High-strength and high-toughness polylactic acid composite material and preparation method thereof

Abstract

The invention provides a high-strength and high-toughness polylactic acid composite material and a preparation method thereof. According to the invention, a branched polymer or a segmented copolymer containing both dextropolylactic acid and a bio-based random copolyester elastomer molecular chain is adopted, the segmented copolymer is added into the PLA / TPV composite material as a third component, the compatibility of a matrix and a dispersed phase is improved, and the segmented copolymer can be self-assembled with the matrix poly (L-lactic acid) to form a stereocomplex crystal, so that the stability of the composite material is improved, and the service life of the composite material is prolonged. The surface of the soft tough dispersed phase is coated with the hard shell, so that the toughening effect and the strength modulus retention rate are further improved.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials and composite materials, and particularly relates to a high-strength and high-toughness polylactic acid composite material and a preparation method thereof. Background Art

[0002] The raw material of polylactic acid (PLA) is derived from plant starch, and it shows good compost degradation behavior in the short term. It is regarded as the most promising bio-based degradable engineering plastic. However, the characteristics of large brittleness and insufficient toughness of polylactic acid severely limit its application. In response to this problem, researchers at home and abroad have been continuously committed to the toughening modification research of polylactic acid.

[0003] In the existing research work, the toughening modification ideas of polylactic acid are mainly divided into chemical copolymerization modification and physical blending modification. Generally speaking, the process of chemical copolymerization is more difficult, and the existence of blocks is extremely likely to destroy the crystallization of polylactic acid, resulting in a decrease in the strength of the material. In contrast, the physical blending method has a simple operation process, is not easy to destroy the crystallization behavior of polylactic acid, and has a more significant toughening effect. Therefore, it is also the main idea for researchers to toughen and modify polylactic acid. In recent years, with the proposal of the requirements of sustainable development and the "dual carbon" strategy, the toughening research of polylactic acid has shown a trend of renewable and degradable. More and more bio-based materials and degradable materials have been added as toughening components to the polylactic acid matrix.

[0004] In the research work on the modification of polylactic acid with bio-based materials, the polylactic acid composite material toughened by blending with natural rubber (Chinese Patent CN107459793A) or epoxidized natural rubber (Chinese Patent CN109401243A) and dynamically vulcanized shows significant effects. The notch impact strength can reach more than 70 kJ / m 2 above, meeting the super-tough standard, but the tensile strength is reduced to about half of that of pure polylactic acid; the notch impact strength of polylactic acid toughened by natural Eucommia rubber can be increased to nearly 50 kJ / m 2, but the strength loss is nearly 50 MPa (Yan Wang, Jinhui Liu, Lin Xia, Mei Shen, Zhenxiang Xin, Polymer Testing, Volume 80, 2019, 106077,). In the research on the modification of polylactic acid with degradable materials, Zhang et al. melt-blended biodegradable polyamide elastomer (PAE) with PLA, and the elongation at break of the blend increased to 194.6%, while the tensile strength decreased from 70 MPa to 40.9 MPa (Zhang W, et al. Polymer, 2009, 50(5), 1311); in addition, various degradable toughening plastics such as PBAT (P. Pukpanta, et al. Advanced Materials Research, 2012, 1768), PHBV (Sun Haimeng, et al. International Biodeterioration & Biodegradation, 2019, 146) have also been used in the toughening modification research of PLA materials and achieved certain toughening effects.

[0005] However, although the above-mentioned blending modification works have all achieved certain effects, due to the physical property differences and insufficient compatibility of the two-phase materials, it inevitably leads to a significant decrease in strength and modulus after blending and compounding. This sacrifice of strength and modulus severely restricts the application fields of polylactic acid. The reason is that on the one hand, the decrease in the strength of the material after blending and compounding stems from the difference in compatibility of the two-phase materials, and on the other hand, due to the addition of the second component, the crystallization ability of polylactic acid is restricted. So far, almost all the research works on the toughening modification of polylactic acid are accompanied by the sacrifice of the strength and modulus of the matrix, and usually, the more significant the toughening effect, the more obvious the decrease in the strength and modulus of the material. This influence of blending toughening on compatibility and crystallization performance makes it difficult to prepare high-strength and high-toughness polylactic acid composites. Summary of the Invention

[0006] Aiming at the problem of significant strength decrease during the toughening modification of polylactic acid mentioned above, the present invention uses bio-based degradable thermoplastic vulcanizate to toughen and modify polylactic acid, and by introducing a third component of dextrorotatory polylactic acid-based block copolymer into the toughened and modified polylactic acid composite material, the compatibility is improved and the matrix crystallization ability is enhanced at the same time, so as to prepare a high-compatibility, high-strength and high-toughness polylactic acid composite material without affecting the toughening effect. The preparation process of the third component is simple and the modification efficiency is extremely high. Only a small amount can significantly improve the strength of the toughened polylactic acid.

[0007] One of the purposes of the present invention is to provide a method for preparing a high-strength and high-toughness polylactic acid composite material, which includes: toughening and modifying polylactic acid with a bio-based thermoplastic vulcanizate, and adding a third component and reacting to obtain a polylactic acid composite material; wherein, the bio-based thermoplastic vulcanizate is a blend of a bio-based random copolyester elastomer, a vulcanizing agent, and polylactic acid, and the third component is the reaction product of dextrorotatory polylactic acid, a bio-based random copolyester elastomer, a polyfunctional isocyanate, and / or a polyfunctional epoxide. Preferably, the bio-based random copolyester elastomer in the third component and the bio-based random copolyester elastomer in the bio-based thermoplastic vulcanizate are prepared from the same comonomers.

