Environment-friendly degradable modified composite material, preparation method and application

Abstract

The present application belongs to the technical field of biodegradable materials, and particularly relates to an environmentally-friendly degradable modified composite material, a preparation method and application. In view of the problems of existing biodegradable materials, such as high brittleness, insufficient low-temperature toughness, poor water resistance, difficult control of degradation rate, and PBAT and PTMO copolymer easy phase separation, the present application is prepared by optimizing the ratio of PBAT, PBS, PLA, inorganic mineral filler, natural plant fiber, PBAT-PTMO block copolymer, etc., through raw material pretreatment, multi-stage mixing and melt plasticization molding. The PBAT-PTMO block copolymer is prepared by thiol-acrylate click reaction, with a number average molecular weight of 20000~30000g / mol and a dispersion degree PDI≤1.96. The material has high strength and high toughness, and the degradation rate is controllable, which can meet the needs of packaging bags, disposable tableware, agricultural mulching film and other fields, and effectively solve the problem that the performance and degradability of traditional materials are difficult to balance.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable materials technology, specifically relating to an environmentally friendly biodegradable modified composite material, its preparation method, and its application. Background Technology

[0002] The widespread use of plastic products has become an indispensable part of modern life; however, the environmental problems they cause are becoming increasingly serious. Due to their structural characteristics, traditional plastics are difficult to degrade in the natural environment. The long-term accumulation of large amounts of waste plastic leads to soil deterioration, increased water pollution, and disruption of ecosystem balance, posing a significant threat to the Earth's ecological environment. According to relevant research reports, the world generates hundreds of millions of tons of plastic waste annually, and this figure is increasing year by year. Against this backdrop, developing highly efficient and environmentally friendly biodegradable plastics has become an urgent task for the global scientific research and industrial communities to replace traditional plastics, alleviate the increasing pressure of environmental pollution, and achieve sustainable development goals.

[0003] In the field of biodegradable plastics research and development, polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) have attracted much attention and are widely used. PLA, due to its high hardness and strength, provides good structural support for biodegradable products. However, its high glass transition temperature significantly increases its brittleness, making it prone to breakage under impact, greatly limiting its application in applications requiring high toughness. To address these issues, Chinese patent CN105542423A discloses a biodegradable mulch film and its preparation method. This method introduces PBAT as an elastomer to improve flexibility and elasticity and reduce brittleness. However, the mulch film degrades too quickly, within 75 days, failing to meet the mulch film duration requirements for long-growing-cycle crops (such as corn and cotton, with growing periods exceeding 90 days). This results in a lack of mulch film protection during critical crop growth periods, affecting yield and quality, and limiting the large-scale promotion and application of biodegradable mulch films.

[0004] Currently, PBAT synthesis processes have evolved to include co-esterification, fractional esterification, and tandem esterification routes, enabling industrial production through one-step or two-step polymerization. For example, in Cao Jie's article "Fully Biodegradable PBAT Synthesis Process," a one-step method directly yields high-molecular-weight products via polycondensation, eliminating the need for chain extension steps, simplifying the process and reducing costs. A two-step method, by first preparing low-molecular-weight PBAT and then using chain extenders to increase its molecular weight, offers advantages such as short reaction time and high production capacity. Although PBAT possesses excellent flexibility and processing properties, meeting the requirements of various molding processes, several problems remain to be solved. First, the rigidity of the aromatic units (butylene terephthalate segments) in the molecular chain leads to insufficient low-temperature toughness, making it prone to embrittlement when used as mulch in cold regions. Second, its poor water resistance leads to mechanical property degradation due to prolonged exposure to humid environments. Third, the balance between melt strength and elastic modulus is difficult to control, limiting its application in elastic materials.

[0005] To overcome the performance limitations of PBAT, recent research has focused on its molecular structure modification. For example, patents CN113956488A and CN113897043A propose embedding flexible polyether segments into the PBAT molecular structure via a catalytic transesterification reaction, forming a block copolymer with stress-induced self-reinforcing properties. This copolymer generates oriented microfibers in situ under stress, simultaneously improving toughness and strength, and the composite material's performance is significantly optimized after blending with PLA. This technology eliminates the need for traditional fiber pre-preparation processes, resulting in a simple and environmentally friendly process. However, it also suffers from drawbacks such as uncontrollable block structure, easy degradation of polyether segments at high temperatures, and insufficient selectivity of the catalytic system, making it difficult to suppress side reactions.

[0006] Polytetrahydrofuran (PTMO), as a flexible polyether segment, has been widely used in materials such as polyurethane (TPU) to improve their flexibility and durability. However, introducing PTMO segments into the molecular structure of PBAT to form PBAT-PTMO block copolymers still faces many technical challenges: (1) PBAT is a semi-aromatic polyester, while PTMO is a polyether. The molecular chain polarity and chemical structure of the two are quite different. Direct copolymerization is prone to phase separation, making it difficult to form a stable block structure, which in turn affects the uniformity of the material's mechanical properties; (2) The ends of PBAT segments are mostly hydroxyl or carboxyl groups, while PTMO commonly ends in hydroxyl groups. It is necessary to carry out transesterification or polycondensation reactions through an efficient catalytic system. However, existing catalysts such as tetrabutyl titanate or Stannous octoate and other substances have insufficient selectivity for ester-ether coupling, which can easily lead to side reactions such as PBAT segment degradation and PTMO cyclization to form tetrahydrofuran; (3) Existing polymerization methods are difficult to achieve precise control of block length, and cannot accurately control the length ratio of PBAT and PTMO segments to balance degradability and mechanical properties; (4) PTMO segments are prone to oxidative degradation at high temperatures, while the polycondensation and processing temperature of PBAT is often as high as 210-280℃. The mismatch in thermal stability between the two may lead to the breakage of PTMO segments during polymerization or processing, affecting the structure and performance of the product.

[0007] To address these challenges, researchers have begun exploring new modification methods, such as reinforcement using nanofillers and improving the compatibility of PLA and PBAT through copolymerization. However, these methods only improve certain mechanical properties of the materials, and have drawbacks such as the failure to simultaneously improve degradation rates, making it difficult for biodegradable plastics to meet the needs of complex applications. Therefore, how to combine the advantages of different polymers to break through the existing compositional framework design, through modification processes and the introduction of novel elastomer materials, has become the key to the next step in developing high-performance biodegradable plastics. This also holds the promise of achieving a perfect balance between mechanical properties and degradability, meeting diverse application requirements. Summary of the Invention

[0008] Given the numerous shortcomings of existing biodegradable plastics, this invention aims to develop a novel environmentally friendly biodegradable modified composite material. By precisely controlling the proportions and properties of various raw materials and introducing innovative modification processes, the material's performance is deeply optimized. Addressing the shortcomings of existing PBAT materials, such as insufficient low-temperature toughness, poor water resistance, and difficulty in controlling melt properties, as well as the technical problems encountered in PBAT-PTMO copolymerization, including phase separation, insufficient catalyst selectivity, difficulty in controlling block length, and mismatched thermal stability, this solution prepares block copolymers through a thiol-acrylate click reaction. Utilizing its high efficiency, high selectivity, and low-temperature reaction characteristics, it overcomes the inherent defects of traditional transesterification or polycondensation reactions, achieving controllable block copolymerization of PBAT and PTMO. This further expands its wide application in packaging bags, disposable tableware, agricultural films, and other fields, comprehensively meeting the increasingly stringent performance standards and functional demands of various industries for environmentally friendly biodegradable materials. It fills the gap in existing technologies in the field of high-performance biodegradable plastics, leading the innovative development and upgrading of the biodegradable materials industry. Based on this, this invention provides an environmentally friendly biodegradable modified composite material, its preparation method, and its applications.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: an environmentally friendly biodegradable modified composite material, which is mainly made of the following raw materials in the following mass percentages: polybutylene adipate / terephthalate: 18%-28%; polybutylene succinate: 10%-16%; polylactic acid: 28%-55%; inorganic mineral filler: 5%-18%, the filler being any one or more combinations of talc, calcium sulfate, calcium silicate, and calcium carbonate, with a particle size of 800 mesh-3000 mesh; natural plant fiber: 2%-5%; PBAT-PTMO block copolymer: 2%-8% The PBAT-PTMO block copolymer is prepared from poly(butylene adipate) / butylene terephthalate prepolymer and polytetrahydrofuran prepolymer in a molar ratio of 1:1.05-1:1.2. The number average molecular weight of the copolymer is 20,000-30,000 g / mol, and the dispersion PDI ≤ 1.96. Nano silica: 0%-2%; additives: 2%-10%, the additives are maleic anhydride, 2-imidazolium ketone and styrene-glycidyl acrylate copolymer, the mass ratio of the three is 0.4:0.4:1; plasticizer: 0%-1%, the plasticizer is preferably tributyl citrate.

[0010] As a further supplement to the above technical solution, the preparation method of the PBAT-PTMO block copolymer includes the following steps:

[0011] Step a, Preparation of PBAT prepolymer with terminal thiol groups: Terephthalic acid, adipic acid, 1,4-butanediol, and 2-mercaptoethanol are mixed in a molar ratio of 1:1:5.5~6.5:0.8~1.2. 0.05%~0.1% of the total monomer mass of the first catalyst, 0.03%~0.05% of the composite antioxidant, and 0.01%~0.03% of the thiol protectant are added. Under nitrogen protection, the temperature is first raised to 160~170℃ for esterification reaction for 1.5~2 h, then raised to 180~190℃ for compression polymerization reaction for 6~8 h, yielding a PBAT prepolymer with terminal thiol groups and a number average molecular weight of 4000~5000 g / mol.

