CN118085697A - PLA barrier film with multi-layer stereocrystal layer and preparation method thereof - Google Patents
PLA barrier film with multi-layer stereocrystal layer and preparation method thereof Download PDFInfo
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- 230000004888 barrier function Effects 0.000 title claims abstract description 66
- 238000002360 preparation method Methods 0.000 title claims abstract description 11
- 229920000747 poly(lactic acid) Polymers 0.000 claims abstract description 62
- 239000011248 coating agent Substances 0.000 claims abstract description 34
- 238000000576 coating method Methods 0.000 claims abstract description 34
- 238000010438 heat treatment Methods 0.000 claims abstract description 21
- 239000001913 cellulose Substances 0.000 claims abstract description 13
- 229920002678 cellulose Polymers 0.000 claims abstract description 13
- 239000002159 nanocrystal Substances 0.000 claims abstract description 5
- RBMHUYBJIYNRLY-UHFFFAOYSA-N 2-[(1-carboxy-1-hydroxyethyl)-hydroxyphosphoryl]-2-hydroxypropanoic acid Chemical compound OC(=O)C(O)(C)P(O)(=O)C(C)(O)C(O)=O RBMHUYBJIYNRLY-UHFFFAOYSA-N 0.000 claims description 77
- JVTAAEKCZFNVCJ-REOHCLBHSA-N L-lactic acid Chemical compound C[C@H](O)C(O)=O JVTAAEKCZFNVCJ-REOHCLBHSA-N 0.000 claims description 77
- 229920001434 poly(D-lactide) Polymers 0.000 claims description 77
- 229920001432 poly(L-lactide) Polymers 0.000 claims description 77
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims description 42
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 27
- 230000005540 biological transmission Effects 0.000 claims description 24
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 15
- 239000011521 glass Substances 0.000 claims description 15
- 238000002844 melting Methods 0.000 claims description 15
- 230000008018 melting Effects 0.000 claims description 15
- 229910052760 oxygen Inorganic materials 0.000 claims description 15
- 239000001301 oxygen Substances 0.000 claims description 15
- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 11
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 9
- 239000003960 organic solvent Substances 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 8
- BYEAHWXPCBROCE-UHFFFAOYSA-N 1,1,1,3,3,3-hexafluoropropan-2-ol Chemical compound FC(F)(F)C(O)C(F)(F)F BYEAHWXPCBROCE-UHFFFAOYSA-N 0.000 claims description 5
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 5
- 239000004626 polylactic acid Substances 0.000 abstract description 58
- 239000000463 material Substances 0.000 abstract description 9
- 239000005022 packaging material Substances 0.000 abstract description 2
- 239000013078 crystal Substances 0.000 abstract 1
- 230000003014 reinforcing effect Effects 0.000 abstract 1
- 239000002245 particle Substances 0.000 description 16
- 238000007664 blowing Methods 0.000 description 12
- 239000013557 residual solvent Substances 0.000 description 12
- 239000002904 solvent Substances 0.000 description 12
- 239000008187 granular material Substances 0.000 description 7
- 239000012528 membrane Substances 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000004014 plasticizer Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229920002472 Starch Polymers 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000007385 chemical modification Methods 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 239000003431 cross linking reagent Substances 0.000 description 2
- 239000012779 reinforcing material Substances 0.000 description 2
- 239000008107 starch Substances 0.000 description 2
- 235000019698 starch Nutrition 0.000 description 2
- 239000004970 Chain extender Substances 0.000 description 1
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- 238000010382 chemical cross-linking Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000013329 compounding Methods 0.000 description 1
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- 239000002270 dispersing agent Substances 0.000 description 1
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- 235000012055 fruits and vegetables Nutrition 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 229920006280 packaging film Polymers 0.000 description 1
- 239000012785 packaging film Substances 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000005014 poly(hydroxyalkanoate) Substances 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 229920006381 polylactic acid film Polymers 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
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- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000012748 slip agent Substances 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
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Abstract
The invention belongs to the technical field of barrier film materials, and discloses a PLA barrier film with a plurality of stereocrystal layers and a preparation method thereof. Alternately coating the L-polylactic acid (PLLA) and the D-polylactic acid (PDLA), reinforcing by adopting cellulose nanocrystals, self-assembling layer by layer to obtain a PLA barrier film, and carrying out heat treatment on the PLA barrier film to induce a plurality of stereo crystal layers, thereby improving the barrier performance of the PLA barrier film. The PLA barrier film material with the multi-layer stereocrystal layer prepared by the invention has the characteristics of biological safety, degradability and high barrier property, and can be used for packaging materials in multiple fields.
