric layer according to Fig. 2
- Fig. 4 shows a scheme of a plain weave fabric made from a two-component linear structure with a multifilament yam core
- Fig. 5 is a scheme of a section through the hierarchically structured self-reinforcing composite system according to the invention with one fabric layer according to Fig. 4.
- Fig. 6 is an SEM image of one variant of PLLA nanofibers at a magnification of 25,000 times
- Fig. 7 shows an SEM image of the two-component linear structure with the monofilament yam core and the sheath formed by the layer of PLLA nanofibers according to Fig. 6 at a magnification of 475 times
- Fig. 8 shows an SEM image of a unidirectional fabric made from the two-component linear structure according to Fig. 7 at a magnification of 109 times
- Fig. 9 shows the DSC curves of the individual components of the hierarchically structured selfreinforcing composite system according to the invention formed using the unidirectional fabric according to Fig. 8
- Fig. 10a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 158 times
- Fig. 10b shows a detail of an interphase interface at the fracture surface in Fig. 10a.
- Fig. 11 shows an SEM image of one variant of sc-PLA nanofibers at a magnification of 15,000 times
- Fig. 12 shows an SEM image of the two- component linear structure with the multifilament yam core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 11 at the point of rupture at a magnification of 183 times
- Fig. 13 shows an SEM image of fabric consisting of the two-component linear structure according to Fig. 12 at a magnification of 125 times
- Fig. 14 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 13, Fig.
- FIG. 15a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 630 times
- Fig. 15b shows a detail of the interphase interface at the fracture surface in Fig. 15a at a magnification of 2,520 times.
- Fig. 16 shows an SEM image of a second variant of sc-PLA nanofibers at a magnification of 25,000 times
- Fig. 17 shows an SEM image of the two- component linear structure with the monofilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 11 at the section point at a magnification of 416 times
- Fig. 18 shows an SEM image of unidirectional fabric made from the two-component linear structure according to Fig. 17 at a magnification of 85 times
- Fig. 19 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using fabric according to Fig. 18, Fig.
- FIG. 20a shows an SEM image of the fracture surface of this hierarchically structured selfreinforcing composite system at a magnification of 349 times
- Fig. 20b shows a detail of the interphase interface at the fracture surface in Fig. 20a at a magnification of 4,320 times.
- Fig. 21 shows an SEM image of a third variant of sc-PLA nanofibers at a magnification of 5,200 times
- Fig. 22 shows an SEM image of the two-component linear structure with the multifilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 21 at the section point at a magnification of 611 times
- Fig. 23 shows an SEM image of twill fabric made of the two-component linear structure according to Fig. 22 at a magnification of 84 times
- Fig. 24 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 23, Fig.
- FIG. 25a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 500 times
- Fig. 25b shows a detail of the interphase interface at the fracture surface in Fig. 25a at a magnification of 2,540 times
- Fig. 26 is an SEM image of a fourth variant of sc-PLA nanofibers at a magnification of 25,000 times
- Fig. 27 shows an SEM image of the two- component linear structure with the monofilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 26 at the section point at a magnification of 191 times
- FIG. 28 shows an SEM image of plain weave fabric made from the two-component linear structure according to Fig. 27 at a magnification of 124 times
- Fig. 29 shows the DSC curves of the individual components of hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 28
- Fig. 30a shows an SEM image of the fracture surface of this hierarchically structured selfreinforcing composite system at a magnification of 405 times
- Fig. 30b shows a detail of the interphase interface at the fracture surface in Fig. 30a at a magnification of 3,100 times.
- Fig. 31 shows an SEM image of a fifth variant of sc-PLA nanofibers at a magnification of 14,800 times
- Fig. 32 shows an SEM image of a two-component linear structure with a multifilament yarn core and a sheath formed by a layer of sc-PLA nanofibers according to Fig. 31 at the section point at a magnification of 396 times
- Fig. 33 shows an SEM image of twill fabric made from the two- component linear structure according to Fig. 32 at a magnification of 221 times
- Fig. 34 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 33, Fig.
- FIG. 35a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 821 times
- Fig. 35b shows a detail of the interphase interface on the fracture surface in Fig. 35a at a magnification of 2,550 times.
- PLA biopolymers, compounds, mixtures and fabrics are dried for at least 12 hours in a vacuum dryer at a temperature of 80 °C to prevent their degradation due to hydrolytic reactions.
- Additives added are similarly dried at a temperature of 50 °C.
- DCM dichloromethane
- DMSO dimethyl sulfoxide
- PY pyridine
- DCM has a specific mass of 1320 kg/m 3 , a molar mass of 85 g/mol and a chemical purity of 99.88 %
- DMSO has a specific mass of 1100 kg/m 3 , a molar mass of 78.13 g/mol, and a chemical purity of 99.88 %
- PY has a specific mass of 983 kg/m 3 , a molar mass of 79.1 g/mol and a chemical purity of 99.5 %.
- PLA monofilament (trade name 6101, Perlon) was used as a fibrous core 2, with a diameter of 0.22 mm, a melting temperature Tm of 170 °C, a fineness of 48 Tex, or PLA multifilament (trade name PLA-DTY dtex 76 f 32, Trevira) was used as a fibrous core 2.
- This multifilament consisted of 32 elementary fibers having a fineness of 7.6 Tex and a melting temperature Tm of 180 °C.
- PLA biopolymers modified with additives e.g., plasticizers, impact modifiers, nucleating agents, lubricants
- other biopolymers e.g., polyester-based thermoplastic elastomer - TPE
- the matrix of the composite was prepared from plates of PLA biopolymer or sc-PLA having dimensions of 145 x 145 x 2 mm prepared by injection molding technology; the mold being cooled to a temperature of 20 °C.
- the resulting hierarchically structured self-reinforcing composite systems were subsequently prepared by inserting at least one layer of fabric between two PLA or sc-PLA plates followed by hot pressing on a heated press.
- Table 1 shows some mechanical parameters of the individual components of the structured self-reinforcing composite system and of the structured selfreinforcing composite systems according to Examples 1 to 6 for comparison.
- PLLA poly(L-lactide)
- Luminy L130 Total Corbion PLA
- Mw weight average molar mass
- Tm 180 °C
- L-enantiomer content of at least 99 % was dissolved under constant stirring at a temperature of 23 ⁇ 1 °C in 63 g of dichloromethane (DCM).
- DCM dichloromethane
- DMSO dimethyl sulfoxide
- PY pyridine
- the polymer solution prepared by this process which contained 10 wt. % of PLLA and 90 wt. % of the solvent mixture (70 % DCM, 20 % DMSO, and 10 % PY) was homogenized under constant stirring for 12 hours and then spun by electric spinning.
- the plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 60 m/min.
- a two-component yam was prepared with a core consisting of PLA monofilament yam and a sheath formed by a layer of PLLA nanofibers, see Fig. 7, which is an SEM image of this yam at a magnification of 475 times, showing its structure.
- the two-component core yam thus prepared showed a fineness of 53 tex.
- the two-component core yam thus prepared was subsequently made into a unidirectional fabric - see Fig. 8, which shows an SEM image of this fabric at a magnification of 109 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yams are visible.
- the plates were made by thermoplastic injection technology at temperatures ranging from 160 °C to 190 °C, and their dimensions were 145 x 145 x 2 mm.
- Unidirectional fabric made from two-component core yam was inserted between these two PLLA plates, and the thus prepared structure was tempered for 5 minutes in a press in contact mode at a temperature of 160 °C.
- the co-PLA plates melt and the co-PLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 9, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is clear that only the material of the plates melted at a temperature of 160 °C.
- the temperature was then increased to 170 °C and after reaching it, pressing took place for 20 seconds with a clamp force of 160 kN.
- the result of the process was a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures.
- the unidirectional fabric layer in this case constituted 9 ⁇ 1 % of the weight of this system.
- Fig. 10a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 158 times and Fig. 10b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 968 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment.
- the polymer solution prepared by this process which contained 8 wt. % of PLA biopolymers (PLLA 90 % and PDLA 10 %) and 92 wt. % of the solvent mixture (60 % DCM, 25 % DMSO, and 15 % PY) was homogenized under constant stirring on a magnetic stirrer for 12 hours and then spun by electric spinning. Alternating current (AC) with a voltage of 20 kV and a frequency of 60 Hz was applied to the spinning electrode, while the polymer solution described above was supplied to its spinning surface at a rate of 15 mL/min. Spinning took place at a laboratory temperature of 23 ⁇ 1 °C and a relative humidity of 35 %.
