Chemical recycling method of bio-based thermoplastic vulcanized rubber, prepared bio-based random copolyester elastomer material and application

Abstract

The invention provides a chemical recycling method of bio-based thermoplastic vulcanized rubber, a prepared bio-based random copolyester elastomer material and application. Based on the characteristic that two-phase polylactic acid and a polyester elastomer main chain of the bio-based thermoplastic vulcanized rubber are both of a polyester structure, the bio-based thermoplastic vulcanized rubber is subjected to alcoholysis by adopting a small-molecular alcohol compound, and a homogeneous low-molecular-weight liquid-phase product is obtained. The product is condensed and polymerized again to obtain the bio-based degradable random copolyester elastomer material containing a lactic acid structural unit and a gel structure, and the polyester elastomer material obtained by repolymerizing the recycled product has a very ideal technical effect in the field of polylactic acid toughening application.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a chemical recycling and reuse method of a bio-based thermoplastic vulcanizate, a prepared bio-based random copolyester elastomer material and its application. Background Art

[0002] With the development of the polymer materials industry, the waste of polymer materials is increasing day by day, and the waste treatment of polymer materials has gradually attracted people's attention. To address this issue, using degradable materials to replace traditional materials and recycling polymer materials are two main ideas. Compared with the replacement of degradable materials, the recycling of materials can often give materials higher added value and is more conducive to forming a carbon footprint closed loop in the service life of materials (The carbon footprint and environmental footprint of plastics - Part 2: The carbon footprint of materials is the amount (mass) of CO2 incorporated into polymer molecules from the air). Therefore, it has received extensive attention from researchers. Among them, the chemical recycling of materials can produce fuels or Raw materials produce new chemicals, which is considered to be one of the most meaningful recycling methods. So far, the chemical recycling of polymer materials in the industrial field mainly stays in the plastic field, including the catalytic short-chain of aliphatic plastics, the alcoholysis of polyester plastics, etc. ([1] Zhang F, Wang F, Wei X, et al. From trash to treasure: Chemical recycling and upcycling of commodity plastic waste to fuels, high-valued chemicals and advanced materials [J]. Journal of Energy Chemistry: English Edition, 2022(6): 21.), but there is little involvement in the rubber and thermoplastic elastomer fields.

[0003] However, thermoplastic elastomers, especially thermoplastic vulcanizates among them, also occupy a quite substantial market share and the demand is increasing day by day. In recent decades, the thermoplastic vulcanizate industry has developed at a high speed. Various types of commercial thermoplastic vulcanizates such as EPDM / PP TPV (CN112135875A) with ethylene propylene diene monomer rubber and polypropylene as raw materials, HNBR / PATPV (CN114350042A) with hydrogenated nitrile butadiene rubber and nylon as raw materials, and SiR / TPU TPV (CN112341824A) with silicone rubber and polyurethane as raw materials have successively appeared in people's sight. Compared with traditional plastic or rubber materials, TPV combines the high elasticity of thermosetting vulcanized rubber and the excellent processing performance of thermoplastic resin. It can be processed and recycled repeatedly, which can fundamentally solve the problem of recycling and reuse of traditional thermosetting rubber, save petroleum resources, and is beneficial to environmental protection (Ning N, Li S, Wu H, et al. Preparation, microstructure, and microstructure-properties relationship of thermoplastic vulcanizates (TPVs): A review[J]. Progress in Polymer ence, 2017: 61-97.). According to the TPE market research report released by the US Transparency Market Research company in 2013, the annual growth rate of TPV demand in the following five years (2013-2018) is expected to be as high as 6.6%. The application fields cover industries such as automotive, fluid handling, consumer goods, medical, and construction. In the current market situation, the annual growth rate of the global TPV market demand exceeds 19%, and it is expected that the global demand will be higher than 1.4 million tons in 2025.

