CN114806113A - Heat-resistant antibacterial PLA full-biodegradable straw and preparation method thereof - Google Patents
Heat-resistant antibacterial PLA full-biodegradable straw and preparation method thereof Download PDFInfo
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- CN114806113A CN114806113A CN202210328390.XA CN202210328390A CN114806113A CN 114806113 A CN114806113 A CN 114806113A CN 202210328390 A CN202210328390 A CN 202210328390A CN 114806113 A CN114806113 A CN 114806113A
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- 239000010902 straw Substances 0.000 title claims abstract description 109
- 230000000844 anti-bacterial effect Effects 0.000 title claims abstract description 58
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
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- 229920000747 poly(lactic acid) Polymers 0.000 claims abstract description 82
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- 239000007822 coupling agent Substances 0.000 claims abstract description 41
- 238000002425 crystallisation Methods 0.000 claims abstract description 30
- 230000008025 crystallization Effects 0.000 claims abstract description 30
- 238000000034 method Methods 0.000 claims abstract description 26
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- IMQLKJBTEOYOSI-UHFFFAOYSA-N Phytic acid Natural products OP(O)(=O)OC1C(OP(O)(O)=O)C(OP(O)(O)=O)C(OP(O)(O)=O)C(OP(O)(O)=O)C1OP(O)(O)=O IMQLKJBTEOYOSI-UHFFFAOYSA-N 0.000 claims description 2
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- 235000021355 Stearic acid Nutrition 0.000 claims description 2
- BGYHLZZASRKEJE-UHFFFAOYSA-N [3-[3-(3,5-ditert-butyl-4-hydroxyphenyl)propanoyloxy]-2,2-bis[3-(3,5-ditert-butyl-4-hydroxyphenyl)propanoyloxymethyl]propyl] 3-(3,5-ditert-butyl-4-hydroxyphenyl)propanoate Chemical compound CC(C)(C)C1=C(O)C(C(C)(C)C)=CC(CCC(=O)OCC(COC(=O)CCC=2C=C(C(O)=C(C=2)C(C)(C)C)C(C)(C)C)(COC(=O)CCC=2C=C(C(O)=C(C=2)C(C)(C)C)C(C)(C)C)COC(=O)CCC=2C=C(C(O)=C(C=2)C(C)(C)C)C(C)(C)C)=C1 BGYHLZZASRKEJE-UHFFFAOYSA-N 0.000 claims description 2
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 2
- FLISWPFVWWWNNP-BQYQJAHWSA-N dihydro-3-(1-octenyl)-2,5-furandione Chemical compound CCCCCC\C=C\C1CC(=O)OC1=O FLISWPFVWWWNNP-BQYQJAHWSA-N 0.000 claims description 2
- FPAFDBFIGPHWGO-UHFFFAOYSA-N dioxosilane;oxomagnesium;hydrate Chemical compound O.[Mg]=O.[Mg]=O.[Mg]=O.O=[Si]=O.O=[Si]=O.O=[Si]=O.O=[Si]=O FPAFDBFIGPHWGO-UHFFFAOYSA-N 0.000 claims description 2
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- RKISUIUJZGSLEV-UHFFFAOYSA-N n-[2-(octadecanoylamino)ethyl]octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(=O)NCCNC(=O)CCCCCCCCCCCCCCCCC RKISUIUJZGSLEV-UHFFFAOYSA-N 0.000 claims description 2
- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 claims description 2
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- SSDSCDGVMJFTEQ-UHFFFAOYSA-N octadecyl 3-(3,5-ditert-butyl-4-hydroxyphenyl)propanoate Chemical compound CCCCCCCCCCCCCCCCCCOC(=O)CCC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 SSDSCDGVMJFTEQ-UHFFFAOYSA-N 0.000 claims description 2
- FATBGEAMYMYZAF-KTKRTIGZSA-N oleamide Chemical compound CCCCCCCC\C=C/CCCCCCCC(N)=O FATBGEAMYMYZAF-KTKRTIGZSA-N 0.000 claims description 2
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-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
- C08L67/04—Polyesters derived from hydroxycarboxylic acids, e.g. lactones
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G81/00—Macromolecular compounds obtained by interreacting polymers in the absence of monomers, e.g. block polymers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2201/00—Properties
- C08L2201/06—Biodegradable
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2201/00—Properties
- C08L2201/08—Stabilised against heat, light or radiation or oxydation
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
- Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- Biological Depolymerization Polymers (AREA)
Abstract
The invention discloses a heat-resistant antibacterial PLA full-biodegradable straw which comprises the following components in parts by mass: 100 parts of polylactic acid, 1-20 parts of inorganic filler, 1-5 parts of functionalized modified crystallization nucleating agent, 0.5-1 part of first coupling agent, 0.2-0.5 part of antioxidant and 0.5-4 parts of lubricant, wherein the functionalized modified crystallization nucleating agent is carboxylated nano microfibrillated cellulose grafted chitosan. The full-biodegradation straw takes the carboxylated nano microfibrillar cellulose grafted chitosan as the functionalized modified crystallization nucleating agent, the crystallinity of the straw material is improved and the crystallization period is shortened through the functionalized modified crystallization nucleating agent, and the method for improving the crystallinity is more economical, so that the heat resistance of the straw is improved, the mechanical property of the straw is improved, and the problems that the current pure PLA straw has poor heat resistance and a small use range are solved. The preparation method of the straw is simple, easy to machine and form and low in cost, and is beneficial to large-scale industrial production.
