Modified polylactic acid plastic and preparation method thereof

Abstract

The invention provides a modified polylactic acid plastic and a preparation method thereof, and relates to the technical field of modified plastics. The modified polylactic acid plastic is prepared by premixing sodium dodecyl sulfate and alkyl amide carboxyl betaine modified nano clay, PLA and an antioxidant, melting, extruding, cooling and granulating. According to the present invention, the sodium dodecyl sulfate and alkyl amide carboxyl betaine compound modifier is adopted to modify the nano-clay, such that the hydrogen-bond interaction between the modified nano-clay and the PLA ester group is enhanced, and the interface bonding force is improved, such that the modified PLA has characteristics of good barrier property, good mechanical property, good impact resistance and good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of modified plastics, and particularly relates to a modified polylactic acid plastic and a preparation method thereof. Background Art

[0002] Degradable plastics refer to plastic materials that can gradually decompose into harmless substances (such as water, carbon dioxide, and inorganic salts) through biological, chemical, or physical actions in the natural environment or under specific conditions. According to the degradation mechanism, degradable plastics can be divided into photo-degradable plastics, bio-degradable plastics, and photo / bio double-degradable plastics. Degradable plastics are widely used in the fields of packaging, agriculture, medical and health, disposable products, etc.

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

[0004] PLA is made from renewable plant resources (such as corn, sugarcane, cassava, etc.). Glucose is obtained by starch hydrolysis, then lactic acid is generated through microbial fermentation, and finally it is polymerized by chemical synthesis methods. Lactic acid has good biocompatibility and can be absorbed and metabolized by the human body. Therefore, it is widely used in the medical field. It is a completely biodegradable material, friendly to the environment, non-toxic, non-irritating, and the decomposition product lactic acid can be metabolized by the human body without accumulating in the body.

[0005] It is of great significance to study modified polylactic acid (PLA) with good mechanical properties and barrier properties, which is mainly reflected in the following aspects:

[0006] At present, the barrier properties, mechanical properties, and impact resistance of pure PLA are poor. This makes it difficult for pure PLA films to meet the requirements for gas and water vapor barrier properties in food preservation, drug packaging, etc. In the fields of medical devices and drug carriers, the mechanical properties of pure PLA also cannot ensure the structural stability and durability. Therefore, it is of great significance to study modified PLA with good mechanical properties and barrier properties.

[0007] The invention patent with the publication number CN103709695A discloses a PLA modified material, its preparation method and a PLA biodegradable ground film. The modified material contains PLA, PBAT, modified talcum powder, antioxidant, ultraviolet absorber, light stabilizer, antiblocking agent, chain extender and initiator. Based on the total weight of the modified material, it contains 58 - 80 wt% of PLA, 15 - 40 wt% of PBAT, 0.1 - 5 wt% of modified talcum powder, 0.1 - 2 wt% of antioxidant, 0.1 - 1 wt% of ultraviolet absorber, 0.1 - 2 wt% of light stabilizer, 0.1 - 2 wt% of antiblocking agent, 0.1 - 1 wt% of chain extender, and 0.0005 - 0.05 wt% of initiator. By adding PBAT to PLA and using a chain extender to compatibilize the polymer in this invention, the prepared material retains the characteristics of high strength, high light transmittance and high cost performance of PLA after blow molding into a film, and at the same time improves the flexibility.

[0008] The invention patent with the publication number CN105199347A discloses a PLA / MMT degradation - enhanced masterbatch - blended and modified PLA / PBAT composite material and its preparation method. This method uses polylactic acid (PLA), poly(butylene adipate - co - terephthalate) (PBAT) and a PLA / MMT degradation - enhanced masterbatch as raw materials. After uniformly mixing 10 - 90 parts of PLA, 10 - 90 parts of PBAT and 5 - 30 parts of the PLA / MMT degradation - enhanced masterbatch, it is melt - blended and modified to prepare a PLA / PBAT composite material with excellent performance. The PLA / MMT degradation - enhanced masterbatch is prepared by using an intercalating agent and a co - intercalating agent to prepare organophilic montmorillonite through ion exchange, increasing the layer spacing between montmorillonite, and then inserting monomers or polylactic acid molecular chains into the interlayer of montmorillonite through in - situ melt polymerization. The PLA / MMT degradation - enhanced masterbatch - blended and 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, these modification methods fail to simultaneously improve the barrier property, mechanical property and impact resistance of PLA. Summary of the Invention