[0012] Step b, Preparation of single-terminated acrylate-based PTMO prepolymer: Add 0.5%~1% of boron trifluoride diethyl ether complex to tetrahydrofuran, and stir and polymerize under nitrogen protection at 0~10℃ for 4~6h to obtain a hydroxyl-terminated PTMO intermediate; add acrylic acid to the hydroxyl-terminated PTMO intermediate, with a molar ratio of acrylic acid to hydroxyl-terminated 1.1:1, add 0.1% of the total mass of the reaction system as a second catalyst, react at 80℃ for 3h, remove unreacted monomers by vacuum distillation, wash three times with 5% NaHCO3 solution, and then dehydrate under vacuum to obtain a single-terminated acrylate-based PTMO prepolymer with a number average molecular weight of 1800~2200 g / mol;

[0013] Step c, block copolymerization reaction: The thiol-terminated PBAT prepolymer from step a and the single-terminated acrylate-terminated PTMO prepolymer from step b are mixed at a molar ratio of 1:1.05~1.2, and 0.1%~0.15% of the total mass of the prepolymer is added as a composite initiator; under nitrogen protection, the copolymerization reaction is carried out at 40~50℃ for 2~2.5h with stirring and ultraviolet light irradiation to form a block copolymer with a number average molecular weight of 20000~30000g / mol and a dispersion PDI≤1.96;

[0014] Step d, purification treatment: The block copolymer from step c is poured into ethanol to precipitate, filtered, washed 2-3 times with deionized water, and vacuum dried to obtain PBAT-PTMO block copolymer.

[0015] The PBAT-PTMO block copolymer has the following chemical structure:

[0016]

[0017] In the formula: the degree of polymerization m of the PBAT chain segment is an integer from 17 to 22; the degree of polymerization n of the PTMO chain segment is an integer from 23 to 28.

[0018] As a further supplement to the above technical solution, in step 1, the first catalyst is tetrabutyl titanate, and the composite antioxidant is a mixture of triphenyl phosphite and hindered phenolic antioxidant 1010, with a mass ratio of 1:1; the thiol protectant is 2,6-dimethylpyridine; in step 2, the second catalyst is p-toluenesulfonic acid; and in step 3, the composite initiator is benzophenone and triethylamine, with a mass ratio of 1:1.2~1.5.

[0019] As a further supplement to the above technical solution, the molar ratio of terephthalic acid, adipic acid, 1,4-butanediol, and 2-mercaptoethanol in step 1 is 1:1:6:1; the molar ratio of PBAT prepolymer to PTMO prepolymer in step 3 is 1:1.08.

[0020] As a further supplement to the above technical solution, the vacuum degree of the compression polymerization reaction in step 1 is 0.08~0.1MPa; the vacuum dehydration temperature in step 2 is 50~60℃, the vacuum degree is 0.09~0.1MPa, and the dehydration time is 2~3h; the wavelength of the ultraviolet light in step 3 is 365nm, and the light intensity is 150~200mW / cm². 2 The stirring rate is 350-400 r / min; the drying temperature in step 4 is 60-70℃, and the drying time is 8-10 h.

[0021] As a further supplement to the above technical solution, the natural plant fiber is any one of cotton fiber, hemp fiber, bamboo fiber, coconut shell fiber, and corn stalk fiber; the natural plant fiber is first steam-exploded into microfibers with a fiber length of 0.5-2mm, then alkalized for 1-2 hours, and then rinsed with deionized water until neutral and dried.

[0022] As a further supplement to the above technical solution, the amount of the silane coupling agent KH550 is 8%-12% of the mass of nano-silica, the ultrasonic power of the ultrasonic cleaner is 300-500W, the processing time is 15-25 minutes, and the ultrasonic cavitation effect works in conjunction with the coupling agent to make the coupling agent more uniformly coat the particle surface, form a stable chemical bond layer, enhance the compatibility and interfacial adhesion with the matrix, improve the tensile strength, elongation at break and thermal stability of the composite material, inhibit the generation of material defects caused by nanoparticle agglomeration, and ensure the uniformity of the microstructure and the consistency of the macroscopic properties of the material.

[0023] A method for preparing an environmentally friendly, biodegradable modified composite material includes the following steps:

[0024] S1 raw material pretreatment: Polylactic acid is vacuum dried at 45-50°C for 4-5 hours; inorganic mineral filler and nano-silica are preheated at 100-110°C for 30-35 minutes; natural plant fiber is pretreated by steam explosion to obtain 0.5-2mm microfiber, then alkalized with 5% NaOH solution for 1-2 hours, rinsed until neutral and then dried.

[0025] S2 Premix: Weigh out PBAT, dried PLA, PBS, preheated inorganic mineral filler, modified natural plant fiber, modified nano silica, PBAT-PTMO block copolymer, tributyl citrate and 70% additives according to the proportion and put them into a high-speed mixer. Mix at 500-900 rpm for 7-8 minutes.

[0026] S3 Secondary Premix: Add the remaining 30% of the additives and premix at a medium speed of 240-260 rpm for 5-6 minutes to optimize the uniformity of raw material distribution, ensure that the additives and raw materials react fully, and improve the compatibility of the system.

[0027] S4 Melting, Plasticizing, and Molding: The mixed material is fed into a co-rotating twin-screw extruder. The screw temperature is set to 60-180°C, the screw speed to 150-250 rpm, and the screw length-to-diameter ratio to 48:1-56:1. Under these conditions, the raw material is fully melted, plasticized, mixed evenly, and extruded stably. The extruded strip is air-cooled, stretched, cut into granules at 4.6-4.8 mm intervals, vibrated, screened, and conveyed to the finished product silo.

[0028] An environmentally friendly, biodegradable modified composite material is used in the manufacture of packaging bags, disposable tableware, and agricultural mulch films. Through precise control of the degradation rate, this composite material can meet the needs of different application scenarios while minimizing environmental impact. Furthermore, its excellent mechanical properties and stability ensure the safety and durability of the products during use, providing strong support for the widespread application of green and environmentally friendly materials.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] This invention redesigns the formulation of bio-based biodegradable materials such as PBAT, PBS, and PLA by introducing PBAT-PTMO block copolymers and adding modified natural plant fibers and nano-silica, combined with inorganic mineral fillers. PLA provides a high-strength framework for the material, while PBAT and the PBAT-PTMO block copolymer synergistically optimize the material's excellent flexibility and impact resistance. Nano-silica and natural plant fibers enhance interfacial bonding, and inorganic mineral fillers optimize mechanical properties, resulting in an overall improvement in the material's comprehensive performance. This allows the composite material to achieve a tensile strength of 30-35 MPa and an elongation at break of 500%-800%, solving the problem of traditional biodegradable materials struggling to balance strength and toughness. Simultaneously, PBS and natural plant fibers form a gradient degradation mechanism, which, combined with the degradation characteristics of PBAT and PLA, achieves a dynamic balance between material stability during its service life in the natural environment and efficient degradation after disposal, meeting the protective needs of long-term agricultural mulch films.

[0031] This invention significantly improves the interfacial compatibility of composite materials through the modification process of natural plant fibers and nano-silica. For example, natural plant fibers are steam-exploded to form microfibers, and then alkalized to enhance interfacial bonding strength. This ensures that the density deviation of the modified granules is only 1.8%, the melt flow rate deviation is 1.7%, and there is no obvious fiber-matrix interface delamination. After treatment with silane coupling agent KH550 and ultrasound, nano-silica forms a stable chemical bond layer on its surface, improves dispersion uniformity, and reduces the agglomeration rate to below 5%. This significantly optimizes the thermal stability and tensile strength of the composite material and avoids material defects caused by particle agglomeration.

[0032] The composite material preparation method of this invention ensures the uniformity and performance stability of the material through a step-by-step pretreatment and multi-stage mixing process. PLA vacuum drying removes moisture, preventing hydrolysis and degradation during processing; preheating of inorganic minerals and nano-silica reduces interfacial bubbles; and ethanol impregnation of natural plant fibers improves wettability. High-speed mixing breaks up raw material agglomerates through strong shear force, while medium-speed secondary premixing ensures uniform dispersion of additives, reducing the dispersion coefficient of each component in the composite material to below 1.2, improving microstructure uniformity, and avoiding performance fluctuations caused by local component differences. Twin-screw extrusion parameters are matched to the raw material melting characteristics, making it suitable for large-scale production and increasing the yield to over 95%.

[0033] This invention involves copolymerizing terminal thiol-based PBAT prepolymers with single-terminated acrylate-based PTMO prepolymers at a specific molar ratio, followed by UV-initiated polymerization to form a structurally controllable block copolymer with a number-average molecular weight of 20,000-30,000 g / mol and a dispersion PDI ≤ 1.96. The low-temperature reaction conditions of 40-50°C in the preparation process prevent high-temperature oxidative degradation of the PTMO segments, and the composite initiator enhances reaction selectivity, resulting in a side reaction inhibition rate of over 90%. The introduction of this block copolymer increases the low-temperature impact strength of the biodegradable composite material to 8-10 kJ / m². 2 This solves the problem of low-temperature embrittlement of traditional PBAT, while enhancing compatibility with the matrix resin, effectively improving the overall mechanical properties of the material, and expanding its application areas.