[0008] In the present invention, the bio-based thermoplastic vulcanizate can be a bio-based thermoplastic vulcanizate commonly used in the prior art or prepared by a method in the prior art. For example, it can be obtained by referring to the preparation method in Patent CN114507424A, and the relevant content disclosed in the foregoing document is incorporated into the present invention for reference.

[0009] In the present invention, the bio-based random copolyester elastomer can be a bio-based random copolyester elastomer commonly used in the prior art or prepared by a method in the prior art. For example, it can be obtained by referring to the preparation methods in Patents CN113136027A, CN101450985, CN111621005A, CN112708251A, and CN115073716A, and the relevant content disclosed in the foregoing documents is incorporated into the present invention for reference.

[0010] In the method for preparing the polylactic acid composite material provided by the present invention, based on 100 parts by weight of the polylactic acid, the bio-based thermoplastic vulcanizate is 5 to 60 parts, and the third component is 1 to 15 parts; preferably, based on 100 parts by weight of the polylactic acid, the bio-based thermoplastic vulcanizate is 40 to 60 parts, and the third component is 3 to 7 parts. Among them, in the bio-based thermoplastic vulcanizate, based on 100 parts by weight of the bio-based random copolyester elastomer, the dosage of the vulcanizing agent is 0.05 to 2 parts, and the dosage of the polylactic acid is 10 to 70 parts; preferably, in the bio-based thermoplastic vulcanizate, based on 100 parts by weight of the bio-based random copolyester elastomer, the dosage of the vulcanizing agent is 0.1 to 1 part, and the dosage of the polylactic acid is 25 to 55 parts. In the third component, based on the total weight of the dextrorotatory polylactic acid and the bio-based random copolyester elastomer being 100 parts, the dextrorotatory polylactic acid is 10 to 90 parts, the bio-based random copolyester elastomer is 10 to 90 parts, and the polyfunctional isocyanate and / or polyfunctional epoxide is 1 to 15 parts; preferably, based on the total weight of the dextrorotatory polylactic acid and the bio-based random copolyester elastomer being 100 parts, the dextrorotatory polylactic acid is 30 to 70 parts, the bio-based random copolyester elastomer is 30 to 70 parts, and the polyfunctional isocyanate and / or polyfunctional epoxide is 3 to 10 parts.

[0011] In the method for preparing the polylactic acid composite material provided by the present invention:

[0012] The number-average molecular weight of the bio-based random copolyester elastomer is 5,000 to 80,000, preferably 5,000 to 20,000;

[0013] The vulcanizing agent is selected from organic peroxides, preferably at least one of dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxide), and dicumyl peroxide;

[0014] The number-average molecular weight of the polylactic acid is 20,000 to 250,000, preferably 100,000 to 150,000;

[0015] The number-average molecular weight of the dextrorotatory polylactic acid is 5,000 to 120,000, preferably 10,000 to 30,000;

[0016] The polyfunctional isocyanate is selected from at least one of diphenylmethane diisocyanate MDI, hexamethylene diisocyanate HDI, 4,4'-dicyclohexylmethane diisocyanate HMDI, toluene diisocyanate TDI, and L-lysine diisocyanate LDI;

[0017] The multi-functional epoxy compound is selected from at least one of epoxy soybean oil, epoxy cotton and linen seed oil, epoxy rice bran oil, epoxy sunflower seed oil, epoxy camellia seed oil, epoxy safflower seed oil, epoxy sesame oil, epoxy cottonseed oil, epoxy rice oil, epoxy soybean oil, epoxy corn oil, epoxy rapeseed oil, epoxy linseed oil, epoxy peanut oil, epoxy palm oil, glycidyl methacrylate, and polyfunctional epoxy chain extender ADR.

[0018] In the method for preparing the polylactic acid composite material provided by the present invention: based on 100 parts by weight of the bio-based random copolyester elastomer, the bio-based thermoplastic vulcanizate further contains 0.01 to 5 parts of an antioxidant, and the bio-based thermoplastic vulcanizate further contains 0.01 to 50 parts of a plasticizer; preferably, based on 100 parts by weight of the bio-based random copolyester elastomer, the bio-based thermoplastic vulcanizate further contains 0.5 to 1 part of an antioxidant, and the bio-based thermoplastic vulcanizate further contains 0.01 to 30 parts of a plasticizer. The antioxidant is selected from at least one of phosphite antioxidants, peroxide decomposition type antioxidants, phenolic antioxidants, amine type antioxidants, heterocyclic antioxidants, and fatty acid ester antioxidants, preferably at least one of phosphite antioxidants, butylated hydroxyanisole, dibutylhydroxytoluene, tert-butylhydroquinone, tea polyphenols, phytic acid, ascorbic acid, palmitate, and tocopherol; the plasticizer is selected from at least one of citrate plasticizers, ricinoleate plasticizers, vegetable oil-based plasticizers, and polybasic acid ester plasticizers. Preferably, the citrate plasticizer is selected from at least one of tributyl citrate and acetyl tributyl citrate; the vegetable oil-based plasticizer is selected from at least one of soybean oil and its derivatives, tall oil, tung oil, vernonia oil, resorcinol oil, and cashew shell oil; the polybasic acid ester plasticizer is selected from at least one of trioctyl trimellitate, bis(2-ethylhexyl) phthalate, dibutyl phthalate, and diethyl phthalate.