[0010] In view of this, the present invention provides a modified polylactic acid plastic and its preparation method. By mixing nano - clay modified with sodium dodecyl sulfate (SDS) and alkylamide carboxybetaine with PLA for granulation, the modified PLA plastic product has good barrier property, mechanical property and impact resistance at the same time.

[0011] The first aspect of the present invention is to provide a preparation method of a modified polylactic acid plastic, which includes the following steps:

[0012] The modified nano-clay and PLA are subjected to vacuum drying treatment; 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 pelletized to obtain the modified polylactic acid plastic.

[0013] Preferably, the addition amount of the modified nano-clay is 2 wt.% to 5 wt.%, and the addition amount of the antioxidant is 0.3 wt.% to 0.5 wt.%. 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 in the present invention includes the following steps:

[0015] Disperse the nano-clay in absolute ethanol to obtain suspension A, then dissolve the modifier in deionized water, and then add the suspension A for modification. After the modification is completed, it is cooled, allowed to stand, filtered, washed, and dried to obtain the 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 sulfate (SDS) and alkylamide carboxybetaine, and the molar ratio of SDS to alkylamide carboxybetaine is (2 - 4):(6 - 8). More preferably, the alkylamide carboxybetaine is composed of coconut oil amide propyl betaine (CAPB) and lauryl amide propyl betaine (LAPB) in a molar ratio of 1:(1 - 2).

[0018] Preferably, the mass-to-volume ratio of the nano-clay to absolute 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 modification pH is 4 ± 0.2, the modification temperature is 70°C to 80°C, and the modification time is 5 - 10 h. More preferably, the modification is carried out under stirring conditions, and the stirring rate is 100 - 300 rpm.

[0020] Preferably, the standing temperature is room temperature, and the standing time is 8 - 12 h.

[0021] Preferably, the drying temperature is 60°C to 70°C.

[0022] Preferably, the D 50 of the nano-clay is 50 - 100 nm, and the layer spacing ≥ 2.5 nm.

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

[0024] The third aspect of the present invention is to provide an application of the modified polylactic acid plastic in the preparation of a degradable, high-barrier and high-strength material, and the modified polylactic acid plastic is the modified polylactic acid plastic described in the above solution.

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

[0026] The present invention uses a compound modifier of sodium dodecyl sulfate and alkylamide carboxybetaine to modify nano-clay. Through charge complementarity and steric hindrance effects, the interlayer exfoliation efficiency of nano-clay layers is improved. Also, the hydrogen bond interaction with the ester group of PLA is enhanced by the polar group of betaine, and the interfacial binding force is improved.

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

[0028] The modified polylactic acid plastic of the present invention has good comprehensive properties, a wide range of applicable scenarios, and the preparation process is the same as that of traditional polylactic acid plastics without additional cost investment, having good application prospects. Detailed Embodiments

[0029] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The present invention provides a modified polylactic acid plastic and its preparation method and application. By modifying polylactic acid, the mechanical properties, processing properties and barrier properties of the polylactic acid plastic are improved.

[0031] The preparation method of 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 °C to 80 °C for 4 to 6 hours;

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

[0034] S1-3. Feed the premix into a twin-screw extruder. During the feeding process, pay attention to the matching of the feeding rate and the screw rotation speed to avoid material blockage. Before using the extruder, preheat it to the set temperature and keep it stable for at least 10 min before feeding. The extruded material is cooled by cooling water at 20°C - 25°C and then pelletized to obtain modified polylactic acid plastic with a pellet length of 2 - 3 mm.