Description
Technical Field
The invention belongs to the field of barrier film materials, and particularly relates to a PLA barrier film with a plurality of stereocrystal layers and a preparation method thereof.
Background
Along with the increasing of living standard and the accelerating of living rhythm, the market has great demands for disposable membrane materials with barrier property, but most of the disposable membrane materials are not degradable at present, and environmental pollution is easily caused after the disposable membrane materials are used and abandoned. With the implementation of the national strategy of 'carbon reaching peak', 'carbon neutralization', the development of degradable disposable membranes is particularly urgent in order to reduce the damage of non-degradable petroleum-based disposable membranes to the environment. In view of the excellent degradability and mechanical properties of polylactic acid (PLA), PLA can be used to prepare degradable disposable films.
Polylactic acid (PLA) is a biodegradable thermoplastic polyester. PLA has good biocompatibility, environmental safety and mechanical property, and excellent processability, and the preparation of the disposable membrane material by using the green and environment-friendly PLA has wide application prospect, but has poor barrier property, so that the application of the polylactic acid membrane is limited to a great extent.
At present, the improvement of barrier properties of polylactic acid barrier films is mainly divided into physical and chemical modification. (1) physical modification: the Chinese patent CN201610145386.4 discloses a multi-layer polylactic acid composite barrier high-strength film which is obtained by multi-layer composite and comprises an outer layer polylactic acid hydrophobic film, an intermediate layer polylactic acid barrier film layer and a bottom layer polylactic acid reinforced film. The Chinese patent CN201610277188.3 discloses an environment-friendly packaging film for fruit and vegetable fresh-keeping, which is formed by compounding 4 layers of films, and sequentially comprises a starch reinforced film, a polylactic acid barrier film, a starch antibacterial film and a polylactic acid wear-resistant film at the outer layer, wherein the four layers of films are edge-sealed by hot melt adhesive. (2) chemical modification: a biodegradable PLA film having improved transparency and heat shrinkage and a method of manufacturing the same are disclosed in korean patent KR 1020200054228. Adding PLA, PHA, plasticizer, silicon dioxide, dispersing agent, slip agent, chain extender and antioxidant, extruding the granules in a T-type extruder. The polylactic acid barrier film prepared by the patent is prepared by adding a reinforcing material and PLA for chemical crosslinking, so that a film with improved barrier performance is obtained, and most of the reinforcing materials are chemical reagents such as plasticizers, crosslinking agents and the like, so that hidden danger exists in the aspect of biological safety.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention provides a PLA barrier film with a plurality of stereocrystalline layers and a preparation method thereof. The PLA barrier film material has the characteristics of biological safety, degradability and high barrier property, and can be used for packaging materials in multiple fields
The invention provides a preparation method of a PLA barrier film with a plurality of stereocrystal layers, which comprises the following steps:
S1, adding PLLA (L-polylactic acid) and Cellulose Nanocrystalline (CNC) into an organic solvent to prepare PLLA solution; adding PDLA (right-handed polylactic acid) and cellulose nanocrystals into an organic solvent to prepare a PDLA solution;
S2, alternately coating the PLLA solution and the PDLA solution on a glass plate, and performing heat treatment after drying to obtain the PLA barrier film with a plurality of stereocrystal layers.
Further, in the step S1, the melting points of PLLA and PDLA are 160-180 ℃; in the PLLA solution, the concentration of PLLA is 4-8wt%, and the addition amount of cellulose nanocrystalline is 0.5-2% of PLLA mass; the concentration of PDLA in the PDLA solution is 4-8wt%, and the addition amount of the cellulose nanocrystalline is 0.5-2% of the mass of the PDLA.
Further, in step S1, the organic solvent is one of chloroform, hexafluoroisopropanol, tetrahydrofuran and N, N-dimethylformamide.
Further, in step S2, the total thickness of the coating is 800-1000 μm.
Further, in step S2, the drying is: placing in a blast oven at 60-80deg.C for 4-24 hr for drying.
Further, in step S2, the heat treatment is: placing into a blast oven for heat treatment at 140-185 ℃ for 30-60min.
