Graft modified PBS / EVA biodegradable foam plastic and preparation method and application thereof

Abstract

This invention provides a grafted or chain-extended modified PBS / EVA biodegradable foam plastic, its preparation method, and its applications. The foam plastic employs two formulation systems: one consists of EVA, PBS, POE, polar monomers, initiator, crosslinking agent, foaming agent, foaming aid, and filler; the other consists of EVA, biodegradable polyester, POE, chain extender, crosslinking agent, foaming agent, foaming aid, and filler. The PBS / EVA composite foam prepared by this invention possesses good biodegradability, high fatigue resistance, and excellent mechanical strength. Furthermore, the system can be remodeled and recycled through transesterification. The PBS / EVA composite foam can be applied to footwear materials, high-end luxury packaging materials, and automotive interiors.

Description

Technical Field

[0001] This invention relates to the field of organic polymer materials and products, specifically to a grafted modified PBS / EVA biodegradable foam plastic, its preparation method, and its application. Background Technology

[0002] With the rapid development of the plastics industry, global annual plastic production has been increasing year by year. On the one hand, most of these plastics use petroleum-based synthetic resins as raw materials. Due to the decreasing petroleum resources and the rapid increase in petroleum consumption, the development of the plastics industry has accelerated the depletion of petroleum resources. On the other hand, since a considerable portion of plastic products are single-use materials, such as packaging materials, agricultural films, and medical materials, these waste plastics have caused serious damage and pollution to the environment, thus causing serious "white pollution."

[0003] Currently, the global green plastics sector has moved from the research and development stage to the industrial production stage, developing rapidly. Major producing countries include the United States, Japan, Germany, Italy, Canada, and China. In overseas markets, demand is growing rapidly; statistics show that the demand for biodegradable plastics will grow at a rate of approximately 12% annually.

[0004] Existing technologies have conducted relevant research on the development of a biodegradable foam plastic.

[0005] Chinese invention patent CN121379082A discloses a biodegradable polylactic acid composite material and its preparation method, relating to the field of polylactic acid material technology. The method includes: firstly, grafting and modifying chitosan activated with hydrochloric acid using KH550 silane coupling agent, and simultaneously surface-modifying nano-zinc oxide with stearic acid; then mixing and spray-drying the two to obtain an antibacterial composite powder; secondly, activating nano-silica with hydrochloric acid and modifying it with KH570 silane coupling agent, and hydroxypropylating modifying alkali lignin; then performing a reflux crosslinking reaction with KH570 modified nano-silica, polycaprolactone, methyl methacrylate, and azobisisobutyronitrile to obtain a heat-resistant reinforcement; finally, uniformly mixing polylactic acid, polybutylene succinate, antibacterial composite powder, heat-resistant reinforcement, tributyl citrate, polyethylene glycol, and talc, and granulating the mixture using a twin-screw extruder to obtain the final product. This invention patent is for non-foamed polylactic acid modified granules, which suffer from problems such as complex composition, lengthy process, high cost, lack of foamed structure, poor cushioning and elasticity, and insufficient degradation efficiency and toughness. It is difficult to directly apply to fields with high requirements for elasticity, low density, and cushioning performance, such as footwear materials, high-end cushioning packaging, and automotive interiors.

[0006] Chinese invention patent CN121378942A discloses a shrinkage-resistant, lightweight, and elastic shoe sole foam material and its preparation method, belonging to the field of footwear technology. The aforementioned lightweight, lightweight, and elastic shoe sole foam material is formed by chemical foaming of EVA composite raw materials. The EVA composite raw materials include: 50-70 parts EVA, 20-40 parts olefinic thermoplastic elastomer, 10-20 parts styrene elastomer, 1.5-3 parts maleic anhydride-grafted ethylene-octene copolymer compatibilizer, 0.4-0.8 parts peroxide crosslinking agent, 3-4 parts foaming agent, 1-1.5 parts zinc oxide, 1-1.5 parts polyethylene wax, 0.5-1.5 parts polybutylene succinate, 0.3-1 parts polyamide 12 microspheres, and 2-3 parts nano-montmorillonite. This foam material, as a shoe sole component, is shrinkage-resistant and has good rebound properties, thus meeting the high-quality requirements and mass production stability of sports shoes. This invention patent is for EVA-based shoe sole foam material, which has problems such as extremely poor biodegradability, complex composition and high cost, insufficient long-term shrinkage stability, shortcomings in mechanical and rebound properties, poor process adaptability, and limited application scenarios. It does not conform to the trend of environmental protection development, and it is difficult to adapt to the needs of high-end shoe materials, high-end packaging and automotive interiors. Compared with biodegradable PBS / EVA composite foam, it has obvious disadvantages in terms of environmental protection, versatility and production cost.