[0034] The composite material of this invention, due to its balanced mechanical properties, controllable degradation rate, and wide processing adaptability, can be widely used in various fields such as agricultural mulch film, packaging bags, and disposable tableware. According to the test report, the tensile strength of the biodegradable express delivery bag reaches 21.2 MPa in the longitudinal direction and 30.7 MPa in the transverse direction, with a nominal strain at break of 713.5% in the longitudinal direction and 525.5% in the transverse direction. This demonstrates the material's excellent performance in both strength and toughness, solving the problem of traditional biodegradable materials struggling to balance strength and toughness. Furthermore, the biodegradable shopping bag achieves a biodegradation percentage of 89.4% and a relative biodegradation percentage of 90.5% after 140 days, while the biodegradable polyester achieves a biodegradation rate of 87.7% after 180 days. This indicates that the material achieves a dynamic balance between stable use and efficient degradation after disposal, meeting the growth cycle requirements of agricultural mulch film under special environmental conditions. Attached Figure Description

[0035] Figure 1 This is a comparison of the FTIR spectra of the PBAT-PTMO block copolymer and the prepolymer in this invention.

[0036] Figure 2 This is a comparison of the proton NMR spectra of the PBAT-PTMO block copolymer and the prepolymer in this invention.

[0037] Figure 3 This is the GPC spectrum of the PBAT-PTMO block copolymer in this invention.

[0038] Figure 4 This is the XPS spectrum of the S-element region of the PBAT-PTMO block copolymer in this invention.

[0039] Figure 5 This is a DSC curve of the PBAT-PTMO block copolymer in this invention.

[0040] Figure 6 This is a conversion curve of the synthesis reaction of PBAT-PTMO block copolymer in this invention.

[0041] Figure 7 This is a graph showing the exothermic reaction curve of the synthesis reaction of the PBAT-PTMO block copolymer in this invention.

[0042] Figure 8 This is a comparison diagram of the tensile strength of different samples in this invention.

[0043] Figure 9 This is a comparison chart of the elongation at break and impact strength of different samples in this invention.

[0044] Figure 10 This is a graph showing the changes in the biodegradation rate of different samples over time in this invention.

[0045] Figure 11 This is a SEM comparison image of the interface before and after modification of natural plant fibers in this invention.

[0046] Figure 12 This is a TEM comparison image of the dispersion of nano-silica before and after surface modification in this invention.

[0047] Figure 13 The image shows a physical sample of granules produced using the raw material formulation and preparation process of this invention.

[0048] Figure 14 The chemical structural formula, FTIR spectrum, and 1H NMR spectrum of the terminal thiol-based PBAT prepolymer in this invention are shown.

[0049] Figure 15 The chemical structural formula, FTIR spectrum, and 1H NMR spectrum of the single-terminated acrylate-based PTMO prepolymer in this invention are shown.

[0050] Figure 16 The chemical structural formula, FTIR spectrum, and 1H NMR spectrum of the PBAT-PTMO block copolymer in this invention are shown. Detailed Implementation

[0051] To further illustrate the technical solution of the present invention, see the appendix. Figures 1 to 13 As shown below, in conjunction with the entire project development process, in order to enable those skilled in the art to better understand and implement it, all raw materials, reagents and catalysts used are commercially available products. In addition to common reagents, such as ethanol, 5% NaHCO3 solution, deionized water and additives, other specific specifications and manufacturers are shown in Tables 1 and 2.

[0052]

[0053]

[0054] To address these issues, polytetrahydrofuran (PTMO) enhances toughness and durability through ether bonds. However, its copolymerization with PBAT suffers from significant differences in molecular chain polarity and chemical structure, leading to easy phase separation during direct copolymerization. Furthermore, PBAT polycondensation and processing require high temperatures, while PTMO segments are prone to oxidative degradation at high temperatures, resulting in a mismatch in thermal stability. Existing catalysts lack sufficient selectivity for ester-ether bond coupling, easily triggering side reactions. The block length is uncontrollable, making it difficult to balance mechanical properties and degradation rates. To resolve these problems, this invention prepares a PBAT-PTMO block copolymer through block copolymerization of a thiol-terminated PBAT prepolymer and a mono-acrylate-terminated PTMO prepolymer. This copolymer has a number-average molecular weight of 20,000-30,000 g / mol and a PDI ≤ 1.96.

[0055] The following section elaborates on the synthesis process, chemical structure characterization methods, and related experimental procedures of PBAT-PTMO block copolymers, combining molecular structure design. Simultaneously, the effects of prepolymer molar ratio, reaction temperature, and initiator dosage on copolymer dispersion, as well as the influence of PBAT and PTMO segment lengths on performance, are verified experimentally. Furthermore, the performance differences between this method and different processes are compared.

[0056] To enable those skilled in the art to replicate the invention, the conventional design parameters that can be obtained through orthogonal experiments are not elaborated upon in this invention. Instead, this invention utilizes adjustments to key parameters and processes for further research and analysis. Therefore, the preparation process of the PBAT-PTMO block copolymer is as follows:

[0057] Step a: Preparation of PBAT prepolymer with terminal thiol groups

[0058] Terephthalic acid, adipic acid, 1,4-butanediol, and 2-mercaptoethanol were mixed uniformly in a molar ratio of 1:1:6:1. Additives included 0.08% tetrabutyl titanate, 0.04% composite antioxidant, and 0.02% 2,6-dimethylpyridine by mass. The composite antioxidant was compounded with antioxidant 1010 in a 1:1 mass ratio using triphenyl phosphite. The reaction was carried out under nitrogen protection, with esterification at 165°C for 2 hours and vacuum polycondensation at 185°C and 0.09 MPa for 7 hours to obtain a thiol-terminated PBAT prepolymer with a number average molecular weight of 4500 g / mol.

[0059] Step b: Preparation of single-terminated acrylate-based PTMO prepolymer

[0060] 0.8% boron trifluoride diethyl ether complex was added to tetrahydrofuran feedstock, and ring-opening polymerization was carried out under nitrogen protection at 5°C for 5 h to obtain a hydroxyl-terminated PTMO intermediate with an average molecular weight of 2000 g / mol. 0.1% p-toluenesulfonic acid was added to the hydroxyl-terminated PTMO intermediate at a molar ratio of acrylic acid to hydroxyl groups of 1.1:1, and the reaction was carried out at 80°C for 3 h. Unreacted monomers were removed by vacuum distillation. The mixture was washed three times with 5% NaHCO3 and dehydrated under vacuum at 55°C and 0.095 MPa for 2.5 h to obtain a single-terminated acrylate-based PTMO prepolymer with a number average molecular weight of 2055 g / mol.

[0061] Step c: Block copolymerization

[0062] A composite initiator, consisting of benzophenone and triethylamine mixed at a mass ratio of 1:1.08, was added to a thiol-terminated PBAT prepolymer and a single-terminated acrylate-terminated PTMO prepolymer at a mass ratio of 1:1.2. The reaction was carried out under nitrogen protection, irradiated with 365 nm ultraviolet light (180 mW / cm²), and stirred at 45 °C and 380 r / min for 2.2 h to obtain a copolymer with a number average molecular weight of 25000 g / mol.

[0063] Step d: Purification treatment

[0064] The block copolymer prepared in step c above was poured into ethanol to precipitate, washed three times with deionized water, and dried under vacuum at 65°C for 9 hours to obtain PBAT-PTMO block copolymer with a dispersion of 1.86. Figure 3 The molecular weight distribution characteristics of the PBAT-PTMO block copolymer are shown: the number average molecular weight is 25,000 g / mol, the weight average molecular weight is 46,500 g / mol, and the dispersion index (PDI) is 1.86, which meets the design specifications of 20,000~30,000 g / mol and PDI≤1.96. This confirms that the molecular weight of the block copolymer can be precisely controlled through the thiol-acrylate click reaction, solving the problems of wide molecular weight distribution and uneven structure in traditional copolymerization.

[0065] The thiol-terminated PBAT prepolymer prepared in step a has the chemical structural formula of formula II:

[0066] like Figure 14 The chemical structure shown in Formula II is a thiol-terminated PBAT prepolymer containing butylene terephthalate and butylene adipate units, with a -SH group at the end. Figure 1 The display shows that FTIR detection is performed at 2550 cm⁻¹. -1 (-SH); Figure 2 show, 1 The structure was confirmed by HNMR analysis, which showed δ=8.1ppm (benzene ring hydrogen of terephthalic acid), δ=2.3ppm (methylene hydrogen of adipate), and δ=2.4ppm (-SH hydrogen).

[0067] The single-terminated acrylate-based PTMO prepolymer prepared in step b has the chemical structural formula of Formula III:

[0068] like Figure 15 The chemical structure shown in Formula III is mainly composed of polytetrahydrofuran segments, with an acrylate group at one end. Figure 1 The results show that FTIR detection at 1630 cm⁻¹... -1 (C=C), 1730cm -1 (Ester group); Figure 2 show, 1 The structure was confirmed by ¹H NMR with δ=3.4 ppm (PTMO methylene hydrogen) and δ=5.8-6.4 ppm (double bond hydrogen).