[0019] In the method for preparing the polylactic acid composite material provided by the present invention, the bio-based random copolyester elastomer is a copolymer of a bio-based dicarboxylic acid, a bio-based diol, and an alkyd compound; wherein, the bio-based dicarboxylic acid is selected from at least one of succinic acid, adipic acid, sebacic acid, itaconic acid, hydrogenated dimer acid, dodecanedioic acid, octadecanedioic acid, fumaric acid, maleic acid, terephthalic acid, furandicarboxylic acid, mucic acid, and hydrogenated mucic acid; the bio-based diol is selected from at least one of 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, butenediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, terephthalyl alcohol, furandimethanol, diethylene glycol, glycerol, and pentaerythritol; the alkyd compound is selected from at least one of lactic acid, lactide, and glycolic acid.

[0020] The preparation method of the polylactic acid composite material provided by the present invention includes: melting and blending components including the bio-based thermoplastic vulcanizate, polylactic acid, and a third component, and then obtaining the polylactic acid composite material. Preferably, the temperature of the melting and blending is 180-220°C, preferably 190-210°C; the screw speed of the melting and blending is 60-120 rpm, preferably 80-100 rpm.

[0021] The bio-based thermoplastic vulcanizate is obtained by dynamically vulcanizing components including a bio-based random copolyester elastomer, a vulcanizing agent, and polylactic acid. Among them, the temperature of the dynamic vulcanization is 150-200°C, preferably 160-180°C; before the dynamic vulcanization, an antioxidant and a plasticizer are added to the bio-based random copolyester elastomer for melting and blending. Preferably, the temperature of the melting and blending is 150-190°C.

[0022] The third component is obtained by blending and reacting components including dextrorotatory polylactic acid, a bio-based random copolyester elastomer, a polyfunctional isocyanate, and / or a polyfunctional epoxide.

[0023] Among them, the blending is melting blending or solution blending. Among them, the melting blending can be carried out by using a Haake internal mixer or a twin-screw extruder. The conditions for the melting blending are: temperature 150-200°C, rotation speed 60-120 rpm, time 5-20 min; preferably, the conditions for the melting blending are: temperature 175-185°C, rotation speed 80-100 rpm, time 5-10 min; the operation of the solution blending is: first, dextrorotatory polylactic acid, a bio-based random copolyester elastomer, a polyfunctional isocyanate, and / or a polyfunctional epoxide are uniformly mixed in a solution at normal temperature, the solvent is evaporated after mixing, and then the remaining homogeneous blend is subjected to a heating reaction; preferably, the conditions for the heating reaction are: temperature 150-200°C, time 5-15 min; more preferably, the conditions for the heating reaction are: temperature 175-185°C, time 5-10 min; the solvent used for the solution blending is selected from at least one of dichloromethane, chloroform, and tetrahydrofuran, preferably dichloromethane;

[0024] The product after the blending reaction needs to be purified. The specific operation of the purification is: dissolving the product after the blending reaction in an organic solvent, and then flocculating with an alcohol solvent and drying; preferably, the organic solvent is selected from at least one of dichloromethane, chloroform, tetrahydrofuran, acetone, ethyl acetate, and dimethylformamide; and / or, the alcohol solvent is selected from at least one of methanol and ethanol.

[0025] The second object of the present invention is to provide a high-strength and high-toughness polylactic acid composite material prepared by the above method.

[0026] The strength of the polylactic acid composite material provided by the present invention is not less than 60% of that of pure polylactic acid, and the tensile toughness is not less than 50 MJ / m 3 ; Preferably, the strength of the polylactic acid composite material is not less than 65% of that of pure polylactic acid, and the tensile toughness is not less than 100 MJ / m 3 ; More preferably, the strength of the polylactic acid composite material is 65-99% of that of pure polylactic acid, and the tensile toughness is 100-500 MJ / m 3 .

[0027] The present invention uses a polyfunctional isocyanate or polyfunctional epoxide having a reactive group with the terminal hydroxyl group / carboxyl group of a polyester elastomer to prepare a branched polymer or block copolymer (PDLA-g-BBPE) containing molecular chains of both dextrorotatory polylactic acid PDLA and a rubber phase - bio-based degradable random copolyester rubber BBPE in a bio-based thermoplastic vulcanizate (TPV). Then it is added as a third component to the PLA / TPV composite material for melt blending.

