Modified polylactic acid plastic and method for preparing the same

Abstract

This invention provides a modified polylactic acid (PLA) plastic and its preparation method, relating to the field of modified plastics technology. The modified PLA plastic of this invention is obtained by premixing, melting, extruding, cooling, and granulating nano-clay modified with sodium dodecyl sulfonate and alkylamide carboxybetaine, PLA, and an antioxidant. This invention uses a compound modifier of sodium dodecyl sulfonate and alkylamide carboxybetaine to modify the nano-clay, enhancing the hydrogen bonding between the modified nano-clay and the PLA ester groups, improving interfacial bonding, and giving the modified PLA excellent barrier properties, mechanical properties, and impact resistance, thus showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of modified plastics technology, and in particular to a modified polylactic acid plastic and its preparation method. Background Technology

[0002] Biodegradable plastics are plastic materials that can gradually decompose into harmless substances (such as water, carbon dioxide, and inorganic salts) through biological, chemical, or physical processes under natural environments or specific conditions. Based on their degradation mechanisms, biodegradable plastics can be classified into photodegradable plastics, biodegradable plastics, and photo / biodegradable plastics. Biodegradable plastics are widely used in packaging, agriculture, healthcare, and disposable products.

[0003] Biodegradable plastics mainly include polylactic acid (PLA), polybutylene terephthalate (PBAT), polybutylene succinate (PBS), polycaprolactone (PCL), and polyhydroxyalkanoates (PHA).

[0004] PLA is produced from renewable plant resources (such as corn, sugarcane, and cassava) through starch hydrolysis to obtain glucose, followed by microbial fermentation to produce lactic acid, and finally polymerized through chemical synthesis. Lactic acid has good biocompatibility and can be absorbed and metabolized by the human body, thus it is widely used in the medical field. It is a completely biodegradable material, environmentally friendly, non-toxic, and non-irritating. The decomposition product, lactic acid, can be metabolized by the human body and will not accumulate in the body.

[0005] Researching modified polylactic acid (PLA) that combines good mechanical and barrier properties is of great significance, mainly in the following aspects:

[0006] Currently, pure PLA exhibits poor barrier properties, mechanical properties, and impact resistance. This makes it difficult for pure PLA films to meet the gas and water vapor barrier requirements of food preservation and pharmaceutical packaging. Furthermore, in fields such as medical devices and drug carriers, the mechanical properties of pure PLA cannot guarantee structural stability and durability. Therefore, researching modified PLA that combines good mechanical and barrier properties is of great significance.

[0007] Chinese patent application CN103709695A discloses a PLA modified material, its preparation method, and a PLA biodegradable mulch film. The modified material contains PLA, PBAT, modified talc, antioxidants, UV absorbers, light stabilizers, opening agents, chain extenders, and initiators. Based on the total weight of the modified material, it contains 58-80% by weight of PLA, 15-40% by weight of PBAT, 0.1-5% by weight of modified talc, 0.1-2% by weight of antioxidants, 0.1-1% by weight of UV absorbers, 0.1-2% by weight of light stabilizers, 0.1-2% by weight of opening agents, 0.1-1% by weight of chain extenders, and 0.0005-0.05% by weight of initiators. This invention, by adding PBAT to PLA and simultaneously using chain extenders to compatibilize the polymer, allows the prepared material to retain the high strength, high light transmittance, and high cost-effectiveness of PLA after blow molding, while also improving its flexibility.

[0008] Chinese patent CN105199347A discloses a PLA / MMT degradation-reinforced masterbatch blend modified PLA / PBAT composite material and its preparation method. This method uses polylactic acid (PLA), poly(terephthalic acid-adipate-butanediol) copolyester (PBAT), and PLA / MMT degradation-reinforced masterbatch as raw materials. 10-90 parts of PLA, 10-90 parts of PBAT, and 5-30 parts of PLA / MMT degradation-reinforced masterbatch are mixed evenly, and then melt-blended to modify PLA / PBAT to prepare a high-performance PLA / PBAT composite material. The PLA / MMT degradation-reinforced masterbatch is prepared by ion exchange using intercalating agents and co-intercalating agents to increase the interlayer spacing of montmorillonite. Then, monomers or polylactic acid molecular chains are intercalated into the interlayer space of montmorillonite through melt in-situ polymerization. The PLA / MMT degradation-reinforced masterbatch blend modified PLA / PBAT composite material prepared by this method has excellent performance and can be used in the production of daily necessities and packaging materials.