[0004] With the increase in demand, the waste generated after the service life of thermoplastic vulcanizates will also cause a huge environmental burden, and the waste treatment of thermoplastic vulcanizates has attracted wide attention. So far, the recycling of thermoplastic vulcanizates only stays in the stage of mechanical recycling (physical recycling), that is, the waste particles of thermoplastic vulcanizates are repeatedly extruded through a screw and remolded to form products. However, the mechanical recycling of thermoplastic vulcanizates will undoubtedly accelerate the thermo-oxidative aging of the material, have a huge impact on the performance of the material, and at the same time, the VOCs emissions generated during the mechanical recycling process will also cause environmental deterioration. Therefore, developing a chemical recycling method for thermoplastic vulcanizates is of great significance.

[0005] Based on this, attempts at chemical recycling (alcoholysis recycling) were carried out on thermoplastic vulcanizates with high current environmental protection value - a bio-based degradable thermoplastic vulcanizate material (CN102827465A) made from bio-based random copolyester elastomer and polylactic acid. The bio-based thermoplastic vulcanizate was subjected to alcoholysis reaction using small molecule diols or small molecule polyols, and was degraded into small molecules or oligomers with a molecular weight between 100 and 5000. The alcoholysis product obtained after the alcoholysis reaction can be reused to prepare a bio-based degradable random copolyester elastomer material and used as a toughening material for polylactic acid, realizing the upgraded reuse of bio-based thermoplastic vulcanizate waste in the field of polylactic acid toughening. It is worth mentioning that due to the existence of a gel network in the thermoplastic vulcanizate itself, the gel network is destroyed after alcoholysis and becomes multi-functional small molecule alcohols or acids, and a certain gel network structure can be formed again during the polymerization process, finally obtaining a bio-based degradable random copolyester elastomer containing lactic acid structural units and a gel structure. This bio-based degradable random copolyester elastomer has good application prospects in the field of polylactic acid toughening. The lactic acid structural units in the polyester elastomer ensure good compatibility between the elastomer and the matrix material polylactic acid, while the existence of the gel structure ensures the high elasticity and stress dissipation ability of the polyester elastomer, which is very beneficial for improving the toughening effect. Generally speaking, this method improves the product added value of bio-based thermoplastic vulcanizate and realizes the carbon footprint closed-loop of the life cycle of bio-based thermoplastic vulcanizate. Using its alcoholysis and repolymerization product as a polylactic acid toughening agent realizes the upgraded utilization of bio-based thermoplastic vulcanizate waste. Summary of the Invention

[0006] To solve the problems of increased treatment costs caused by the degradation of bio-based degradable thermoplastic vulcanizate waste discharged into the environment and the decrease in the added value of the material itself, the present invention provides a method for chemical recycling and reuse of bio-based thermoplastic vulcanizate. The bio-based thermoplastic vulcanizate is subjected to alcoholysis reaction using small molecule diols or small molecule polyols, and is degraded into small molecules or oligomers with a molecular weight between 100 and 5000. The alcoholysis product obtained after the alcoholysis reaction can be reused to prepare a bio-based degradable random copolyester elastomer material and used as a toughening material for polylactic acid, realizing the upgraded reuse of bio-based thermoplastic vulcanizate waste in the field of polylactic acid toughening.

[0007] One object of the present invention is to provide a method for chemical recycling and reuse of bio-based thermoplastic vulcanizate, including the steps of subjecting the bio-based thermoplastic vulcanizate and small molecule alcohol compounds to an alcoholysis reaction to obtain small molecule compounds, and continuing the polymerization reaction using the small molecule compounds as raw materials. Among them, the plastic phase of the bio-based thermoplastic vulcanizate is polylactic acid, and the rubber phase is a bio-based random copolyester elastomer.