Description
Technical Field
The invention relates to the field of biodegradable materials, in particular to a heat-resistant antibacterial PLA full-biodegradable straw and a preparation method thereof.
Background
The straw is a common product in daily life, is widely applied to the fields of food, catering and medicine, and brings great convenience to the life of people. However, the conventional straw is made of plastic materials such as polypropylene, which cannot be degraded in the natural environment. The disposable straws are used and discarded in a large amount, which causes great harm to soil, atmosphere and ocean. With the rapid development of the industries such as takeaway and tea drinking in China, the demand of the disposable plastic straws is increased sharply, and according to big data, 15 hundred million disposable plastic straws can be used in one day in China. Therefore, the development of the environment-friendly plastic straw is extremely important for environmental protection and industrial development.
The biodegradable plastic straw can satisfy the above requirements, wherein polylactic acid (PLA) is a good material for preparing the biodegradable plastic straw. The biomass is derived from biomass such as starch, cellulose and the like, can be composted and degraded into carbon dioxide and water under the action of microorganisms after being discarded, and is a bio-based fully biodegradable green high polymer material. PLA has the service performance very close to that of polypropylene, and when used as a straw, the PLA has enough strength and hardness, good water resistance and solvent resistance, and is nontoxic and tasteless. However, PLA has a slow crystallization rate, and the Heat Distortion Temperature (HDT) of PLA products in industrial production is only about 58 ℃, which is poor in heat resistance, thereby limiting heat-resistant applications of PLA straws.
The reason for the poor heat resistance of the PLA straw is that the crystallization speed of PLA is slow and the crystallinity of the product is low. The ester groups on the PLA main chain only have one methylene carbon atom, the molecular chain is in a spiral conformation, the mobility of the molecular chain is much lower than that of PET, and the crystallization is hardly caused in the processing and forming process. Cellulose particles increase crystallinity and are an effective method for improving the heat resistance of PLA straws. In the prior art of cellulose reinforced polylactic acid materials, chinese patent application No. CN202110755637.1 discloses a rare earth modified fiber reinforced polylactic acid and a preparation method thereof, which combines a solution blending method and a hot pressing method to improve the compactness of cellulose fibers and polylactic acid and fix the orientation of cellulose fibers, and finally obtains biodegradable rare earth modified fiber reinforced polylactic acid with ultrahigh tensile strength and tensile modulus. The Chinese patent application with the application number of CN202110362497.1 discloses a preparation method of a high-length-diameter-ratio bamboo cellulose nanofiber-reinforced polylactic acid composite material, which carries out enzymolysis, oxidation and modification treatment on bamboo cellulose, further improves the interface compatibility of the treated bamboo cellulose and polylactic acid, realizes better fusion of the polylactic acid and the bamboo fiber, and plays a role in strengthening and toughening.
In addition, the straw is generally in contact with human bodies and food when in use, when an outer packaging plastic bag of the straw is damaged or the outer packaging paper bag is moistened and damaged, bacteria are easily bred in the straw inside, so that the antibacterial property of the straw material is very important, and the antibacterial property of the straw on the market is generally poor.
Disclosure of Invention
The invention aims to solve the technical problem that aiming at the defects of the prior art, the invention provides the heat-resistant antibacterial PLA full-biodegradable straw and the preparation method thereof, which can improve the high-temperature resistance of the straw and endow the straw with good antibacterial property.
The technical scheme adopted by the invention for solving the technical problems is as follows: a heat-resistant antibacterial PLA full-biodegradable straw comprises the following components in parts by mass: 100 parts of polylactic acid, 1-20 parts of inorganic filler, 1-5 parts of functionalized modified crystallization nucleating agent, 0.5-1 part of first coupling agent, 0.2-0.5 part of antioxidant and 0.5-4 parts of lubricant, wherein the functionalized modified crystallization nucleating agent is carboxylated nano microfibrillated cellulose grafted chitosan.
The heat-resistant antibacterial PLA full-biodegradation straw takes the carboxylated nano microfibrillated cellulose grafted chitosan as the functionalized modified crystallization nucleating agent, the crystallization degree of the straw material is improved and the crystallization period is shortened through the functionalized modified crystallization nucleating agent, and the method for improving the crystallization degree is economic, so that the heat resistance of the straw is improved, the mechanical property of the straw is improved, and the current situations of poor heat resistance and small use range of the current pure PLA straw are solved.
The functionalized modified crystallization nucleating agent adopted by the invention is carboxylated nano microfibrillated cellulose grafted chitosan. The nano microfibrillated cellulose (NFC) is a material with a three-dimensional network structure, not only has nano microfiber fibers, but also has a nano network structure, has large specific surface area, high strength, high crystallinity and good chemical activity and biocompatibility, and can form more mechanical lock catches with polymer molecules, so that PLA molecular chains inside the material are more easily attached to the NFC for crystallization, a crystallization area with regular orientation and compact structure is formed, and the high temperature resistance and toughness of the material can be greatly improved. In addition, DSC test and analysis of the inventor show that the NFC serving as the nucleating agent material can accelerate crystallization growth and enhance heterogeneous nucleation, compared with pure PLA, the crystal nucleus density is improved, the spherulite size is reduced, the crystallization speed is accelerated, the rheological property and the crystallization characteristic of the PLA are remarkably improved, and meanwhile, the degradation performance test and analysis show that the degradation rate of the straw material is remarkably increased along with the increase of the content of the NFC.