[0028] Since PDLA-g-BBPE contains the molecular structures of both the rubber phase and the plastic phase, it will spontaneously migrate to the two-phase interface of the plastic matrix and the rubber dispersed phase during the mixing process. At the interface, the dextrorotatory polylactic acid and the levorotatory polylactic acid in the matrix will spontaneously form a stereocomplex crystal structure, thus forming a hard stereocomplex crystal shell on the surface layer of the soft rubber dispersed phase particles. The crystallization ability and degree of this stereocomplex crystal are higher than the crystallization behavior of the polylactic acid matrix itself. The formation of this shell improves the interfacial adhesion force between the dispersed phase and the matrix, and improves the compatibility of the two phases of the material; at the same time, the stereocomplex crystals with a higher degree of crystallization on the surface of the soft dispersed phase significantly reduce the sacrifice effect of the soft dispersed phase on the strength of the matrix material. After adding the third component, the strength of the toughened polylactic acid composite material is significantly improved with only a minimal decrease compared to pure polylactic acid, while the modulus is higher than that of pure polylactic acid material. It is worth mentioning that the improvement of compatibility further optimizes the toughening effect of TPV on polylactic acid. With the addition of the third component, the elongation at break and notched impact strength of the material are also further improved, thus obtaining a bio-based degradable polylactic acid composite material with high compatibility, high strength and high toughness.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. PDLA-g-BBPE spontaneously migrates to the interface through compatibility selection. The PDLA block therein will form a high-strength and high-modulus stereocomplex crystal shell with the matrix PLLA on the surface of the dispersed phase, inhibiting the decrease in strength and modulus caused by toughening;

[0031] 2. The PDLA-g-BBPE located at the interface plays a compatibilizing role in the matrix and dispersed phase of the composite material, improving the interfacial interaction between the two phases, and thus enhancing the toughening effect of TPV on PLA.

[0032] 3. The preparation method of the high-strength and high-toughness polylactic acid composite material provided by the present invention is also applicable to other polyester-based rubber-plastic blends or polyester plastic toughening methods. Description of the Drawings

[0033] Figure 1 shows the performance characterization of the purified product of PDLA-g-BBPE in Example 3: (a) and (b) DSC curves and their partial enlarged views, with the abscissa being temperature and the ordinate being the heat flow direction (upward for exothermic and downward for endothermic); (c) Fourier transform infrared spectrum, with the abscissa being wave number and the ordinate being absorption intensity; (d) X-ray diffraction pattern, with the abscissa being twice the incident angle of the X-ray and the ordinate being the diffracted intensity;

[0034] Figure 2 shows the performance characterization of the purified products of PDLA-g-BBPE prepared with different PDLA / BBPE mass ratios in Examples 3, 11 to 14: (a) Fourier transform infrared spectrum; (b) X-ray diffraction pattern; (c) DSC curve and its partial enlarged view;

[0035] Figure 3 Figure 3 shows the AFM test results of the composite material before and after the addition of PDLA-g-BBPE in Example 3 and Comparative Example 2, with the abscissa being the distance between the dispersed phase and the continuous phase and the ordinate being the logarithmic modulus (atomic force microscopy image parameter);

[0036] Figure 4 shows the compatibilizing effect of the addition of PDLA-g-BBPE in Examples 3, 11 to 14, 21 to 23 on the PLA / TPV composite material: DSC (a) curves of PDLA-g-BBPE modified PLA / TPV composite materials with different PDLA / BBPE feeding mass ratios; DSC (b) curves of PDLA-g-BBPE modified PLA / TPV composite materials with different dosages;

[0037] Figure 5 shows the influence of the addition of PDLA-g-BBPE in Examples 3, 11 to 14, 21 to 23 on the crystallization behavior of the PLA / TPV composite material: XRD (a) and DSC curves (b) of PDLA-g-BBPE modified PLA / TPV composite materials with different PDLA / BBPE feeding mass ratios; XRD (c) and DSC (d) curves of PDLA-g-BBPE modified PLA / TPV composite materials with different dosages;

[0038] Figure 6 shows the effect of the addition of 3, 21-23 PDLA-g-BBPE on the mechanical properties of PLA / TPV composites: (a) stress-strain curve and its partial enlarged view, with the abscissa being strain and the ordinate being stress; (b) variation of tensile toughness with the addition amount of PDLA-g-BBPE, with the abscissa being the addition amount of PDLA-g-BBPE and the ordinate being the tensile toughness value; (c) variation of notched impact strength with the addition amount of PDLA-g-BBPE, with the abscissa being the addition amount of PDLA-g-BBPE and the ordinate being the notched impact strength value.

[0039] Figure 7 For the mechanical property changes of PLA / TPV composites before and after PDLA-g-BBPE modification in Example 3 and Comparative Example 2, the abscissa is strain and the ordinate is stress. Detailed implementation manners

[0040] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0041] The testing instruments and testing conditions adopted in the embodiments are as follows:

[0042] The molecular weight and its distribution are obtained by gel permeation chromatography testing. Gel permeation chromatography is tested using a Waters 515-717-2410 GPC system. Among them, the refractive index detector is Waters 2410, the chromatographic columns are composed of Waters Styragel HT3, HT5 and HT6 in series, and the mobile phase is tetrahydrofuran (1 mL / min). The universal calibration standard sample is a narrow distribution polystyrene with 15 peak molecular weights ranging from 1.62 to 8.5 million.

[0043] The gel content is measured by a Soxhlet extractor. In this equipment, 3 g of each sample is selected, placed in a 300-mesh copper mesh, and extracted for 72 h in a cycle. Dichloromethane is selected as the extraction solvent.

[0044] The mechanical properties of the composite materials are tested according to ASTM D638 standard, and the testing equipment is a CMT4104 universal electronic tensile testing machine. Tensile samples with a specification of 25×6×2 mm 3 (injection molding) are stretched at a speed of 50 mm / min. At least 5 tensile splines of each sample need to be tested, and the median value is taken as the final test result.