[0008] Among them, the bio-based thermoplastic vulcanizate is obtained by melt blending a bio-based random copolyester elastomer, a vulcanizing agent, and polylactic acid. Specifically, the bio-based random copolyester elastomer and polylactic acid are first melt blended at a high temperature, and then the vulcanizing agent is added and blended evenly at room temperature. Finally, dynamic vulcanization is completed at a high temperature to prepare the bio-based thermoplastic vulcanizate. Among them, the comonomers of the bio-based random copolyester elastomer are a diol and an organic acid. The diol is selected from at least one of 1,4-butenediol and C2-C14 branched or unbranched saturated aliphatic diols, preferably selected from at least one of 1,4-butenediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, and glycerol; the organic acid is selected from at least one of a dicarboxylic acid and an alcohol acid, preferably selected from at least one of succinic acid, adipic acid, sebacic acid, dodecanedioic acid, glycolic acid, oxalic acid, lactic acid, terephthalic acid, furandicarboxylic acid, and hydrogenated dimer acid; the vulcanizing agent is selected from at least one of sulfur, sulfur monochloride, selenium, tellurium, organic peroxides, quinone oxime compounds, polysulfide polymers, urethanes, and maleimide derivatives, and more preferably selected from organic peroxides; based on 100 parts by weight of the bio-based random copolyester elastomer, the vulcanizing agent is 0-5 parts, and the polylactic acid is 1-100 parts. More preferably, based on 100 parts by weight of the bio-based random copolyester elastomer, the vulcanizing agent is 0.25-2 parts, and the polylactic acid is 25-100 parts.

[0009] In the chemical recycling and reuse method of the bio-based thermoplastic vulcanizate provided by the present invention:

[0010] The small molecule alcohol compound is selected from at least one of small molecule diols and small molecule polyols, preferably selected from at least one of ethylene glycol, 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 mass ratio of the bio-based thermoplastic vulcanizate to the small molecule alcohol compound is (0.25-64):1, preferably (1-16):1; the number average molecular weight of the small molecule compound obtained by alcoholysis is 100-5000, preferably 500-4500. The small molecule compound after alcoholysis is preferably a small molecule or oligomer with a molecular weight of 500-4500. When the molecular weight of the oligomer obtained by degradation is higher than 5000, the terminal group activity of the oligomer is low during the repolymerization process, and the polymerization reaction ability is poor; when the molecular weight of the oligomer obtained by degradation is lower than 100, the small molecule is volatile during the repolymerization process, resulting in loss of repolymerization raw materials, which is not conducive to the preparation of the bio-based degradable random copolyester elastomer.

[0011] In the method for chemical recycling and reuse of the bio-based thermoplastic vulcanizate provided by the present invention, the conditions for the alcoholysis reaction are as follows: the reaction temperature is 160-220°C, and the reaction time is 0.5-4 h; preferably, the reaction temperature is 180-200°C, and the reaction time is 0.5-2 h; after the alcoholysis reaction, vacuum distillation is required. Preferably, the conditions for the vacuum distillation are as follows: the distillation temperature is 160-220°C, and the distillation pressure is -0.05 to -0.1 MPa; preferably, the conditions for the vacuum distillation are as follows: the distillation temperature is 180-200°C, and the distillation pressure is -0.08 to -0.1 MPa.

[0012] The second object of the present invention is to provide a bio-based random copolyester elastomer material, which is obtained by polycondensation of the small molecule compounds obtained in the chemical recycling and reuse method of the above-mentioned bio-based thermoplastic vulcanizate. The polycondensation reaction is optionally carried out under the action of a catalyst. Among them, the catalyst is selected from at least one of antimony trioxide, antimony acetate, antimony glycolate, germanium dioxide, potassium fluorotitanate, titanium dioxide, tetrabutyl titanate, titanium glycolate, stannous octoate, stannous chloride, dibutyltin dilaurate, p-toluenesulfonic acid, zinc acetate, cobalt acetate, aluminum isopropoxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, and magnesium acetate. The dosage of the catalyst is 0-5 wt% of the alcoholysis product, preferably 0.05-1 wt%. The conditions for the polycondensation reaction are as follows: the temperature is 200-250°C, preferably 220-240°C; the pressure is -0.05 to -0.1 MPa, preferably -0.08 to -0.1 MPa.