[0007] Chinese invention patent CN121362444A discloses an environmentally degradable plastic, its preparation method, and its application, belonging to the field of degradable plastics technology. The raw materials for preparing the degradable modified plastic of this invention include polylactic acid, polybutylene terephthalate-adipate, modified thermoplastic starch, modified cellulose, polybutylene succinate, epoxidized soybean oil, polyvinyl alcohol, glyceryl monolaurate, and ethylenediaminetetraacetic acid; wherein, the modified thermoplastic starch is obtained by thermoplastic modification of starch with plasticizers followed by further modification with castor oil and toluene diisocyanate; the modified cellulose is obtained by modifying cellulose acetate with chitosan. By controlling the types and proportions of the raw materials used in plastic preparation, this invention can obtain a plastic with excellent degradation and mechanical properties. When made into shopping bags, it can significantly improve load-bearing capacity and is easily degraded by microorganisms in the environment after disposal, without causing environmental pollution. However, it has significant drawbacks: First, the plastic is non-foamed, with complex components and numerous modification processes, resulting in high production costs and poor mass production stability, which is not conducive to large-scale production. Second, the main component is rigid, lacking toughness and the cushioning and resilience properties of foamed materials, making it unsuitable for applications such as shoe materials and automotive interiors. Third, its application scenarios are limited, suitable only for simple packaging, resulting in poor versatility. Fourth, modified starch and cellulose easily lead to water absorption, mold growth, and performance degradation, with poor controllability of the degradation rate. Compared with the biodegradable PBS / EVA composite foam of this application, the existing technology has significant disadvantages in terms of cost, process, mechanical properties, application scope, and degradation stability, and cannot meet the needs of high-end, multi-scenario applications. Summary of the Invention

[0008] The purpose of this invention is to provide a grafted or chain-extended modified PBS / EVA biodegradable foam plastic, its preparation method, and its applications. This invention employs two parallel modification methods—grafting modification and chain-extending modification—to enhance and compatibilize the system: on the one hand, an initiator and polar monomer can be introduced into PBS to achieve PBS grafting modification, followed by blending with EVA and hot-pressing foaming to prepare composite foam materials; on the other hand, a one-step process can be used to simultaneously complete chain-extending modification, melt blending, and foaming, simplifying the preparation process. This invention aims to study the gas barrier properties, crystallinity, mechanical properties, and degradation properties of PBS composite materials through formulation design and process adjustment, and to explore the mechanism of action. A rotational rheometer is used to study the relationship between changes in the structure and morphology of the composite material and the resulting changes in performance.

[0009] To achieve the above objectives, the present invention provides the following solution:

[0010] A biodegradable foam plastic based on grafted or chain-extended modified PBS / EVA, comprising one of the following two formulations by weight:

[0011] Formula 1: 60-90 parts of ethylene-vinyl acetate copolymer (EVA), 10-40 parts of biodegradable polyester, 5-20 parts of polyolefin elastomer (POE), 0.5-2.5 parts of polar monomer, 0.2-0.6 parts of initiator, 0.2-0.9 parts of crosslinking agent, 1-3 parts of foaming agent, 1.5-4 parts of foaming aid, and 2.5-10 parts of filler;

[0012] Formula 2: 60-90 parts of ethylene-vinyl acetate copolymer (EVA), 10-40 parts of biodegradable polyester, 5-20 parts of polyolefin elastomer (POE), 0.1-1.0 parts of chain extender, 0.2-0.9 parts of crosslinking agent, 1-3 parts of foaming agent, 1-3 parts of foaming aid, and 2.5-10 parts of filler;

[0013] Degradable polyester molecular chains are modified by free radical grafting or melt chain extension. Grafting introduces polar groups, while chain extension achieves molecular chain growth and branching, forming a multi-layer cross-linked network structure under the action of a cross-linking agent. This effectively improves the mechanical properties, thermal stability, melt strength, and interfacial compatibility of the system, while maintaining good biodegradability, achieving both toughening and functional modification. The polar groups include at least one of carboxyl groups, anhydride groups, and epoxy groups. The static water contact angle of the foam is 122.9°~134.4°, and the tear strength is 1.5~2.1 kN / m.

[0014] This invention provides two parallel modification systems: grafting and chain extension. Grafting is used to introduce polar groups to improve interfacial compatibility. Chain extension achieves molecular chain growth and branching in situ through a one-step method, constructing a stable cross-linked network, which significantly improves melt strength, mechanical properties and cell structure stability. The process is simple, and the biodegradability is fully preserved, making it more suitable for industrial production and high-end applications.

[0015] Furthermore, the ethylene-vinyl acetate copolymer EVA has a melt index of 4–20 g / 10min (190℃ / 2.16 kg) and a VA content of 10–40 wt%; the polyolefin elastomer POE has a melt index of 20–50 g / 10min (190℃ / 2.16 kg).