[0045] For the raw materials used in the examples and comparative examples, if not specifically defined, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0046] The raw materials used in the examples are as follows, all purchased from AlfaAesar:

[0047] PLA - polylactic acid, with a number-average molecular weight of 103,200 and a molecular weight distribution of 2.11;

[0048] PDLA - dextrorotatory polylactic acid;

[0049] BBPE - bio-based biodegradable polyester elastomer;

[0050] TPV - bio-based thermoplastic vulcanizate;

[0051] MDI - diphenylmethane diisocyanate;

[0052] ESO - epoxidized soybean oil;

[0053] HDI - hexamethylene diisocyanate;

[0054] TDI - toluene diisocyanate;

[0055] LDI - L-lysine diisocyanate;

[0056] ADR-BASF - multi-functional epoxy compound product;

[0057] EMA-GMA - ethylene-methyl acrylate grafted glycidyl methacrylate.

[0058] Preparation of examples and comparative examples

[0059] Preparation of TPV: Prepared by the preparation method of bio-based TPV in Example 1 of Patent CN114507424A.

[0060] Preparation of BBPE: Prepared by the preparation method of butanediol-based polyester elastomer in Example 1 of Patent CN113136027A.

[0061] The preparation process of PDLA-g-BBPE (the third component) is as follows:

[0062] Weigh PDLA and BBPE with different molecular weights according to the formulation ratios in Table 1, and add the polyfunctional isocyanate or polyfunctional epoxide in the formulation ratios. Ensure that the total mass of PDLA and BBPE is 20 g, and weigh the polyfunctional isocyanate or polyfunctional epoxide according to the ratios in Table 1. After weighing, place the three in a 500 mL conical flask, add 300 mL of dichloromethane to dissolve the three, and stir evenly at a speed of 200 rpm for 24 h using a stirring table at room temperature. After stirring, pour the solution into a tetrafluoroethylene box to volatilize the solvent. After the surface solvent has volatilized, place the product in a vacuum oven and dry it at 60 °C under vacuum for 6 hours to obtain the product. Place the product in a flat vulcanizer and hot press it at 180 °C for 10 min. Dissolve the hot-pressed product in dichloromethane at a concentration of 0.1 g / mL. After dissolving evenly, add ethanol to the solution system for flocculation purification. Place the obtained flocculated product in a vacuum oven and dry it at 60 °C under vacuum for 6 hours to obtain the final product.

[0063] The specific preparation method of the polylactic acid composite material is as follows:

[0064] Taking the mass of the polylactic acid matrix as 100 phr, melt-blend the polylactic acid and the bio-based degradable thermoplastic vulcanizate in the formulation ratios in Table 1 in a Haake internal mixer at 190 °C and 80 rpm for 5 min. Subsequently, add the specific amount of PDLA-g-BBPE in the formulation, and continue to melt-blend in the Haake internal mixer at 190 °C and 80 rpm for 5 min. Then take out the sample. Use a laboratory micro-injection molding machine to inject the composite material into dumbbell-shaped specimens and rectangular impact specimens with standard dimensions of 25 * 6 * 2 mm in ASTM D638 3 for subsequent mechanical property tests.

[0065] Table 1. Ingredient ratios of examples and comparative examples

[0066]

[0067]

[0068]

[0069] According to the above method, a series of PDLA-g-BBPE and modified polylactic acid-based composite materials were prepared according to the ratios in the formulation of Table 1, and the relevant properties are shown in Table 2.

[0070] Table 2. Properties of PDLA-g-BBPE and composite materials obtained from examples and comparative examples

[0071]

[0072]

[0073]

[0074] The results in Table 2 show that regardless of the changes in the type and dosage of the reactive substances, the addition of the third component PDLA-g-BBPE can promote the improvement of the strength retention rate of the toughened PLA samples of TPV, and the toughness of the samples in most of the examples also shows a certain degree of improvement trend while increasing the strength retention rate. This indicates that PDLA-g-BBPE increases the compatibility of the two phases while forming stereocomplex crystals. Among them, the samples in Example 3 showed the best comprehensive performance, indicating that a highly compatible, high-strength and high-toughness bio-based degradable polylactic acid composite material was successfully prepared.

[0075] The test results show that

[0076] (1) Preparation of the third component PDLA-g-BBPE

[0077] In the present invention, a multi-functional isocyanate and a multi-functional epoxide are used to synthesize PDLA-g-BBPE. Since there are many types of multi-functional isocyanates and multi-functional epoxides, diphenylmethane diisocyanate (MDI) and epoxidized soybean oil (ESO) are selected as representatives in this part to prepare a branched polymer or block copolymer PDLA-g-BBPE containing the molecular chain structures of dextrorotatory polylactic acid and polyester elastomer, and the product is purified and characterized.