[0009] However, none of these modification methods could simultaneously improve the barrier properties, mechanical properties, and impact resistance of PLA. Summary of the Invention

[0010] In view of this, the present invention provides a modified polylactic acid plastic and a method for preparing the same. The method involves mixing and granulating nano-clay modified with sodium dodecyl sulfonate (SDS) and alkyl amide carboxybetaine with PLA, so that the modified PLA plastic product has good barrier properties, mechanical properties and impact resistance.

[0011] The first aspect of this invention is to provide a method for preparing modified polylactic acid plastic, comprising the following steps:

[0012] Modified nano-clay and PLA are vacuum dried; then the dried modified nano-clay, PLA and antioxidant are mixed at high speed to obtain a premix; the premix is ​​melted, extruded, cooled and granulated to obtain modified polylactic acid plastic.

[0013] Preferably, the modified nano-clay is added at a rate of 2 wt.% to 5 wt.%, and the antioxidant is added at a rate of 0.3 wt.% to 0.5 wt.%, wherein the antioxidant is antioxidant 1010 and / or antioxidant 168. More preferably, the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2.

[0014] The preparation method of the modified nano-clay of the present invention includes the following steps:

[0015] Nano-clay was dispersed in anhydrous ethanol to obtain suspension A. Then, a modifier was dissolved in deionized water and added to suspension A for modification. After modification, the mixture was cooled, allowed to stand, filtered, washed, and dried to obtain modified nano-clay.

[0016] Preferably, the molar ratio of the modifier to the nano-clay is (2-3):1.

[0017] Preferably, the modifier is sodium dodecyl sulfonate (SDS) and alkylamide carboxybetaine, wherein the molar ratio of SDS to alkylamide carboxybetaine is (2-4):(6-8). More preferably, the alkylamide carboxybetaine is composed of cocamidopropyl betaine (CAPB) and lauramide propyl betaine (LAPB) in a molar ratio of 1:(1-2).

[0018] Preferably, the mass-to-volume ratio of the nano-clay to anhydrous ethanol is 1 g / (50-100) mL, and the mass-to-volume ratio of the modifier to deionized water is 1 g / (10-20) mL.

[0019] Preferably, the modified pH is 4±0.2, the modified temperature is 70℃~80℃, and the modified time is 5~10h. More preferably, the modification is carried out under stirring conditions, and the stirring rate is 100~300rpm.

[0020] Preferably, the settling temperature is room temperature, and the settling time is 8 to 12 hours.

[0021] Preferably, the drying temperature is 60℃~70℃.

[0022] Preferably, the D of the nano-clay 50 The wavelength range is 50–100 nm, and the interlayer spacing is ≥2.5 nm.

[0023] A second aspect of the present invention is to provide a modified polylactic acid plastic prepared according to the above method.

[0024] A third aspect of the present invention is to provide an application of a modified polylactic acid plastic in the preparation of a biodegradable, high-barrier, and high-strength material, wherein the modified polylactic acid plastic is the modified polylactic acid plastic described in the above-mentioned scheme.

[0025] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0026] This invention uses sodium dodecyl sulfonate and alkyl amide carboxybetaine compound modifier to modify nano clay. Through charge complementarity and steric hindrance effect, the interlayer peeling efficiency of nano clay is improved. Furthermore, the interfacial bonding is enhanced by the polar group of betaine and the hydrogen bonding of PLA ester group.

[0027] The modified nano-clay of the present invention also acts as a nucleating agent and a solubilizer, reducing the amount of additives and lowering the preparation cost of modified polylactic acid plastics.

[0028] The modified polylactic acid plastic of this invention has good comprehensive properties, is applicable to a wide range of scenarios, and its preparation process is the same as that of traditional polylactic acid plastic, requiring no additional cost investment, and has good application prospects. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a modified polylactic acid plastic, its preparation method, and its application. By modifying polylactic acid, this invention improves the mechanical properties, processing properties, and barrier properties of polylactic acid plastic.

[0031] The method for preparing the modified polylactic acid plastic of the present invention includes the following steps:

[0032] S1-1. Vacuum dry the modified nano-clay and PLA at 60℃~80℃ for 4~6h;

[0033] S1-2. Weigh the dried PLA, modified nano clay, and antioxidant according to the proportion, put them into a high-speed mixer, and mix at 500-800 rpm for 10-15 minutes to obtain a premix.