[0016] Further, the polar monomer is selected from at least one of itaconic acid (ITA), maleic anhydride (MAH), glycidyl methacrylate (GMA), and acrylic acid (AA); the biodegradable polyester is selected from at least one of polybutylene succinate (PBS), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polybutylene adipate succinate (PBSA), and polybutylene adipate terephthalate (PBAT); the initiator is selected from at least one of benzoyl peroxide (BPO), dicumyl peroxide (DCP), and bis(tert-butylperoxy)diisopropylbenzene (BIBP / BIPB); the crosslinking agent is selected from 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, 1,1-bis(tert-butylperoxy)-3,3,5- At least one of trimethylcyclohexane and bis(tert-butylperoxy)diisopropylbenzene (BIBP); the chain extender is selected from at least one of epoxy chain extenders, isocyanate chain extenders, and oxazoline chain extenders; the melt index of the PBS is 5–70 g / 10 min (190 °C / 2.16 kg).

[0017] Furthermore, the foaming agent is selected from at least one of azodicarbonamide (AC / ADC), p-toluenesulfonyl hydrazine (TSH), and 4,4'-oxobisbenzenesulfonyl hydrazine (OBSH); the foaming aid is selected from at least one of zinc oxide (ZnO), magnesium oxide (MgO), zinc stearate, calcium stearate, and triethanolamine.

[0018] Furthermore, the filler is selected from at least one of calcium carbonate, talc, silica, and barium sulfate.

[0019] Furthermore, in the biodegradable foam plastic, the ester group of PBS is the main structural site for biodegradation.

[0020] Furthermore, the POE, as a toughening modifier, can improve the toughness and melt strength of the system; the talc, as a nucleating agent and reinforcing filler, can improve the uniformity and thermal stability of the cells; the zinc stearate, as a lubricant and foaming agent, has the functions of internal and external lubrication, activating the foaming agent, and aiding in demolding; the zinc oxide, as a foaming activator, has the functions of assisting crosslinking and thermal stabilization; the initiator can initiate grafting and crosslinking reactions to form a multi-layer crosslinked network; and the AC, as a chemical foaming agent, decomposes upon heating to generate gas and form a cell structure.

[0021] A method for preparing grafted or chain-extended modified PBS / EVA biodegradable foam plastic includes the following steps:

[0022] Step 1: Add biodegradable polyester PBS to a mixing device and preheat and melt it at a temperature of 120–170℃, a rotation speed of 50–70 r / min, and a time of 1–3 min to obtain molten PBS;

[0023] Step 2: Rapidly add polar monomers and initiators or directly add chain extenders to molten PBS, and carry out free radical grafting or melt chain extension reaction for 5–15 min to obtain grafted or chain-extended modified PBS blends.

[0024] Step 3: Melt-blend EVA with the PBS blend obtained in Step 2, then add POE, foaming agent, foaming aid, crosslinking agent and filler, and mix evenly to obtain a foamable composite system; Step 4: Place the blend in an open mixing equipment and mix evenly at 100–150℃ to obtain PBS / EVA compound; Step 5: Hot press the compound in a hot press at 150–190℃ for 2–30 min, preferably 170℃ for 12 min, to obtain PBS / EVA composite foam plastic.

[0025] When using the chain extension modification route, the reaction step is a chain extension reaction, which can be carried out in a one-step process: biodegradable polyester, ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), chain extender, crosslinking agent, foaming agent, foaming aid, and filler are added to a mixing device in proportion, and the chain extension reaction, blending and compounding are completed simultaneously in the molten state at 130-160℃ and 50-70r / min. Then, the composite foam plastic is obtained by hot pressing.

[0026] In this invention, composite foam plastics are applied to footwear materials, packaging, building insulation materials, medical protective cushioning materials, and automotive interiors; the packaging is a cushioning packaging material; the footwear material is a midsole for sports shoes or an insole for casual shoes; the automotive interior is a seat cushioning layer, door panel lining, and headliner cushioning material.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) Traditional EVA foam materials, due to their non-degradability, can no longer meet the market's goal of "energy saving and carbon reduction". This paper introduces polybutylene succinate-itaconic acid copolymer (PBS-COOH), an environmentally friendly material with biodegradable properties, and combines it with EVA. By grafting or chain extension, a multi-linked network is constructed to improve the mechanical strength and structural toughness of PBS.

[0029] (2) Due to the multiple cross-linking effects induced by grafting / chain extension, the resulting foam plastic has lightweight characteristics (about 0.15 g / cm³), including tear strength (3.2 kN / m), tensile strength (1.28 MPa) and compressive stress under 50% compression deformation (about 0.23 MPa).

[0030] (3) The PBS / EVA composite foam obtained by grafting or chain extension to construct a multi-crosslinked network in this invention can completely change the shortcomings of traditional EVA being non-degradable, making the foamed foam more green and environmentally friendly while also possessing mechanical strength and material toughness. Attached Figure Description

[0031] Figure 1 These are scanning electron microscope images of the internal pores and pore diameter distribution of the PBS / EVA composite foam in Examples 1-4.

[0032] Figure 2 The statistics are the grafting rate, hardness, density, and tear strength in Examples 1-4.

[0033] Figure 3 The diagram shows the hydrophobic and antifouling properties of the PBS / EVA composite foam prepared in this invention.