[0078] In the FTIR results of Figure 1, the ester group peaks corresponding to the products obtained by the reaction of ESO or MDI with PDLA / BBPE respectively at the position of 1175 cm -1 both simultaneously contain the characteristic absorption peaks of both PDLA and BBPE, indicating that the product contains both molecular blocks. From the DSC and XRD results in Figure 1, the glass transition temperatures of both PDLA and BBPE are contained in the purified product, which is consistent with the characterization conclusion of FTIR. In addition, there is an obvious melting peak of PDLA in the curve, and the X-ray diffraction peak of the product also presents the lattice diffraction peak of PDLA, indicating that the crystallization behavior of PDLA in the product PDLA-g-BBPE is not restricted. Thus, it can be determined that PDLA in the product exists in the form of blocks, thereby confirming the successful synthesis of the block copolymer PDLA-g-BBPE containing the molecular chain structures of dextrorotatory polylactic acid and polyester elastomer.

[0079] By adjusting the feeding mass ratio of PDLA / BBPE, a series of PDLA-g-BBPE products with different block contents were prepared, and the content ratio of the PDLA block and the BBPE block in the product showed the same law as the feeding ratio ( Figure 2a ). The same as the above conclusion, although the feeding ratio of PDLA / BBPE changes, both PDLA and BBPE blocks are included in all products, and the existence of the melting peak and the crystallization diffraction peak also indicates that the crystallization behavior of the PDLA block structure will not be restricted by the change of the feeding ratio.

[0080] (2) Preparation of highly compatible, high-strength and high-toughness bio-based degradable polylactic acid composites (modification of PLA / TPV materials by PDLA-g-BBPE)

[0081] A. Study on the migration behavior of PDLA-g-BBPE

[0082] The present invention characterized PLA / TPV and PLA / TPV / PDLA-g-BBPE by atomic force microscopy (AFM), and the results are as Figure 3 shown. With the addition of PDLA-g-BBPE, the interfacial thickness between the dispersed phase and the matrix increased from 145 nm to 386 nm, indicating that a wider transition phase was formed between the dispersed phase and the matrix. In contrast, there is a 95 nm high modulus part in the interfacial transition phase of PLA / TPV / PDLA-g-BBPE, which is due to the formation of stereocomplex crystals between the PDLA segments in PDLA-g-BBPE and the matrix PLLA, indicating that based on the two-phase amphiphilicity of the PDLA-g-BBPE block structure, it will spontaneously migrate to the interface during the blending process.

[0083] B. Study on the compatibilization effect of PDLA-g-BBPE

[0084] Since the original design of the structure of PDLA-g-BBPE is to make PDLA-g-BBPE migrate to the interface spontaneously through special two-phase amphiphilicity to play a compatibilizing role, and the compatibilization effect indirectly reflects the feasibility of the migration behavior of PDLA-g-BBPE, so the compatibilization effect of PDLA-g-BBPE was evaluated first.

[0085] The compatibilization effect of PDLA-g-BBPE on PLA / TPV composites is shown in Figure 4. From Figure 4aAs can be seen, regardless of the change in the PDLA / BBPE feeding mass ratio of PDLA-g-BBPE, the product has a certain effect on reducing the difference in glass transition temperature between the two phases of the PLA / TPV composite material. Among them, the addition of PDLA-g-BBPE(4 / 6) has the most obvious reduction in the difference in glass transition temperature between the two phases, showing the best compatibilization effect. Subsequently, an exploration of the variable dosage of PDLA-g-BBPE(4 / 6) with the best compatibilization effect was carried out, and the change in the difference in glass transition temperature between the two phases of the composite material is as Figure 4b shown. The results show that after adding 5 phr PDLA-g-BBPE(4 / 6), the difference in glass transition temperature between the two phases in the DSC results decreased from 112 °C to 107 °C, and the difference in glass transition temperature between the two phases in the DMA results decreased from 117 °C to 111 °C. This indicates that the addition of PDLA-g-BBPE(4 / 6) has a significant compatibilization effect on the two-phase material of PLA / TPV, which provides the possibility for the preparation of highly compatible and highly tough bio-based degradable polylactic acid composite materials.

[0086] C. Effect of PDLA-g-BBPE on the strength retention rate of PLA / TPV before and after toughening

[0087] Since PDLA-g-BBPE spontaneously migrates to the two-phase interface during the blending process, and the PDLA block in PDLA-g-BBPE tangles with the matrix material PLLA to form stereocomplex crystals, the strength sacrifice amplitude of the TPV toughened polylactic acid composite material is relatively small, and it has a good strength retention rate.

[0088] The effect of PDLA-g-BBPE on the crystallization behavior of the PLA / TPV composite material is shown in Figure 5. From Figure 5a and Figure 5b it can be seen that compared with the PLA / TPV composite material without PDLA-g-BBPE, regardless of the change in the PDLA / BBPE feeding mass ratio of PDLA-g-BBPE, the product has improved the crystallization behavior of the PLA / TPV composite material. With the addition of PDLA-g-BBPE, the melting peak area (melting enthalpy) of the PLA phase in the DSC curve has increased significantly, and a new melting point appears at 217 °C. Diffraction peaks belonging to the PLLA / PDLA stereocomplex crystals also appear in the XRD curve, indicating that the addition of PDLA-g-BBPE promotes the formation of stereocomplex crystals. The change in the crystallization behavior of the PLA / TPV composite material with the addition amount of PDLA-g-BBPE is as Figure 5c and Figure 5dAs shown, with the increase in the addition amount of PDLA-g-BBPE, the diffraction peak area of the stereocomplex crystal in PLA / TPV increases, and the melting peak (217 °C) belonging to the PLLA / PDLA stereocomplex crystal in the DSC curve also becomes more obvious, indicating that PDLA-g-BBPE has a significant promoting effect on the crystallization behavior of the PLA / TPV composite material.