- AC Alternating current
- Two PLLA plates with a content of 15 wt % plasticizer - acetyl tributy I citrate (ATBC, CITROFLEX* A-4, Vertellus LLC) were used for the preparation of the matrix of the composite.
- the plates were made by thermoplastic injection technology at temperatures ranging from 170 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
- the temperature was then increased to 170 °C and after reaching it, pressing took place for 30 seconds with a clamp force of 170 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 170 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force.
- the result of the process was a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures. In this case, the layers of plain weave fabric constituted 13 ⁇ 1 % of the weight of this system.
- Fig. 15 shows an SEM image of the fracture surface of the above- mentioned hierarchically structured self-reinforcing composite system at a magnification of 630 times and Fig. 15b shows an SEM image of a detail of the interphase interface on this fracture surface at a magnification of 2,520 times. It can be seen from the two images that neither the core nor the sheath of the two- component core yarn melted during the heat treatment.
- the plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 40 m/min.
- a two-component yarn was prepared with a core made from PLA monofilament yarn and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 17, which shows an SEM image of this yarn at a magnification of 416 times and from which its structure is visible.
- the two-component core yarn prepared in this way showed a fineness of 57 tex.
- the two-component core yam thus prepared was subsequently made into a unidirectional fabric - see Fig. 18, which shows an SEM image of this fabric at a magnification of 85 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yarns are visible.
- TPE thermoplastic elastomer
- the temperature was increased to 175 °C, and after reaching it, pressing took place for 40 seconds with a clamp force of 185 kN.
- the result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures.
- the layers of unidirectional fabric constituted 19 ⁇ 1 % of the weight of the above-mentioned system.
- Fig. 20a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 349 times
- Fig. 20b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 4,320 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment. Furthermore, the morphology of the matrix is visible in the two images, where TPE is dispersed in co-PLA in the form of spherical particles.
- PDLA poly(D-lactide)
- Luminy D120 Total Corbion PLA
- the polymer solutions thus prepared were mixed and to the mixture obtained, 27.9 g DMSO and 18.6 g PY was added.
- the thus prepared polymer solution which contained 7 wt. % of PLA biopolymers (PLLA 70 % a PDLA 30 %) and 93 wt. % of the solvent mixture (50 % DCM, 30 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electris spinning.
- a two-component yam was prepared with a core consisting of PLA multifilament yam and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 22, which shows an SEM image of this yam at a magnification of 611 times, and from which its structure is visible.
- the two-component core yam thus prepared showed a fineness of 14 tex.
- twill fabric was then formed - see Fig. 23, which shows an SEM image of this fabric at a magnification of 84 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yams are visible.
- Two PLLA plates (trade name Luminy 130, Total Corbion PLA) containing a PLA-based impact modifier (masterbatch) were used to prepare the matrix of the composite.
- the impact modifier content was 10 wt. %.
- the plates were made by thermoplastic injection technology at temperatures ranging from 170 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
- the temperature was then increased to 180 °C, and after reaching it, pressing took place for 30 seconds with a clamp force of 190 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 190 kN until a temperature of 100 °C was reached. At this temperature, the composite crystallized isothermally for 2 minutes. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 190 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force.
- the result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. In this case, the layers of twill fabric constituted 21 ⁇ 2 % of the weight of the above-mentioned system.
- Fig. 25a shows an SEM image of the fracture surface of this structured self-reinforcing composite system at a magnification of 500 times
- Fig. 25b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 2,540 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment. Furthermore, the morphology of the matrix with cavities caused by the addition of the masterbatch can be seen in both images.
- the polymer solutions thus prepared were mixed and 28.2 g of DMSO and 23.5 g of PY was added to the mixture obtained.
- the thus prepared polymer solution which contained 6 wt. % of PLA biopolymers (PLLA 60 % and PDLA 40 %) and 93 wt. % of the solvent mixture (50 % DCM, 30 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electric spinning.
- the plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 25 m/min.
- a two-component yam was prepared with a core consisting of PLA monofilament yam and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 27, which shows an SEM image of this yam at a magnification of 191 times and from which its structure is visible.
- PLLA plates (trade name Luminy 130, Total Corbion PLA) containing 0.3 wt.% of the nucleating agent - orotic acid monohydrate (OA, Merck) were used.
- the plates were made by thermoplastic injection moulding at temperatures ranging from 160 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
- the temperature was then increased to 180 °C, and after reaching it, pressing took place for 40 seconds with a clamp force of 200 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 200 kN until a temperature of 90 °C was reached. At this temperature, the composite crystallized isothermally for 3 minutes. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 190 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force.
- the result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures.
- the layers of twill fabric constituted 30 ⁇ 1 % of the weight of the above-mentioned system.
- Fig. 30a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 405 times
- Fig. 30b shows an SEM image a detail of the interphase interface on the fracture surface at a magnification of 3,100 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment. Furthermore, the morphology of the matrix with a nucleating agent based on orotic acid can be seen in the two images.
- the polymer solutions thus prepared were mixed and 33.3 g of DMSO and 28.5 g of PY was added to the mixture obtained.
- the thus prepared polymer solution which contained 5 wt. % of PLA biopolymers (PLLA 50 % and PDLA 50 %) and 95 wt. % of the solvent mixture (35 % DCM, 35 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electric spining.
- the plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA multifilament yarn which was unwound at a speed of 20 m/min.
- a two-component yam was prepared with a core made from PLA multifilament yarn and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 32, which shows an SEM image of this yarn at a magnification of 396 times and from which its structure is visible.
- twill weave fabric was formed from the two-component core yarn thus prepared - see Fig. 33, which shows an SEM image of this fabric at a magnification of 221 times, on which both the cores and the nanofibrous sheaths of the individual two-component core yarns are visible.
- Two PLLA plates (trade name Luminy 130, Total Corbion PLA) with a content of 0.5 wt. % of a lubricant based on N,N'-Ethylenebis(stearamide) (EBS, Merck) were used for the preparation of the composite of the matrix.
- the plates were made by thermoplastic injection technology at temperatures ranging from 180°C to 210°C, and their dimensions were 145 x 145 x 2 mm.
- twill weave fabric made from two-component core yarn, rotated relative to each other by 45°, were inserted, and the thus prepared structure was tempered for 5 minutes in a press in contact mode at a temperature of 170 °C.
- the PLLA plates melt and the co-PLLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 34, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is visible that at a temperature of 170 °C only the material of the plates melted.
- the temperature was then increased to 180 °C, and after reaching it, pressing took place for 60 seconds with a clamp force of 220 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 220 kN until a temperature of 110 °C was reached. At this temperature, the composite crystallized isothermally for 1 minute. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 220 kN until a temperature of 50 °C was reached; subsequent cooling was without force.
- the result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. In this case, the layers of twill fabric constituted 27 ⁇ 1 % of the weight of this system.
- Fig. 35a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 821 times and Fig. 35b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 2,550 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment.
- the tensile test of two-component nanofibrous core yams according to Examples 1 to 6 was carried out according to ISO 2062, the standard is intended for threads on packages and determines the breaking strength and elongation at break of individual threads using an apparatus with a constant elongation rate.
- the results of the test are the values of modulus of elasticity in tension (Et), ultimate tensile strength (Om) and nominal relative elongation at break (stb).
- Et modulus of elasticity in tension
- Om ultimate tensile strength
- stb nominal relative elongation at break
- the tensile test of the hierarchically structured self-reinforcing biocomposites according to Examples 1 to 6 was conducted according to ISO 527-4, the standard is intended for isotropic and orthotropic plastic composites reinforced with fibrous filler.
- the result of the test was modulus of elasticity in tension (Et), ultimate tensile strength (Om) and nominal relative elongation at break (stb).
- a preload of 2 N was used to measure the samples.
- a speed of 1 mm/min was used, and a speed of 5 mm/min was used to determine the ultimate strength and ultimate tensile strength.
- the impact strength test of the hierarchically structured self-reinforcing biocomposites according to Examples 1 to 6 was carried out according to standard ISO 179-1 and complement ISO 179-1 Z1 fll by the Charpy method with a nominal hammer energy of 5 J.
- Determination of the temperature of deflection of the hierarchically structured self-reinforcing biocomposites of Examples 1 to 6 under load (HDT) was performed according to ISO 75-2, method A using a bending stress of 1.8 MPa at a heating rate of 120 °C/h.