[0069] like Figure 16 As shown, the PBAT-PTMO block copolymer has the chemical structure of Formula I as follows:

[0070] In the formula: the degree of polymerization m of the PBAT chain segment is an integer from 17 to 22; the degree of polymerization n of the PTMO chain segment is an integer from 23 to 28.

[0071] Figure 1 The display shows that Formula II is at 2550cm. -1 The -SH characteristic peak appears at 1630 cm⁻¹, and Equation III shows a peak at 1630 cm⁻¹. -1 The presence of a C=C characteristic peak at this point confirms the existence of terminal functional groups in the prepolymer; the aforementioned characteristic peak disappears in Equation I, leaving only the peak at 1725 cm⁻¹. -1 (Ester bond, PBAT segment) and 1110cm -1 (Ether bond, PTMO segment) Direct verification of the complete conduction of the thiol-acrylate click reaction and the formation of the block copolymer structure.

[0072] Figure 2 The results show that Formula II exhibits a -SH hydrogen nucleus signal at δ=2.4ppm, and Formula III exhibits a double bond hydrogen nucleus signal at δ=5.8~6.4ppm, consistent with the chemical structure of the prepolymer. In Formula I, the above signals disappear, while δ=8.1ppm (benzene ring hydrogen of PBAT segment) and δ=3.4ppm (methylene hydrogen of PTMO segment) appear, further confirming that PBAT and PTMO are connected by thioether bonds to form a block structure, which is completely consistent with the chemical structure of Formula I.

[0073] Figure 4As shown, XPS analysis of sulfur showed characteristic peaks of thioether bonds at 163.8 eV and 165.0 eV, corresponding to spin-orbit splitting of the 2p orbital. This directly confirms that PBAT and PTMO segments form a stable chemical connection through a thiol-acrylate click reaction, providing elemental evidence for the block structure shown in Formula I and explaining the molecular mechanism of the reduced phase separation size.

[0074] The purified PBAT-PTMO block copolymer particles were added to a twin-screw extruder and melt-plasticized at 160-180℃. After extrusion into strips, the strips were granulated. The granules were then injection molded to produce tensile test strips (150 mm long and 10 mm wide) and notched impact test strips (80 mm long and 10 mm wide) according to GB / T1040.3-2006 and GB / T1843-2008 standards for mechanical property testing. A portion of the granules was also pressed into a 0.5 mm thick film and cut into 50 mm × 50 mm samples for water resistance and thermal stability testing, ensuring that the sample size accuracy was consistent with the testing standards.

[0075] The test methods are as follows: Tensile strength and elongation at break were tested according to GB / T1040.3-2006 at a rate of 50 mm / min. Low-temperature impact strength at -20℃ was tested according to GB / T1843-2008 using the simply supported beam notch method. By-products were qualitatively analyzed by gas chromatography-mass spectrometry, and their content was calculated as a percentage of the total mass of by-products to the total mass of raw materials. The cross-sectional morphology was observed using scanning electron microscopy, and the phase separation dimensions were statistically analyzed. After 1 hour of thermo-oxidative aging at 200℃, the molecular weight retention rate (i.e., the percentage of the number-average molecular weight after aging to the initial number-average molecular weight) was determined by gel permeation chromatography.

[0076] To verify the effects of prepolymer molar ratio, reaction temperature, and initiator dosage on copolymer dispersion, as shown in Table 3, we set the prepolymer molar ratio, reaction temperature, and initiator dosage as variables, with each group repeated three times, and a fixed UV light intensity of 180 mW / cm². 2 The stirring rate was 380 r / min, the reaction time was 2.2 hours, and the other conditions were the same as those in the preparation process.

[0077]

[0078] The orthogonal experimental results are shown in Table 3. When the prepolymer molar ratio is 1:1.05-1:1.20, the reaction temperature is 40-50℃, and the initiator dosage is 0.10%-0.15%, the dispersity is ≤1.96, indicating a uniform copolymer structure. Among them, the combination of 1:1.08, 45℃, and 0.12% has the lowest dispersity (1.86), which is the optimal parameter. Below or above this range, the dispersity increases significantly, indicating that the core parameter range is scientifically designed. Exceeding the range will lead to incomplete reaction or aggravated side reactions. Figure 5The block copolymer exhibits the following thermal properties: two glass transition temperatures (PTMO segment Tg = -70℃, PBAT segment Tg = 40℃) and a melting peak (Tm = 160℃) for the PBAT segment, indicating that the flexible PTMO segment and the rigid PBAT segment form a microphase separation structure. This structure is the key reason why the material simultaneously possesses high toughness (elongation at break 500%-800%) and high strength (30-35MPa), solving the defect of low-temperature embrittlement in traditional PBAT.

[0079] To investigate the effect of PBAT and PTMO segment length on their properties, as shown in Table 4, we followed these steps: We fixed the PBAT segment degree of polymerization (m=20) and adjusted the PTMO prepolymer's degree of polymerization (n) by changing synthesis parameters such as the ring-opening polymerization time; we also fixed the PTMO segment degree of polymerization (n=25) and adjusted the PBAT prepolymer's degree of polymerization (m) by changing the condensation time. PBAT-PTMO block copolymers with different segment parameters were prepared using a prepolymer molar ratio of 1:1.08, reaction at 45℃, and initiator dosage of 0.12%. Each group was tested in triplicate. Tensile strength, elongation at break, and other mechanical properties, as well as water resistance after 30 days of immersion in water, were tested. The correlation between segment length and properties was analyzed.

[0080]

[0081] The results of the gradient experiment are shown in Table 4. When the PTMO chain segment n=23-28, the elongation at break and the low temperature impact strength are optimal, and the improvement slows down after n>28. When the PBAT chain segment m=17-22, the tensile strength and water resistance are balanced, and the toughness decreases after m>22. Figure 6 The results showed that under UV initiation at 40-50℃, the conversion rate reached 95% after 2 hours, and the complete reaction with a conversion rate of 98% was achieved after 2.2 hours. This verified the high efficiency of the thiol-acrylate click reaction, which is consistent with the designed efficient reaction time of 2-2.5 hours, avoiding the chain segment degradation problem caused by the excessively long reaction time in traditional high-temperature transesterification reactions. Therefore, m=17-22 and n=23-28 are the optimal chain segment ranges for industrial production.

[0082] To compare the performance differences of this invention with different preparation processes, we set up the following four groups of comparative experiments: Control group 1 was the traditional transesterification process (preparation process according to CN113897043A, PBAT raw material used was Zhuhai TH-801T, PTMO used was PTMG2000 from Mitsubishi Chemical, Japan, tetrabutyl titanate catalysis, reaction at 230℃ for 4 hours); Control group 2 was the thiol-deficient group (2,6-dimethylpyridine was removed, the rest was the same as the above preparation process); Control group 3 was the composite antioxidant-deficient group (only antioxidant 1010 was added, the rest was the same as the above preparation process); Control group 4 was the high-temperature click reaction group (in step c, the reaction temperature was adjusted from 45℃ to 80℃, the rest was the same as the above preparation process). The by-product content, dispersibility, mechanical properties, and other indicators of each group were tested according to the above-mentioned relevant test methods.

[0083]

[0084] The experimental results are shown in Table 5. Compared with the traditional transesterification process, this invention reduces by-products by 76%, decreases dispersion by 21%, and increases low-temperature impact strength by 53%, solving the degradation and phase separation problems caused by high temperatures. Furthermore, the thiol protectant reduces thiol oxidation side reactions by 42%, the composite antioxidant improves thermal stability by 10%, and the low-temperature reaction reduces PTMO degradation by 40%, demonstrating the necessity of each process step. Figure 7 As shown, the exothermic process of this invention exhibits significant stability. Within the reaction temperature range of 40-50℃, the exothermic rate remains stable at 0.4-0.65 mW / g, without any dramatic exothermic peaks. This characteristic is attributed to the low-temperature reaction characteristics of the thiol-acrylate click reaction, effectively preventing PTMO segments from undergoing oxidative degradation at high temperatures and ensuring the integrity of the block copolymer molecular structure. In contrast, control group 1, using a traditional transesterification process, exhibited a sharp exothermic peak of 2.1 mW / g at a high temperature of 230℃. This dramatic exothermic phenomenon directly led to PTMO segment breakage, severely affecting the structure and properties of the product. Control group 2, lacking a thiol protectant, showed an overall higher and more volatile exothermic rate than this invention, indicating that the thiol protectant plays a crucial role in suppressing thiol oxidation side reactions and stabilizing the exothermic reaction. Control group 3, lacking a composite antioxidant, showed a continuous increase in exothermic activity in the later stages of the reaction, further verifying the key significance of the composite antioxidant in maintaining the thermal stability of the reaction. Control group 4 employed a high-temperature click reaction process. The reaction temperature of 80°C resulted in a significantly higher exothermic rate than that of this invention, indicating that even with the same click reaction, high temperature still exacerbates the risk of thermal degradation of PTMO segments. Therefore, the low-temperature click reaction process employed in this invention, through precise control of the exothermic reaction, effectively protects the PTMO segments while ensuring efficient reaction, providing a reliable process guarantee for the preparation of high-performance PBAT-PTMO block copolymers.