[0013] The present invention adds a catalyst to the alcoholysis product and carries out condensation polymerization at high temperature and high vacuum until the Weissenberg effect appears and then stops the reaction. Since the reaction raw materials are small molecule products obtained by the common alcoholysis of polyester elastomer and polylactic acid, the random copolymerization characteristics during the polycondensation process introduce a large amount of lactic acid monomers or lactic acid-based oligomers as raw materials into the original monomers of the polyester elastomer. The final polyester elastomer contains a large number of lactic acid structural units. In addition, due to the existence of a gel network in the thermoplastic vulcanizate itself, the gel network is destroyed after alcoholysis to become multi-functional small molecule alcohols or acids, and a certain gel network structure can be formed again during the repolymerization process, finally obtaining a bio-based degradable random copolyester elastomer containing lactic acid structural units and gel structure. This bio-based degradable random copolyester elastomer has good application prospects in the field of toughening polylactic acid. The lactic acid structural units in the polyester elastomer ensure good compatibility between the elastomer and the matrix material polylactic acid, while the existence of the gel structure guarantees the high elasticity and stress dissipation ability of the polyester elastomer, which is very beneficial for improving the toughening effect.

[0014] The third object of the present invention is to provide an application of the above-mentioned bio-based random copolyester elastomer material in the field of toughening polylactic acid.

[0015] A fourth object of the present invention is to provide a bio-based random copolyester elastomer toughened polylactic acid material, which is obtained by melt blending the above-mentioned bio-based random copolyester elastomer material and polylactic acid. Among them, the number average molecular weight of the polylactic acid is 20,000 to 250,000, preferably 100,000 to 150,000; based on 100 parts by weight of polylactic acid, the bio-based random copolyester elastomer material is 10 to 50 parts, preferably 10 to 30 parts; the conditions for the melt blending are: the temperature is 160 to 200 °C, preferably 170 to 180 °C.

[0016] The present invention completes the melt blending of the elastomer material obtained by polycondensing the alcoholysis product and polylactic acid in a Haake mixer or a twin-screw extruder to obtain a bio-based degradable polylactic acid composite material with significantly improved toughness, thereby realizing the upgrading and reuse of bio-based thermoplastic vulcanizate waste in the field of toughening polylactic acid.

[0017] Advantages of the present invention:

[0018] 1. Chemically recycling the bio-based thermoplastic vulcanizate waste and finding an application way for reuse in the present invention is the most effective means to solve the above problems. Chemical recycling saves the treatment cost of waste composting degradation, and the reuse of the recycled product can further increase the added value of the product.

[0019] 2. The small molecule compounds obtained after the alcoholysis reaction in the present invention are repolymerized, and the obtained polyester elastomer contains lactic acid structural units and has the structural characteristics of gels, which can effectively toughen the polylactic acid material and is suitable for the application field of toughening modification of polylactic acid.

[0020] 3. The chemical recycling and reuse method provided by the present invention is also applicable to polyester-based rubber-plastic blends or other bio-based thermoplastic vulcanizates based on polyester, and the recycled and repolymerized products are also applicable to toughening the same plastic in rubber-plastic blends. Description of the Drawings

[0021] Figure 1 shows the alcoholysis reaction results of the bio-based thermoplastic vulcanizate waste in Examples 3, 16 to 19 under different mass ratios of waste particles to small molecule alcohol compounds: (a) the change of the apparent state of the mixture with the alcoholysis time; (b) the change of the number average molecular weight with the alcoholysis time; (c) the change of the molecular weight distribution coefficient with the alcoholysis time.

[0022] Figure 2 shows the nuclear magnetic resonance hydrogen spectrum ( Figure 2a ) and infrared spectrum ( Figure 2b ) of the samples at different alcoholysis times of the bio-based thermoplastic vulcanizate waste in Examples 3, 16 to 19 under different mass ratios of waste particles to small molecule alcohol compounds.

[0023] Figure 3 Molecular weight change of the repolymerization product of the alcoholysis solution of the bio-based thermoplastic vulcanizate waste in Example 3.

[0024] Figure 4 shows the molecular structure characterization of the repolymerization product of the alcoholysis solution of the bio-based thermoplastic vulcanizate waste in Example 3: (a) 1H NMR spectrum and its corresponding structure; (b) infrared spectrum.