Chitosan is similar to nano microfibrillated cellulose in chemical structure, except that the C2 position is amino and hydroxyl respectively, so that it can be graft-modified. The chitosan has broad-spectrum antibacterial activity, has obvious inhibition effect on the growth of dozens of bacteria and fungi, and endows the straw with excellent antibacterial property.
Preferably, the preparation process of the carboxylated nano microfibrillated cellulose grafted chitosan comprises the following steps:
a) preparing nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid, water, an alkaline catalyst, an esterifying agent and a second coupling agent, wherein the mass part ratio of the nano microfibrillated cellulose to the chitosan is 80: 1-5: 200-250: 5-20: 300-500: 5: 1-1.5: 0.5-1;
b) adding the prepared nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid and water into a ball milling tank of a planetary ball mill for ball milling, wherein a grinding medium is zirconia or ceramic balls, the temperature is 40-70 ℃, the ball milling revolution speed is 80-120 rpm, the rotation speed is 150-200 rpm, and the ball milling time is 30-120 min;
c) after the step b) is finished, adding the prepared alkaline catalyst, esterification agent and second coupling agent into a ball milling tank, and continuously milling at the temperature of 50-80 ℃, the ball milling revolution speed of 100-140 rpm, the rotation speed of 160-220 rpm, and the ball milling time of 40-120 min;
d) and c), after the step c) is finished, taking out the powder in the ball milling tank, putting the powder into a drying oven, and drying at the temperature of 80-105 ℃ to be completely dry to obtain the carboxylated nano microfibrillated cellulose grafted chitosan.
The chitosan surface has a large amount of hydroxyl and amino, so that the hydroxyl on the chitosan surface is firstly carboxylated by chloroacetic acid in the process of preparing the carboxylated nano microfibrillated cellulose grafted chitosan; the surface of the nanometer microfibrillated cellulose (NFC) is provided with a large amount of hydroxyl, so that the NFC has higher polarity, and the compatibility of the NFC and an organic matrix is not strong.
According to the invention, through a ball milling mode, unreacted hydroxyl groups on positions C2 and C3 of NFC or positions C6 and modified carboxyl groups on chitosan are subjected to esterification reaction, and simultaneously, the modified carboxyl groups on the NFC and amino groups on the position C2 of the chitosan are subjected to amide reaction, so that the finally compounded carboxylated nano microfibrillated cellulose grafted chitosan (NFC-CS) has excellent biocompatibility and biodegradability, and as a functional modified crystallization nucleating agent, on one hand, the crystallinity of a straw material serving as a biological composite material is improved, the heat resistance temperature and the mechanical property of the straw material are obviously improved, and on the other hand, the chitosan can improve the antibacterial property of the straw material. In addition, the invention carries out ball milling on the mixture of the nano microfibrillated cellulose, the chitosan and the like by a specific grinding medium under specific grinding conditions in a ball milling mode, and the mechanical force generated by the ball milling can destroy the crystal structure, reduce the particle size, even break molecular chains, expose more groups on the cellulose and the chitosan, and is beneficial to the carboxylation and the grafting modification of the cellulose and the chitosan. The invention enables all phases to be uniformly dispersed by ball milling, is beneficial to the esterification reaction when the nano microfibrillated cellulose and chitosan are grafted, is beneficial to the implementation of the amide reaction, and can effectively avoid the agglomeration of the nano microfibrillated cellulose due to overlarge polarity. Under the action of extremely strong impact force, shearing force and friction force generated by ball milling, the collision probability among substances is increased due to the action of mechanical force on the nano microfibrillated cellulose, the chitosan, the alkaline catalyst solution and the esterifying agent, so that the contact state of reactants is obviously improved, and the problems of poor reaction uniformity and the like existing in solid-phase reaction are effectively solved.
The preparation method of the straw utilizes the natural chemical structural characteristics of the nano microfibrillated cellulose and the chitosan to graft the chitosan after the nano microfibrillated cellulose is carboxylated so as to enable the nano microfibrillated cellulose to become the functionalized modified crystallization nucleating agent. The straw prepared by the method has high crystallinity, good heat resistance and good antibacterial performance.
Further, the alkaline catalyst is one or a combination of more of NaOH, KOH, sodium methoxide and sodium carbonate; the esterifying agent is one or a combination of more of anhydrous sodium acetate, propionate, maleic anhydride and octenyl succinic anhydride; the second coupling agent is a titanate coupling agent or an aluminate coupling agent. Specifically, the second coupling agent may be selected from titanate coupling agent 101, titanate coupling agent 102, and titanate coupling agent 105, or selected from aluminate coupling agent DL-411, aluminate coupling agent DL-411AF, aluminate coupling agent DL-411D, and aluminate coupling agent DL-411D.
Further, the chitosan is acid-soluble chitosan, and is dried for 10-18 hours at the temperature of 80-105 ℃ before the ball milling in the step b).
Preferably, the inorganic filler is one or a combination of several of talcum powder, calcium carbonate, silicon dioxide and barium sulfate, the first coupling agent is a silane coupling agent, the antioxidant is one or a combination of several of tea polyphenol, phytic acid, antioxidant 1010, antioxidant 168, antioxidant 1076 and antioxidant 1790, and the lubricant is one or a combination of several of stearic acid, ethylene bis stearamide, oleamide and erucamide. The inorganic filler has low price and can reduce the material cost. Specifically, the first coupling agent may be a silane coupling agent such as KH550, KH570, a171, KH590, or a 151.