[0085] In summary, this invention, through precise molecular structure design and optimized process parameters, utilizes a thiol-acrylate click reaction to effectively solve the problems of easy phase separation, thermal stability mismatch, and frequent side reactions in the direct copolymerization of PBAT and PTMO. The prepared copolymer, verified by orthogonal, gradient, and comparative experiments, exhibits a dispersion ≤1.96 and uniform structure under conditions of a prepolymer molar ratio of 1:1.05-1:1.20, a reaction temperature of 40-50℃, and an initiator dosage of 0.10%-0.15%. When the degree of polymerization (m) of PBAT segments is 17-22 and the degree of polymerization (n) of PTMO segments is 23-28, the overall performance reaches its optimal level, with tensile strength of 30-34 MPa, elongation at break of 650%-800%, and low-temperature impact strength of 8.2-9.8 kJ / m². Water resistance and thermal stability are significantly improved, and byproducts are reduced. This process is repeatable and easily industrialized, providing reliable technical support for the widespread application of biodegradable materials.

[0086] This invention uses PBAT, PBS, and PLA as main raw materials, and inorganic mineral fillers and additives as auxiliary components. By introducing and adjusting PBAT-PTMO block copolymers, modified natural plant fibers and nano-silica, and plasticizers, the proportions of bio-based biodegradable materials such as PBAT, PBS, and PLA are optimized. This results in composite materials with balanced mechanical properties, controllable degradation rates, and wide processing adaptability, making them widely applicable in various fields such as agricultural mulch films, packaging bags, and disposable tableware. We further illustrate this through 15 examples and 7 comparative examples, targeting biodegradable bags, disposable tableware, and granules as products.

[0087] I. Material composition selection and proportion design

[0088] The environmentally friendly biodegradable modified composite material developed in this invention, through preliminary research, determined the proportions of each raw material as follows: poly(butylene adipate / terephthalate): 18%-28%; polybutylene succinate: 10%-16%; polylactic acid: 28%-55%; inorganic mineral filler: 5%-18%; natural plant fiber: 2%-5%; PBAT-PTMO block copolymer: 2%-8%, wherein the PBAT-PTMO block copolymer is composed of materials with a molar ratio of 1:1.05-1:1.2. Poly(butylene adipate) / terephthalate prepolymer and polytetrahydrofuran prepolymer are prepared by block copolymerization. The number average molecular weight of the copolymer is 20,000~30,000 g / mol, and the dispersion PDI ≤ 1.96. Nano-silica: 0%-2%; Additives: 2%-10%, the additives being maleic anhydride, 2-imidazolium ketone, and a copolymer of styrene and glycidyl acrylate in a mass ratio of 0.4:0.4:1; Plasticizer: 0%-1%, preferably tributyl citrate. Inorganic mineral fillers are any one of talc, calcium sulfate, calcium silicate, and calcium carbonate, and the specific appropriate inorganic minerals can be selected according to the product's application.

[0089] II. Preparation process of composite materials

[0090] To facilitate reproducibility by those skilled in the art, additional information on common raw materials is provided: nano-silica was purchased from Taiyuan Kepona Nano Engineering Co., Ltd.; bamboo fiber from Hebei Jigao Chemical Fiber; hemp fiber from Wuhan Hanma Biotechnology; corn fiber from Shandong Xinrui New Materials; and talc powder (800 mesh) and calcium carbonate (3000 mesh) were purchased from Shanxi Yishunda Kaolin Co., Ltd. Referring to Tables 1 and 2, we list the following optimal preparation process as the basis for subsequent research examples. The specific preparation process is as follows:

[0091] 1. Raw material pretreatment: Place PLA in a vacuum drying oven and vacuum dry at 45℃ for 4.5h; use a steam explosion device (pressure 2.0MPa, maintained for 12 seconds) to obtain 0.5-2mm microfibers, then alkalize with 5% NaOH solution in a stirred tank for 1.5h, rinse with deionized water until neutral, and then dry in a forced-air drying oven at 80℃; place talc powder and calcium carbonate in an oven and preheat at 105℃ for 30 minutes; add 10% by weight of silane coupling agent KH550 to nano silica, ultrasonically treat in an ultrasonic cleaner (400W) for 20 minutes, and then dry in a vacuum drying oven for later use.

[0092] 2. Premixing: Weigh PBAT, PLA, PBS, pretreated plant fiber, inorganic filler, PBAT-PTMO block copolymer and 70% additives according to the formula, add them to a high-speed mixer and stir at 700 rpm for 7.5 minutes.

[0093] 3. Secondary mixing: Transfer the premixed materials to the same high-speed mixer, add the remaining 30% of the additives, and adjust the speed to 250 rpm and stir for 5 minutes.

[0094] 4. Melting, plasticizing and molding: (1) The mixture is added to a twin-screw extruder (TE-35, length-to-diameter ratio 48:1), with screw temperatures of 60℃ in zone 1, 120℃ in zone 2, 160℃ in zone 3, 180℃ in zone 4, and 170℃ at the die head, and a rotation speed of 200 rpm. After the extruded strip is air-cooled and stretched, it is granulated at a spacing of 4.7 mm and then formed by a blown film machine (matching film thickness 0.03-0.05 mm) to produce film products. (2) The mixture is extruded and granulated by a twin-screw extruder (length-to-diameter ratio 56:1) (temperature 160-190℃, rotation speed 180 rpm), and then formed by an injection molding machine (mold temperature 60℃, injection pressure 80 MPa) to produce tableware. (3) The mixture is extruded and granulated using a co-rotating twin-screw extruder (TE-35, Nanjing Keya Chemical Equipment Co., Ltd., length-to-diameter ratio 56:1); the granules are screened by a vibrating screen to control the particle size at 1-3 mm, and are used to produce granules (such as...). Figure 13 As shown, see Examples 8 and 9 below.

[0095] 5. Post-processing: After the molded product cools and sets, remove burrs. After sampling inspection and passing the inspection, package and store the product. (See attached...) Figure 5 As shown, in the finished product silo, the granules are packaged by a semi-automatic granule packaging machine. After being sealed, these packaged materials can be sold to customers in the market or used directly in the downstream product manufacturing process.

[0096] Currently, our company's workshop is equipped with vertical mixers, express delivery bag blown film machines, mulch film blown film machines, single-layer blown film machines, ABA blown film machines, various bag making machines, slitting machines, and low-temperature granulators. The preparation process involves step-by-step pretreatment and multi-stage mixing. After mixing, the film is blown using a biodegradable blown film machine, printed with environmentally friendly water-based inks (most air column cushioning bags do not require printing), and finally heat-cut and formed by a bag making machine to obtain biodegradable film bags. Mulch film-specific materials are mixed and blown using an ABC three-layer co-extrusion blown film machine, and then slit to obtain biodegradable mulch film.

[0097] In addition, existing film bag manufacturing workshops, based on production plans or customer order specifications, utilize the biodegradable modified composite masterbatch developed in this invention as raw material to produce qualified fully biodegradable customized products and package them through processes such as film blowing, printing, winding, and bag making. The main products produced are PE and fully biodegradable plastic products, including express delivery bags, mulch films, pet bags, garbage bags, seedling bags, and shopping bags.

[0098] III. Implementation Plan Design

[0099] Based on preliminary research, the environmentally friendly biodegradable modified composite material developed in this invention was designed in the following embodiments in combination with different application scenarios (membranes, tableware, granules). All embodiments contain 7 raw materials: PBAT, PBS, PLA, PBAT-PTMO, inorganic mineral filler, natural plant fiber, and additives. Nano silica and plasticizers are added according to the performance requirements of the application field, and the total mass percentage of each component is 100%.

[0100] Example 1 (MD): The formulation consisted of 20% PBAT, 10% PBS, 40% PLA, 15% calcium carbonate, 3% bamboo fiber, 7% additives, 3% PBAT-PTMO, 1.5% nano-silica, and 0.5% plasticizer. The process followed the blown film blowing procedure of the basic example, with a thickness of 0.03 mm. Performance was as follows: infrared analysis showed that the main component was PBAT; longitudinal tensile strength was 21.2 MPa, and transverse tensile strength was 30.7 MPa; longitudinal elongation at break was 713.5%, and transverse elongation was 525.5%; and the biodegradability after 140 days was 89.4%.

[0101] Example 2 (ST): Compared with Example 1, the composition was adjusted as follows: PBAT 23%, PBS 12%, PLA 41%, talc replaced calcium carbonate at 10%, hemp fiber 4%, auxiliaries 4.5%, PBAT-PTMO 5%, plasticizer 0.5%, and nano-silica removed. The process was the same as in Example 1, with a thickness of 0.04 mm. Performance was as follows: infrared analysis showed PBAT as the main component; longitudinal tensile strength 20.8 MPa, transverse tensile strength 29.5 MPa; longitudinal elongation at break 680.2%, transverse elongation 510.3%; 140-day biodegradability 88.7%.

[0102] Example 3 (CJ01 knife): Compared with Example 1, the composition was adjusted as follows: PBAT was increased to 18%, PBS remained at 10%, PLA was increased to 53%, talc replaced calcium carbonate at 5%, hemp fiber accounted for 3%, auxiliaries were 5%, PBAT-PTMO was adjusted to 5%, nano-silica remained at 1%, and plasticizer was removed. The process was changed to injection molding, with a length set at 160mm. The performance was as follows: infrared analysis showed PLA as the main component; tensile strength was 45MPa; elongation at break was 35%; and heat distortion temperature was 65℃.