[0034] Figure 4 This is a diagram showing the tear strength properties. Figure 5 This is a stress variation diagram; Figure 6 Tear strength variation graph Figure 7 This is a graph showing the variation of the compressive stress-strain curve. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. However, the described embodiments are only some embodiments of the present invention, and not all embodiments. In both the embodiments and the comparative examples, the PBS was dried in a drying oven at 60°C for 8 hours before use.

[0036] The raw materials and sources of the following comparative examples and embodiments:

[0037] The EVA copolymer used in this experiment (VA content 26 mol%, 7470M grade, purchased from Yanshan Petrochemical) had the following MFI performance parameters: melt flow rate (MFI) 190 ℃ (2.16 kg = 4 g / 10 min), density 0.948 g / cm³. The blowing agent AC was purchased from Jiangsu Honglibao Composite Materials Technology Co., Ltd., ethylene-octene copolymer (POE) from China Petroleum & Chemical Corporation, itaconic acid (ITA) from Shandong Youshuo Chemical Technology Co., Ltd., dimethacrylate peroxide (DCP) from Shanghai Maclean Biochemical Co., Ltd., PBS (MFI = 77 g / 10 min) from Xinjiang Lanshan Tunhe, and bis(tert-butylperoxide) diisopropylbenzene (BIPB) from Maclean Biochemical (Shanghai) Co., Ltd.

[0038] Comparative Example 1

[0039] EVA (100 parts), bis(tert-butylperoxide) diisopropylbenzene (BIPB) (0.9 parts), foaming agent AC (3 parts), zinc stearate (1.5 parts), zinc oxide (3 parts), POE (20 parts), DCP (0.9 parts), and talc (5 parts) were first mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The mixture was then kneaded for 10 minutes under high-speed shear force to obtain EVA compound. The EVA compound was then hot-pressed at 170°C for 12 minutes to obtain EVA foam.

[0040] Comparative Example 2

[0041] PBS (30 parts), EVA (70 parts), bis(tert-butylperoxide) diisopropylbenzene (BIPB) (0.9 parts), foaming agent AC (3 parts), zinc stearate (1.5 parts), zinc oxide (3 parts), POE (20 parts), DCP (0.9 parts), and talc (5 parts) were first mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The mixture was then mixed for 10 minutes under high-speed shear force to obtain PBS / EVA compound. The PBS / EVA compound was then hot-pressed at 170℃ for 12 minutes to obtain PBS / EVA composite foam.

[0042] Comparative Example 3

[0043] EVA (100 parts), bis(tert-butylperoxide) diisopropylbenzene (BIPB) (0.9 parts), foaming agent AC (3 parts), zinc stearate (1.5 parts), zinc oxide (3 parts), POE (20 parts), DCP (0.9 parts), talc (5 parts), and chain extender PL3468 (0.8 parts) were first mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The mixture was then mixed for 10 minutes under high-speed shear force to obtain EVA compound. The EVA compound was then hot-pressed at 170°C for 12 minutes to obtain EVA foam.

[0044] Example 1

[0045] In a torque rheometer, 10 g of PBS (MFI = 77 g / 10 min, provided by Xinjiang Lanshan Tunhe) was melted for 1 min at 170 °C under shear force (60 r / min). Then, 0.04 g of DCP (purchased from Shanghai Maclean Biochemical Co., Ltd.) and 0.175 g of ITA (purchased from Shandong Youshuo Chemical Technology Co., Ltd.) were added to carry out a free radical grafting reaction for 2 min 30 s. After the grafting reaction was completed, an epoxy-functionalized PBS mixture was obtained. After the torque rheometer temperature was reduced to 140℃, 90g of EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g of BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g of foaming agent AC, 1.5g of zinc stearate, 3g of zinc oxide, 20g of POE, and 5g of talc were added and mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed for 10 minutes under high-speed shear force to obtain PBS / EVA compound. The PBS / EVA compound was then hot-pressed at 170℃ for 12 minutes to obtain PBS / EVA composite foam.

[0046] Example 2

[0047] In a torque rheometer, 20 g of PBS (MFI = 77 g / 10 min, provided by Xinjiang Lanshan Tunhe) was melted for 1 min at 170 °C under shear force (60 r / min). Then, 0.04 g of DCP (purchased from Shanghai Maclean Biochemical Co., Ltd.) and 0.175 g of ITA (purchased from Shandong Youshuo Chemical Technology Co., Ltd.) were added to carry out a free radical grafting reaction for 2 min 30 s. After the grafting reaction was completed, an epoxy-functionalized PBS mixture was obtained. After the torque rheometer temperature was reduced to 140℃, 80g of EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g of BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g of foaming agent AC, 1.5g of zinc stearate, 3g of zinc oxide, 20g of POE, and 5g of talc were added and mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed for 10 minutes under high-speed shear force to obtain PBS / EVA compound. The PBS / EVA compound was then hot-pressed at 170℃ for 12 minutes to obtain PBS / EVA composite foam.