A preparation method of the heat-resistant antibacterial PLA full-biodegradable straw comprises the following steps:
1) extracting alpha cellulose from plant raw materials, swelling, and mechanically shearing the alpha cellulose at a high speed to prepare nano microfibrillated cellulose;
2) uniformly mixing polylactic acid, inorganic filler, carboxylated nano microfibrillated cellulose grafted chitosan, a first coupling agent, an antioxidant and a lubricant at a high speed to obtain a premix;
3) and melting and blending the obtained premix, extruding and molding, cooling and cutting, and annealing to obtain the heat-resistant antibacterial PLA full-biodegradable straw.
Preferably, the specific process of step 1) is as follows: firstly, crushing plant fibers into particles of 40-100 meshes, bleaching with 10-15% of sodium chlorite by mass for 0.5-3 h, drying, treating with 2-6% of sodium hydroxide by mass for 0.5-2 h, filtering, and washing with water to be neutral to obtain alpha cellulose; secondly, adding the alpha cellulose into a urea alkali solution according to a solid-to-liquid ratio of 1: 5-8 for swelling treatment for 1-5 hours at a treatment temperature of 20-60 ℃ to obtain swelled alpha cellulose, wherein the mass ratio of sodium hydroxide, urea and pure water in the urea alkali solution is 5-10: 10-15: 80-85; and finally, mechanically shearing the swollen alpha cellulose at a high speed for 0.5-3 h, centrifugally washing the swollen alpha cellulose at a rotating speed of 8000-12000 rpm until the swollen alpha cellulose is neutral, and freeze-drying the precipitate to obtain the white nano microfibrillated cellulose.
Further, the specific process of step 2) is as follows: firstly, drying polylactic acid at 50-80 ℃ to be absolute dry, drying an inorganic filler at 80-105 ℃ to be absolute dry, then mixing the inorganic filler, a first coupling agent, an antioxidant and a lubricant at a low speed of 100-300 rpm for 5-10 min to obtain a mixture, then adding the polylactic acid and the carboxylated nano microfibrillated cellulose grafted chitosan into the mixture, and mixing at a high speed of 300-600 rpm at a temperature of 50-70 ℃ for 5-15 min to obtain the premix.
Further, the specific process of step 3) is as follows: putting the obtained premix into a double-screw extruder or an internal mixer for melt blending, and then extruding and granulating to obtain blended granules; then placing the obtained blended granules in a single-screw extruder, extruding and molding through a circular die head, cooling to 20-40 ℃, and cutting into a straw; and then annealing the obtained straw at 100-120 ℃ for 3-10 min to obtain the heat-resistant antibacterial PLA full-biodegradable straw.
Further, the temperature of extrusion granulation is 100-190 ℃, the temperature of extrusion molding is 130-190 ℃, and the heating mode of annealing treatment is infrared heating, microwave heating or blast heating.
Compared with the prior art, the invention has the following advantages:
(1) the heat-resistant antibacterial PLA full-biodegradable straw material has excellent heat resistance and wide application range, and can be applied to the field of other biodegradable materials besides straws.
(2) The straw of the invention is made of raw materials without environment-friendly materials, and compared with the traditional polypropylene straw, the straw of the invention belongs to a full-biodegradable straw, and is a compostable full-biodegradable material.
(3) The raw materials of the straw are biodegradable natural antibacterial chitosan, so that the straw has excellent antibacterial property.
(4) The preparation method of the straw is simple, easy to machine and form and low in cost, and is beneficial to large-scale industrial production.
Drawings
FIG. 1 shows the tensile strength and impact strength of heat-resistant antibacterial PLA full-biodegradation straw with different addition amounts of functionalized modified crystallization nucleating agents;
FIG. 2 shows the crystallinity and heat-resistant temperature of heat-resistant antibacterial PLA full biodegradation straw with different addition amounts of functionalized modified crystallization nucleating agent;
FIG. 3 shows the tensile strength and impact strength of heat-resistant antibacterial PLA full-biodegradable straws with different inorganic filler addition amounts;
FIG. 4 shows the crystallinity and heat-resistant temperature of heat-resistant antibacterial PLA full biodegradation straw with different inorganic filler addition amounts;
FIG. 5 shows the tensile strength and impact strength of heat-resistant antibacterial PLA full-biodegradable straws with different addition amounts of esterifying agents;
FIG. 6 shows the crystallinity and heat-resistant temperature of heat-resistant antibacterial PLA full biodegradation straws with different addition amounts of esterifying agents;
FIG. 7 shows the tensile strength and impact strength of heat-resistant antibacterial PLA full-biodegradable straws with different chitosan addition amounts;
FIG. 8 shows the crystallinity and heat-resistant temperature of heat-resistant antibacterial PLA full biodegradation straws with different chitosan addition amounts;
FIG. 9 shows the bacteriostatic rates of the heat-resistant antibacterial PLA full-biodegradation straw on Escherichia coli and Staphylococcus aureus with different chitosan addition amounts.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
The compositions of the heat-resistant antibacterial PLA full-biodegradable straws of examples 1 to 5 in parts by mass are shown in Table 1, and the single-factor experiments were performed by respectively designating examples 1 to 5 as numbers C1, C2, C3, C4 and C5.