- Transition temperatures and enthalpies, ratios of homo- and stereocomplex crystallites were obtained from differential scanning calorimetry (DSC) measurements according to ISO 11357, which describes thermoanalytical DSC testing methods. A heating rate of 10 °C/min was selected.
- Table 1 shows the mechanical properties of the two-component nanofibrous core yams used in Examples 1 to 6, and Table 2 shows the mechanical properties of the hierarchically structured self-reinforcing composite systems based on polylactic acid biopolymers according to Examples 1 to 6 created using these two-component nanofibrous core yams.
- able 1 part 1/2
- able 2 part 1/6
- able 2 part 2/6)
- able 2 part 3/6)
- able 2 part 4/6) able 2 (part 5/6) able 2 (part 6/6)
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Abstract
The invention relates to a method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid, in which a polymer solution is prepared, containing 5 to 15 wt. % of poly(L- lactide) or symmetric or asymmetric mixtures of poly(L-lactide) and poly(D- lactide) and 85 to 95 wt. % of a solvent system consisting of a mixture of dichloromethane, dimethyl sulfoxide and pyridine in the ratio (3 to 7.5) : (1.5 to 4) : (0.5 to 3.5). This solution is transformed into nanofibers of poly(L-lactide) or mixtures of poly(L-lactide) and poly(D-lactide) by spinning, wherein these nanofibers, after their formation, are deposited on the surface of a fibrous core (2) made from polylactic acid biopolymer, which rotates or balloons around its longitudinal axis, whereby a two-component core yarn based on polylactic acid is prepared. Subsequently, a flat fabric is formed from this yarn, wherein at least one layer of the flat fabric is deposited at elevated temperature and pressure in a matrix (5) based on a polylactic acid biopolymer with a melting temperature lower than or equal to the melting temperature of a nanofibrous sheath (3) of the two- component core yarn, wherein during deposition the structure of the flat fabric is saturated with the matrix (5), thereby creating a hierarchically structured self- reinforcing composite system based on polylactic acid biopolymers, which consists of 5 to 35 wt. % of a two-component core yarn based on polylactic acid.
Description
Method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid, and such composite systems
Technical field
The invention relates to a method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid.
In addition, the invention relates to composite systems prepared by this method.
Background art
In recent years, biodegradable polymers, which are prepared from renewable raw material sources, have been the subject of ever-increasing interest. The advantages of these materials primarily include their effect on reducing the carbon footprint, environmental benefits resulting from their ability to biodegrade and the potential to be sustainable material systems of the future. Among the most studied biopolymers falling into this group are aliphatic polyesters, such as polyhydroxyalkanoates (PHA) and polylactic acid (PLA), which is also often called polylactide.
With intensive research into the production of second and third generation high molecular weight PLA using lignocellulose-based raw material sources and direct conversion of greenhouse gases to lactic acid using microorganisms, PLA will gain in importance.
Since lactic acid contains a chiral carbon atom, there are two optical isomeric forms of lactic acid monomer, referred to as L and D, i.e. , poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA). Depending on the purity of the individual homopolymers, the stereochemistry of their polymer chains and the process conditions, an amorphous or semicrystalline polymer can be prepared at a glass transition temperature (Tg) in the range of 50 °C to 60 °C and a melting temperature (Tm) in the range of 130 °C to 180 °C.
Under the conditions of industrial composting, PLA is subject to biodegradation and, thanks to its good biocompatibility and bioresorbability, it belongs to the most widely studied polymers in clinical biomedical studies. In
recent years, it has attracted interest not only as a replacement for traditional petroleum-based synthetic polymers, but also as a special polymer in various applications.
On the other hand, PLA also exhibits some properties that limit its use in technical applications. These properties mainly include low impact resistance and high brittleness, which are related to the glassy state of PLA at normal room temperature. The low temperature resistance of PLA is mainly related to poor homonucleation of PLA and insufficient mobility of macromolecular chains during crystallization from melts. Since there is an ever-increasing interest in a long-term sustainable economy that is environmentally friendly, it is necessary to overcome the shortcomings mentioned above. Thus, many strategies have been implemented in the last decades to improve the utility properties of PLA. The most commonly used strategies include heterogeneous nucleation, plasticization using plasticizers, copolymerization and mixing (blending) with other polymers.
Another option to improve the utility properties of PLA is stereocomplexation, which was described for the first time in 1987 by Ikada et al. [1 ], The formation of a PLA stereocomplex (sc-PLA) between the optical isomers poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) leads not only to an increase in mechanical properties, but also to an increase in thermal and hydrolytic resistance. The interactions responsible for the formation of sc-PLA are weak multicentred hydrogen bonding interactions (-CH3 ■ ■■ O=C < and =CH ■ ■ ■ O=C <) between PLLA and PDLA enantiomers, which keep both helical coiled macromolecular chains with opposite configurations together [2], As a result of these interactions, sc-PLA crystallites have a melting temperature approximately by 50 °C higher than PLLA or PDLA homocrystallites when equimolar mixed.
The preparation of sc-PLA melt samples by blending (mixing) PLLA/PDLA followed by an additional crystallisation step in the presence of steam or supercooled water at a temperature of 120 to 200 °C is disclosed in international application W02016172011A1 . Application WO2014147132A1 describes the preparation of sc-PLA by mixing solutions or melts using specific nucleating agents. The production of sc-PLA based samples by injection molding of PLLA/PDLA mixtures (blends) under specific temperature and pressure conditions is disclosed in international application W02008104757A1 . International application W02009045877A1 deals with the preparation of fibers
by melt spinning of PLLA/PDLA blends and subsequent heat treatment, where a high sc-PLA content is achieved. The preparation of nanofibrous membranes based on sc-PLA is the subject of international application WO2015155182A1. Nanofibers are obtained by a complex process of spinning the PLLA/PDLA blend from a melt, which is followed by heat treatment, washing, selective extraction, drying and hot pressing.
The preparation of stereocomplexed PLA nanofibers by electrostatic spinning was first described in 2006 by Tsuji et al. [3], Since then, numerous laboratory procedures for the preparation of sc-PLA nanofibers using various solvent systems under the action of direct electric current have been described. The preparation of a flat film from non-woven sc-PLA nanofibers using direct current and an injection needle electrode placed on a syringe is described, for example, in CN107142610B.
The concept of single-polymer composites, often referred to as "selfreinforcing" composites, was first described in 1975 by Capiati and Porter [4], who used oriented polyethylene (PE) fibers and PE powder with different melting temperatures in their research. Since then, various techniques have been developed to combine oriented fibers with a separate homogeneous phase of the matrix of the composite. The advantages of such self-reinforcing systems mainly include the ability to achieve an excellent interphase interface and, due to their relative chemical homogeneity, they increase their added value by their recyclability compared to composites based on heterogeneous components. The preparation of such polymer structures is dealt with in documents WO1 997033017A1 , WO1993011204A1 and W02009127864A1 .
The preparation of self-reinforcing P LA-based composites was for the first time described by Makela et al. [5], Li and Yao [6] later prepared self-reinforcing PLA composites by stacking amorphous PLA films and highly-oriented PLA fibers using hot pressing. The preparation of unidirectionally oriented self-reinforced PLA composites was addressed by Gao et al. [7], Self-reinforcing transparent stereocomplexed PLA nanocomposites were then prepared by Kurokawa and Hotta [8], Their study utilized electrostatic spinning to prepare sc-PLA nanofibrous nonwoven structure, which was subsequently inserted between two PLA films and hot-molded. The disadvantage of this process is that the nonwoven fabric lacks the orientation of the nanofibers in the loading direction of the
composite and the resulting material therefore does not exhibit high mechanical properties.
Thus, neither the preparation nor the composition of practically applicable hierarchically structured self-reinforcing composite systems based on PLA biopolymers with uniform structure and uniform distribution of mechanical properties has been described so far.
The object of the invention is to provide a method of preparation of hierarchically structured self-reinforcing composite systems based on polylactic acid biopolymers and such composite systems. These systems will significantly improve the mechanical properties and temperature resistance of traditional PLA- based products, increasing their applicability in replacing fossil based polymers. Other advantages of such systems can be seen especially in the reduction of the carbon footprint and the fact that these materials can be completely based on renewable raw materials with targeted recyclability or biodegradability.