[0025] Figure 5 Stress-strain curves of the toughened polylactic acid with the repolymerization products of the alcoholysis of bio-based thermoplastic vulcanizates in Examples 3, 45 to 47.

[0026] Figure 6 Notched impact strength test results of the toughened polylactic acid with the repolymerization products of the alcoholysis of bio-based thermoplastic vulcanizates in Examples 3, 45 to 47. Detailed implementation manners

[0027] 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 for further illustration of the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the content of the present invention still fall within the protection scope of the present invention.

[0028] The raw materials used in the examples and comparative examples, if not specifically limited, 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.

[0029] Examples 1 to 47

[0030] According to the description of the invention content, the experimental conditions and experimental formulations are shown in the following table. According to the claims of the invention content, during the experimental design process of the examples, the types of small molecule alcohols, the mass ratio of waste to small molecule alcohols, the alcoholysis reaction temperature and time, the types and dosages of catalysts used in repolymerization, the temperature and pressure of repolymerization, and the fraction of the repolymerization product elastomer required for blending during the final toughening of polylactic acid were changed.

[0031] The specific operation of the alcoholysis of the bio-based thermoplastic vulcanizate waste is as follows:

[0032] Weigh the bio-based thermoplastic vulcanizate waste particles and small molecule alcohol compounds according to the ratios in Table 1, and place the two in a reactor and carry out pulping at room temperature at a speed of 30 rpm. After the pulping is uniform, raise the temperature of the reaction kettle to the corresponding alcoholysis temperature in Table 1, and heat for the corresponding time after reaching the temperature. After the heating is completed, the alcoholysis product is discharged through the product flow channel to obtain a homogeneous liquid phase of small molecules or oligomers.

[0033] The specific operation process for preparing bio-based random copolyester elastomer by polycondensation of alcoholysis products is as follows:

[0034] Take the alcoholysis product from the previous step, add the corresponding type of catalyst with the corresponding mass fraction in Table 1 thereto, and carry out condensation polymerization in a polycondensation reactor under the temperature and pressure conditions shown in Table 1 until the Weissenberg effect appears in the system, then the reaction stops. The polymerization product is taken out through the product flow channel for standby.

[0035] The preparation process of the bio-based random copolyester elastomer toughened polylactic acid material is as follows:

[0036] Take polylactic acid (purchased from Natureworks, grade Natureworks 2003D, number average molecular weight of 103,200, distribution of 2.11) as 100 phr, and melt-blend the polyester elastomer synthesized from the recycled thermoplastic vulcanizate with the corresponding mass fraction in Table 1 and polylactic acid in a Haake mixer or twin-screw extruder at 170 °C and 80 rpm. Use a laboratory micro-injection molding machine to inject the composite material into dumbbell-shaped specimens with standard dimensions of 25*6*2 mm in ASTM D638 3 and rectangular impact specimens with dimensions of 80*10*4 mm in GB / T 1843-2008 3 for subsequent mechanical property tests.

[0037] Comparative Examples

[0038] Comparative Examples 1 to 3 respectively compared three situations: the alcoholysis reaction without the presence of alcohol, the repolymerization reaction without the presence of a catalyst, and the polylactic acid toughened with the elastomer of the repolymerization product. The other preparation processes were the same as those in Example 1, and the dosages of each component and the reaction conditions are shown in Table 1. Among them, in Comparative Example 1, small molecule alcohol compounds were not added during the alcoholysis process, in Comparative Example 2, a catalyst was not added during the preparation process of the bio-based random copolyester elastomer, and in Comparative Example 3, it was the performance of pure polylactic acid. In addition, in Comparative Example 4, the bio-based thermoplastic vulcanizate was used to directly toughen the polylactic acid material without undergoing an alcoholysis reaction.