[0048] Example 3

[0049] In a torque rheometer, 30 g of PBS (MFI = 77 g / 10 min, provided by Xinjiang Lanshan Tunhe) was melted for 1 min at 170 °C under shear force (60 r / min). Then, 0.04 g of DCP (purchased from Shanghai Maclean Biochemical Co., Ltd.) and 0.175 g of ITA (purchased from Shandong Youshuo Chemical Technology Co., Ltd.) were added to carry out a free radical grafting reaction for 2 min 30 s. After the grafting reaction was completed, an epoxy-functionalized PBS mixture was obtained. After the torque rheometer temperature was reduced to 140℃, 70g of EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g of BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g of foaming agent AC, 1.5g of zinc stearate, 3g of zinc oxide, 20g of POE, and 5g of talc were added and mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed for 10 minutes under high-speed shear force to obtain PBS / EVA compound. The PBS / EVA compound was then hot-pressed at 170℃ for 12 minutes to obtain PBS / EVA composite foam.

[0050] Example 4

[0051] In a torque rheometer, 40 g of PBS (MFI = 77 g / 10 min, provided by Xinjiang Lanshan Tunhe) was melted for 1 min at 170 °C under shear force (60 r / min). Then, 0.04 g of DCP (purchased from Shanghai Maclean Biochemical Co., Ltd.) and 0.175 g of ITA (purchased from Shandong Youshuo Chemical Technology Co., Ltd.) were added to carry out a free radical grafting reaction for 10 min. After the grafting reaction was completed, an epoxy-functionalized PBS mixture was obtained. After the torque rheometer temperature was reduced to 140℃, 60g of EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g of BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g of foaming agent AC, 1.5g of zinc stearate, 3g of zinc oxide, 20g of POE, and 5g of talc were added and mixed in an internal mixer. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed for 10 minutes under high-speed shear force to obtain PBS / EVA compound. The PBS / EVA compound was then hot-pressed at 170℃ for 12 minutes to obtain PBS / EVA composite foam.

[0052] Example 5

[0053] In a torque rheometer, 10g PBS (MFI=77g / 10min, provided by Xinjiang Lanshan Tunhe), 0.08g PL3468 (purchased from Dongguan Yutai Plastics Co., Ltd.), 90g EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g foaming agent AC, 1.5g zinc stearate, 3g zinc oxide, 20g POE, and 5g talc were mixed in a mixer at 150℃ for 4min30s. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed under high-speed shear force for 10min to obtain a PBS / EVA blend. The PBS / EVA blend was then hot-pressed at 170℃ for 12min to obtain a PBS / EVA composite foam.

[0054] Example 6

[0055] In a torque rheometer, 20g PBS (MFI=77g / 10min, provided by Xinjiang Lanshan Tunhe), 0.08g PL3468 (purchased from Dongguan Yutai Plastics Co., Ltd.), 80g EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g foaming agent AC, 1.5g zinc stearate, 3g zinc oxide, 20g POE, and 5g talc were mixed in a mixer at 150℃ for 4min30s. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed under high-speed shear force for 10min to obtain a PBS / EVA blend. The PBS / EVA blend was then hot-pressed at 170℃ for 12min to obtain a PBS / EVA composite foam.

[0056] Example 7

[0057] In a torque rheometer, 30g PBS (MFI=77g / 10min, provided by Xinjiang Lanshan Tunhe), 0.08g PL3468 (purchased from Dongguan Yutai Plastics Co., Ltd.), 70g EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g foaming agent AC, 1.5g zinc stearate, 3g zinc oxide, 20g POE, and 5g talc were mixed in a mixer at 150℃ for 4min30s. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed under high-speed shear force for 10min to obtain a PBS / EVA blend. The PBS / EVA blend was then hot-pressed at 170℃ for 12min to obtain a PBS / EVA composite foam.

[0058] Example 8

[0059] In a torque rheometer, 40g PBS (MFI=77g / 10min, provided by Xinjiang Lanshan Tunhe), 0.08g PL3468 (purchased from Dongguan Yutai Plastics Co., Ltd.), 60g EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g foaming agent AC, 1.5g zinc stearate, 3g zinc oxide, 20g POE, and 5g talc were mixed in a mixer at 150℃ for 4min30s. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed under high-speed shear force for 10min to obtain a PBS / EVA blend. The PBS / EVA blend was then hot-pressed at 170℃ for 12min to obtain a PBS / EVA composite foam.

[0060] Example 9

[0061] In a torque rheometer, 50g PBS (MFI=77g / 10min, provided by Xinjiang Lanshan Tunhe), 0.08g PL3468 (purchased from Dongguan Yutai Plastics Co., Ltd.), 50g EVA (VA content 26mol%, 7470M grade, purchased from Yanshan Petrochemical), 0.9g BIPB (provided by Maclean Biochemical (Shanghai) Co., Ltd.), 3g foaming agent AC, 1.5g zinc stearate, 3g zinc oxide, 20g POE, and 5g talc were mixed in a mixer at 150℃ for 4min30s. After the torque showed no significant change, the mixture was added to an open mill and mixed evenly. The blend was then mixed under high-speed shear force for 10min to obtain a PBS / EVA blend. The PBS / EVA blend was then hot-pressed at 170℃ for 12min to obtain a PBS / EVA composite foam.