List of non-patent literature:
[1 ] Ikada, Y., Jamshidi K., Tsuji H., and Hyon, S. H. Stereocomplex formation between enantiomeric poly (lactides), Macromolecules, 20(4), 904-906, 1987
[2] Sarasua, J. R., Rodriguez, N. L., Arraiza, A. L., and Meaurio, E., Stereoselective crystallization and specific interactions in polylactides. Macromolecules, 38(20), 8362-8371 , 2005
[3] Tsuji, H., Nakano, M., Hashimoto, M., Takashima, K., Katsura, S., and Mizuno, A. Electrospinning of poly (lactic acid) stereocomplex nanofibers. Biomacromolecules, 7(12), 3316-3320, 2006
[4] Capiati, N. J. and Porter, R. S. The concept of one polymer composites modelled with high density polyethylene. Journal of materials science, 10(10), 1671 -1677, 1975,
[5] Makela, P., Pohjonen, T., Tdrmala, P., Waris, T., and Ashammakhi, N. Strength retention properties of self-reinforced poly l-lactide (SR-PLLA) sutures compared with polyglyconate (MaxonR) and polydioxanone (PDS) sutures. An in vitro study. Biomaterials, 23(12), 2587-2592, 2002
[6] Li, R., and Yao, D. Preparation of single poly (lactic acid) composites. Journal of applied polymer science, 107(5), 2909-2916, 2008
[7] Gao, C., Meng, L., Yu, L., Simon, G. P., Liu, H., Chen, L., and Petinakis, S. Preparation and characterization of uniaxial poly (lactic acid)-based selfreinforced composites. Composites Science and Technology, 117, 392-397, 2015
[8] Kurokawa, N., & Hotta, A. Thermomechanical properties of highly transparent self-reinforced polylactide composites with electrospun stereocomplex polylactide nanofibers. Polymer, 153, 214-222, 2018.
Principle of the invention
The object of the invention is achieved by a method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid (PLA), which include nanofibers based on poly(L- lactide) (PLLA) or based on an asymmetric or symmetrical blend of poly(L-lactide) and poly(D-lactide) (PDLA). Preferably, these nanofibers are prepared by spinning a solution, preferably, for example, by the method according to WO2014094694A1 , using alternating current, where an electric field for spinning is alternately created between a spinning electrode to which alternating voltage is applied and air and/or gas ions created and/or brought into its vicinity. In this process, a polymer dosing device known from W02019047990A1 and/or a spinning electrode in one of the embodiments known from W02017108012A1 can be used. During spinning with the use of alternating current, the nanofibers formed are carried in the direction of the gradient of the electric field away from the spinning electrode, forming a hollow plume (sleeve). This is then deposited according to the method of WO2016192697A2 on a supporting fibrous core which rotates around its own axis and/or balloons, creating a nanofibrous sheath on its surface. Another method of creating such a two-component linear structure is also known from WO2008149488A1 .
The formed two-component core yam 1. contains a fibrous core 2 on which a nanofibrous sheath 3 is deposited, the nanofibrous sheath 3 being formed by a nanofibrous plume wound in a helix. The fibrous core 2 consists of a monofilament (see Figure 1 ) or multifilament (see Figure 2) textile yarn made from PLA biopolymer. This yam unwinds and simultaneously rotates around its own axis and/or balloons in the working space of the device in which the electrically neutral nanofibrous plume is created. Upon contact of the plume with the fibrous
core 2, the plume is transformed into a flat stripe of oriented nanofibers and spirally wraps around the fibrous core 2. The density of the nanofibrous sheath 3 thus formed can be controlled by the rate at which the solution is dispensed onto the surface of the spinning electrode and/or by the rate at which the continuous fibrous core 2 is unwound.
Both the fibrous core 2 and the nanofibrous sheath 3 are made from PLA biopolymer, wherein in the case of the fibrous core 2, the biopolymer usually has the same or lower melting temperature than in the case of the nanofibrous sheath 3, as will be explained below.
Before entering the working space and the path of the nanofibrous plume, the fibrous core 2 is preferably preheated to a desired working temperature in the range of 25 to 55 ± 1 °C.
The formed two-component core yarn 11 can, if necessary, be heat-fixed by passing through a die heated to a temperature of 55 to 100 ± 1 °C and then dried in a tempering chamber located behind the working space of the device.
The two-component core yam 1. thus formed is subsequently processed by standard textile techniques into strands, planar (2D) and spatial (3D) textile structures which can serve independently or as self-reinforcing elements of hierarchically structured biodegradable composite systems based on PLA biopolymers, or PLA copolymers, mixtures with other biopolymers, their combination, or with the addition of additives (plasticizers, nucleating agents, flame retardants, lubricants, UV stabilizers, antioxidants, dyes, antistatic agents, blowing agents, impact modifiers, etc.), fillers and/or discontinuous fiber reinforcement. As a rule, these modifications must not compromise the biodegradability of the resulting material research.
In the preparation of hierarchically structured self-reinforcing composite systems according to the invention, the two-component core yarn 1. is processed into a flat (2D) textile, e.g., fabric - see Figs. 2 and 4, and deposited in a PLA- based matrix 4 - see Figs. 3 and 5. All components of this system have a melting temperature equal to or lower than the nanofibrous sheath 3 of the used two- component linear structure. Analogously, a knitted fabric made from the two- component core yarn 1. can also be used.
A PLA-based spinning solution is prepared by dissolving PLLA or a mixture of PLLA and PDLA in a suitable solvent system which contains dichloromethane
(DCM), dimethyl sulfoxide (DMSO) and pyridine (PY). The concentration of the polymer in this solution is 5 to 15 wt. %, the ratio of solvents in the solvent system DCM : DMSO : PY is (3 to 7.5) : (1 .5 to 4) : (0.5 to 3.5).
In the case of using the mixture of PLLA and PDLA, solutions of these polymers in DCM are preferably prepared separately, and after their mixing and homogenization, DMSO and PY are added to them. The polymer solution thus prepared is homogenized and then spun using one of the methods of preparation of polymer nanofibers. A particularly advantageous method is spinning using alternating current, during which an electrically neutral plume of nanofibers is created, which moves in the direction of the gradient of the electric field away from the spinning electrode, and at the same time is caught on a monofilament or multifilament PLA yam rotating or ballooning around its longitudinal axis, on which it creates a uniform and continuous nanofibrous sheath 3. Thus, a two- component yarn 1_ is prepared.
From the thus prepared two-component core yarn 1., a flat textile, e.g., a fabric or knitted fabric of any type, is then prepared by a suitable textile technique and is subsequently incorporated into a PLA-based matrix 4. In a suitable procedure, at least one layer of this fabric is inserted between two plates of PLA polymer or co-PLA and together with them is exposed to elevated temperature (150 to 200 °C) and pressure (150 to 250 kN). In a preferred variant, this semiproduct is heated for 3 to 8 minutes to a temperature of 150 to 180 °C, at which the material of the plates melts and the flat fabric is saturated with this matrix 4, and then it is heated for 15 to 80 seconds to a temperature of 160 to 200 °C, at which the textile is saturated with the matrix 4 and the entire structure is fixed. However, due to the different melting temperatures, the core 2 and the sheath 3 of the two-component core yam 1_ do not melt, and consequently, the yam 1_ and its components retain their morphology and character. The result of this process is a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures, which contains at least one layer of fabric prepared from the two-component core yam 1_ based on PLA deposited in a PLA or co-PLA matrix 4. The textile constitutes 5 to 35 wt. % of this composite.
In order to achieve the required mechanical properties of hierarchically structured self-reinforcing composite systems when multiple layers of fabric are
used, these layers can be suitably oriented relative to each other, e.g., by rotating them by a suitable angle, e.g., 45 °, 90 °, or in any other way, or by combining textiles of different types.
In the enclosed drawings, Fig. 1 a shows a scheme of a two-component linear structure with a monofilament yam core, Fig. 1 b shows a scheme of a two- component linear structure with a multifilament yam core, Fig. 2 shows a scheme of a plain weave fabric made from a two-component linear structure with a monofilament yam core, Fig. 3 shows a scheme of a section through the hierarchically structured self-reinforcing composite system according to the invention with one fabric layer according to Fig. 2, Fig. 4 shows a scheme of a plain weave fabric made from a two-component linear structure with a multifilament yam core, Fig. 5 is a scheme of a section through the hierarchically structured self-reinforcing composite system according to the invention with one fabric layer according to Fig. 4.