[0039] Table 1

[0040]

[0041]

[0042]

[0043]

[0044] Test Examples

[0045] The molecular weight and its distribution were obtained by gel permeation chromatography (GPC). The GPC test was carried out using a Waters 515-717-2410 GPC system. Among them, the refractive index detector was Waters 2410, the chromatographic columns were composed of Waters Styragel HT3, HT5 and HT6 in series, and the mobile phase was tetrahydrofuran (1 mL / min). The universal calibration standard samples were narrow-distribution polystyrenes with molecular weights in the range of 1.62 to 8.5 million at 15 peak positions.

[0046] The gel content was measured by a Soxhlet extractor. For each sample, 3 g was selected and placed in a 300-mesh copper mesh, and extraction was carried out for 72 h in a cycle. Dichloromethane was selected as the extraction solvent.

[0047] The mechanical properties of the composite materials were tested according to ASTM D638 standard, and the test equipment was a CMT4104 universal electronic tensile testing machine. Samples with a specification of 25×6×2 mm 3 (injection molding) were stretched at a speed of 50 mm / min. At least 5 tensile specimens were tested for each sample, and the median value was taken as the final test result.

[0048] Related samples were prepared according to the above operation method, and characterizations such as the molecular weight and its distribution, gel content, and mechanical properties of the toughened polylactic acid were carried out. The results are shown in Table 2. The results show that the small-molecule alcohol compounds used in the present invention can all cause the bio-based thermoplastic vulcanizate to be alcoholyzed into small molecules or oligomers, and the gel structure is significantly damaged. After repolymerization, the molecular weight increases again and contains the corresponding gel structure. Finally, the product of alcoholysis and repolymerization of the bio-based thermoplastic vulcanizate waste shows a significant toughening effect on polylactic acid. Compared with pure polylactic acid, the elongation at break and notched impact strength are both significantly improved.

[0049] Table 2

[0050]

[0051]

[0052]

[0053] Description of the test results:

[0054] (1) Alcoholysis recovery of bio-based thermoplastic vulcanizate waste

[0055] Examples 1 to 47 record the apparent states and molecular weight changes of the products of alcoholysis of bio-based thermoplastic vulcanizate waste for different durations, and the relevant results are shown in Figure 1. As Figure 1aAs shown, with the progress of the alcoholysis reaction, the system gradually changes from a turbid solid-liquid co-suspension to a clear homogeneous system, indicating that the macromolecular solids in the solid-liquid blend system are gradually degraded under the action of alcohol and transformed into liquid-phase small molecules, and the system is transformed into a homogeneous liquid-phase system. From Figure 1b the perspective of the change in molecular weight, the initial number-average molecular weight of the soluble part of the thermoplastic vulcanizate waste is about 30,000. Under the action of alcoholysis, the number-average molecular weight of the material shows a significant downward trend and finally drops to 100 - 5000 (the final molecular weight obtained from the mass ratio of waste particles to small molecule alcohol is different). From Figure 1c the perspective of the molecular weight distribution coefficient, with the progress of the alcoholysis reaction, the distribution coefficient shows a trend of first increasing and then decreasing. This is because in the initial stage of alcoholysis, the linear polylactic acid molecular chains are first broken, resulting in a decrease in the number-average molecular weight, but the change in the weight-average molecular weight is not obvious; after the polylactic acid degrades into oligomers, the alcoholysis reaction occurs in the gel network, leading to a significant downward trend in the weight-average molecular weight, thus causing the distribution coefficient to decrease.

[0056] To further understand the mechanism of the alcoholysis reaction, taking the sample with a mass ratio of waste particles to small molecules of 64:1 as an example, the change in the molecular structure of the sample with the alcoholysis time was explored, and the results are shown in Figure 2. As shown in Figure 2, under the action of the alcoholysis reaction, due to the destruction of the long molecular chains, the absorption peak shift in the nuclear magnetic resonance hydrogen spectrum decreases, and the ester group absorption peak (1175 cm -1 ) in the infrared spectrum also shows a significant downward trend. Figure 2a Among them, the ester group peak of polylactic acid in the sample with a shorter alcoholysis time decreases first, while the ester group peak of the polyester rubber does not change significantly. After further reaction, the ester group peak of the polyester rubber decreases, corresponding to the results shown in Figure 1.