The invention also provides the PLA barrier film prepared by the preparation method, and the number of the stereocrystal layers of the PLA barrier film is 3-7.
Further, the PLA barrier film has a film thickness of 100-180 μm, an oxygen transmission amount of 5-20cm 3/(m2.24 h.0.1 MPa, and a water vapor transmission rate of 75X 10 -16-95×10-16kg·m/(m2 s.Pa).
Compared with the prior art, the invention is characterized in that the reinforcing agents such as a micromolecule cross-linking agent, a plasticizer and the like are not added, CNC is added into the PLLA solution and the PDLA solution, then the PLLA solution and the PDLA solution are alternately coated, and a continuous stereocrystal layer is induced by a heat treatment process, so that the barrier property is regulated and controlled, the water vapor transmission amount and the oxygen transmission rate are reduced, and the layer-by-layer self-assembled barrier film has the characteristics of high biosafety, degradability and high barrier property, has low manufacturing cost, can be better applied to the field of environment-friendly functional materials, and meets the production requirements of the polymer material industry.
Drawings
Fig. 1 is a flowchart of the preparation of the PLA barrier film provided by the invention.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the preparation method of the PLA barrier film with a plurality of stereocrystal layers provided by the invention comprises the following steps: the method comprises the following steps:
S1, adding PLLA and Cellulose Nanocrystalline (CNC) into an organic solvent to prepare PLLA solution; adding PDLA and cellulose nanocrystals into an organic solvent to prepare a PDLA solution; the PLLA and the PDLA are preferably materials with melting points of 160-180 ℃; in the PLLA solution, the concentration of PLLA is 4-8wt%, and the addition amount of cellulose nanocrystalline is 0.5-2% of PLLA mass; the concentration of PDLA in the PDLA solution is 4-8wt%, and the addition amount of the cellulose nanocrystalline is 0.5-2% of the mass of the PDLA. The organic solvent is preferably one of chloroform, hexafluoroisopropanol, tetrahydrofuran and N, N-dimethylformamide.
S2, alternately coating PLLA solution and PDLA solution on a glass plate to obtain a layer-by-layer self-assembled PLA barrier film, wherein the coating thickness is preferably 800-1000 mu m; the total number of coating times is 4-8.
S3, drying the layer-by-layer self-assembled PLA barrier film obtained in the step S2, and then performing heat treatment to obtain the PLA barrier film with the multi-layer stereocrystal layer. In theory, PLLA and PDLA are coated at intervals, the coating times are 4-8 times, the interface where PLLA/PDLA contacts is a layer of stereocrystal layer, and the stereocrystal layer of the PLA barrier film is 3-7 layers. The drying mode is preferably drying for 4-24 hours by adopting a blast oven at 60-80 ℃. The heat treatment mode is preferably to use a blast oven at 140-185 ℃ for heat treatment for 30-60min.
Example 1
(1) PLLA and PDLA particles with the corresponding mass and melting point of 160 ℃ are weighed and dried at 70 ℃ for 24 hours, then PLLA and PDLA particles are respectively dissolved in Chloroform (CHL), and CNC with the mass of 0.5% of PLLA or PDLA is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating the PLLA solution and the PDLA solution obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 800 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 24 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film obtained in the step (3) in a baking oven at 140 ℃ for 30min for heat treatment to obtain the PLA barrier film with the multi-layer stereocrystal layer. The thickness of the PLA barrier film obtained was 174. Mu.m, the oxygen transmission amount was 20cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 95X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 2
(1) PLLA and PDLA particles with the corresponding mass and melting point of 160 ℃ are weighed and dried at 70 ℃ for 24 hours, then PLLA and PDLA particles are respectively dissolved in Hexafluoroisopropanol (HFIP), and CNC with the mass of PLLA or PDLA of 1% is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating the PLLA solution and the PDLA solution obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 1000 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 70 ℃ for 10 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film obtained was 142. Mu.m, the oxygen transmission amount was 18cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 93X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 3
(1) PLLA and PDLA particles with the corresponding mass and melting point of 180 ℃ are weighed, dried at 70 ℃ for 24 hours, then the PLLA and PDLA particles are respectively dissolved in Tetrahydrofuran (THF), and CNC accounting for 1% of the mass of the PLLA or PDLA is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating the PLLA solution and the PDLA solution obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 1000 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 80 ℃ for 4 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film was 146. Mu.m, the oxygen transmission amount was 18cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 94X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 4
(1) PLLA and PDLA particles with the corresponding mass and melting point of 180 ℃ are weighed, dried at 70 ℃ for 24 hours, then PLLA and PDLA particles are respectively dissolved in DMF, and CNC accounting for 1% of the mass of PLLA or PDLA is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating PLLA and PDLA solutions on a glass plate by adopting an adjustable coater under the room temperature condition, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 1000 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 20 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 40min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film obtained was 123. Mu.m, the oxygen transmission amount was 17cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 86X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 5
(1) PLLA and PDLA particles with the corresponding mass and melting point of 180 ℃ are weighed and dried at 70 ℃ for 24 hours, then PLLA and PDLA particles are respectively dissolved in Chloroform (CHL), and CNC with the mass of 1.5% of PLLA or PDLA is respectively added to obtain a 6wt% PLLA solution and a 6wt% PDLA solution.