[0034] S1-3. Feed the premixed material into the twin-screw extruder. During the feeding process, pay attention to matching the feeding rate with the screw speed to avoid material blockage. Before using the extruder, preheat it to the set temperature and stabilize it for at least 10 minutes before feeding. After the extruded material is cooled by cooling water at 20℃~25℃, it is granulated to obtain modified polylactic acid plastic with a particle length of 2~3mm.

[0035] In some specific embodiments of the present invention, the amount of modified nano-clay added is 2 wt.% to 5 wt.% of PLA, and the amount of antioxidant added is 0.3 wt.% to 0.5 wt.% of PLA.

[0036] The modified nanoclay of this invention exhibits good dispersibility and compatibility in PLA, thus reducing the amount of modified nanoclay required to some extent, but it still needs to be kept within a reasonable range. Too little nanoclay will fail to form a continuous and uniform network structure, resulting in insufficient performance improvement. Conversely, too much modified nanoclay will reduce dispersibility, leading to agglomerates observed during SEM, increased melt viscosity, decreased processing performance, and problems such as strip breakage during extrusion, significantly reducing the overall performance of PLA. Therefore, this invention limits the amount of modified nanoclay added to 2 wt.% to 5 wt.% of PLA. Within this range, the dispersibility of the modified nanoclay and the number of modified groups are within an optimal range, thereby improving the overall performance of PLA.

[0037] In some specific embodiments of the present invention, the antioxidant is antioxidant 1010 and / or antioxidant 168. In some preferred embodiments of the present invention, the antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:(1.5 to 2.5).

[0038] Antioxidant 1010 is a hindered phenolic antioxidant, and antioxidant 168 is a phosphite antioxidant. Antioxidant 1010 is the primary antioxidant, mainly used to inhibit free radical-initiated oxidation chain reactions. Antioxidant 168 is a secondary antioxidant, mainly used to decompose peroxides generated during polymer processing, thereby inhibiting the chain propagation of oxidation reactions and reducing the secondary generation of free radicals. This invention preferably uses a composite antioxidant composed of antioxidant 1010 and antioxidant 168, which inhibits the thermal oxidative degradation of PLA through a free radical capture-peroxide decomposition synergistic mechanism. However, in this invention, the ratio of antioxidant 1010 to antioxidant 168 is affected by the free radical generation rate and the peroxide accumulation rate; therefore, the ratio needs to be adjusted according to actual conditions to achieve the best antioxidant effect.

[0039] In some specific embodiments of the present invention, the temperature of the feeding section of the twin-screw extruder is 160℃~170℃, the temperature of the melting section is 175℃~185℃, the temperature of the mixing section is 180℃~190℃, the temperature of the die section is 175℃~180℃, and the screw speed is 200~300rpm. High speed can enhance shear dispersion, but excessive speed will generate excessive shear force and heat, leading to a sharp increase in local temperature, which in turn causes PLA molecular chains to break and the molecular weight to decrease. Therefore, it is necessary to limit the screw speed.

[0040] The preparation method of the modified nano-clay of the present invention includes the following steps:

[0041] S2-1. Disperse the nano-clay in anhydrous ethanol to obtain suspension A;

[0042] S2-2. Dissolve the modifier in deionized water to obtain a modifier solution;

[0043] S2-3. The modifier solution is added to the suspension A for modification;

[0044] S2-4. After modification, the material is cooled, allowed to stand, filtered, washed, and dried to constant weight to obtain modified nano-clay.

[0045] In some specific embodiments of the present invention, the molar ratio of the modifier to the nano-clay is (2-3):1.

[0046] In some specific embodiments of the present invention, the modifier is SDS and alkylamide carboxybetaine, the molar ratio of SDS to alkylamide carboxybetaine is (2-4):(6-8), and the alkylamide carboxybetaine is composed of CAPB and LAPB in a molar ratio of 1:(1-2).

[0047] In the modifiers used in this invention, SDS can replace the metal cations between nano-clay layers through ion exchange, expanding the interlayer spacing (≥2.5 nm) and promoting clay exfoliation into nanosheets. Meanwhile, the hydrophobic alkyl chains of CAPB and LAPB synergistically insert into the interlayer with SDS, while the hydrophilic carboxyl and quaternary ammonium groups inhibit interlayer re-aggregation through steric hindrance, improving the dispersibility of the modified nano-clay in PLA. Simultaneously, the long-chain alkyl groups of SDS and the hydrophobic groups of betaine cover the clay surface, reducing its surface energy and making it more compatible with the hydrophobic PLA matrix, reducing phase separation, and further improving the compatibility of the modified nano-clay in PLA. The carboxylic acid groups of betaine form hydrogen bonds with the ester groups of PLA, strengthening the interfacial bonding and improving the mechanical properties of the modified PLA.