[0057] From the above results, it can be seen that under the action of small molecule alcohol compounds, the bio-based thermoplastic vulcanizate waste becomes small molecules or oligomers with a number-average molecular weight of 100 - 5000. The gel network of the rubber phase and the linear molecular chains of the plastic phase are both damaged, and the apparent state changes from a suspension to a homogeneous liquid-phase system, realizing the preliminary recycling of the bio-based thermoplastic vulcanizate waste.

[0058] (2) Repolymerization of the alcoholysis product of bio-based thermoplastic vulcanizate waste

[0059] To determine the synthesis effect of the alcoholysis product and the repolymerization product, the molecular weight and structure of the alcoholysis product and the repolymerization product of the bio-based thermoplastic vulcanizate waste were characterized. Figure 3 The results show that the number-average molecular weight of the repolymerized sample is 22,400 g / mol, and the gel content (about 25%) is slightly lower than that of the TPV waste. From Figure 4a nuclear magnetic resonance and Figure 4bFrom the infrared spectroscopy test results, the product contains the structural units of both polylactic acid and polyester elastomer, indicating that a bio-based degradable random copolyester elastomer containing lactic acid structural units and gel structure has been successfully synthesized.

[0060] (3) Toughening of polylactic acid with the alcoholysis and repolymerization product of bio-based degradable thermoplastic vulcanizate

[0061] Based on the structural characteristics that the above product contains both lactic acid structural units and gel structure, it has good application prospects in the field of toughening modification of polylactic acid. The repolymerization product was blended with polylactic acid according to the above process, and mechanical properties were characterized as Figures 5 - 6 shown. As shown in the figure, under the toughening effect of the alcoholysis and repolymerization product, the toughness of polylactic acid shows a significant improvement. When the dosage of the alcoholysis and repolymerization product is 20 phr, the composite material shows the best toughness. The elongation at break of the material increases from 14% to 120%, and the notched impact strength increases from 5.84 kJ / m 2 to 30.21 kJ / m 2 , achieving a significant toughening effect.

[0062] In summary, under the action of small molecule alcohol compounds, the bio-based thermoplastic vulcanizate waste undergoes alcoholysis reaction. Both polylactic acid and polyester elastomer undergo chain scission reactions, and the gel network of the rubber phase is damaged, transforming from solid powder into a homogeneous liquid phase system of oligomers without gel and with a number average molecular weight of 100 - 5000. Under the action of a catalyst, the oligomers in the alcoholysis product undergo polycondensation reaction to form a bio-based degradable random copolyester elastomer containing lactic acid structural units and gel structure. The molecular weight of this elastomer is comparable to that of the bio-based thermoplastic vulcanizate waste, the gel content is slightly lower than that of the bio-based thermoplastic vulcanizate waste, and it contains both the structural units of polyester elastomer and polylactic acid. This product shows excellent application effects in the field of toughening polylactic acid, which can increase the elongation at break to 9 times that of pure polylactic acid and the notched impact strength to 6 times that of pure polylactic acid.

Claims

1. A method for chemical recycling and reuse of bio-based thermoplastic vulcanizates, comprising the steps of subjecting the bio-based thermoplastic vulcanizates to alcoholysis reaction with small molecule alcohol compounds to obtain small molecule compounds, and continuing the polymerization reaction with the small molecule compounds as raw materials, wherein, The plastic phase of the bio-based thermoplastic vulcanizate is polylactic acid, and the rubber phase is a bio-based random copolyester elastomer.