TABLE 1
The preparation method of the heat-resistant antibacterial PLA full-biodegradable straw in the embodiment 1 comprises the following steps:
1) extracting alpha cellulose from plant raw materials, swelling, and mechanically shearing the alpha cellulose at a high speed to prepare nano microfibrillated cellulose; the specific process is as follows: firstly, crushing plant fibers into 50-mesh particles, bleaching the particles with 10 mass percent of sodium chlorite for 1 hour, drying the particles, treating the particles with 5 mass percent of sodium hydroxide for 1 hour, filtering the particles, and washing the particles with water to be neutral to obtain alpha cellulose; secondly, adding the alpha cellulose into a urea alkali solution according to a solid-liquid ratio of 1:5 for swelling treatment for 3 hours at a treatment temperature of 50 ℃ to obtain swelled alpha cellulose, wherein the mass ratio of sodium hydroxide, urea and pure water in the urea alkali solution is 5:10: 80; finally, mechanically shearing the swollen alpha cellulose at a high speed for 1.5h, then centrifugally washing the swollen alpha cellulose at a rotating speed of 8000rpm until the swollen alpha cellulose is neutral, and freeze-drying a precipitate to obtain white nano microfibrillated cellulose;
2) preparing carboxylated nano microfibrillated cellulose grafted chitosan:
a) preparing nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid, water, an alkaline catalyst, an esterifying agent and a second coupling agent, wherein the mass part ratio of the nano microfibrillated cellulose to the chitosan is 80:3:200:15:400:5:1.5: 1;
b) adding the prepared nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid and water into a ball milling tank of a planetary ball mill for ball milling, wherein a grinding medium adopts zirconia or ceramic balls, the temperature is 50 ℃, the ball milling revolution speed is 100rpm, the rotation speed is 150rpm, and the ball milling time is 80 min;
c) after the step b) is finished, adding the prepared alkaline catalyst, esterifying agent and second coupling agent into a ball milling tank, and continuously milling at the temperature of 60 ℃, the ball milling revolution speed of 100rpm, the rotation speed of 180rpm and the ball milling time of 100 min;
d) after the step c) is finished, taking out the powder in the ball milling tank, putting the powder into a drying oven, and drying at 105 ℃ to be absolutely dry to obtain carboxylated nano microfibrillated cellulose grafted chitosan;
3) uniformly mixing polylactic acid, inorganic filler, carboxylated nano microfibrillated cellulose grafted chitosan, a first coupling agent, an antioxidant and a lubricant at a high speed to obtain a premix; the specific process is as follows: firstly, drying polylactic acid at 50-80 ℃ to be absolute dry, drying an inorganic filler at 80-105 ℃ to be absolute dry, then mixing the inorganic filler, a first coupling agent, an antioxidant and a lubricant at a low speed of 200rpm for 8min to obtain a mixture, then adding the polylactic acid and the carboxylated nano microfibrillated cellulose grafted chitosan into the mixture, and mixing at a high speed of 500rpm for 10min at a temperature of 60 ℃ to obtain a premix;
4) melting and blending the obtained premix, extruding and molding, cooling and cutting, and annealing to obtain the heat-resistant antibacterial PLA full-biodegradable straw; the specific process is as follows: putting the obtained premix into a double-screw extruder or an internal mixer for melt blending, and then extruding and granulating at 160 ℃ to obtain blended granules; then placing the obtained blended granules into a single-screw extruder, extruding and molding the blended granules at 140 ℃ through a circular die head, cooling the extruded granules to 20 ℃, and cutting the extruded granules into a suction pipe; and then carrying out infrared heating annealing treatment on the obtained straw at 100 ℃ for 5min to obtain the heat-resistant antibacterial PLA full-biodegradable straw.
In example 1, talc was used as the inorganic filler, KH550 as the first coupling agent, 1076 as the antioxidant, erucamide as the lubricant, acid-soluble chitosan as the chitosan, 20% NaOH solution as the basic catalyst, anhydrous sodium acetate as the esterifying agent, and 101 as the titanate coupling agent as the second coupling agent.
The heat-resistant antibacterial PLA full-biodegradable straws of examples 2 to 5 were prepared in the same manner as in example 1.
The pipette of comparative example 1 was prepared without the addition of chitosan, with NFC as nucleating agent. The mass parts of the straw of comparative example 1 were: 100 parts of polylactic acid, 2 parts of NFC, 15 parts of inorganic filler, 1 part of first coupling agent, 0.2 part of antioxidant and 2 parts of lubricant, wherein the materials selected for the inorganic filler, the first coupling agent, the antioxidant and the lubricant are the same as those in the embodiment 1.
The straw of comparative example 1 was prepared by the following method:
A1) extracting alpha cellulose from plant raw materials, swelling, and mechanically shearing the alpha cellulose at a high speed to prepare nano microfibrillated cellulose, wherein the specific preparation process and parameters of the step are the same as those in the example 1;
B1) uniformly mixing polylactic acid, inorganic filler, NFC, a first coupling agent, an antioxidant and a lubricant at a high speed to obtain a premix, wherein the specific preparation process and parameters of the step are the same as those in the embodiment 1;
C1) and (3) melting and blending the obtained premix, extruding and molding, cooling and cutting, and annealing to obtain the straw of the comparative example 1, wherein the specific processes and parameters of the step are the same as those in the example 1.