[0103] Example 4 (CJ02 fork): Compared with Example 3, the composition was adjusted as follows: PBAT 19%, PBS 11%, PLA 52%, talc 6%, bamboo fiber replaced hemp fiber at 3%, additives 4%, PBAT-PTMO 4%, and nano-silica maintained at 1%. The process was the same as in Example 3, maintaining a length of 160 mm. The performance was as follows: infrared analysis showed PLA as the main component; tensile strength 44 MPa; elongation at break 38%; heat distortion temperature 64℃.

[0104] Example 5 (CJ03 spoon): Compared with Example 3, the composition was adjusted as follows: PBAT 20%, PBS 12%, PLA 48%, talc 6%, bamboo fiber replaced hemp fiber at 3%, additives 5%, PBAT-PTMO 5%, and nano-silica 1%. The process was the same as in Example 3, but the length was kept at 160 mm. The performance was as follows: infrared analysis showed PLA as the main component; tensile strength 42 MPa; elongation at break 40%; heat distortion temperature 63℃.

[0105] Example 6 (CH01 lunchbox): Compared with Example 1, the components were adjusted as follows: PBAT 25%, PBS 15%, PLA 35%, talc replaced calcium carbonate at 12%, hemp fiber 3%, auxiliaries 5.5%, PBAT-PTMO 3%, nano silica 1.5%, and plasticizer removed. The process was changed to injection molding, with dimensions set at 190×135×56mm. Performance: Infrared analysis showed the main components were a mixture of PBAT, PLA, PBS, talc, and calcium carbonate; tensile strength 38MPa; elongation at break 60%; and biodegradability after 180 days 87.7%.

[0106] Example 7 (CH02 Tabletop): Compared with Example 6, the composition was adjusted as follows: PBAT remained at 25%, PBS was adjusted to 16%, PLA remained at 35%, calcium carbonate replaced talc at 14%, bamboo fiber replaced hemp fiber at 3%, additives were 4%, PBAT-PTMO was adjusted to 2%, and nano-silica was adjusted to 1%. The process was the same as in Example 6, but the dimensions were adjusted to 190×135×7mm. The performance was as follows: infrared analysis showed the main components were a mixture of PBAT, PLA, PBS, talc, and calcium carbonate; tensile strength was 36MPa; elongation at break was 70%; and biodegradability after 180 days was 87.2%.

[0107] Example 8 (HYSCST01): Compared with Example 1, the composition was adjusted as follows: PBAT 22%, PBS 14%, PLA 36%, calcium carbonate 12%, corn stalk fiber replaced bamboo fiber at 4%, additives 5%, PBAT-PTMO 5%, nano-silica 1%, and plasticizer 1%. The process was changed to extrusion granulation. Performance was as follows: infrared analysis showed PBAT as the main component; starch content 44%; density deviation 1.8%; MFR deviation 1.7%.

[0108] Example 9 (HYSCMD01): Compared with Example 8, the components were adjusted as follows: PBAT to 24%, PBS to 13%, PLA to 36%, talc to replace calcium carbonate at 10%, corn stalk fiber to 3%, additives to 5%, PBAT-PTMO to 6%, nano-silica to 2%, and plasticizer to 1%. The process was the same as in Example 8. The performance was as follows: infrared analysis showed the main components were PBAT, PLA, PBS, and calcium carbonate; starch content was 42%; density deviation was 2.0%; and MFR deviation was 1.9%.

[0109] Example 10 (Membrane): Compared with Example 1, the composition remained PBAT 20%, PBS 10%, PLA 36%, calcium carbonate 18%, bamboo fiber 3%, additives 4%, PBAT-PTMO 8%, plasticizer 1%, and nano-silica was removed. The process used was a three-layer co-extrusion blown film with a thickness adjusted to 0.01 mm. The properties were: longitudinal tensile strength 22.1 MPa; transverse tensile strength 31.2 MPa; longitudinal elongation at break 650.4%.

[0110] Example 11 (Membrane): Compared with Example 1, the composition was adjusted as follows: PBAT 28%, PBS 16%, PLA 29%, calcium carbonate 10%, bamboo fiber 5%, additives 4%, PBAT-PTMO 8%, and nano-silica and plasticizer were removed. The process was the same as in Example 1, but the blown film thickness was adjusted to 0.05 mm. The properties were: longitudinal tensile strength 19.5 MPa; transverse tensile strength 28.3 MPa; longitudinal elongation at break 750.6%.

[0111] Example 12 (Tableware): Compared with Example 3, the composition was adjusted as follows: PBAT 22%, PBS 13%, PLA 48%, talc 8%, hemp fiber 3%, auxiliaries 4%, PBAT-PTMO 2%, and nano-silica removed. The process was the same as in Example 3, with a length of 160 mm. The properties were: tensile strength 40 MPa; elongation at break 50%; heat distortion temperature 62°C.

[0112] Example 13 (Tableware): Compared with Example 3, the composition was adjusted as follows: PBAT 24%, PBS 14%, PLA 42%, talc 10%, hemp fiber 3%, auxiliaries 4%, PBAT-PTMO 3%, and nano-silica removed. The properties were: tensile strength 39 MPa; elongation at break 55%; heat distortion temperature 61°C.

[0113] Example 14 (granules): Compared with Example 8, the composition was adjusted as follows: PBAT 23%, PBS 12%, PLA 38%, calcium carbonate 12%, corn stalk fiber 4%, additives 4%, PBAT-PTMO 6%, plasticizer 1%, and nano-silica removed. The process was the same as in Example 8. The performance was: starch content 41%; density deviation 2.1%; MFR deviation 2.0%.

[0114] Example 15 (granules): Compared with Example 8, the composition was adjusted as follows: PBAT 26%, PBS 13%, PLA 35%, calcium carbonate 11%, corn stalk fiber 3%, additives 4%, PBAT-PTMO 7%, plasticizer 1%, and nano silica removed. The performance was: starch content 43%; density deviation 1.9%; MFR deviation 1.8%.

[0115] IV. Proportional Design

[0116] Comparative Example 1 (corresponding to Example 1): The formulation is the same as in Example 1, but the plant fibers were not subjected to steam explosion and alkalization treatment. The properties are: longitudinal tensile strength 18.5 MPa; transverse tensile strength 26.3 MPa; longitudinal elongation at break 550%; interfacial peel rate 15%.

[0117] Comparative Example 2 (corresponding to Example 1): The formulation is the same as in Example 1, but PBAT-PTMO is removed, and PBAT is adjusted to 23%. The properties are: longitudinal tensile strength 19.2 MPa; transverse tensile strength 27.5 MPa; longitudinal elongation at break 450%; impact strength at -20℃ 4.5 kJ / m².

[0118] Comparative Example 3 (corresponding to Example 3): The formulation consisted of 70% PLA, 15% PBAT, 8% PBS, 5% 800-mesh talc, and 2% additives. Compared with Example 3, the proportion of PLA was too high. The properties were: tensile strength 52 MPa; elongation at break 12%; impact strength 3.0 kJ / m².

[0119] Comparative Example 4 (corresponding to Example 6): The formulation consisted of 35% PBAT, 30% PLA, 10% PBS, 15% 800-mesh talc, and 10% additives. Compared to Example 6, the PBAT ratio was too high. The performance was a tensile strength of 22 MPa and a biodegradability of 95% after 180 days.

[0120] Comparative Example 5 (corresponding to Example 8): The formulation is the same as in Example 8, but the nano-silica was not treated with KH550. The properties are: starch content 38%; density deviation 4.5%; MFR deviation 5.2%; agglomeration rate 22%.

[0121] Comparative Example 6 (corresponding to Example 1): The formulation is the same as in Example 1, except the secondary mixing step is omitted. The properties are: longitudinal tensile strength 19.2 MPa; transverse tensile strength 28.1 MPa; component dispersion coefficient 1.8.

[0122] Comparative Example 7 (corresponding to Example 1): The formulation consisted of 95% PBAT and 5% additives, and was a pure PBAT material compared to Example 1. The properties were: longitudinal tensile strength 16.8 MPa; transverse tensile strength 25.1 MPa; and 85% biodegradability after 180 days.

[0123] V. Sampling and Testing Methods

[0124] The following is the detailed information of the sampled specimens for testing:

[0125] The biodegradable bag (MD brand) is in accordance with "2021C0816 Biodegradable Bag (Brand: MD)", with a sampling quantity of 50g. The sample is a white semi-transparent bag with a blue pattern on one side of the outer surface, and the specifications are 550×(350+90×2)×0.03mm.

[0126] The biodegradable bag (ST brand) is in accordance with "2021C0817 Biodegradable Bag (Brand: ST)", with a sampling quantity of 50g. The sample is a beige semi-transparent bag with a blue pattern on one side of the outer surface, and the specifications are 400×(250+55×2)×0.03mm.

[0127] The biodegradable material (HYSCST01 grade) was sampled according to "2021C0850 Biodegradable Materials (Grade: HYSCST01)", with a sampling quantity of 50g and the sample being light brownish-yellow granules.

[0128] The biodegradable disposable knife (CJ01 grade) was sampled according to the "2021C0851 Biodegradable Disposable Knife (Grade: CJ01)" standard. The sampling quantity was 50g, the sample was a white knife, and the specification was 160mm.

[0129] The biodegradable disposable table lid (brand name CH02) was sampled according to "2021C0852 Biodegradable Disposable Table Lid (brand name: CH02)", with a sampling quantity of 50g. The sample was a white lid with a size of 190×135×7mm.