[0048] However, studies have found that the mixture of alkylamide carboxybetaine and sodium dodecyl sulfate in pure water exhibits antagonistic effects. To address this issue, this invention specifies a modification pH of 4 ± 0.2, which is adjusted using hydrochloric acid. Under these conditions, the antagonistic effect of the mixture of alkylamide carboxybetaine and SDS is almost nonexistent, allowing for smooth modification, promoting intercalation, optimizing intercalation efficiency, and preventing aggregation.

[0049] Furthermore, the sulfonic acid groups and quaternary ammonium groups of betaine can neutralize the surface charge of the clay, reducing agglomeration caused by electrostatic attraction and further improving the uniform distribution of nano-clay in PLA. The hydrophobic surface of the modified clay is more easily wetted with molten PLA, improving processing fluidity and thus enhancing processing performance.

[0050] In the alkylamide carboxybetaine modifiers used in this invention, CAPB has a longer alkyl chain (a mixed C12-C18 chain). Its larger hydrophobic volume provides a stronger steric hindrance effect, significantly increasing the interlayer spacing of the nanoclay and promoting the exfoliation of clay into nanosheets. However, the presence of the long chain also leads to a decrease in intercalation efficiency. CAPB's long hydrophobic chain has better compatibility with the hydrophobic groups of PLA, but its carboxylic acid group density is lower (due to its large molecular volume), resulting in weaker hydrogen bonding compared to LAPB. LAPB, on the other hand, has a shorter alkyl chain (a single C12 chain), a smaller molecular volume, and higher intercalation efficiency. However, its steric hindrance effect is weaker, its interlayer spacing is smaller than CAPB, and its ability to inhibit interlayer recombination is weaker, resulting in poorer long-term stability than CAPB. Nevertheless, LAPB has a higher carboxylic acid group density, enabling it to form more hydrogen bonds with the ester groups of PLA.

[0051] Therefore, this invention uses a mixture of CAPB and LAPB, combined with SDS, to modify nano-clay and achieve better modification results. When CAPB and LAPB are used in combination, the long chains of CAPB widen the interlayer spacing, while the short chains of LAPB fill the interlayer gaps, forming a more stable intercalation structure and inhibiting clay aggregation. The long chains of CAPB enhance hydrophobic compatibility, while the carboxylic acid groups of LAPB strengthen hydrogen bonding, comprehensively improving interfacial bonding. The mixed surfactants can also form composite micelles, accelerating the intercalation process.

[0052] Finally, in order to achieve a good synergistic effect, the present invention limits the ratio of CAPB to LAPB, that is, the molar ratio of CAPB to LAPB is 1:(1~2), so as to take into account the interlayer spacing, dispersion and interfacial bonding performance.

[0053] In some specific embodiments of the present invention, the mass-to-volume ratio of the nano-clay to anhydrous ethanol is 1g:(50-100)mL, and the mass-to-volume ratio of the modifier to deionized water is 1g:(10-20)mL.

[0054] In some specific embodiments of the present invention, the modified pH is 4±0.2, the modification temperature is 70℃~80℃, and the modification time is 5~10h; the standing temperature is room temperature, and the standing time is 8~12h; the drying temperature is 60℃~70℃. In some preferred embodiments of the present invention, the modification is carried out under stirring conditions, and the stirring rate is 100~300rpm.

[0055] A second aspect of the present invention is to provide a modified polylactic acid plastic prepared according to the above method.

[0056] A third aspect of the present invention is to provide an application of a modified polylactic acid plastic in the preparation of a biodegradable, high-barrier, and high-strength material, wherein the modified polylactic acid plastic is the modified polylactic acid plastic described in the above-mentioned scheme.

[0057] The modified PLA plastic of this invention exhibits high barrier properties, effectively preventing the penetration of oxygen and water vapor and extending the shelf life of food. Simultaneously, its excellent mechanical and processing properties allow it to be manufactured into packaging containers, films, and food storage boxes of various shapes. In pharmaceutical packaging, the modified PLA plastic of this invention provides excellent barrier properties, preventing the medicine from becoming damp and oxidized. In electronic product packaging, the modified PLA plastic of this invention can also prevent electronic components from becoming damp and provide sufficient protection for them.