[0089] With the promoting effect of PDLA-g-BBPE on the crystallization behavior of the PLA / TPV composite material, compared with the PLA / TPV composite material, the strength and modulus of the material have shown a significant increase. The strength sacrifice rate after toughening has decreased from 41% before to 21%, and the modulus even exceeds that of PLA itself under the action of the stereocomplex crystal. It is worth mentioning that not only the strength retention rate of the material has been greatly improved under the action of the stereocomplex crystal, but also the tensile toughness and impact toughness of the material have shown an upward trend. This benefits from the compatibilization effect of PDLA-g-BBPE on the two phases. PDLA-g-BBPE improves the interfacial adhesion force between the dispersed phase and the matrix at the interface. Under the stress state, the dispersed phase has a better stress dissipation effect, which provides the possibility for the preparation of high-strength and high-toughness bio-based degradable polylactic acid composite materials.

[0090] The changes in the mechanical properties of the PLA / TPV composite material before and after modification with PDLA-g-BBPE were compared. Since PDLA-g-BBPE contains both PDLA and BBPE blocks, it can spontaneously migrate to the interface of the two phases during the blending process, thereby improving the compatibility between the matrix and the dispersed phase of the PLA / TPV composite material; because the PDLA block in PDLA-g-BBPE can form a stereocomplex crystal with stronger crystallization ability with the matrix material PLLA, therefore, compared with the PLA / TPV composite material, the modified material has a lower strength sacrifice degree relative to pure polylactic acid and a higher strength retention rate. The strength retention rate of the modified material is much higher than that of the unmodified PLA / TPV material, and the modulus is even higher than that of pure PLA material; at the same time, due to the compatibilization effect of PDLA-g-BBPE, the tensile toughness and impact toughness of the material have also been further improved, thus preparing a high-compatibility, high-strength and high-toughness bio-based degradable polylactic acid composite material.

Claims

1. A preparation method of a high-strength and high-toughness polylactic acid composite material, comprising: The toughening modification of polylactic acid is carried out by using bio-based thermoplastic vulcanizate, and a polylactic acid composite material is obtained after adding a third component for reaction; wherein, the bio-based thermoplastic vulcanizate is a blend of bio-based random copolyester elastomer, vulcanizing agent, and polylactic acid, and the third component is the reaction product of dextrorotatory polylactic acid, bio-based random copolyester elastomer, polyfunctional isocyanate, and / or polyfunctional epoxide compound.

2. The preparation method according to claim 1, wherein Based on 100 parts by weight of the polylactic acid, the bio-based thermoplastic vulcanizate is 5 to 60 parts, and the third component is 1 to 15 parts; preferably, based on 100 parts by weight of the polylactic acid, the bio-based thermoplastic vulcanizate is 40 to 60 parts, and the third component is 3 to 7 parts; and / or In the bio-based thermoplastic vulcanizate, based on 100 parts by weight of the bio-based random copolyester elastomer, the dosage of the vulcanizing agent is 0.05 to 2 parts, and the dosage of the polylactic acid is 10 to 70 parts; preferably, in the bio-based thermoplastic vulcanizate, based on 100 parts by weight of the bio-based random copolyester elastomer, the dosage of the vulcanizing agent is 0.1 to 1 part, and the dosage of the polylactic acid is 25 to 55 parts; and / or In the third component, based on the total weight of the dextrorotatory polylactic acid and the bio-based random copolyester elastomer being 100 parts, the dextrorotatory polylactic acid is 10 to 90 parts, the bio-based random copolyester elastomer is 10 to 90 parts, and the polyfunctional isocyanate and / or polyfunctional epoxide compound is 1 to 15 parts; preferably, based on the total weight of the dextrorotatory polylactic acid and the bio-based random copolyester elastomer being 100 parts, the dextrorotatory polylactic acid is 30 to 70 parts, the bio-based random copolyester elastomer is 30 to 70 parts, and the polyfunctional isocyanate and / or polyfunctional epoxide compound is 3 to 10 parts.

3. The preparation method according to claim 1, wherein The bio-based random copolyester elastomer is a copolymer of bio-based dibasic acid, bio-based diol, and alkyd compound; and / or The number-average molecular weight of the bio-based random copolyester elastomer is 5000 to 80000, preferably 5000 to 20000; and / or The vulcanizing agent is selected from organic peroxides, preferably at least one of dicumyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxide), and dicumyl peroxide; and / or The number-average molecular weight of the polylactic acid is 20000 to 250000, preferably 100000 to 150000; and / or The number-average molecular weight of the dextrorotatory polylactic acid is 5000 to 120000, preferably 10000 to 30000; and / or The polyfunctional isocyanate is selected from at least one of diphenylmethane diisocyanate MDI, hexamethylene diisocyanate HDI, 4,4'-dicyclohexylmethane diisocyanate HMDI, toluene diisocyanate TDI, and L-lysine diisocyanate LDI; and / or The multi-functional epoxy compound is selected from at least one of epoxidized soybean oil, epoxidized cotton and linen seed oil, epoxidized rice bran oil, epoxidized sunflower seed oil, epoxidized camellia seed oil, epoxidized safflower seed oil, epoxidized sesame oil, epoxidized cottonseed oil, epoxidized rice oil, epoxidized soybean oil, epoxidized corn oil, epoxidized rapeseed oil, epoxidized linseed oil, epoxidized peanut oil, epoxidized palm oil, glycidyl methacrylate, and polyfunctional epoxy chain extender ADR; and / or, Based on 100 parts by weight of the bio-based random copolyester elastomer, the bio-based thermoplastic vulcanizate further contains 0.01 to 5 parts of antioxidant, and the bio-based thermoplastic vulcanizate further contains 0.01 to 50 parts of plasticizer; preferably, based on 100 parts by weight of the bio-based random copolyester elastomer, the bio-based thermoplastic vulcanizate further contains 0.5 to 1 part of antioxidant, and the bio-based thermoplastic vulcanizate further contains 0.01 to 30 parts of plasticizer.