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

[0036] The modified nano-clay of the present invention has good dispersibility and compatibility in PLA. Therefore, the amount of the modified nano-clay can be reduced to a certain extent, but still needs to be maintained within a reasonable range. If the amount of nano-clay is too low, a continuous and uniform network structure cannot be formed, and the performance improvement is insufficient. When the addition amount of the modified nano-clay is too high, the dispersibility decreases. Aggregates can be found by SEM observation, the melt viscosity increases, the processing performance deteriorates, and problems such as broken strips will occur during the extrusion process, and the comprehensive performance of PLA will decrease significantly. Therefore, the present invention limits the addition amount of the modified nano-clay to 2 wt.% - 5 wt.% of PLA. Within this range, the dispersibility of the modified nano-clay and the number of modified groups are in a better interval, thereby improving the comprehensive 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 - 2.5).

[0038] Antioxidant 1010 is a hindered phenol antioxidant, and antioxidant 168 is a phosphite antioxidant. Among them, antioxidant 1010 is the main antioxidant, mainly used to inhibit the oxidation chain reaction initiated by free radicals. Antioxidant 168 is an auxiliary antioxidant, mainly used to decompose the peroxides generated during the processing of polymers, thereby inhibiting the chain propagation of the oxidation reaction and reducing the secondary generation of free radicals. The present invention preferably uses a composite antioxidant composed of antioxidant 1010 and antioxidant 168 to inhibit the thermal oxidative degradation of PLA through a free radical capture - peroxide decomposition synergistic mechanism. In the present invention, the ratio of antioxidant 1010 and antioxidant 168 is affected by the free radical generation rate and the peroxide accumulation rate. Therefore, the ratio of the two needs to be adjusted according to the actual situation 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°C to 170°C, the temperature of the melting section is 175°C to 185°C, the temperature of the mixing section is 180°C to 190°C, the temperature of the die head section is 175°C to 180°C, and the screw speed is 200 to 300 rpm. High screw speed can enhance shear dispersion, but too high a speed will generate excessive shear force and heat, resulting in a sharp rise in local temperature, which will break the PLA molecular chains and reduce the molecular weight. 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 absolute ethanol to obtain suspension A;

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

[0043] S2-3: Add the modifier solution to suspension A for modification;

[0044] S2-4: After the modification is completed, cool, stand, filter, wash, and dry to constant weight to obtain the 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] Among the modifiers used in the present invention, SDS can replace the metal cations between the nano-clay layers through ion exchange, expand the nano-clay layer spacing (≥2.5 nm), and promote the clay to peel into nano-sheets. The hydrophobic alkyl chains of CAPB and LAPB are inserted into the layers synergistically with SDS, and the hydrophilic carboxyl and quaternary ammonium groups inhibit the re-aggregation between the layers through steric hindrance effects, improving the dispersion of the modified nano-clay in PLA. At the same time, the long-chain alkyl group of SDS and the hydrophobic group of betaine cover the surface of the clay, reducing its surface energy, 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 group of betaine forms hydrogen bonds with the ester group of PLA, strengthening the interfacial binding force and enhancing the mechanical properties of the modified PLA.

[0048] However, in the research, it was found that the mixed system of alkyl amide carboxy betaine and sodium dodecyl sulfonate in a pure water system showed an antagonistic effect. To solve this problem, the present invention defines the modified pH as 4 ± 0.2, and the adjustment of this pH is carried out by hydrochloric acid. Under this condition, the antagonistic effect of the mixed system of alkyl amide carboxy betaine and SDS hardly exists, and thus the modification can be carried out smoothly, promoting intercalation, optimizing the intercalation efficiency, and avoiding agglomeration.

[0049] In addition, the sulfonic acid group and the quaternary ammonium group of betaine can neutralize the surface charge of the clay, reduce the agglomeration caused by electrostatic attraction, and further improve the uniform distribution of nano-clay in PLA. The hydrophobic surface of the modified clay is more easily infiltrated by molten PLA, enhancing the processing fluidity, that is, improving the processing performance.