[0058] The agricultural mulch film made of the modified PLA plastic of the present invention has good barrier properties and mechanical properties, which can effectively prevent water evaporation and weed growth. At the same time, its biodegradability avoids the soil pollution caused by traditional plastic mulch films.

[0059] The modified PLA plastic of this invention can also be used to produce disposable products, and its biodegradability can reduce its environmental impact.

[0060] The modified PLA of this invention can be processed into fibers, which can be spun into high-strength fibers, while its barrier properties can give the fabric a certain degree of water resistance.

[0061] The modified PLA plastic of this invention has excellent processing and mechanical properties, making it suitable as a consumable for 3D printing and applicable to the manufacture of various products.

[0062] To further illustrate the present invention, the following embodiments provide a detailed description. All raw materials used in the following embodiments of the present invention are commercially available, with the nano-clay purchased from Shanghai Maclean Reagent Co., Ltd.

[0063] Unless otherwise specified, all experiments were repeated three times. Analysis of variance (ANOVA) and Duncan's multiple comparison analysis were performed using SPSS 21.0. Results are expressed as mean ± standard deviation, and p < 0.05 was considered statistically significant.

[0064] Example 1: A method for preparing modified polylactic acid plastic, the steps of which are as follows:

[0065] S1-1. The modified nano-clay and PLA were vacuum dried at 60℃ for 6 hours.

[0066] S1-2. Weigh the dried PLA, modified nano-clay, and antioxidant (composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2) according to the proportion, put them into a high-speed mixer, and mix at 800 rpm for 10 min to obtain a premix. The mass percentage of modified nano-clay in the premix is ​​3%, and the mass percentage of antioxidant in the premix is ​​0.4%.

[0067] S1-3. Feed the premixed material into the twin-screw extruder. During the feeding process, pay attention to matching the feeding rate with the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: feed section temperature is 170℃, melt section temperature is 185℃, mixing section temperature is 190℃, die section temperature is 180℃, and screw speed is 200rpm. Before use, the extruder should be preheated to the set temperature and stabilized for 10 minutes before feeding. After the extruded material is cooled by 20℃ cooling water, it is granulated to obtain modified polylactic acid plastic with a particle length of 2-3mm.

[0068] The preparation steps of the modified nano-clay are as follows:

[0069] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0070] S2-2. Dissolve the modifier in deionized water at a ratio of 1g:20mL to obtain a modifier solution. The modifier is composed of SDS and alkylamide carboxybetaine in a molar ratio of 3:7, and the alkylamide carboxybetaine is composed of CAPB and LAPB in a molar ratio of 1:1.5.

[0071] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0072] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0073] Example 2: A method for preparing modified polylactic acid plastic, the steps of which are as follows:

[0074] S1-1. The modified nano-clay and PLA were vacuum dried at 80℃ for 4 hours.

[0075] S1-2. Weigh the dried PLA, modified nano-clay, and antioxidant (composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5) according to the proportion, put them into a high-speed mixer, and mix them at 500 rpm for 15 min to obtain a premix. The mass percentage of modified nano-clay in the premix is ​​2%, and the mass percentage of antioxidant in the premix is ​​0.3%.

[0076] S1-3. Feed the premixed material into the twin-screw extruder. During the feeding process, pay attention to matching the feeding rate with the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: feed section temperature is 160℃, melt section temperature is 175℃, mixing section temperature is 180℃, die section temperature is 175℃, and screw speed is 300rpm. Before use, preheat the extruder to the set temperature and stabilize it for 10 minutes before feeding. After the extruded material is cooled by 25℃ cooling water, it is granulated to obtain modified polylactic acid plastic with a particle length of 2-3mm.

[0077] The preparation steps of the modified nano-clay are as follows:

[0078] S2-1. Disperse nano-clay in anhydrous ethanol at a ratio of 1g:50mL to obtain suspension A;

[0079] S2-2. Dissolve the modifier in deionized water at a ratio of 1g:10mL to obtain a modifier solution. The modifier is composed of SDS and alkylamide carboxybetaine in a molar ratio of 2:8. The alkylamide carboxybetaine is composed of CAPB and LAPB in a molar ratio of 1:1.