[0130] The biodegradable disposable spoon (CJ03 grade) was sampled according to "2021C0854 Biodegradable Disposable Spoon (Grade: CJ03)", with a sampling quantity of 50g. The sample was a white spoon with a specification of 160mm.

[0131] The biodegradable disposable fork (CJ02 grade) was sampled according to "2021C0855 Biodegradable Disposable Fork (Grade: CJ02)", with a sampling quantity of 50g. The sample was a white fork with a specification of 160mm.

[0132] The biodegradable disposable lunch box (brand name CH01) was sampled according to the standard "2021C0871 Biodegradable Disposable Lunch Box (brand name: CH01)". The sample size was 50g, and the sample was a white box with a size of 190×135×56mm.

[0133] The biodegradable material (HYSCMD01 grade) was sampled according to "2021C0962 Biodegradable Materials (Grade: HYSCMD01)", with a sampling quantity of 50g and the sample being white granules.

[0134] According to the "2022C0410 Biodegradation Rate Test Report (Biodegradable Polyester)", the sampling quantity was 500g, the sample was white granules, and the client specified that the material was single-component PBAT (see Table 1 Jinfa).

[0135] The starch-based injection molding compound (corresponding to the granular material example) was sampled according to the "Inspection Report on Starch-Based Injection Molding Compound". The sampling quantity was 300g + 20 sample strips, and the sample was light yellow granules.

[0136] According to the "Inspection Report - Express Bag", the sample size for the express bag (corresponding film type example) is 50 pieces. The sample is a printed film bag with the following specifications: thickness 0.05 mm × length (including sealing tongue) (560+50) × width 540 mm.

[0137] Biodegradable shopping bags (physical properties, corresponding to membrane examples) were tested according to the "Inspection Report - Physical Properties of Biodegradable Shopping Bags". The sample size was 30 bags. The samples were shopping bags with printing and handles, with a length of 540 × width (400+200) × thickness of 0.04 mm.

[0138] Biodegradable shopping bags (biodegradability performance, corresponding membrane examples) were sampled according to the "Biodegradable Shopping Bag Inspection Report Biodegradability Performance". The sample size was 50 bags. The samples were shopping bags with printing and handles, with a length of 540 × width (400+200) × thickness of 0.04 mm.

[0139] The above performance tests were performed according to the following standards: Material analysis was performed using the infrared method (GB / T6040-2019); biodegradability was determined according to GB / T19277.1-2011, with three replicate compost containers per group, under composting conditions of 58±2℃ and 55±5% humidity, using the CO2 release method; tensile strength and elongation at break were tested according to GB / T1040.3-2006 (rate 50mm / min), with five parallel samples prepared for each group, and the average value was taken, with a relative standard deviation (RSD) ≤3.2%; low-temperature impact strength was tested according to GB / T1843-2008 at -20℃ using the simply supported beam notch method, with six parallel samples tested, and outliers with a deviation >10% were removed before taking the average value, with an RSD ≤4.5%. Referring to GB / T 43196-2023, with magnification set to 200x and scale bars of 50μm and 5μm respectively, the cross-sectional morphology of the composite material before and after modification with natural plant fibers was observed using scanning electron microscopy. After gold sputtering treatment, the dispersion state of the fibers and their interfacial bonding with the matrix were observed before and after modification. Transmission electron microscopy was used to analyze the dispersibility of nano-silica before and after modification. The samples were prepared into ultrathin sections with a thickness of 50-100nm to observe the size, distribution, and aggregation of nanoparticles after ultrasonic modification.

[0140] VI. Analysis of Experimental Results

[0141] This invention achieves precise matching of materials and application scenarios through differentiated design of the proportions of key components such as PBAT, PLA, and PBS. For membrane products such as express delivery bags and agricultural mulch films, 20%-28% PBAT and 29%-41% PLA are used, combined with 5%-8% PBAT-PTMO block copolymer. For example, in Example 1, 20% PBAT and 40% PLA have a longitudinal elongation at break of 713.5% and a transverse elongation at break of 525.5%, with a 140-day biodegradability of 89.4%. In Example 11, 28% PBAT, 29% PLA, and 8% PBAT-PTMO have a longitudinal elongation at break of 750.6%, meeting the requirements for high toughness and controllable degradation. For tableware such as knives, forks, and lunch boxes, 35%-53% PLA and 18%-25% PBAT are used, as in Example 3, 53% PLA. Example 6, with 18% PLA and 25% PBAT, has a tensile strength of 45 MPa and a heat distortion temperature of 65°C. Example 7, with 35% PLA and 25% PBAT, has a tensile strength of 38 MPa and an elongation at break of 60%, meeting the requirements for high strength and heat resistance. For subsequent processing, the granular material uses 35%-38% PLA, 22%-26% PBAT, and 12%-14% PBS, as shown in Example 8, with a density deviation of 1.8% and a melt flow rate deviation of 1.7%, ensuring compositional stability. Comparative experiments show that Comparative Example 3, with 70% PLA, has an elongation at break of only 12%, and Comparative Example 4, with 35% PBAT, has a tensile strength of only 22 MPa. Deviating from the suitable ratio will lead to performance degradation.

[0142] Figure 8 The results show that in Example 8, after PLA vacuum drying, inorganic filler preheating, and secondary mixing, the MFR fluctuation range within 15 minutes was ≤0.1g / 10min, and the curve was stable, proving that the components were uniformly dispersed. In contrast, the PLA group without vacuum drying showed a continuous increase in MFR over time due to hydrolysis and degradation; the inorganic filler group without preheating showed drastic curve fluctuations due to moisture introduction; and the group without secondary premixing showed fluctuations of ±0.5g / 10min due to uneven dispersion of additives. These results indicate that step-by-step pretreatment and multi-stage mixing processes can significantly improve melt stability, providing a uniform material basis for subsequent molding processes such as blown film and injection molding, consistent with the detection result of only a 1.7% deviation in melt mass flow rate in the examples. Furthermore, PLA vacuum drying avoids hydrolysis, and preheating of inorganic minerals reduces bubbles; high-speed premixing combined with medium-speed secondary mixing resulted in a component dispersion coefficient ≤1.2, while in Comparative Example 6, omitting secondary mixing increased the coefficient to 1.8, resulting in a 10% decrease in strength. The molding process adaptability is significant, with blown film technology used in Example 1, where the film thickness deviation was ≤0.002mm. The tableware is manufactured using injection molding, and in Example 3, the heat distortion temperature reaches 65°C. The synergistic design of the process and materials avoids performance fluctuations caused by traditional single-process methods.

[0143] like Figure 9 As shown, the tensile stress-strain curves intuitively demonstrate the optimization of mechanical properties by the synergistic effect of the components. Example 1, containing PBAT-PTMO block copolymer, exhibits a clear elastic-plastic transition stage, with an elongation at break of 713.5%, while maintaining a tensile strength of 21.2 MPa, achieving a balance between strength and toughness. Comparative Example 2, lacking PBAT-PTMO, suffers from a shortened plastic stage, with the elongation at break dropping to 450%, demonstrating the crucial role of the block copolymer in improving toughness. Comparative Example 3, with an excessively high PLA proportion, results in a steep curve and no plastic stage, with an elongation at break of only 12%, exhibiting high brittleness. Comparative Example 7, with pure PBAT, has a low stress peak, failing to meet high strength requirements. These comparisons verify the scientific validity of the component ratio and synergistic design of the PBAT-PTMO block copolymer in this invention, solving the problem of balancing strength and toughness in traditional biodegradable materials. Furthermore, orthogonal experiments show that with a prepolymer molar ratio of 1:1.08 and a reaction temperature of 45℃, the copolymer dispersion of 1.86 and a phase separation size of 0.3-0.5 μm are far superior to traditional transesterification processes. In terms of mechanical properties, Example 1, with the addition of 2% of the copolymer, showed a low-temperature impact strength of 9.5 kJ / m² at -20°C, while Comparative Example 2, without the copolymer, showed an impact strength that decreased to 4.5 kJ / m² and an elongation at break that decreased from 713.5% to 450%.

[0144] Figure 10The results show that the agricultural mulch film of Example 10 achieved a degradation rate of 86.8% after 180 days, with only 35% degradation in the first 90 days, making it suitable for the coverage needs of long-cycle crops such as corn. The biodegradable bag of Example 1 achieved a degradation rate of 89.4% after 140 days, with a faster degradation rate in the middle stage, meeting the requirement for rapid degradation after short-term use. The disposable lunch box of Example 6 achieved a degradation rate of 87.7% after 180 days, with a steady upward curve, meeting the stability requirements of tableware usage cycles. In contrast, Comparative Example 4, due to its excessively high PBAT ratio, achieved a degradation rate of 95% after 180 days, resulting in functional failure due to excessively rapid degradation. These results demonstrate that precise matching of degradation rates can be achieved through component ratio control, solving the problem of adapting to scenarios where traditional mulch films degrade too quickly or incompletely, and further verifying the material's adaptability to different application scenarios.

[0145] Figure 11 The results, observed using scanning electron microscopy, show that the samples from Example 1 and Comparative Example 1 are different. In Comparative Example 1, the untreated fibers exhibit a raw, entangled state, with the fiber bundles adhering to each other and having a loose structure. When in contact with the matrix, the irregular shape easily creates gaps. In Example 1, the modified fibers are more regularly dispersed, with a roughened surface and a more ordered microstructure. This modification provides a more stable interface with the PBAT / PLA matrix. This structural change directly results in Example 1 having a significantly higher longitudinal tensile strength than Comparative Example 1, without any interfacial delamination. This steam explosion synergistic alkalization process demonstrates the optimization of fiber morphology and interfacial compatibility.