(2) And (3) alternately coating the PLLA solution and the PDLA solution obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 800 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 8 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 140 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film obtained was 174. Mu.m, the oxygen transmission amount was 13cm 3/(m2. Multidot.24 h.multidot.0.1 MPa, and the water vapor transmission rate was 93X 10 -16kg·m/(m2. Multidot.s.Pa).
Example 6
(1) PLLA and PDLA particles with the corresponding mass and melting point of 160 ℃ are weighed and dried at 70 ℃ for 24 hours, then PLLA and PDLA particles are respectively dissolved in Chloroform (CHL), and CNC with the mass of 1.5% of PLLA or PDLA is respectively added to obtain 8wt% PLLA solution and 8wt% PDLA solution.
(2) And (3) alternately coating the PLLA and PDLA solutions in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 4 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 800 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 15 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 140 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film was 167. Mu.m, the oxygen transmission amount was 15cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 90X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 7
(1) PLLA and PDLA particles with the corresponding mass and melting point of 180 ℃ are weighed, dried at 70 ℃ for 24 hours, then the PLLA and PDLA particles are respectively dissolved in Chloroform (CHL), and CNC with the mass of 1.8% of the PLLA or PDLA is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating the PLLA and PDLA solutions obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 6 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 1000 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 15 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film obtained was 161. Mu.m, the oxygen transmission amount was 9cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 81X 10 -16kg·m/(m2. Multidot.s. Pa).
Example 8
(1) PLLA and PDLA particles with the corresponding mass and melting point of 180 ℃ are weighed, dried at 70 ℃ for 24 hours, then the PLLA and PDLA particles are respectively dissolved in Chloroform (CHL), and CNC with the mass of 2% of PLLA or PDLA is respectively added to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) And (3) alternately coating the PLLA and PDLA solutions obtained in the step (1) on a glass plate by adopting an adjustable coater at room temperature, wherein the coating times are 8 times, the thickness of each layer of solution is kept basically consistent, and the total coating thickness is 1000 mu m.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 24 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 30min for heat treatment to obtain the PLA barrier film with a plurality of stereocrystal layers. The thickness of the PLA barrier film obtained was 135. Mu.m, the oxygen transmission amount was 5cm 3/(m2. Multidot.24 h.multidot.0.1 MPa, and the water vapor transmission rate was 75X 10 -16kg·m/(m2. Multidot.s.Pa).
Comparative example 1
(1) PLLA granules having a melting point of 180℃were weighed and dried at 70℃for 24 hours, and then dissolved in Chloroform (CHL) to obtain a 4wt% PLLA solution.
(2) The PLLA solution was applied to the glass plate using an adjustable applicator at room temperature for 1 pass with a total thickness of 1000 μm.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 48 hours to volatilize the water and the residual solvent. The thickness of the PLLA barrier film was 28. Mu.m, the oxygen permeation amount was 491cm 3/(m2. Multidot.24 h.multidot.0.1 MPa, and the water vapor permeation rate was 125X -16kg·m/(m2. Multidot.s.Pa).
Comparative example 2
(1) The PDLA granules with the corresponding mass and 180 ℃ melting point were weighed and dried at 70 ℃ for 24 hours, and then dissolved in Chloroform (CHL) to obtain 4wt% PDLA solution.
