A rigid polybutylene succinate biodegradable sheet and a method for preparing the same

Abstract

This invention provides a rigid polybutylene succinate (PBS) biodegradable sheet and its preparation method. The biodegradable sheet comprises, by weight: 40-55 parts PBS, 40-50 parts core-shell composite material, 3-5 parts polylactic acid (PLA), 1-2 parts compatibilizer, 0.3-0.5 parts lubricant, and 0.5-1.0 parts nucleating agent. This invention utilizes anhydride to mechanically modify starch under dry conditions, causing esterification and anhydride adhesion to the surface of starch particles. Low molecular weight PBS is then extended and anchored onto the surface of the starch particles via hot-melt extrusion to form a core-shell composite material. This core-shell composite material significantly increases rigidity, prevents starch particles from being exposed, and exhibits excellent compatibility with the PBS matrix. The prepared sheet does not swell or precipitate after boiling. This production technology uses simple raw materials, the hot-melt extrusion equipment is suitable for large-scale production, the biodegradable sheet has a high starch content, and the overall cost is low.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable plastics technology, specifically relating to a rigid polybutylene succinate biodegradable sheet and its preparation method. Background Technology

[0002] Polybutylene succinate (PBS) is a high-performance biodegradable plastic that completely biodegrades under natural conditions. Its processing properties fall between those of polyethylene and polypropylene, allowing for direct processing using conventional plastic molding processes and equipment, including injection molding, thermoforming, blow molding, and blown film forming. In recent years, mature PBS production lines have been established and capacity is continuously expanding, resulting in significant cost reductions and accelerating its replacement of traditional petroleum-based PE and PP plastics. Consequently, PBS is being widely used in food packaging trays, pharmaceutical packaging, industrial parts packaging, and electronic product packaging, with new application scenarios constantly emerging.

[0003] Because PBS is an aliphatic saturated polyester with flexible butanediol segments in its main chain, its molecular chain has high flexibility, resulting in relatively soft biodegradable sheets. While this inherent softness provides good toughness, it lacks supporting rigidity. During vacuum forming, the sheets sag significantly after heating, preventing them from fully conforming to the mold and affecting forming accuracy. Vacuum-formed trays and packaging shells are prone to deformation, failing to effectively secure the contents. Thickening is generally required to prevent deformation during handling, increasing costs.

[0004] Therefore, there is a need for engineers to develop rigid polybutylene succinate (PBS) biodegradable sheets to promote the widespread application of biodegradable sheets in the packaging field. Currently disclosed theoretical technologies mainly utilize the rigidity of PBS modified with highly rigid polylactic acid (PLA), wood flour, lignin, starch, and inorganic powders. Patent CN115926408B discloses a biodegradable polymer composition, its preparation method, and its application. By compounding PLA with PBS and adding inorganic fillers, the biodegradable polymer composition exhibits excellent mechanical properties, possessing both good rigidity and toughness, making it suitable for biodegradable tableware. Patent CN114133758B discloses a modified wood flour / PBS biodegradable base material and its preparation method. By grafting and modifying wood flour fibers before applying them to PBS, the biodegradability of the material can be greatly improved, and the problem of poor material rigidity can be solved. Patent CN109575534B discloses a biomass enhancer, modified PBS material, and its preparation method. Utilizing the large number of stable benzene rings in modified lignin, which act as a nucleating agent, the crystallinity of PBS is improved, thereby enhancing the thermal stability of PBS.

[0005] Polylactic acid (PLA) itself has very high rigidity. Alloying PLA with PBS can significantly increase the rigidity of PBS, and this is currently the most widely used method. However, PLA requires a relatively high addition amount to improve rigidity, and its high cost limits its large-dosage addition. Adding inorganic powders (such as talc, calcium carbonate, and clay) to PBS can improve its modulus and hardness, thus giving PBS better rigidity and providing significant rigidity support for sheet thermoforming products. However, excessive addition of inorganic powders is not advisable; generally, adding more than 10% will reduce interfacial compatibility and drastically decrease mechanical properties. Furthermore, excessive use of inorganic powders can easily cause tearing in sheet thermoforming of deep-cavity products, and also causes significant wear on the mold during thermoforming, requiring strict control. When using large amounts of biomass materials such as lignin and wood fibers, lignin itself is brownish-red, significantly affecting the color and appearance quality of the sheet; wood fibers are difficult to disperse, easily causing defects such as roughness and pitting on the surface of the product.

[0006] Our aim is to use starch to modify the rigidity of PBS. Starch not only has good biodegradability, but also low raw material cost, is renewable, and has high food contact safety. Adding it to biodegradable sheets significantly reduces costs. Existing technologies mostly use small-molecule plasticizers such as glycerol to thermoplasticize starch to obtain thermoplastic starch (TPS). TPS has good thermal processing properties, but glycerol thermoplasticization completely transforms starch from rigid to flexible, with almost no stiffness-enhancing effect. Furthermore, PBS sheets using TPS will absorb moisture and soften further after being left indoors for one day. Incompletely plasticized starch has better rigidity, but the addition amount is low when used for tableware packaging. Excessive addition will lead to a significant decrease in strength, and there is a risk of starch swelling and precipitation when tableware made from the sheet contains liquids. Summary of the Invention

[0007] To improve the rigidity of polybutylene succinate (PBS) at a low cost and realize its industrial application in sheet blister packaging, this invention proposes a rigid PBS biodegradable sheet and its preparation method. The main technique involves surface esterification of starch during micronization. Unreacted anhydrides adhere to the surface of the starch granules, and the anhydrides extend the chain of low molecular weight PBS, firmly anchoring it to the surface of the starch particles to form a core-shell structure composite material. High addition amounts to the PBS resin not only increase the rigidity of the PBS biodegradable sheet but also provide excellent water resistance, exhibiting no water absorption or swelling in humid environments.