[0146] like Figure 12 As shown, the microstructure of the materials prepared in Comparative Example 5 and Example 8 was observed using transmission electron microscopy. In Comparative Example 5, the untreated nano-silica, lacking interface modification, exhibited strong interparticle aggregation, forming numerous aggregates exceeding 500 nm in size. Some aggregates were interconnected, with the largest reaching 1 μm in size. The nanoparticle distribution was extremely uneven, with almost no effectively dispersed individual particles between the aggregates. In contrast, Example 8, after KH550 modification and synergistic ultrasonic dispersion, showed that the coupling agent grafted onto the nanoparticle surface effectively reduced the aggregation energy barrier. Combined with the mechanical dispersion effect of ultrasound, the particles were uniformly dispersed in the matrix, with individual particle sizes <50 nm and approximately spherical shapes. The interparticle spacing was stable at 50-100 nm, with a consistent distribution density within the field of view and an aggregation rate ≤5%. This demonstrates that the synergistic effect of KH550 and ultrasonic treatment can fundamentally improve the dispersion stability of nano-silica.

[0147] In summary, the present invention has demonstrated its innovation in five aspects—component ratio, modification process, copolymer design, process matching, and application adaptability—through systematic experiments using 15 examples and 7 comparative examples. Experimental data show that the composite material exhibits a tensile strength of 30-45 MPa, an elongation at break of 500%-800%, and a biodegradability of 87%-89%. These key indicators are superior to traditional solutions, and the performance can be precisely adapted to various applications such as membranes, tableware, and granular materials, fully demonstrating the inventiveness and practicality of the proposed solution.

[0148] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An environmentally degradable modified composite material, characterized in that, The mass percentage of each raw material is as follows: Polybutylene adipate terephthalate: 18%-28%; Polybutylene succinate: 10%-16%; Poly lactic acid: 28%-55%; Natural plant fiber: 2%-5%; PBAT-PTMO block copolymer: 2%-8%; Inorganic mineral filler: 5%-18%, the filler is any one or a combination of more than one of talc, calcium sulfate, calcium silicate and calcium carbonate, and the particle size is 800-3000 mesh; Auxiliary agent: 2%-10%, the auxiliary agent is maleic anhydride, 2-imidazolidone and a copolymer of styrene and glycidyl acrylate, and the mass ratio of the three is 0.4:0.4:1; The PBAT-PTMO block copolymer is prepared from polybutylene adipate terephthalate prepolymer and polytetrahydrofuran prepolymer with a molar ratio of 1:1.05-1:1.2, and the number average molecular weight of the copolymer is 20000-30000 g / mol, and the dispersity PDI is less than or equal to 1.96; The preparation method of the PBAT-PTMO block copolymer comprises the following steps: Step a, preparation of thiol-terminated PBAT prepolymer: mix terephthalic acid, adipic acid, 1,4-butanediol and 2-mercaptoethanol in a molar ratio of 1:1:5.5-6.5:0.8-1.2, and add 0.05%-0.1% of the total mass of the monomers of the first catalyst, 0.03%-0.05% of the composite antioxidant and 0.01%-0.03% of the thiol protecting agent; under nitrogen protection, first heat to 160-170℃ for esterification reaction for 1.5-2h, then heat to 180-190℃, and reduce the pressure for polycondensation reaction for 6-8h to obtain thiol-terminated PBAT prepolymer with a number average molecular weight of 4000-5000 g / mol; Step b, preparation of PTMO prepolymer with a single end acrylate group: add 0.5%-1% of boron trifluoride etherate complex to tetrahydrofuran, and stir under 0-10℃ and nitrogen protection for 4-6h to obtain a hydroxyl-terminated PTMO intermediate; add acrylic acid to the hydroxyl-terminated PTMO intermediate, the molar ratio of acrylic acid to the hydroxyl-terminated group is 1.1:1, and add 0.1% of the total mass of the reaction system of the second catalyst, and react at 80℃ for 3h, remove the unreacted monomers by reduced pressure distillation, wash with 5% NaHCO3 solution for 3 times, and then dehydrate under vacuum to obtain PTMO prepolymer with a single end acrylate group with a number average molecular weight of 1800-2200 g / mol; Step c, block copolymerization: mix the thiol-terminated PBAT prepolymer of step a and the PTMO prepolymer with a single end acrylate group of step b in a molar ratio of 1:1.05-1.2, and add 0.1%-0.15% of the total mass of the prepolymers of the composite initiator; under nitrogen protection, stir and irradiate with ultraviolet light at 40-50℃ for 2-2.5h for copolymerization reaction to form a block copolymer with a number average molecular weight of 20000-30000 g / mol; Step d, purification treatment: the block copolymer of step c is poured into ethanol for precipitation, after filtration, washed with deionized water for 2~3 times, vacuum drying, to obtain PBAT-PTMO block copolymer, dispersity PDI≤1.96, the PBAT-PTMO block copolymer has the following formula I chemical structure: ， Formula I In the formula: the polymerization degree m of PBAT segment is an integer of 17~22; the polymerization degree n of PTMO segment is an integer of 23~28.

2. The environmentally friendly degradable modified composite material according to claim 1, characterized in that, Also includes nano silicon dioxide 0%-2% and plasticizer 0%-1%, the plasticizer is tributyl citrate.

3. The environmentally friendly degradable modified composite material according to claim 1, characterized in that, The first catalyst in step a is tetrabutyl titanate, the composite antioxidant is a mixture of triphenyl phosphite and hindered phenolic antioxidant 1010, the mass ratio of which is 1:1; the thiol protective agent is 2,6-dimethylpyridine; the second catalyst in step b is p-toluenesulfonic acid; the composite initiator in step c is benzophenone and triethylamine, the mass ratio of which is 1:1.2~1.

5.

4. The environmentally friendly degradable modified composite material according to claim 1, characterized in that, The molar ratio of terephthalic acid, adipic acid, 1,4-butanediol and 2-mercaptoethanol in step a is 1:1:6:1; the molar ratio of PBAT prepolymer and PTMO prepolymer in step c is 1:1.

08.

5. The environmentally friendly degradable modified composite material according to claim 1, characterized in that, The vacuum degree of the reduced pressure condensation reaction in step a is 0.08-0.1 MPa, the temperature of vacuum dehydration in step b is 50-60℃, the vacuum degree is 0.09-0.1 MPa, and the dehydration time is 2-3 h; the wavelength of the ultraviolet light in step c is 365 nm, the light intensity is 150-200 mW / cm 2 , and the stirring rate is 350-400 r / min; the drying temperature in step d is 60-70℃, and the drying time is 8-10 h.

6. The environmentally friendly degradable modified composite material according to claim 2, characterized in that, The natural plant fiber is any one of cotton fiber, hemp fiber, bamboo fiber, coconut shell fiber and corn straw fiber; the natural plant fiber is first treated by steam explosion to form microfibers with a fiber length of 0.5-2mm, then alkalized for 1-2 hours, then washed with deionized water to neutral and dried.

7. The environmentally friendly degradable modified composite material according to claim 2, characterized in that, The nano silicon dioxide is treated by adding 8%-12% silane coupling agent KH550, ultrasonic treatment for 15-25 minutes, using the acoustic cavitation effect to cooperate with the coupling agent, so that the coupling agent is more evenly coated on the surface of the particles to form a stable chemical bond layer.

8. A method for preparing the environmentally friendly biodegradable modified composite material as described in claim 2, characterized in that, The method comprises the following steps: S1 raw material pretreatment: the polylactic acid is vacuum dried at 45-50°C for 4-5 hours; the inorganic mineral filler and nano silicon dioxide are preheated at 100-110°C for 30-35 minutes; the natural plant fiber is pretreated by steam explosion to obtain microfibers with a length of 0.5-2mm, then alkalized with 5% NaOH solution for 1-2 hours, washed to neutral and dried; S2 premixing: PBAT, dried PLA, PBS, preheated inorganic mineral filler, modified natural plant fiber, modified nano silicon dioxide, PBAT-PTMO block copolymer, tributyl citrate and 70% auxiliary agent are weighed according to the proportion and put into a high-speed mixer, and mixed at a high speed of 500-900rpm for 7-8 minutes; S3 secondary premixing: the remaining 30% auxiliary agent is added, and secondary premixing is carried out at a medium speed of 240-260rpm for 5-6 minutes, so as to optimize the uniformity of the raw materials, ensure that the auxiliary agent fully acts on each raw material, and improve the compatibility of the system; S4 melt plasticization and molding: the mixture is fed into a co-rotating twin-screw extruder, the screw temperature is set to 60-180°C, the screw rotation speed is 150-250 rpm, the screw length-diameter ratio is 48:1-56:1, under the conditions, the raw materials are fully melt plasticized, mixed uniformly, and stably extruded; the extruded strip is air-cooled and drawn, cut into particles at a spacing of 4.6-4.8 mm, vibrated and sieved, and then conveyed to a finished product bin.

9. Use of the environmentally friendly degradable modified composite material according to any one of claims 1-7 in the preparation of packaging bags, disposable tableware, and agricultural mulching films.

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