The pipette of comparative example 2 was added directly with chitosan without the addition of NFC. The mass parts of the straw of comparative example 2 were: 100 parts of polylactic acid, 2 parts of chitosan, 15 parts of inorganic filler, 1 part of first coupling agent, 0.2 part of antioxidant and 2 parts of lubricant, wherein the materials selected from the chitosan, the inorganic filler, the first coupling agent, the antioxidant and the lubricant are the same as those in the embodiment 1.
The manufacturing method of the straw of comparative example 2 was:
A2) uniformly mixing polylactic acid, inorganic filler, chitosan, a first coupling agent, an antioxidant and a lubricant at a high speed to obtain a premix, wherein the specific preparation process and parameters of the step are the same as those in the example 1;
B2) and (3) melting and blending the obtained premix, extruding and molding, cooling and cutting, and annealing to obtain the straw of the comparative example 2, wherein the specific processes and parameters of the step are the same as those in the example 1.
For examples 1 to 5, the blended pellets obtained in step 4) were injection molded to prepare tensile and impact test samples, and annealed at 100 ℃ for 5 min. For comparative examples 1 to 2, the blended pellets obtained in step C1) and step B2) were injection-molded to prepare tensile and impact test specimens, respectively, and annealed at 100 ℃ for 5min as in example 1. The tensile test of the samples is according to the test standard ATSM D638, the samples are dumbbell-shaped test specimens, the length is 120mm, the gauge length is 50mm, and the width and the thickness of the middle part are respectively about 10mm and 5 mm. The tensile speed is 10mm/min, at least 5 samples are tested in each group, and the average values of the tensile strength and the tensile elongation at break of the samples are taken. The impact test was according to the ATSM D6110 test standard, with a sample length of 100mm, width of 10mm and thickness of 4 mm. At least 5 specimens per group were tested and the average value of the impact strength of the samples was taken. The test results are shown in FIG. 1.
The crystallinity of the samples of examples 1 to 5 and comparative examples 1 to 2 was measured by a DSC tester. The DSC instrument is German Netzsch DSC 204, the temperature is raised from 20 ℃ to 180 ℃ at 10 ℃/min under nitrogen atmosphere, and the temperature-raising enthalpy curve is recorded. The formula for calculating the crystallinity of polylactic acid by DSC method is as follows:
Xc＝(△Hm-△Hc)/△Hm 0 ×100％
in the formula, Δ Hm and Δ Hc represent melting enthalpy and cold crystallization enthalpy of a polylactic acid sample, respectively; Δ Hm 0 Represents the melting enthalpy (theoretical enthalpy, equal to 96.30J/g) of the polylactic acid which is completely crystallized.
The load heat distortion temperature of the samples of examples 1-5 and comparative examples 1-2 was tested according to GB/T1634-1979.
The crystallinity and heat distortion temperature results of examples 1-5 are shown in FIG. 2.
According to the antibacterial performance of the samples in the examples 1-5 and the comparative examples 1-2 tested by the Q/BT 2591-2003, the strains select escherichia coli and staphylococcus aureus.
According to tests, the tensile strength and the impact strength of the sample of the comparative example 1 are 45.5MPa and 27J/m, the crystallinity is 23.8 percent, the heat distortion temperature is 85 ℃, and the bacteriostasis rates to escherichia coli and staphylococcus aureus are 11.2 percent and 8.3 percent respectively; the tensile strength and impact strength of the sample of comparative example 2 were 39MPa and 21J/m, the crystallinity was 3.0%, the heat distortion temperature was 50 ℃, and the bacteriostatic rates for E.coli and S.aureus were 94.2% and 96.9%, respectively.
As can be seen from FIG. 1, as the addition amount of the functionalized and modified crystallization nucleating agent increases, the tensile strength and the impact strength of the straw materials of examples 1 to 5 both increase and then decrease. Of these performance values, even the minimum value is advantageous over comparative example 2 without NFC. Among them, the tensile strength and impact strength of example 4 were improved by about 30% and 42%, respectively, compared to comparative example 2 without NFC reinforcement. The crystallinity of example 4 was increased by 11.4 times compared to comparative example 2, and the heat resistance temperature was increased from 50 ℃ to 100 ℃. In addition, the bacteriostatic rates of the straw material of example 3 on escherichia coli and staphylococcus aureus are 79.2% and 82.3% respectively, which are improved by 6 times and 8.9 times respectively compared with the straw material of comparative example 1 without chitosan.
The compositions of the heat-resistant antibacterial PLA full-biodegradable straws of examples 6 to 10 in parts by mass are shown in Table 2, and the single-factor experiments were performed by respectively designating examples 6 to 10 as numbers S1, S2, S3, S4 and S5.
TABLE 2
The heat-resistant antibacterial PLA full-biodegradable straws of examples 6 to 10 were prepared in the same manner as in example 1.
In the same manner as in example 1, the blend pellets of examples 6 to 10 were injection-molded to prepare tensile and impact test specimens, and the tensile and impact tests, crystallinity, heat distortion temperature and antibacterial properties were performed after annealing at 100 ℃ for 5 min. The results of the tensile strength and impact strength tests are shown in FIG. 3, and the results of the crystallinity and heat distortion temperature are shown in FIG. 4.