[0080] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 9.5 h at pH 4±0.2, 70℃, and 300 rpm, wherein the molar ratio of modifier to nano-clay is 2:1.

[0081] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 8 hours, filtered, washed, and dried at 70℃ to constant weight to obtain modified nano-clay.

[0082] Example 3: A method for preparing modified polylactic acid plastic, the steps of which are as follows:

[0083] S1-1. The modified nano-clay and PLA were vacuum dried at 70℃ for 5 hours.

[0084] S1-2. Weigh the dried PLA, modified nano-clay, and antioxidant (composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:2.5) according to the proportion, put them into a high-speed mixer, and mix them at 800 rpm for 10 min to obtain a premix. The mass percentage of modified nano-clay in the premix is ​​5%, and the mass percentage of antioxidant in the premix is ​​0.5%.

[0085] S1-3. Feed the premixed material into the twin-screw extruder. During the feeding process, pay attention to matching the feeding rate with the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: feed section temperature is 165℃, melt section temperature is 180℃, mixing section temperature is 185℃, die section temperature is 180℃, and screw speed is 250rpm. Before use, the extruder should be preheated to the set temperature and stabilized for 10 minutes before feeding. After the extruded material is cooled by 20℃ cooling water, it is granulated to obtain modified polylactic acid plastic with a particle length of 2-3mm.

[0086] The preparation steps of the modified nano-clay are as follows:

[0087] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:80mL to obtain suspension A;

[0088] S2-2. Dissolve the modifier in deionized water at a ratio of 1g:15mL to obtain a modifier solution. The modifier is composed of SDS and alkylamide carboxybetaine in a molar ratio of 1:2. The alkylamide carboxybetaine is composed of CAPB and LAPB in a molar ratio of 1:2.

[0089] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 6 hours at pH 4±0.2, 80℃, and 100rpm, wherein the molar ratio of modifier to nano-clay is 3:1.

[0090] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 10 hours, filtered, washed, and dried at 65℃ to constant weight to obtain modified nano-clay.

[0091] Comparative Example 1

[0092] Same as Example 1, except that: the nano-clay was not modified, and the specific steps for preparing polylactic acid plastic are as follows:

[0093] The preparation method of modified polylactic acid plastics includes the following steps:

[0094] S1-1. Vacuum dry nano-clay and PLA at 60℃ for 6h;

[0095] S1-2. Weigh the dried PLA, nano clay, and antioxidant (composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.5) according to the proportion, put them into a high-speed mixer, and mix at 800 rpm for 10 minutes to obtain a premix. The mass percentage of nano clay in the premix is ​​2.5%, and the mass percentage of antioxidant in the premix is ​​0.4%.

[0096] S1-3. Feed the premixed material into the twin-screw extruder. During the feeding process, pay attention to matching the feeding rate with the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: feed section temperature is 170℃, melt section temperature is 185℃, mixing section temperature is 190℃, die section temperature is 180℃, and screw speed is 200rpm. Before use, the extruder should be preheated to the set temperature and stabilized for 10 minutes before feeding. After the extruded material is cooled by 20℃ cooling water, it is granulated to obtain modified polylactic acid plastic with a particle length of 2-3mm.

[0097] Comparative Example 2

[0098] Same as Example 1, except that: only SDS is used to modify the nano-clay. The specific preparation steps of the modified nano-clay are as follows:

[0099] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0100] S2-2. Dissolve SDS in deionized water at a ratio of 1g:20mL to obtain a modifier solution;

[0101] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0102] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0103] Comparative Example 3

[0104] Same as Example 1, except that: only alkylamide carboxybetaine is used to modify the nano-clay. The specific preparation steps of the modified nano-clay are as follows:

[0105] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0106] S2-2. Dissolve the modifier in deionized water at a ratio of 1g:20mL to obtain a modifier solution. The modifier is composed of CAPB and LAPB in a molar ratio of 1:1.5.