Fig. 6 is an SEM image of one variant of PLLA nanofibers at a magnification of 25,000 times, Fig. 7 shows an SEM image of the two-component linear structure with the monofilament yam core and the sheath formed by the layer of PLLA nanofibers according to Fig. 6 at a magnification of 475 times, Fig. 8 shows an SEM image of a unidirectional fabric made from the two-component linear structure according to Fig. 7 at a magnification of 109 times, Fig. 9 shows the DSC curves of the individual components of the hierarchically structured selfreinforcing composite system according to the invention formed using the unidirectional fabric according to Fig. 8, Fig. 10a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 158 times, and Fig. 10b shows a detail of an interphase interface at the fracture surface in Fig. 10a.
Fig. 11 shows an SEM image of one variant of sc-PLA nanofibers at a magnification of 15,000 times, Fig. 12 shows an SEM image of the two- component linear structure with the multifilament yam core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 11 at the point of rupture at a magnification of 183 times, Fig. 13 shows an SEM image of fabric consisting
of the two-component linear structure according to Fig. 12 at a magnification of 125 times, Fig. 14 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 13, Fig. 15a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 630 times, and Fig. 15b shows a detail of the interphase interface at the fracture surface in Fig. 15a at a magnification of 2,520 times.
Fig. 16 shows an SEM image of a second variant of sc-PLA nanofibers at a magnification of 25,000 times, Fig. 17 shows an SEM image of the two- component linear structure with the monofilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 11 at the section point at a magnification of 416 times, Fig. 18 shows an SEM image of unidirectional fabric made from the two-component linear structure according to Fig. 17 at a magnification of 85 times, Fig. 19 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using fabric according to Fig. 18, Fig. 20a shows an SEM image of the fracture surface of this hierarchically structured selfreinforcing composite system at a magnification of 349 times, and Fig. 20b shows a detail of the interphase interface at the fracture surface in Fig. 20a at a magnification of 4,320 times.
Fig. 21 shows an SEM image of a third variant of sc-PLA nanofibers at a magnification of 5,200 times, Fig. 22 shows an SEM image of the two-component linear structure with the multifilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 21 at the section point at a magnification of 611 times, Fig. 23 shows an SEM image of twill fabric made of the two-component linear structure according to Fig. 22 at a magnification of 84 times, Fig. 24 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 23, Fig. 25a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 500 times, and Fig. 25b shows a detail of the interphase interface at the fracture surface in Fig. 25a at a magnification of 2,540 times.
Fig. 26 is an SEM image of a fourth variant of sc-PLA nanofibers at a magnification of 25,000 times, Fig. 27 shows an SEM image of the two- component linear structure with the monofilament yarn core and the sheath formed by the layer of sc-PLA nanofibers according to Fig. 26 at the section point at a magnification of 191 times, Fig. 28 shows an SEM image of plain weave fabric made from the two-component linear structure according to Fig. 27 at a magnification of 124 times, Fig. 29 shows the DSC curves of the individual components of hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 28, Fig. 30a shows an SEM image of the fracture surface of this hierarchically structured selfreinforcing composite system at a magnification of 405 times, and Fig. 30b shows a detail of the interphase interface at the fracture surface in Fig. 30a at a magnification of 3,100 times.
Fig. 31 shows an SEM image of a fifth variant of sc-PLA nanofibers at a magnification of 14,800 times, Fig. 32 shows an SEM image of a two-component linear structure with a multifilament yarn core and a sheath formed by a layer of sc-PLA nanofibers according to Fig. 31 at the section point at a magnification of 396 times, Fig. 33 shows an SEM image of twill fabric made from the two- component linear structure according to Fig. 32 at a magnification of 221 times, Fig. 34 shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite system according to the invention formed using the fabric according to Fig. 33, Fig. 35a shows an SEM image of the fracture surface of this hierarchically structured self-reinforcing composite system at a magnification of 821 times, and Fig. 35b shows a detail of the interphase interface on the fracture surface in Fig. 35a at a magnification of 2,550 times.
Examples of embodiment
Illustrative examples of the preparation of hierarchically structured selfreinforcing composite systems based on biopolymers of polylactic acid (PLA) and composite systems thus obtained are given below for clarity.
Before each technological processing, all PLA biopolymers, compounds, mixtures and fabrics are dried for at least 12 hours in a vacuum dryer at a
temperature of 80 °C to prevent their degradation due to hydrolytic reactions. Additives added are similarly dried at a temperature of 50 °C. Parameters in the examples of the used solvents based on dichloromethane (DCM, CH2CI2), dimethyl sulfoxide (DMSO, (CH3)2SO) and pyridine (PY, C5H5N) correspond to the following specifications, only their concentrations differ: DCM has a specific mass of 1320 kg/m3, a molar mass of 85 g/mol and a chemical purity of 99.88 %; DMSO has a specific mass of 1100 kg/m3, a molar mass of 78.13 g/mol, and a chemical purity of 99.88 %. PY has a specific mass of 983 kg/m3, a molar mass of 79.1 g/mol and a chemical purity of 99.5 %.
PLA monofilament (trade name 6101, Perlon) was used as a fibrous core 2, with a diameter of 0.22 mm, a melting temperature Tm of 170 °C, a fineness of 48 Tex, or PLA multifilament (trade name PLA-DTY dtex 76 f 32, Trevira) was used as a fibrous core 2. This multifilament consisted of 32 elementary fibers having a fineness of 7.6 Tex and a melting temperature Tm of 180 °C.
PLA biopolymers modified with additives (e.g., plasticizers, impact modifiers, nucleating agents, lubricants) and with other biopolymers (e.g., polyester-based thermoplastic elastomer - TPE) were compounded on a twin- screw extruder to achieve the desired weight in the resulting material system. The matrix of the composite was prepared from plates of PLA biopolymer or sc-PLA having dimensions of 145 x 145 x 2 mm prepared by injection molding technology; the mold being cooled to a temperature of 20 °C. The resulting hierarchically structured self-reinforcing composite systems were subsequently prepared by inserting at least one layer of fabric between two PLA or sc-PLA plates followed by hot pressing on a heated press.
Table 1 shows some mechanical parameters of the individual components of the structured self-reinforcing composite system and of the structured selfreinforcing composite systems according to Examples 1 to 6 for comparison. Example 1
10 g of poly(L-lactide) (PLLA, with the trade name Luminy L130, Total Corbion PLA) with a weight average molar mass Mw = 180 kg/mol, a melting temperature Tm = 180 °C and an L-enantiomer content of at least 99 % was dissolved under constant stirring at a temperature of 23 ± 1 °C in 63 g of dichloromethane (DCM). 18 g of dimethyl sulfoxide (DMSO) and then 9 g of pyridine (PY) was further added to the thus obtained solution. DMSO has a higher
boiling point than DCM, so it evaporates later during spinning and thus aids in the elongation and orientation of the nanofibers. Pyridine is added to the mixture to increase the conductivity of the resulting solution. The polymer solution prepared by this process, which contained 10 wt. % of PLLA and 90 wt. % of the solvent mixture (70 % DCM, 20 % DMSO, and 10 % PY) was homogenized under constant stirring for 12 hours and then spun by electric spinning.
Alternating current (AC) with a voltage of 10 kV and a frequency of 50 Hz was applied to the spinning electrode, while the polymer solution described above was supplied to its spinning surface at a rate of 10 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 200 ± 62 nm was formed - see Fig. 6, which shows an SEM image of these nanofibers at a magnification of 25,000 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 60 m/min. In this manner, a two-component yam was prepared with a core consisting of PLA monofilament yam and a sheath formed by a layer of PLLA nanofibers, see Fig. 7, which is an SEM image of this yam at a magnification of 475 times, showing its structure. The two-component core yam thus prepared showed a fineness of 53 tex.
The two-component core yam thus prepared was subsequently made into a unidirectional fabric - see Fig. 8, which shows an SEM image of this fabric at a magnification of 109 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yams are visible.
To prepare the matrix of the composite, two plates based on PLA copolymer were used (co-PLA, trade name Luminy LX175, Total Corbion PLA) with a weight average molar mass Mw= 163 kg/mol, a melting temperature Tm = 155 °C and an L-enantiomer content of 96 %. The plates were made by thermoplastic injection technology at temperatures ranging from 160 °C to 190 °C, and their dimensions were 145 x 145 x 2 mm.