As can be seen from FIG. 3, the straw materials of examples 6 to 10 both increased in tensile strength and decreased in impact strength as the amount of the inorganic filler added increased. Of these performance values, even the minimum value is advantageous over comparative example 2 without NFC. Among them, the tensile strength and impact strength of example 9 were improved by about 16% and 15%, respectively, compared to comparative example 2 without NFC reinforcement. The crystallinity of example 10 was increased 8.7 times as compared to comparative example 2, and the heat-resistant temperature was increased from 50 ℃ to 100 ℃. In addition, the bacteriostatic rates of the straw material of example 10 on escherichia coli and staphylococcus aureus are respectively 78.3% and 81.9%, which are respectively 5.9 and 8.8 times higher than those of comparative example 1 without chitosan.
The compositions of the heat-resistant antibacterial PLA full-biodegradable straws of examples 11 to 15 in parts by mass are shown in Table 3, and single-factor experiments were performed by respectively designating examples 11 to 15 as numbers B1, B2, B3, B4 and B5.
TABLE 3
The heat-resistant antibacterial PLA full-biodegradation straw of examples 11 to 15 is prepared by the same method as example 1, except that in the step 2) of preparing the carboxylated nano-microfibrillated cellulose grafted chitosan, the mass ratios of the alkaline catalyst to the esterifying agent are 5:1, 5:1.1, 5:1.2, 5:1.3 and 5:1.4, respectively.
Tensile and impact test samples were prepared by injection molding the blend pellets of examples 11 to 15 in the same manner as in example 1, and the tensile and impact test, the crystallinity, the heat distortion temperature and the antibacterial property were tested after annealing at 100 ℃ for 5 min. The results of the tensile strength and impact strength tests are shown in FIG. 5, and the results of the crystallinity and heat distortion temperature are shown in FIG. 6.
As can be seen from FIG. 5, the straw materials of examples 11 to 16 both increased in tensile strength and impact strength as the amount of the esterification agent added increased. Among them, the tensile strength and impact strength of example 15 were improved by about 20% and 30% respectively compared to comparative example 2 without NFC reinforcement, and also improved appropriately compared to comparative example 1 with only NFC. It can be seen that the esterification agent promotes the reaction of the nano microfibrillated cellulose grafted chitosan, and the functionalized modified crystallization nucleating agent further improves the mechanical properties of the composite material. The crystallinity of example 15 was improved by 7.4 times compared to comparative example 2, and the heat resistance temperature was increased from 50 ℃ to about 90 ℃. In addition, the bacteriostatic rates of the straw material of example 14 on escherichia coli and staphylococcus aureus are respectively 80.2% and 84.3%, which are respectively 6.2 and 9.5 times higher than those of comparative example 1 without chitosan.
The compositions of the heat-resistant antibacterial PLA full-biodegradable straws of examples 16 to 19 in parts by mass are shown in Table 4, and the straws of examples 16 to 19 in parts by mass are respectively shown as numbers E1, E2, E3 and E4, and single-factor experiments are performed.
TABLE 4
The heat-resistant antibacterial PLA full-biodegradation straw of examples 16 to 19 was prepared in substantially the same manner as in example 1, except that in the step 2) of preparing the carboxylated nano-microfibrillated cellulose grafted chitosan, the mass ratios of the nano-microfibrillated cellulose to the chitosan were 80:1, 80:2, 80:4, and 80:5, respectively.
Tensile and impact test samples were prepared by injection molding the blend pellets of examples 16 to 19 in the same manner as in example 1, and the tensile and impact test, the crystallinity, the heat distortion temperature and the antibacterial property were tested after annealing at 100 ℃ for 5 min. The test results of tensile strength and impact strength are shown in fig. 7, the results of crystallinity and heat distortion temperature are shown in fig. 8, and the results of antibacterial property are shown in fig. 9.
As can be seen from FIG. 7, the straw materials of examples 16 to 19 both increased in tensile strength and impact strength as the amount of chitosan added increased. The tensile strength and the impact strength of example 19 are respectively improved by about 30% and 28% compared with those of comparative example 2 without adding NFC reinforcement, and are also improved appropriately compared with those of comparative example 1 only adding NFC, and it can be seen that the chitosan grafted nano microfibrillated cellulose is beneficial to improving the mechanical properties of the straw material. The crystallinity of example 18 was increased by 7.3 times compared to comparative example 2, and the heat resistance temperature was increased from 50 ℃ to about 100 ℃. In addition, as can be seen from fig. 9, the antibacterial properties of the straw with respect to escherichia coli and staphylococcus aureus are improved as the content of chitosan is increased.
Claims (10)
1. The heat-resistant antibacterial PLA full-biodegradation straw is characterized by comprising the following components in parts by mass: 100 parts of polylactic acid, 1-20 parts of inorganic filler, 1-5 parts of functionalized modified crystallization nucleating agent, 0.5-1 part of first coupling agent, 0.2-0.5 part of antioxidant and 0.5-4 parts of lubricant, wherein the functionalized modified crystallization nucleating agent is carboxylated nano microfibrillated cellulose grafted chitosan.