[0062] Performance testing

[0063] Grafting rate test: Weigh 0.5g of epoxy-functionalized PBS and dissolve it in 70 mL of xylene by heating. Then add 10 mL of 0.1 mol / L trichloroacetic acid-xylene standard solution, heat under reflux for 2 h, add 2 drops of phenolphthalein indicator (10g / L), and titrate to the endpoint with 0.1 mol / L KOH-ethanol standard solution. Perform a blank experiment and calculate the grafting rate according to the following formula. The test results are shown in Table 1.

[0064]

[0065] Where GD is the grafting degree (%), N is the concentration of KOH / CH3OH solution used in the titration process (mol / L), V2 and V1 are the volumes (mL) of KOH / CH3OH solution consumed in titrating the blank sample and the epoxy-functionalized PBS, respectively, M is the molecular weight of the polar monomer (g / mol), and m is the mass of the epoxy-functionalized PBS titrated (g).

[0066] Contact angle test: The water contact angle was tested according to GB / T 30693-2014 standard. A contact angle measuring instrument was used to perform a static water contact angle test on the foam plastic surface at room temperature. Five points were tested for each sample and the average value was taken.

[0067] Tear strength test: The tear strength of the sample is tested using a right-angled specimen in accordance with GB / T 529-2008 standard.

[0068] The performance of the comparative examples and the embodiments is shown in Table 1.

[0069] Tensile and tear tests were conducted according to GB / T1040-2006 standard.

[0070] The formula for calculating the foaming ratio is as follows:

[0071]

[0072] Where ρ1 is ρ2 is .

[0073] The formula for calculating bubble density is as follows:

[0074]

[0075] Where A represents the actual area of ​​the cross-section of the composite foam in the scanning electron microscope (SEM) image; n is the total number of cells counted in the image; and M represents the magnification of the image.

[0076] Table 1

[0077]

[0078] As shown in Table 1, the addition of itaconic acid (introducing carboxyl groups during the grafting modification step) significantly improved the compatibility and foaming ability of the blends by constructing a multi-layered interfacial network with carboxyl groups. Under constant expansion ratio conditions, the cross-system changes from pure EVA to PBS / EVA and then to PBS-COOH / EVA (where the carboxyl groups are introduced by itaconic acid during the grafting modification step, with a blending ratio of 3:7) followed the basic physical laws of foaming, manifested as gradual cell refinement and synchronous gradient thinning of the cell wall. For the PBS / EVA system, due to its poor compatibility, the effect of its heterogeneous nucleation sites is limited, but the number is still greater than that of the homogeneous nucleation sites in pure EVA, thus achieving a higher nucleation density than pure EVA, achieving basic cell refinement and cell wall thinning. Through interface modification, the PBS-COOH / EVA interface is transformed into a highly efficient nucleation site, significantly increasing the nucleation density and further achieving cell refinement and continuous wall thinning. At the same time, it avoids the cracking and collapse problems common in thin cell walls. Enhanced interfacial compatibility helps to achieve more uniform stress transfer, avoiding early failure caused by local stress concentration, thereby providing more reliable structural stability. As a result, while the content of modified PBS gradually increases in Examples 1-4, the tear strength and tensile strength do not decrease significantly, and the mechanical properties can remain on par with EVA foam.

[0079] Figure 1The images show SEM images of the cells in Examples 1-4, where the content of PBS grafted with itaconic acid to replace EVA increased sequentially from 10% to 40%. As the PBS-COOH content increased, the material showed a thickening trend, which is closely related to the improved melt strength of the grafted segments. This phenomenon stems from the increased proportion of rigid segments in the PBS-COOH: more multiple crosslinking points enhance the melt strength gradient, while additional heterogeneous nucleation sites reduce the gas supply to each unit cell, thereby suppressing excessive stretching and thinning of the cell walls.

[0080] Figure 2 The trends of four key performance indicators of the PBS / EVA composite foam of the present invention under different formulations and process conditions (Comparative Example 1, Examples 1-4) are shown in the following details:

[0081] Density: Comparative Example 1 had the highest density (approximately 0.18 g / cm³), Example 1 showed a slight decrease, Example 2 reached the lowest density (approximately 0.16 g / cm³), and Examples 3 and 4 showed a slight increase followed by stabilization, exhibiting an overall trend of initial decrease followed by stabilization. Hardness (Shore C): From Comparative Example 1 to Example 4, the hardness continuously decreased, gradually decreasing from approximately 48 HA to approximately 39 HA, indicating that the material's softness continuously improved with formulation and process optimization. Resilience (%): Comparative Example 1 had a resilience of approximately 47%, Example 1 showed a slight decrease, Example 2 recovered to approximately 46%, and subsequently gradually decreased to approximately 39% in Examples 3 and 4, exhibiting an overall trend of fluctuation followed by a decrease. Tear Strength (kN / m): From Comparative Example 1 to Example 4, the tear strength continuously decreased, gradually decreasing from approximately 8.5 kN / m to approximately 7.0 kN / m, indicating that the material's toughness weakened with adjustments to the formulation and process.