Unidirectional fabric made from two-component core yam was inserted between these two PLLA plates, and the thus prepared structure was tempered for 5 minutes in a press in contact mode at a temperature of 160 °C. During the tempering process, the co-PLA plates melt and the co-PLA fabric is saturated
with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 9, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is clear that only the material of the plates melted at a temperature of 160 °C. The temperature was then increased to 170 °C and after reaching it, pressing took place for 20 seconds with a clamp force of 160 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 160 kN until a temperature of 50 °C was reached; subsequent cooling was already without force. The result of the process was a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures. The unidirectional fabric layer in this case constituted 9 ± 1 % of the weight of this system.
Fig. 10a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 158 times and Fig. 10b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 968 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment.
Example 2
7.2 g of PLLA same as in Example 1 was dissolved in 49 g of DCM under constant stirring at a temperature of 23 ± 1 °C.
0.8 g of poly(D-lactide) (PDLA, with the trade name Luminy D070, Total Corbion PLA) with a weight average molar mass Mw = 85 kg/mol, a melting temperature Tm = 180 °C and a D-enantiomer content of at least 99 % was dissolved in 6.2 g of DCM.
The polymer solutions thus prepared were mixed and to the mixture formed 23 g of DMSO and 13.8 g of PY was added.
The polymer solution prepared by this process, which contained 8 wt. % of PLA biopolymers (PLLA 90 % and PDLA 10 %) and 92 wt. % of the solvent mixture (60 % DCM, 25 % DMSO, and 15 % PY) was homogenized under constant stirring on a magnetic stirrer for 12 hours and then spun by electric spinning.
Alternating current (AC) with a voltage of 20 kV and a frequency of 60 Hz was applied to the spinning electrode, while the polymer solution described above was supplied to its spinning surface at a rate of 15 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 310 ± 43 nm was formed - see Fig. 11 , which shows an SEM image of these nanofibers at a magnification of 15,000 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA multifilament yarn which was unwound at a speed of 50 m/min. In this manner, a two-component yam was prepared with a core consisting of PLA multifilament yam and a sheath formed by a layer of sc-PLA nanofibers (PLLA 90 % and PDLA 10 %) with a fineness of 10 tex - see Fig. 12, which shows an SEM image of this yam at a magnification of 183 times and in which the structure of this yam is visible.
From the two-component core yam thus prepared, plain weave fabric was then formed - see Fig. 13, which shows an SEM image of this fabric at a magnification of 125 times and in which both the cores and the nanofibrous sheaths of the individual two-component core yams are visible.
Two PLLA plates with a content of 15 wt % plasticizer - acetyl tributy I citrate (ATBC, CITROFLEX* A-4, Vertellus LLC) were used for the preparation of the matrix of the composite. The plates were made by thermoplastic injection technology at temperatures ranging from 170 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
Between these two PLLA plates, two identical layers of plain weave fabric made from two-component core yam, rotated relative to each other by 90°, were inserted, and the thus prepared structure was tempered for 5 minutes in a press in contact mode at a temperature of 165 °C. During the tempering process, the PLLA plates melt and the PLLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 14, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is apparent that at a temperature of 165 °C only the material of the plates melted. The temperature was then increased to 170 °C and after reaching it, pressing took place for 30 seconds with a clamp force of 170 kN. This was followed by non-isothermal
cooling while maintaining the clamp force of 170 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force. The result of the process was a hierarchically structured self-reinforcing composite system based on PLA biopolymers with different melting temperatures. In this case, the layers of plain weave fabric constituted 13 ± 1 % of the weight of this system.
Fig. 15 shows an SEM image of the fracture surface of the above- mentioned hierarchically structured self-reinforcing composite system at a magnification of 630 times and Fig. 15b shows an SEM image of a detail of the interphase interface on this fracture surface at a magnification of 2,520 times. It can be seen from the two images that neither the core nor the sheath of the two- component core yarn melted during the heat treatment.
Example 3
6.4 g of poly(L-lactide) (PLLA, with the trade name Luminy L175, Total Corbion PLA) with a weight average molar mass Mw= 210 kg/mol, a melting temperature Tm = 180 °C and an L-enantiomer content of at least 99 % was dissolved under constant stirring at a temperature of 35 ± 1 °C in 40 g of DCM.
1 .6 g of PDLA same as in Example 2 was dissolved in 6.2 g DCM.
The polymer solutions thus prepared were mixed and 27.6 g of DMSO and 13.8 g of PY was added to the mixture obtained. The thus obtained polymer solution, which contained 8 wt. % of PLA biopolymers (PLLA 80 % and PDLA 20 %) and 92 wt. % of the solvent mixture (55 % DCM, 30 % DMSO and 15 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electric spinning.
Alternating current (AC) with a voltage of 30 kV and a frequency of 70 Hz was applied to the spinning electrode, while the above-described polymer solution was supplied to its spinning surface at a rate of 20 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 245 ± 71 nm was formed - see Fig. 16, which shows an SEM image of these nanofibers at a magnification of 25,000 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 40 m/min.
In this manner, a two-component yarn was prepared with a core made from PLA monofilament yarn and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 17, which shows an SEM image of this yarn at a magnification of 416 times and from which its structure is visible. The two-component core yarn prepared in this way showed a fineness of 57 tex.
The two-component core yam thus prepared was subsequently made into a unidirectional fabric - see Fig. 18, which shows an SEM image of this fabric at a magnification of 85 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yarns are visible.
To prepare the matrix of the composite, two plates based on PLA copolymer (co-PLA, trade name Luminy 130, Total Corbion PLA) with biodegradable polyester-based thermoplastic elastomer (TPE, trade name NP EL 208-65A, NaturePlast) were used. The TPE content was 20 wt. %. The plates were made by thermoplastic injection technology at temperatures in the range of 160 °C to 190 °C, and their dimensions were 145 x 145 x 2 mm.
Between these two co-PLA plates, two identical layers of unidirectional fabric made from two-component core yarn, rotated relative to each other by 90°, were inserted, and the thus prepared structure was tempered for 3 minutes in a press in contact mode at a temperature of 170 °C. During the tempering process, the co-PLA plates melt and the co-PLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 19, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, showing that at a temperature of 170 °C only the material of the plates melted. Subsequently, the temperature was increased to 175 °C, and after reaching it, pressing took place for 40 seconds with a clamp force of 185 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 185 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force. The result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. In this case, the layers of unidirectional fabric constituted 19 ± 1 % of the weight of the above-mentioned system.
Fig. 20a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 349
times and Fig. 20b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 4,320 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment. Furthermore, the morphology of the matrix is visible in the two images, where TPE is dispersed in co-PLA in the form of spherical particles.
Example 4
4.9 g of PLLA same as in Example 1 was dissolved in 32 g of DCM under constant stirring at a temperature of 35 ± 1 °C.
2.1 g poly(D-lactide) (PDLA, with trade name Luminy D120, Total Corbion PLA) with a weight average molar mass Mw= 154 kg/mol, a melting temperature Tm = 180 °C and an L-enantiomer content of at least 99 % was dissolved under constant stirring in 14.5 g of DCM.
The polymer solutions thus prepared were mixed and to the mixture obtained, 27.9 g DMSO and 18.6 g PY was added. The thus prepared polymer solution, which contained 7 wt. % of PLA biopolymers (PLLA 70 % a PDLA 30 %) and 93 wt. % of the solvent mixture (50 % DCM, 30 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electris spinning.
Alternating current (AC) with a voltage of 35 kV and a frequency of 75 Hz was applied to the spinning electrode, while the above-described polymer solution was supplied to its spinning surface at a rate of 25 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 402 ± 37 nm was formed - see Fig. 21 , which shows an SEM image of these nanofibers at a magnification of 5,200 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA multifilament yam which was unwound at a speed of 30 m/min. In this manner, a two-component yam was prepared with a core consisting of PLA multifilament yam and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 22, which shows an SEM image of this yam at a magnification of 611 times, and from which its structure is visible. The two-component core yam thus prepared showed a fineness of 14 tex.
From the two-component core yam thus prepared, twill fabric was then formed - see Fig. 23, which shows an SEM image of this fabric at a magnification of 84 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yams are visible.