[0050] In the alkyl amide carboxy betaine modifier used in the present invention, the alkyl chain of CAPB is relatively long (C12-C18 mixed chain), and its relatively large hydrophobic volume can provide a stronger steric hindrance effect, significantly expanding the layer spacing of nano-clay and promoting the clay to peel into nano-sheets. However, the presence of the long chain will lead to a decrease in the intercalation efficiency. The long hydrophobic chain of CAPB has better compatibility with the hydrophobic groups of PLA, but the density of carboxylic acid groups is relatively low (due to the large molecular volume), and the hydrogen bond interaction is relatively weak compared to LAPB. While the alkyl chain of LAPB is shorter (C12 single chain), the molecular volume is smaller, and the intercalation efficiency is higher, but the steric hindrance effect is weak, the layer spacing is smaller than that of CAPB, and the ability to inhibit the re-packing between layers is relatively weak, and the long-term stability is worse than that of CAPB. However, LAPB has a higher density of carboxylic acid groups and can form more hydrogen bonds with the ester groups of PLA.

[0051] Therefore, the present invention uses CAPB and LAPB in combination, and combines with SDS to modify nano-clay to achieve better modification effects. When CAPB and LAPB are used in combination, the long chain of CAPB expands the layer spacing, the short chain of LAPB fills the interlayer voids, forming a more stable intercalation structure and inhibiting clay agglomeration; the long chain of CAPB enhances the hydrophobic compatibility, and the carboxylic acid groups of LAPB strengthen the hydrogen bond interaction, comprehensively improving the interfacial binding force; the mixed surfactant can also form composite micelles to accelerate the intercalation process.

[0052] Finally, in order to achieve good synergistic effects, the present invention defines 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 layer spacing, dispersibility and interfacial binding performance.

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

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

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

[0056] The third aspect of the present invention is to provide an application of the modified polylactic acid plastic in the preparation of degradable, high-barrier, and high-strength materials, and the modified polylactic acid plastic is the modified polylactic acid plastic described in the above solution.

[0057] The high-barrier performance of the modified PLA plastic of the present invention can effectively prevent the penetration of oxygen and water vapor, and extend the shelf life of food. At the same time, its good mechanical properties and processing properties enable it to be made into various-shaped packaging containers, films, and fresh-keeping boxes. In pharmaceutical packaging, the modified PLA plastic of the present invention can provide good barrier properties to prevent drugs from being affected by moisture and oxidation. In electronic product packaging, the modified PLA plastic of the present invention can also prevent electronic components from being affected by moisture and provide sufficient protection for electronic components.

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

[0059] The modified PLA plastic of the present invention can also be used for the production of disposable products, and its degradability can also reduce the impact on the environment.

[0060] Processing the modified PLA of the present invention into fibers can spin high-strength fibers, and at the same time its barrier properties can endow the fabric with certain waterproof properties.

[0061] The good processing properties and mechanical properties of the modified PLA plastic of the present invention enable it to be used as a consumable for 3D printing and can be used to manufacture various products.

[0062] To further illustrate the present invention, the following examples are used for detailed description. The raw materials used in the following examples of the present invention are all commercially available, and the nano-clay is purchased from Shanghai Macklin Reagent.

[0063] Unless otherwise specified, all tests are repeated 3 times. ANOVA (Analysis of Variance) and Duncan multiple comparison analysis are performed using SPSS 21.0, and the results are expressed as mean ± standard deviation. A significant difference is indicated when P < 0.05.

[0064] Example 1 A preparation method of modified polylactic acid plastic is as follows:

[0065] S1-1. Vacuum dry the modified nano-clay and PLA at 60 °C for 6 h;

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

[0067] S1-3. Feed the premix into a twin-screw extruder. During the feeding process, pay attention to the matching of the feeding rate and the screw rotation speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: the temperature of the feeding section is 170 °C, the temperature of the melting section is 185 °C, the temperature of the mixing section is 190 °C, the temperature of the die head section is 180 °C, the screw rotation speed is 200 rpm. The extruder is preheated to the set temperature before use and stabilized for 10 min before feeding. The extruded material is cooled by 20 °C cooling water and then pelletized to obtain modified polylactic acid plastic with a particle length of 2 - 3 mm.