2. The chemical recycling method of the bio-based thermoplastic vulcanizate according to claim 1, wherein the bio-based thermoplastic vulcanizate is obtained by blending a bio-based random copolyester elastomer, a vulcanizing agent, and polylactic acid; preferably, the comonomers of the bio-based random copolyester elastomer are a diol and an organic acid, wherein the diol is selected from at least one of 1,4-butenediol, C2-C14 branched or unbranched saturated aliphatic diols, preferably selected from at least one of 1,4-butenediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol; the organic acid is selected from at least one of dibasic acids and alkanoic acids, preferably selected from at least one of succinic acid, adipic acid, sebacic acid, dodecanedioic acid, glycolic acid, oxalic acid, lactic acid, terephthalic acid, furandicarboxylic acid, hydrogenated dimer acid; and / or, the vulcanizing agent is selected from at least one of sulfur, sulfur monochloride, selenium, tellurium, organic peroxides, quinone oxime compounds, polysulfide polymers, urethanes, maleimide derivatives, more preferably selected from organic peroxides; and / or, based on 100 parts by weight of the bio-based random copolyester elastomer, the vulcanizing agent is 0-5 parts, and the polylactic acid is 1-100 parts. More preferably, based on 100 parts by weight of the bio-based random copolyester elastomer, the vulcanizing agent is 0.25-2 parts, and the polylactic acid is 25-100 parts.

3. The chemical recycling method of the bio-based thermoplastic vulcanizate according to claim 1, wherein the small molecule alcohol compounds are selected from at least one of small molecule diols and small molecule polyols, preferably selected from at least one of ethylene glycol, 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, pentaerythritol; and / or, the mass ratio of the bio-based thermoplastic vulcanizate to the small molecule alcohol compounds is (0.25-64):1, preferably (1-16):1; and / or, the number average molecular weight of the small molecule compounds obtained by the alcoholysis reaction is 100-5000, preferably 500-4500.

4. The chemical recycling method of the bio-based thermoplastic vulcanizate according to claim 1, wherein the conditions of the alcoholysis reaction are: the reaction temperature is 160-220 °C, and the reaction time is 0.5-4 h; preferably, the reaction temperature is 180-200 °C, and the reaction time is 0.5-2 h; and / or, After the alcoholysis reaction, vacuum distillation is also required. Preferably, the conditions for the vacuum distillation are as follows: the distillation temperature is 160-220 °C, and the distillation pressure is -0.05 to -0.1 MPa; more preferably, the conditions for the vacuum distillation are as follows: the distillation temperature is 180-200 °C, and the distillation pressure is -0.08 to -0.1 MPa.

5. A bio-based random copolyester elastomer material is obtained by polycondensation of small molecule compounds obtained from the chemical recycling method of the bio-based thermoplastic vulcanizate according to any one of claims 1 to 4.

6. The bio-based random copolyester elastomer material according to claim 5, characterized in that the polycondensation reaction is optionally carried out under the action of a catalyst; and / or the conditions for the polycondensation reaction are as follows: the temperature is 200-250 °C, preferably 220-240 °C; the pressure is -0.05 to -0.1 MPa, preferably -0.08 to -0.1 MPa.

7. The bio-based random copolyester elastomer material according to claim 6, characterized in that the catalyst is selected from at least one of antimony trioxide, antimony acetate, antimony glycolate, germanium dioxide, potassium fluotitanate, titanium dioxide, tetrabutyl titanate, titanium glycolate, stannous octoate, stannous chloride, dibutyltin dilaurate, p-toluenesulfonic acid, zinc acetate, cobalt acetate, aluminum isopropoxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, magnesium acetate; and / or the dosage of the catalyst is 0-5 wt% of the alcoholysis product, preferably 0.05-1 wt%.

8. Use of the bio-based random copolyester elastomer material according to any one of claims 5 to 7 in the field of toughening polylactic acid.

9. A bio-based random copolyester elastomer toughened polylactic acid material is obtained by melt blending the bio-based random copolyester elastomer material according to any one of claims 5 to 7 and polylactic acid.

10. The bio-based random copolyester elastomer toughened polylactic acid material according to claim 9, characterized in that the number average molecular weight of the polylactic acid is 20,000-250,000, preferably 100,000-150,000; and / or based on 100 parts by weight of polylactic acid, the bio-based random copolyester elastomer material is 10-50 parts, preferably 10-30 parts; and / or the conditions for the melt blending are as follows: the temperature is 160-200 °C, preferably 170-180 °C.

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