Two PLLA plates (trade name Luminy 130, Total Corbion PLA) containing a PLA-based impact modifier (masterbatch) were used to prepare the matrix of the composite. The impact modifier content was 10 wt. %. The plates were made by thermoplastic injection technology at temperatures ranging from 170 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
Between these two PLLA plates, three identical layers of twill weave fabric made from two-component core yam, rotated relative to each other by 90 °, were inserted and the thus prepared structure was tempered for 4 minutes in a press in contact mode at a temperature of 170 °C. During the tempering process, the PLLA plates melt and the PLLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 24, which represents the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, showing that at a temperature of 170 °C only the material of the plates melted. The temperature was then increased to 180 °C, and after reaching it, pressing took place for 30 seconds with a clamp force of 190 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 190 kN until a temperature of 100 °C was reached. At this temperature, the composite crystallized isothermally for 2 minutes. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 190 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force. The result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. In this case, the layers of twill fabric constituted 21 ± 2 % of the weight of the above-mentioned system.
Fig. 25a shows an SEM image of the fracture surface of this structured self-reinforcing composite system at a magnification of 500 times and Fig. 25b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 2,540 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the
heat treatment. Furthermore, the morphology of the matrix with cavities caused by the addition of the masterbatch can be seen in both images.
Example 5
3.6 g of PLLA same as in Example 3 was dissolved in 25 g of DCM under constant stirring at a temperature of 35 ± 1 °C.
2.4 g of PDLA same as in Example 4 was dissolved under constant stirring in 17.3 g of DCM.
The polymer solutions thus prepared were mixed and 28.2 g of DMSO and 23.5 g of PY was added to the mixture obtained. The thus prepared polymer solution, which contained 6 wt. % of PLA biopolymers (PLLA 60 % and PDLA 40 %) and 93 wt. % of the solvent mixture (50 % DCM, 30 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electric spinning.
Alternating current (AC) with a voltage of 40 kV and a frequency of 80 Hz was applied to the spinning electrode, while the above-described polymer solution above was supplied to its spinning surface at a rate of 30 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 290 ± 29 nm was formed - see Fig. 26, which shows an SEM image of these nanofibers at a magnification of 25,000 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA monofilament yam which was unwound at a speed of 25 m/min. In this manner, a two-component yam was prepared with a core consisting of PLA monofilament yam and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 27, which shows an SEM image of this yam at a magnification of 191 times and from which its structure is visible.
From the two-component core yam thus prepared, plain weave fabric was then formed - see Fig. 28, which shows an SEM image of this fabric at a magnification of 124 times, in which both the cores and the nanofibrous sheaths of the individual two-component core yams can be seen.
To prepare the matrix of the composite, two PLLA plates (trade name Luminy 130, Total Corbion PLA) containing 0.3 wt.% of the nucleating agent - orotic acid monohydrate (OA, Merck) were used. The plates were made by
thermoplastic injection moulding at temperatures ranging from 160 °C to 200 °C, and their dimensions were 145 x 145 x 2 mm.
Between these two PLLA plates, three identical layers of plain weave fabric made from two-component core yarn, rotated relative to each other by 45°, were inserted, and the thus prepared structure was tempered for 6 minutes in a press in contact mode at a temperature of 170 °C. During the tempering process, the PLLA plates melt and the PLLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 29, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is visible that at a temperature of 170 °C only the material of the plates melted. The temperature was then increased to 180 °C, and after reaching it, pressing took place for 40 seconds with a clamp force of 200 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 200 kN until a temperature of 90 °C was reached. At this temperature, the composite crystallized isothermally for 3 minutes. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 190 kN until a temperature of 50 °C was reached; the following cooling process was already without applying clamp force. The result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. The layers of twill fabric constituted 30 ± 1 % of the weight of the above-mentioned system.
Fig. 30a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 405 times and Fig. 30b shows an SEM image a detail of the interphase interface on the fracture surface at a magnification of 3,100 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment. Furthermore, the morphology of the matrix with a nucleating agent based on orotic acid can be seen in the two images.
Example 6
2.5 g of PLLA same as in Example 1 was dissolved in 16.6 g of DCM under constant stirring at a temperature of 40 ± 1 °C.
2.5 g of PDLA same as in Example 4 was dissolved in 17.3 g of DCM under constant stirring.
The polymer solutions thus prepared were mixed and 33.3 g of DMSO and 28.5 g of PY was added to the mixture obtained. The thus prepared polymer solution, which contained 5 wt. % of PLA biopolymers (PLLA 50 % and PDLA 50 %) and 95 wt. % of the solvent mixture (35 % DCM, 35 % DMSO, and 20 % PY) was left to homogenize under constant stirring for 12 hours and then spun by electric spining.
Alternating current (AC) with a voltage of 50 kV and a frequency of 90 Hz was applied to the spinning electrode, while the above-described polymer solution was supplied to its spinning surface at a rate of 35 mL/min. Spinning took place at a laboratory temperature of 23 ± 1 °C and a relative humidity of 35 %. During this process, a spatial hollow plume consisting of nanofibers with a diameter of 480 ± 61 nm was formed - see Fig. 31 , which shows an SEM image of these nanofibers at a magnification of 14,800 times. The plume was fed into the working space of the device, where it was continuously wound onto a core made from PLA multifilament yarn which was unwound at a speed of 20 m/min. In this manner, a two-component yam was prepared with a core made from PLA multifilament yarn and a sheath formed by a layer of sc-PLA nanofibers - see Fig. 32, which shows an SEM image of this yarn at a magnification of 396 times and from which its structure is visible.
Subsequently, twill weave fabric was formed from the two-component core yarn thus prepared - see Fig. 33, which shows an SEM image of this fabric at a magnification of 221 times, on which both the cores and the nanofibrous sheaths of the individual two-component core yarns are visible.
Two PLLA plates (trade name Luminy 130, Total Corbion PLA) with a content of 0.5 wt. % of a lubricant based on N,N'-Ethylenebis(stearamide) (EBS, Merck) were used for the preparation of the composite of the matrix. The plates were made by thermoplastic injection technology at temperatures ranging from 180°C to 210°C, and their dimensions were 145 x 145 x 2 mm.
Between these two PLLA plates, four identical layers of twill weave fabric made from two-component core yarn, rotated relative to each other by 45°, were inserted, and the thus prepared structure was tempered for 5 minutes in a press in contact mode at a temperature of 170 °C. During the tempering process, the
PLLA plates melt and the co-PLLA fabric is saturated with the matrix; however, there is no melting of the core and the sheath of the two-component core - see Fig. 34, which shows the DSC curves of the individual components of the hierarchically structured self-reinforcing composite, from which it is visible that at a temperature of 170 °C only the material of the plates melted. The temperature was then increased to 180 °C, and after reaching it, pressing took place for 60 seconds with a clamp force of 220 kN. This was followed by non-isothermal cooling while maintaining the clamp force of 220 kN until a temperature of 110 °C was reached. At this temperature, the composite crystallized isothermally for 1 minute. Subsequently, non-isothermal cooling continued while maintaining the clamp force of 220 kN until a temperature of 50 °C was reached; subsequent cooling was without force. The result of the process was a hierarchically structured self-reinforcing composite system with a crystalline structure based on PLA biopolymers with different melting temperatures. In this case, the layers of twill fabric constituted 27 ± 1 % of the weight of this system.
Fig. 35a shows an SEM image of the fracture surface of the above- mentioned structured self-reinforcing composite system at a magnification of 821 times and Fig. 35b shows an SEM image of a detail of the interphase interface on the fracture surface at a magnification of 2,550 times. It can be seen from the two images that neither the core nor the sheath of the two-component core yarn melted during the heat treatment.
Methods of measuring the properties of the resulting material systems:
The tensile test of two-component nanofibrous core yams according to Examples 1 to 6 was carried out according to ISO 2062, the standard is intended for threads on packages and determines the breaking strength and elongation at break of individual threads using an apparatus with a constant elongation rate. The results of the test are the values of modulus of elasticity in tension (Et), ultimate tensile strength (Om) and nominal relative elongation at break (stb). The sample was fixed in jaws spaced Io = 250 mm apart, which moved away from each other at a speed of 100 mm/min.
The tensile test of the hierarchically structured self-reinforcing biocomposites according to Examples 1 to 6 was conducted according to ISO 527-4, the standard is intended for isotropic and orthotropic plastic composites reinforced with fibrous filler. The result of the test was modulus of elasticity in tension (Et), ultimate tensile strength (Om) and nominal relative elongation at break (stb). A preload of 2 N was used to measure the samples. To determine the modulus of elasticity in tension, a speed of 1 mm/min was used, and a speed of 5 mm/min was used to determine the ultimate strength and ultimate tensile strength.