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

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

[0070] S2-2. Dissolve the modifier in deionized water at a ratio of 1 g:20 mL 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 suspension A, stir and modify at pH 4 ± 0.2, 75 °C, and 200 rpm for 8 h, where the molar ratio of the modifier to the nano-clay is 2.5:1;

[0072] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nano-clay.

[0073] Example 2 A preparation method of modified polylactic acid plastic is as follows:

[0074] S1-1. Vacuum dry the modified nano-clay and PLA at 80 °C for 4 h;

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

[0076] S1-3. Feed the premix into a twin-screw extruder. During the feeding process, pay attention to the matching of the feeding rate and the screw rotation speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: the temperature of the feeding section is 160 °C, the temperature of the melting section is 175 °C, the temperature of the mixing section is 180 °C, the temperature of the die head section is 175 °C, the screw rotation speed is 300 rpm. The extruder is preheated to the set temperature before use and stabilized for 10 minutes before feeding. The extruded material is cooled by 25 °C cooling water and then pelletized to obtain modified polylactic acid plastic with a pellet length of 2 - 3 mm.

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

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

[0079] S2-2. Dissolve the modifier in deionized water at a ratio of 1 g:10 mL 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 suspension A, stir and modify it at pH 4 ± 0.2, 70 °C, and 300 rpm for 9.5 hours, where the molar ratio of the modifier to the nano-clay is 2:1;

[0081] S2-4. After the modification is completed, cool it, let it stand at room temperature for 8 hours, filter, wash, and dry it at 70 °C to constant weight to obtain the modified nano-clay.

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

[0083] S1-1. Vacuum-dry the modified nano-clay and PLA at 70 °C for 5 hours;

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

[0085] S1-3. Feed the premix into a twin-screw extruder. During the feeding process, pay attention to the matching of the feeding rate and the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: the temperature of the feeding section is 165 °C, the temperature of the melting section is 180 °C, the temperature of the mixing section is 185 °C, the temperature of the die head section is 180 °C, the screw speed is 250 rpm. The extruder is preheated to the set temperature before use and stabilized for 10 min before feeding. The extruded material is cooled by 20 °C cooling water and then pelletized to obtain modified polylactic acid plastic with a pellet length of 2 - 3 mm.

[0086] The preparation steps of the modified nanoclay are as follows:

[0087] S2-1. Disperse the nanoclay in absolute ethanol at a ratio of 1 g:80 mL to obtain suspension A.

[0088] S2-2. Dissolve the modifier in deionized water at a ratio of 1 g:15 mL to obtain a modifier solution. The modifier is composed of SDS and alkylamide carboxybetaine in a molar ratio of 1:2, and 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 suspension A, stir and modify at pH 4 ± 0.2, 80 °C, and 100 rpm for 6 h, where the molar ratio of the modifier to the nanoclay is 3:1.

[0090] S2-4. After the modification is completed, cool, let it stand at room temperature for 10 h, filter, wash, and dry at 65 °C to constant weight to obtain the modified nanoclay.

[0091] Comparative Example 1

[0092] Same as Example 1, the difference is that the nanoclay is not modified. The specific preparation steps of the polylactic acid plastic are as follows:

[0093] The preparation method of the modified polylactic acid plastic is as follows:

[0094] S1-1. Vacuum-dry the nanoclay and PLA at 60 °C for 6 h.

[0095] S1-2. Weigh the dried PLA, nano-clay, and antioxidant (composed of antioxidant 1010 and antioxidant 168 with a mass ratio of 1:1.5) proportionally, put them into a high-speed mixer, and mix at 800 rpm for 10 min 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 premix into a twin-screw extruder. During the feeding process, pay attention to the matching of the feeding rate and the screw speed to avoid material blockage. The parameters of the twin-screw extruder are set as follows: the temperature of the feeding section is 170 °C, the temperature of the melting section is 185 °C, the temperature of the mixing section is 190 °C, the temperature of the die head section is 180 °C, the screw speed is 200 rpm. The extruder is preheated to the set temperature before use and stabilized for 10 min before feeding. The extruded material is cooled by 20 °C cooling water and then pelletized to obtain modified polylactic acid plastic with a pellet length of 2 - 3 mm.