2. The heat-resistant antibacterial PLA full-biodegradation straw according to claim 1, wherein the preparation process of the carboxylated nano-microfibrillated cellulose grafted chitosan is as follows:
a) preparing nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid, water, an alkaline catalyst, an esterifying agent and a second coupling agent, wherein the mass part ratio of the nano microfibrillated cellulose to the chitosan is 80: 1-5: 200-250: 5-20: 300-500: 5: 1-1.5: 0.5-1;
b) adding the prepared nano microfibrillated cellulose, chitosan, ammonium persulfate, chloroacetic acid and water into a ball milling tank of a planetary ball mill for ball milling, wherein a grinding medium is zirconia or ceramic balls, the temperature is 40-70 ℃, the ball milling revolution speed is 80-120 rpm, the rotation speed is 150-200 rpm, and the ball milling time is 30-120 min;
c) after the step b) is finished, adding the prepared alkaline catalyst, esterification agent and second coupling agent into a ball milling tank, and continuously milling at the temperature of 50-80 ℃, the ball milling revolution speed of 100-140 rpm, the rotation speed of 160-220 rpm, and the ball milling time of 40-120 min;
d) and c) after the step c) is finished, taking out the powder in the ball milling tank, putting the powder into a drying oven, and drying the powder at the temperature of 80-105 ℃ to be absolutely dry to obtain the carboxylated nano microfibrillated cellulose grafted chitosan.
3. The heat-resistant antibacterial PLA total biodegradation straw as claimed in claim 2, wherein the alkaline catalyst is one or a combination of NaOH, KOH, sodium methoxide and sodium carbonate; the esterifying agent is one or a combination of more of anhydrous sodium acetate, propionate, maleic anhydride and octenyl succinic anhydride; the second coupling agent is a titanate coupling agent or an aluminate coupling agent.
4. The heat-resistant antibacterial PLA full-biodegradation straw according to claim 2, wherein the chitosan is acid-soluble chitosan, and the chitosan is dried at a temperature of 80-105 ℃ for 10-18 h before the ball milling in the step b).
5. The heat-resistant antibacterial PLA full-biodegradation straw according to claim 1, wherein the inorganic filler is one or a combination of several of talcum powder, calcium carbonate, silicon dioxide and barium sulfate, the first coupling agent is a silane coupling agent, the antioxidant is one or a combination of several of tea polyphenol, phytic acid, antioxidant 1010, antioxidant 168, antioxidant 1076 and antioxidant 1790, and the lubricant is one or a combination of several of stearic acid, ethylene bis-stearamide, oleamide and erucamide.
6. A method for preparing the heat-resistant antibacterial PLA full-biodegradable straw as claimed in any one of claims 1 to 5, which is characterized by comprising the following steps:
1) extracting alpha cellulose from plant raw materials, swelling, and mechanically shearing the alpha cellulose at a high speed to prepare nano microfibrillated cellulose;
2) uniformly mixing polylactic acid, inorganic filler, carboxylated nano microfibrillated cellulose grafted chitosan, a first coupling agent, an antioxidant and a lubricant at a high speed to obtain a premix;
3) and melting and blending the obtained premix, extruding and molding, cooling and cutting, and annealing to obtain the heat-resistant antibacterial PLA full-biodegradable straw.
7. The method for preparing the heat-resistant antibacterial PLA full-biodegradable straw as claimed in claim 6, wherein the specific process of the step 1) is as follows: firstly, crushing plant fibers into particles of 40-100 meshes, bleaching with 10-15% of sodium chlorite by mass for 0.5-3 h, drying, treating with 2-6% of sodium hydroxide by mass for 0.5-2 h, filtering, and washing with water to be neutral to obtain alpha cellulose; secondly, adding the alpha cellulose into a urea alkali solution according to a solid-to-liquid ratio of 1: 5-8 for swelling treatment for 1-5 hours at a treatment temperature of 20-60 ℃ to obtain swelled alpha cellulose, wherein the mass ratio of sodium hydroxide, urea and pure water in the urea alkali solution is 5-10: 10-15: 80-85; and finally, mechanically shearing the swollen alpha cellulose at a high speed for 0.5-3 h, centrifugally washing the swollen alpha cellulose at a rotating speed of 8000-12000 rpm until the swollen alpha cellulose is neutral, and freeze-drying the precipitate to obtain the white nano microfibrillated cellulose.
8. The method for preparing the heat-resistant antibacterial PLA full-biodegradable straw as claimed in claim 6, wherein the specific process of the step 2) is as follows: firstly, drying polylactic acid at 50-80 ℃ to be absolute dry, drying an inorganic filler at 80-105 ℃ to be absolute dry, then mixing the inorganic filler, a first coupling agent, an antioxidant and a lubricant at a low speed of 100-300 rpm for 5-10 min to obtain a mixture, then adding the polylactic acid and the carboxylated nano microfibrillated cellulose grafted chitosan into the mixture, and mixing at a high speed of 300-600 rpm at a temperature of 50-70 ℃ for 5-15 min to obtain the premix.
9. The method for preparing the heat-resistant antibacterial PLA full-biodegradation straw according to claim 6, wherein the specific process of the step 3) comprises the following steps: putting the obtained premix into a double-screw extruder or an internal mixer for melt blending, and then extruding and granulating to obtain blended granules; then placing the obtained blended granules in a single-screw extruder, extruding and molding through a circular die head, cooling to 20-40 ℃, and cutting into a straw; and then annealing the obtained straw at 100-120 ℃ for 3-10 min to obtain the heat-resistant antibacterial PLA full-biodegradable straw.
10. The preparation method of the heat-resistant antibacterial PLA full-biodegradable straw as claimed in claim 9, wherein the temperature of extrusion granulation is 100-190 ℃, the temperature of extrusion molding is 130-190 ℃, and the heating mode of annealing treatment is infrared heating, microwave heating or blast heating.
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