The impact strength test of the hierarchically structured self-reinforcing biocomposites according to Examples 1 to 6 was carried out according to standard ISO 179-1 and complement ISO 179-1 Z1 fll by the Charpy method with a nominal hammer energy of 5 J.
Determination of the temperature of deflection of the hierarchically structured self-reinforcing biocomposites of Examples 1 to 6 under load (HDT) was performed according to ISO 75-2, method A using a bending stress of 1.8 MPa at a heating rate of 120 °C/h.
Transition temperatures and enthalpies, ratios of homo- and stereocomplex crystallites were obtained from differential scanning calorimetry (DSC) measurements according to ISO 11357, which describes thermoanalytical DSC testing methods. A heating rate of 10 °C/min was selected.
Below, Table 1 shows the mechanical properties of the two-component nanofibrous core yams used in Examples 1 to 6, and Table 2 shows the mechanical properties of the hierarchically structured self-reinforcing composite systems based on polylactic acid biopolymers according to Examples 1 to 6 created using these two-component nanofibrous core yams.
able 1 (part 1/2)
able 2 (part 1/6)
able 2 (part 2/6)
able 2 (part 3/6)
able 2 (part 4/6)
able 2 (part 5/6)
able 2 (part 6/6)
Industrial applicability
Increasing the application possibilities of sustainable polymers in various industries in replacing traditional polymers that are based on notorious nonrenewable fossil resources. Possibilities of targeted recycling or biodegradation of prepared parts with the aid of industrial composting. The potential for use in biomedical applications or the transport industry due to good temperature resistance, biocompatibility and bioresorbability with the possibility of controlling the breakdown of hierarchical structures depending on the ratio of the individual isomers and the degree of crystallinity.
Claims
1. A method of preparation of hierarchically structured self-reinforcing composite systems based on biopolymers of polylactic acid, characterized in that a polymer solution is prepared, containing 5 to 15 wt. % of poly(L-lactide) or symmetric or asymmetric mixture of poly(L-lactide) and poly(D-lactide) and 85 to 95 wt. % of a solvent system consisting of a mixture of dichloromethane, dimethyl sulfoxide and pyridine in the ratio (3 to 7.5) : (1 .5 to 4) : (0.5 to 3.5), this solution is transformed into nanofibers of poly(L-lactide) or mixtures of poly(L-lactide) and poly(D-lactide) by spinning, wherein these nanofibers, after their formation, are deposited on the surface of a fibrous core (2) made from polylactic acid biopolymer, which rotates or balloons around its longitudinal axis, whereby a two- component core yam based on polylactic acid is prepared, a flat fabric is formed from this yarn, wherein at least one layer of the flat fabric is deposited at elevated temperature and pressure in a matrix (5) based on a polylactic acid biopolymer with a melting temperature lower than or equal to the melting temperature of a nanofibrous sheath (3) of the two-component core yam, wherein during deposition the structure of the flat fabric is saturated with the matrix (5), thereby creating a hierarchically structured self-reinforcing composite system based on polylactic acid biopolymers, which consists of 5 to 35 wt. % of a two-component core yam based on polylactic acid.
2. The method according to claim 1 , characterized in that before forming the fabric, the two-component core yam is heat-fixed by passing through a die at a temperature of 55 to 100 ± 1 °C.
3. The method according to claim 1 or 2, characterized in that the fibrous core (2) from two-component core yam consists of monofilament or multifilament yam from polylactic acid biopolymer.
4. The method according to claim 1 , characterized in that a solution of poly(L-lactide) and a solution of poly(D-lactide) in dichloromethane are prepared separately and after mixing them, dimethyl sulfoxide and pyridine are added to the mixed solution thus obtained.
5. The method according to claim 1 or 4, characterized in that the polymer solution of poly(L-lactide) or symmetric or asymmetric mixture of poly(L- lactide) and poly(D-lactide) is spun by spinning using alternating current, in which
an electrically neutral plume of nanofibers is formed, which moves in the direction of the electric field gradient away from a spinning electrode.
6. The method according to claim 1 , characterized in that at least one layer of fabric from the two-component core yarn based on polylactic acid is inserted between two plates of biopolymer or copolymer of polylactic acid and together with them is exposed to a temperature of 150 to 200 °C for 3 to 8 minutes and then to a temperature of 160 to 200 °C and a pressure of 150 to 250 kN for 15 to 80 seconds, whereby the material of the plates from biopolymer or copolymer of polylactic acid melts, which saturates the structure of the fabric from the two-component core yam based on polylactic acid, without melting the material of the core yam.
7. The method according to claim 1 or 6, characterized in that after saturating the structure of fabric from the two-component core yam based on polylactic acid, the created composite is cooled non-isothermally to a temperature of 50 °C under a pressure of 150 to 250 kN.
8. The method according to claim 1 or 7, characterized in that after saturating the structure of the fabric from the two-component core yam based on polylactic acid, the formed composite is non-isothermally cooled to a temperature of 80 to 120 °C, at which temperature it is maintained for 0.5 to 5 minutes under a pressure of 150 to 250 kN, wherein the matrix material is isothermally crystallized, and then non-isothermally cooled down to a temperature of 50 °C.
9. A hierarchically structured self-reinforcing composite systems based on polylactic acid biopolymers prepared by the method according to any of claims 1 to 8, characterized in that it contains at least one layer of fabric from a two- component core yam composed of a fibrous core (2) from polylactic acid biopolymer and a sheath (3) formed by nanofibers of poly(L-lactide) or symmetric or asymmetric blend of poly(L-lactide) and poly(D-lactide), deposited in a matrix (5) based on polylactic acid biopolymer, wherein the fabric layer is saturated with this matrix (5) and constitutes 5 to 35 wt. % of this composite.
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US20100148404A1 (en) * | 2007-05-29 | 2010-06-17 | Hiroto Smida | Nanofiber spinning method and device |
CZ2016822A3 (en) * | 2016-12-22 | 2018-03-21 | SINTEX, a.s. | A method of producing a linear fibrous structure comprising a polymeric nanofibre coating, a linear fibrous structure formed therefrom, and a fabric formed at least partially by this linear fibrous structure |
US20180355521A1 (en) * | 2015-06-05 | 2018-12-13 | Technicka Univerzita V Liberci | Linear Fibrous Formation with a Coating of Polymeric Nanofibers Enveloping a Supporting Linear Formation Constituting a Core, a Method and a Device for Producing It |
US20190352803A1 (en) * | 2018-05-16 | 2019-11-21 | University Of Georgia Research Foundation, Inc. | Methods and devices for multi-layer nanofibers |
CN110564119A (en) * | 2019-08-23 | 2019-12-13 | 浙江理工大学 | Mulberry silk composite thread reinforced PCL modified PLA biodegradable composite material and preparation method thereof |
US20220136137A1 (en) * | 2020-11-02 | 2022-05-05 | The Secant Group, Llc | Poly(glycerol sebacate) urethane fibers, fabrics formed therefrom, and methods of fiber manufacture |
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US20100148404A1 (en) * | 2007-05-29 | 2010-06-17 | Hiroto Smida | Nanofiber spinning method and device |
US20180355521A1 (en) * | 2015-06-05 | 2018-12-13 | Technicka Univerzita V Liberci | Linear Fibrous Formation with a Coating of Polymeric Nanofibers Enveloping a Supporting Linear Formation Constituting a Core, a Method and a Device for Producing It |
CZ2016822A3 (en) * | 2016-12-22 | 2018-03-21 | SINTEX, a.s. | A method of producing a linear fibrous structure comprising a polymeric nanofibre coating, a linear fibrous structure formed therefrom, and a fabric formed at least partially by this linear fibrous structure |
US20190352803A1 (en) * | 2018-05-16 | 2019-11-21 | University Of Georgia Research Foundation, Inc. | Methods and devices for multi-layer nanofibers |
CN110564119A (en) * | 2019-08-23 | 2019-12-13 | 浙江理工大学 | Mulberry silk composite thread reinforced PCL modified PLA biodegradable composite material and preparation method thereof |
US20220136137A1 (en) * | 2020-11-02 | 2022-05-05 | The Secant Group, Llc | Poly(glycerol sebacate) urethane fibers, fabrics formed therefrom, and methods of fiber manufacture |
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