[0107] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0108] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0109] Comparative Example 4

[0110] Same as Example 1, except that only CAPB was used to modify the nano-clay. The specific preparation steps of the modified nano-clay are as follows:

[0111] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0112] S2-2. Dissolve CAPB in deionized water at a ratio of 1g:20mL to obtain a modifier solution;

[0113] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0114] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0115] Comparative Example 5

[0116] Same as Example 1, except that only LAPB was used to modify the nano-clay. The specific preparation steps of the modified nano-clay are as follows:

[0117] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0118] S2-2. Dissolve LAPB in deionized water at a ratio of 1g:20mL to obtain a modifier solution;

[0119] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0120] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0121] Comparative Example 6

[0122] Same as Example 1, except that: alkyl amide carboxybetaine CAPB and LAPB are replaced with an equal amount of carboxybetaine—N-alkyl carboxybetaine. The specific preparation steps of the modified nanoclay are as follows:

[0123] S2-1. Disperse the nano-clay in anhydrous ethanol at a ratio of 1g:100mL to obtain suspension A;

[0124] S2-2. Dissolve N-alkylcarboxybetaine in deionized water at a ratio of 1g:20mL to obtain a modifier solution;

[0125] S2-3. After adding the modifier solution to the suspension A, stir and modify it for 8 hours at pH 4±0.2, 75℃, and 200rpm, wherein the molar ratio of modifier to nano-clay is 2.5:1.

[0126] S2-4. After modification, the material is cooled, allowed to stand at room temperature for 12 hours, filtered, washed, and dried at 60℃ to constant weight to obtain modified nano-clay.

[0127] Pure PLA and the modified PLA obtained in Examples 1-3 and Comparative Examples 1-6 were prepared into samples of the same specifications. The performance of the samples was tested under the same conditions, and the results are shown in Tables 1 and 2.

[0128] Table 1 Results of mechanical property tests on samples

[0129] Tensile strength / MPa Elongation at break / % <![CDATA[Impact strength / kJ·m 2 > PLA 51.67±0.33h 6.88±0.12g 2.75±0.25d Example 1 77.50±0.54a 20.64±0.36a 7.59±0.41a Example 2 76.89±0.11b 19.76±0.24b 7.40±0.49a Example 3 78.54±0.46b 20.91±0.39a 7.67±0.35a Comparative Example 1 59.42±0.42g 13.07±0.27f 4.25±0.25c Comparative Example 2 69.75±0.25c 13.76±0.24e 5.31±0.31b Comparative Example 3 63.29±0.29d 16.51±0.49c 5.07±0.23b Comparative Example 4 64.59±0.41e 15.96±0.24d 4.64±0.36bc Comparative Example 5 62.78±0.22ef 16.79±0.21c 4.98±0.32b Comparative Example 6 62.54±0.37f 16.05±0.41d 5.01±0.14b

[0130] Note: Different lowercase letters in the same column in the table indicate a significant difference between the two (P < 0.05).

[0131] Table 2 Results of sample barrier performance testing

[0132]

[0133] Note: Different lowercase letters in the same column in the table indicate a significant difference between the two (P < 0.05).

[0134] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a modified polylactic acid plastic, characterized by, Includes the following steps: Modified nano-clay and PLA are vacuum dried; then the dried modified nano-clay, PLA and antioxidant are mixed at high speed to obtain a premix; the premix is ​​melted, extruded, cooled and granulated to obtain modified polylactic acid plastic. The preparation method of the modified nano-clay includes the following steps: Nano-clay was dispersed in anhydrous ethanol to obtain suspension A; then the modifier was dissolved in deionized water, added to suspension A for modification, and after modification, cooled, allowed to stand, filtered, washed and dried to obtain modified nano-clay. The modifier is composed of sodium dodecyl sulfonate and alkylamide carboxybetaine; The alkylamide carboxybetaine is composed of cocamidopropyl betaine and lauramide propyl betaine in a molar ratio of 1:(1~2); The modifier is composed of sodium dodecyl sulfonate and alkylamide carboxybetaine in a molar ratio of (2~4):(6~8); The molar ratio of the modifier to the nano-clay is (2~3):1; The modification temperature is 70°C~80°C, the modification time is 5~10 h, and the modification pH is 4±0.

2.

2. The production method according to claim 1, characterized by, The amount of modified nano-clay added in the premix is ​​2wt.%~5wt.%.

3. The preparation method according to claim 1, characterized in that, The amount of antioxidant added in the premix is ​​0.3 wt.% to 0.5 wt.%.

4. The method of claim 1, wherein, The mass-to-volume ratio of the nano-clay to anhydrous ethanol is 1 g / (50~100) mL.

5. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the modifier to deionized water is 1 g / (10~20) mL.

6. The production method according to claim 1, characterized by, The D of the nanoclay 50 The wavelength range is 50~100 nm, and the interlayer spacing is ≥2.5 nm.

7. A modified polylactic acid plastic, characterized in that, Prepared by the method described in any one of claims 1-6.

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