[0082] Figure 3 This invention demonstrates that the PBS / EVA composite foam prepared in this invention is particularly well-suited for applications in the footwear industry. Static water contact angle testing showed a contact angle range of 122.9°~134.4°, exhibiting excellent hydrophobic and stain-resistant properties. It can effectively resist daily rain and sweat, keeping the shoe midsole / insole dry. Furthermore, combining the material's good cushioning and rebound properties with its biodegradability, it balances comfort, weather resistance, durability, and environmental friendliness, providing an ideal material solution for high-performance biodegradable footwear materials.

[0083] Figure 4 The results show that the PBS / EVA composite foam prepared by this invention has a tear strength of up to 2.1 kN / m, which is about 31% higher than that of the comparative example, while maintaining a high specific strength. It can significantly improve the tear resistance and bending resistance of the material. Combined with its excellent hydrophobic and stain-resistant properties and compression cushioning performance, it can better meet the comprehensive needs of the footwear industry for durability, comfort and environmental protection.

[0084] Figure 5 The results show that, compared with Comparative Example 3, the PBS / EVA composite foam materials prepared in Examples 5-9 of this invention achieve a synergistic improvement in strength and toughness while maintaining a high elongation at break. Comparative Example 3 fractured at a low strain (approximately 350%), while the elongation at break of the embodiments of this invention can reach over 600%, indicating that the modified material has excellent ductility and resistance to deformation. Furthermore, the tensile strength of some embodiments is close to or exceeds that of the comparative example, demonstrating that the composite crosslinking network constructed by chain extension modification in this invention significantly improves the toughness of the material without sacrificing its mechanical strength, effectively solving the technical bottleneck of the traditional PBS / EVA system where "strength and toughness are difficult to balance."

[0085] Figure 6 The results show that, compared with Comparative Example 3, the tear strength of some embodiments of the present invention was significantly improved. The tear strength of Example 7 reached a maximum of approximately 6.1 kN / m, significantly better than Comparative Example 3 (approximately 5.4 kN / m). This indicates that the crosslinked network constructed by grafting or chain extension modification in the present invention effectively enhances the molecular chain interactions and interfacial bonding forces within the material, inhibits crack propagation, and improves tear resistance. Furthermore, it can be seen that the tear strength of the material first increases and then decreases with changes in the PBS ratio in the formulation, indicating that under a specific ratio, chain extension modification achieves the best optimization effect on interfacial compatibility and molecular chain network; however, when the PBS content is too high, the interfacial defects in the system increase, leading to a decrease in tear resistance. These results verify the effectiveness of the present invention in optimizing tear resistance by controlling the PBS / EVA system structure through chain extension.

[0086] from Figure 7The compressive stress-strain curves show that the compression process of all samples exhibits the typical three-stage characteristics of foamed materials: the low strain region (<30%) is the elastic deformation stage, where stress increases slowly and linearly with strain; the medium strain region (30%~60%) is the transition stage from cell collapse plateau to densification, where the stress growth rate accelerates; and the high strain region (>60%) is the densification stage, where the cells are completely compacted, and stress increases sharply with strain. Comparison of different formulations reveals that Comparative Example 3 (only the EVA system with chain extender) has the lowest overall compressive stress, indicating poor cell structure stability and weak resistance to compressive deformation. With the increase of PBS-CE content (Examples 5~9), the compressive stress of the composite system gradually increases, and the load-bearing capacity under the same strain is significantly enhanced. Example 9 exhibits the best compressive performance, with stress in the high strain region being much higher than other samples, indicating that the mechanical strength and cell structure stability of the material are significantly improved after introducing PBS-CE and modifying it through a one-step chain extension method. This result demonstrates that introducing PBS-CE into the EVA matrix and employing a one-step chain extension foaming process can effectively improve the compressibility of foamed materials, providing a feasible path for preparing high-strength, structurally stable composite foamed materials.

Claims

1. A biodegradable foam plastic based on grafted or chain-extended modified PBS / EVA, characterized in that, By weight, it includes one of the following two formulations: Formula 1: 60-90 parts of ethylene-vinyl acetate copolymer (EVA), 10-40 parts of biodegradable polyester, 5-20 parts of polyolefin elastomer (POE), 0.5-2.5 parts of polar monomer, 0.2-0.6 parts of initiator, 0.2-0.9 parts of crosslinking agent, 1-3 parts of foaming agent, 1-3 parts of foaming aid, and 2.5-10 parts of filler; Formula 2: 60-90 parts of ethylene-vinyl acetate copolymer (EVA), 10-40 parts of biodegradable polyester, 5-20 parts of polyolefin elastomer (POE), 0.1-1.0 parts of chain extender, 0.2-0.9 parts of crosslinking agent, 1-3 parts of foaming agent, 1-3 parts of foaming aid, and 2.5-10 parts of filler; Degradable polyester molecular chains are modified by free radical grafting or melt chain extension. Grafting introduces polar groups, while chain extension achieves molecular chain growth and branching, forming a multi-layer cross-linked network structure under the action of a cross-linking agent. This effectively improves the mechanical properties, thermal stability, melt strength, and interfacial compatibility of the system, while maintaining good biodegradability, achieving both toughening and functional modification. The polar groups include at least one of carboxyl groups, anhydride groups, and epoxy groups. The static water contact angle of the foam is 122.9°~134.4°, and the tear strength is 1.5~2.1 kN / m.