(2) The PDLA solution was applied to a glass plate using an adjustable coater at room temperature for 1 pass with a total thickness of 1000 μm.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 24 hours to volatilize the water and the residual solvent. The thickness of the PDLA barrier film was 20. Mu.m, the oxygen permeation amount was 480cm 3/(m2. Multidot.24 h.multidot.0.1 MPa, and the water vapor permeation rate was 130X 10 -16kg·m/(m2. Multidot.s.Pa).
Comparative example 3
(1) PLLA and PDLA granules with the corresponding mass and melting point of 180 ℃ are weighed, dried at 70 ℃ for 24 hours, and then the PLLA and PDLA granules are blended and dissolved in Chloroform (CHL) to obtain 4wt% PLLA and PDLA blend solution.
(2) The blend solution was applied to a glass plate using an adjustable coater at room temperature for 1 pass with a total thickness of 1000 μm.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 24 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 200 ℃ for 30min for heat treatment to obtain the PLA barrier film with the stereocrystal. The thickness of the obtained PLLA and PDLA blend barrier film was 23. Mu.m, the oxygen permeation amount was 300cm 3/(m2.24 h.0.1 MPa, and the water vapor permeation rate was 110X 10 -16kg·m/(m2 s.Pa).
Comparative example 4
(1) PLLA and PDLA granules with the corresponding mass and melting point of 160 ℃ are weighed, dried at 70 ℃ for 24 hours, and then the PLLA and PDLA granules are respectively dissolved in Chloroform (CHL) to obtain 4wt% PLLA solution and 4wt% PDLA solution.
(2) The PLLA and PDLA solutions were alternately coated on the glass plates using an adjustable coater at room temperature for 4 times, keeping the thickness of each layer of solution substantially uniform, with a total coating thickness of 800 μm.
(3) And (3) placing the film obtained in the step (2) at room temperature for 24 hours to fully volatilize the solvent, and placing the film in an electrothermal blowing oven at 60 ℃ for 24 hours to volatilize the water and the residual solvent.
(4) And (3) placing the film in the step (3) in a baking oven at 140 ℃ for 30min for heat treatment, and obtaining the PLA barrier film with the multilayer structure. The thickness of the PLA barrier film obtained was 174. Mu.m, the oxygen transmission amount was 68cm 3/(m2. Multidot.24 h. Multidot.0.1 MPa, and the water vapor transmission rate was 102X 10 -16kg·m/(m2. Multidot.s. Pa).
Claims (8)
1. A method for preparing a PLA barrier film with multiple stereocrystalline layers, comprising the steps of:
S1, adding PLLA and cellulose nanocrystals into an organic solvent to prepare PLLA solution; adding PDLA and cellulose nanocrystals into an organic solvent to prepare a PDLA solution;
S2, alternately coating the PLLA solution and the PDLA solution on a glass plate, and performing heat treatment after drying to obtain the PLA barrier film with a plurality of stereocrystal layers.
2. The method according to claim 1, wherein in step S1, the melting points of PLLA and PDLA are each 160-180 ℃; in the PLLA solution, the concentration of PLLA is 4-8wt%, and the addition amount of cellulose nanocrystalline is 0.5-2% of PLLA mass; the concentration of PDLA in the PDLA solution is 4-8wt%, and the addition amount of cellulose nanocrystalline is 0.5-2% of the mass of PDLA.
3. The method according to claim 1, wherein in step S1, the organic solvent is one of chloroform, hexafluoroisopropanol, tetrahydrofuran and N, N-dimethylformamide.
4. The method of claim 1, wherein in step S2, the total thickness of the coating is 800-1000 μm.
5. The method according to claim 1, wherein in step S2, the drying is: placing in a blast oven at 60-80deg.C for 4-24 hr for drying.
6. The method according to claim 1, wherein in step S2, the heat treatment is: placing into a blast oven for heat treatment at 140-185 ℃ for 30-60min.
7. The PLA barrier film prepared by the preparation method of any one of claims 1 to 6, wherein the number of the stereocrystal layers of the PLA barrier film is 3 to 7.
8. The PLA barrier film of claim 7, wherein the PLA barrier film has a film thickness of 100-180 μm, an oxygen transmission of 5-20cm 3/(m2 -24 h 0.1 MPa), and a water vapor transmission of 75 x 10 -16-95×10- 16kg·m/(m2 s Pa.
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