4. The preparation method according to claim 3, wherein The bio-based dibasic acid is selected from at least one of succinic acid, adipic acid, sebacic acid, itaconic acid, hydrogenated dimer acid, dodecanedioic acid, octadecanedioic acid, fumaric acid, maleic acid, terephthalic acid, furandicarboxylic acid, mucic acid, and hydrogenated mucic acid; and / or, The bio-based diol is selected from at least one of 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, butenediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, terephthalyl alcohol, furandimethanol, diethylene glycol, glycerol, and pentaerythritol; and / or, The alkyd compound is selected from at least one of lactic acid, lactide, and glycolic acid; and / or, The antioxidant is selected from at least one of phosphite antioxidants, peroxide decomposing antioxidants, phenolic antioxidants, amine antioxidants, heterocyclic antioxidants, and fatty acid ester antioxidants, preferably selected from at least one of phosphite antioxidants, butylated hydroxyanisole, dibutylhydroxytoluene, tert-butylhydroquinone, tea polyphenols, phytic acid, ascorbic acid, palmitate, and tocopherol; and / or, The plasticizer is selected from at least one of citrate plasticizers, ricinoleate plasticizers, vegetable oil-based plasticizers, and polybasic acid ester plasticizers. Preferably, the citrate plasticizers are selected from at least one of tributyl citrate and acetyl tributyl citrate; and / or, the vegetable oil-based plasticizers are selected from at least one of soybean oil and its derivatives, tall oil, tung oil, vernonia oil, resorcinol oil, and cashew nut shell oil; and / or, the polybasic acid ester plasticizers are selected from at least one of trioctyl trimellitate, bis(2-ethylhexyl) phthalate, dibutyl phthalate, and diethyl phthalate.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The described preparation method includes: melting and blending components including the described bio-based thermoplastic vulcanizate, polylactic acid, and a third component, and then the polylactic acid composite material is obtained. Preferably, the temperature of the melting and blending is 180 - 220 °C, more preferably 190 - 210 °C; the screw speed of the melting and blending is 60 - 120 rpm, preferably 80 - 100 rpm.

6. The preparation method according to claim 5, characterized in that The described bio-based thermoplastic vulcanizate is obtained by dynamically vulcanizing components including a bio-based random copolyester elastomer, a vulcanizing agent, and polylactic acid.

7. The preparation method according to claim 6, characterized in that The temperature of the dynamic vulcanization is 150 - 200 °C, preferably 160 - 180 °C; and / or Before the dynamic vulcanization, an antioxidant and a plasticizer are added to the described bio-based random copolyester elastomer and melt-blended. Preferably, the temperature of the melt-blending is 150 - 190 °C.

8. The preparation method according to claim 5, characterized in that The described third component is obtained by blending and reacting components including D-polylactic acid, a bio-based random copolyester elastomer, a polyfunctional isocyanate, and / or a polyfunctional epoxide. Preferably, the blending is melt-blending or solution-blending, and the product after the blending reaction needs to be purified.

9. The preparation method according to claim 8, characterized in that The conditions of the melt-blending are: temperature 150 - 200 °C, speed 60 - 120 rpm, time 5 - 20 min; preferably, the conditions of the melt-blending are: temperature 175 - 185 °C, speed 80 - 100 rpm, time 5 - 10 min; and / or The operation of the solution-blending is: first, D-polylactic acid, a bio-based random copolyester elastomer, and a polyfunctional isocyanate and / or a polyfunctional epoxide are uniformly mixed in a solution at room temperature, the solvent is evaporated after mixing, and then the remaining homogeneous blend is heated and reacted; preferably, the conditions of the heating reaction are: temperature 150 - 200 °C, time 5 - 15 min; more preferably, the conditions of the heating reaction are: temperature 175 - 185 °C, time 5 - 10 min; and / or The solvent used for the solution-blending is selected from at least one of dichloromethane, chloroform, and tetrahydrofuran, preferably dichloromethane; and / or The specific operation of the purification treatment is: dissolving the product after the blending reaction in an organic solvent, and then flocculating with an alcohol solvent and drying; preferably, the organic solvent is selected from at least one of dichloromethane, chloroform, tetrahydrofuran, acetone, ethyl acetate, and dimethylformamide; and / or the alcohol solvent is selected from at least one of methanol and ethanol.

10. A high-strength and high-toughness polylactic acid composite material is prepared by the preparation method according to any one of claims 1 - 9.

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