[0097] Comparative Example 2

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

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

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

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

[0102] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nano-clay.

[0103] Comparative Example 3

[0104] Same as Example 1, the difference is that: only alkyl amide carboxy betaine is used to modify the nano-clay, and the specific preparation steps of the modified nano-clay are as follows:

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

[0106] S2-2. Dissolve the modifier in deionized water at a ratio of 1 g:20 mL 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 for 8 h at pH 4 ± 0.2, 75 °C, and 200 rpm, where the molar ratio of the modifier to the nanoclay is 2.5:1;

[0108] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nanoclay.

[0109] Comparative Example 4

[0110] Same as Example 1, except that: only CAPB is used to modify the nanoclay, and the specific preparation steps of the modified nanoclay are as follows:

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

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

[0113] S2-3. After adding the modifier solution to the suspension A, stir and modify for 8 h at pH 4 ± 0.2, 75 °C, and 200 rpm, where the molar ratio of the modifier to the nanoclay is 2.5:1;

[0114] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nanoclay.

[0115] Comparative Example 5

[0116] Same as Example 1, except that: only LAPB is used to modify the nanoclay, and the specific preparation steps of the modified nanoclay are as follows:

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

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

[0119] S2-3. After adding the modifier solution to the suspension A, stir and modify for 8 h at pH 4 ± 0.2, 75 °C, and 200 rpm, where the molar ratio of the modifier to the nanoclay is 2.5:1;

[0120] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nanoclay.

[0121] Comparative Example 6

[0122] Same as Example 1, with the difference that: the alkylamide carboxybetaines CAPB and LAPB are replaced with an equal amount of carboxybetaine - N-alkyl carboxybetaine. The specific preparation steps of the modified nano-clay are as follows:

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

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

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

[0126] S2-4. After the modification is completed, cool, let stand at room temperature for 12 h, filter, wash, and dry at 60 °C to constant weight to obtain the modified nano-clay.

[0127] Prepare the pure PLA and the modified PLA obtained in Examples 1-3 and Comparative Examples 1-6 into samples of the same specification, and test the performance of the samples under the same conditions. The results are shown in Tables 1 and 2.

[0128] Table 1 Test results of the mechanical properties of the 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 ± 0.36 bc Comparative Example 5 62.78 ± 0.22 ef 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 Test results of the barrier properties of the samples

[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 above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing modified polylactic acid plastic, characterized in that: The following steps are involved: The modified nanoclay and PLA are vacuum dried; the dried modified nanoclay, PLA and antioxidant are then mixed at high speed to obtain a premix; the premix is ​​melted, extruded, cooled and granulated to obtain a modified polylactic acid plastic; The preparation method of the modified nanoclay comprises the following steps: The nanoclay is dispersed in anhydrous ethanol to obtain a suspension A; then a modifier is dissolved in deionized water, and the suspension A is added thereto for modification, and after the modification is completed, the suspension is cooled, allowed to stand, filtered, washed, and dried to obtain a modified nanoclay; The modifier consists of sodium dodecyl sulfate and alkylamide carboxy betaine.

2. The preparation method according to claim 1, characterized in that: The added amount of modified nanoclay in the premix is ​​2wt.%~5wt.%.

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

4. The preparation method according to claim 1, characterized in that: The molar ratio of the modifier to the nanoclay is (2-3):1, and the modifier is sodium dodecyl sulfate and alkylamide carboxy betaine.

5. The preparation method according to claim 1, characterized in that: The mass volume ratio of the nanoclay and anhydrous ethanol is 1 g / (50-100) mL.

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

7. The preparation method according to claim 1, characterized in that: The modification temperature is 70°C to 80°C, and the modification time is 5 to 10 h.

8. The preparation method according to claim 1, characterized in that: The D 50 The thickness of the nanostructured carbon nanotubes is 50~100 nm, and the interlayer spacing is ≥2.5 nm.

9. A modified polylactic acid plastic, characterized in that: Prepared by the method according to any one of claims 1 to 8.

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