2. The grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 1, characterized in that, The ethylene-vinyl acetate copolymer EVA has a melt index of 4–20 g / 10min (190℃ / 2.16kg) and a VA content of 10–40 wt%; the polyolefin elastomer POE has a melt index of 20–50 g / 10min (190℃ / 2.16kg).

3. The grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 1, characterized in that, The polar monomer is selected from at least one of itaconic acid (ITA), maleic anhydride (MAH), glycidyl methacrylate (GMA), and acrylate (AA); the biodegradable polyester is selected from at least one of polybutylene succinate (PBS), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polybutylene adipate succinate (PBSA), and polybutylene adipate terephthalate (PBAT); the initiator is a free radical initiator, selected from at least one of benzoyl peroxide (BPO), dicumyl peroxide (DCP), and bis(tert-butylperoxy)diisopropylbenzene (BIBP); the crosslinking agent is selected from 2,5-dimethyl-2,5-bis(tert-butylperoxy) The PBS contains at least one of hexane, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, and bis(tert-butylperoxy)diisopropylbenzene (BIBP); the chain extender is selected from at least one of epoxy chain extenders, isocyanate chain extenders, and oxazoline chain extenders; the PBS has a melt index of 50–80 g / 10 min (190 °C / 2.16 kg).

4. The grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 1, characterized in that, The foaming agent is selected from at least one of azodicarbonamide AC / ADC, p-toluenesulfonyl hydrazine TSH, and 4,4'-oxobisbenzenesulfonyl hydrazine OBSH; the foaming aid is selected from at least one of zinc oxide ZnO, magnesium oxide MgO, zinc stearate, calcium stearate, and triethanolamine.

5. The grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 1, characterized in that, The filler is selected from at least one of calcium carbonate, talc, silica, and barium sulfate.

6. The method for preparing a biodegradable foam plastic of grafted or chain-extended modified PBS / EVA as described in claim 1, characterized in that, The preparation method sequentially includes melting, grafting or chain extension, blending, mixing, and molding steps; specifically, it includes the following steps: (1) First, the biodegradable polyester is preheated in the mixing equipment to make it melt; (2) Then, polar monomers and initiators are quickly added or chain extenders are added directly to carry out free radical grafting or melt chain extension reaction. After the reaction is completed, a biodegradable polyester mixture with multiple cross-linked networks is obtained. (3) Weigh the ethylene-vinyl acetate copolymer EVA and the biodegradable polyester mixture obtained in step (2) and blend them in a mixing device. Add the polyolefin elastomer POE, foaming agent, foaming aid, crosslinking agent and filler into the mixing device to obtain a biodegradable polyester / EVA blend. (4) The biodegradable polyester / EVA blend obtained in step (3) is added to an open mixing equipment for mixing. The blend is mixed evenly under the action of mechanical shear force to obtain biodegradable polyester / EVA blend. (5) The biodegradable polyester / EVA compound is hot-pressed in a hot press to obtain biodegradable polyester / EVA composite foam.

7. The method for preparing grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 6, characterized in that, In step (1), the temperature inside the mixing equipment is 120-170℃, the shearing condition is 50-70r / min, and the melting time is 1-3min; in step (2), the proportion of polar monomer itaconic acid is 1-8%, the mass ratio of initiator / polar monomer is 10-30%, and the grafting or chain extension reaction time is 5-15min; in step (4), the temperature of the open mixing equipment is 100-150℃; in step (5), the temperature and time of the hot pressing are 150-190℃ and 2-30min, respectively.

8. The method for preparing grafted or chain-extended modified PBS / EVA biodegradable foam plastic according to claim 6, characterized in that, In step (3), the mass ratio of the crosslinking agent to PBS is 0.2-5%, and the mass ratio of the foaming agent to the crosslinking agent is 10-50%; in step (4), the mixing time of the open mill is 1-15 min, and the roller temperature of the open mill is controlled at 80-120℃ during the mixing process; the mechanical shearing conditions are 50-70 r / min.

9. The composite foam plastic according to any one of claims 1 to 5 is applied to the fields of shoe materials, packaging, building insulation materials, medical protective cushioning materials and automotive interiors.

10. The application according to claim 9, characterized in that, The packaging is a cushioning packaging material; the shoe material is a midsole for sports shoes or an insole for casual shoes; the car interior is a seat cushioning layer, door panel lining, and headliner cushioning material.

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