[0008] The specific technical solution of this invention is as follows: A rigid polybutylene succinate biodegradable sheet is made from the following raw materials in parts by weight: 40-55 parts polybutylene succinate, 40-50 parts core-shell structure composite material, 3-5 parts polylactic acid, 1-2 parts compatibilizer, 0.3-0.5 parts lubricant, and 0.5-1.0 parts nucleating agent; The core-shell composite material is prepared by the following method: starch and acid anhydride are mechanically and dryly modified to obtain modified starch; the modified starch and low molecular weight polybutylene succinate are chain extended by hot melt extrusion to form a core-shell composite material with polybutylene succinate as the shell and starch as the core.

[0009] Starch possesses good rigidity. Through mechanical force (such as air jet milling and grinding), the hydroxyl groups on the surface of fine starch particles undergo esterification with acid anhydrides, forming a flexible interface with intermolecular connections. While retaining its rigidity, the starch retains the acid anhydride attached to the interface. During the hot-melt extrusion of modified starch and low molecular weight polybutylene succinate (PPS), the acid anhydride undergoes a melt chain extension reaction with the hydroxyl groups (-OH) at the ends of the PPS molecular chains, achieving interchain linkage. This chain extension increases the molecular weight of PPS, anchoring it at the interface of the starch particles, forming a core-shell composite material with PPS as the shell and starch as the core. In this core-shell composite material, the PPS and starch particles are firmly anchored at the interface, and the starch particles are not easily exposed. Biodegradable sheets were prepared by adding a high amount of shell-core structured composite material to polybutylene succinate matrix resin. The composite material is easily dispersed, has good compatibility, and the sheets have excellent supporting rigidity and tensile strength. Moreover, the composite material with polybutylene succinate as the shell and starch as the core shields the starch from exposure, resulting in sheets with excellent water resistance and no water absorption and swelling. This meets the requirements for thermoforming various thermoforming trays, food boxes, electronic trays, disposable tableware, etc.

[0010] Preferably, the mass ratio of starch to acid anhydride is 100:(1-1.5); the starch is at least one of corn starch and tapioca starch; the acid anhydride is at least one of maleic anhydride, itaconic anhydride, and succinic anhydride. When formulating the mixture, avoid using excessive amounts of acid anhydride, as overuse of acid anhydride-modified starch will cause the starch granules to completely gelatinize and disintegrate, losing their rigidity. While ensuring esterification of the starch granule surface and subsequent chain extension with low molecular weight polybutylene succinate, reduce the use of acid anhydride to avoid residues in the final product. If there is a large amount of residual acid anhydride in the core-shell composite material, there will be a noticeable sour smell; the amount of acid anhydride used can be appropriately reduced. Acid anhydride is irritating; when dry mechanically modifying starch, a mask should be worn to avoid inhaling dust.

[0011] Preferably, the modified starch and low molecular weight polybutylene succinate are chain extended by hot melt extrusion at a mass ratio of 100:(30-35). The modified starch surface is esterified and contains acid anhydrides. During hot melt extrusion, the acid anhydrides connect to PBS segments to extend the chain and increase the molecular weight, and are firmly anchored to the surface of the starch granules to form a shell-core bonded composite material. This composite material can be added in high amounts to polybutylene succinate, and not only is it compatible and well dispersed with polybutylene succinate, but the high addition amount has little impact on the material strength and significantly improves rigidity. Due to the firm anchoring, the starch granules are not easily exposed or precipitated, and the resulting sheet has excellent water resistance and maintains good mechanical properties in a humid environment, fully meeting the requirements for holding tableware.

[0012] Preferably, the number average molecular weight (Mn) of the low molecular weight polybutylene succinate is 3000-8000 Da. Low molecular weight polybutylene succinate has low hot melt viscosity and terminal hydroxyl groups (-OH) at the chain ends, making it easy to uniformly disperse modified starch during hot melt extrusion. The chain is extended by the acid anhydride on the surface of the starch granules, forming high molecular weight polybutylene succinate, which is uniformly anchored on the surface of the starch granules.

[0013] Preferably, the compatibilizer is at least one of ethylene-acrylic acid copolymer (EAA), ethylene-vinyl acetate copolymer (EVA), PLA grafted glycidyl methacrylate (PLA-g-GMA), and PBS grafted glycidyl methacrylate (PBS-g-GMA).

[0014] Preferably, the lubricant is at least one of glyceryl tristearate, ethylene bis-stearamide, stearic acid, and pentaerythritol stearate. The lubricant reduces the adhesion of the sheet during calendering, facilitates rapid demolding during vacuum forming, and improves processing efficiency and product quality. Preferably, the nucleating agent is an ultrafine inorganic powder nucleating agent and / or an organic nucleating agent. The ultrafine inorganic powder nucleating agent is at least one of precipitated barium sulfate with a particle size less than 5 μm or ultrafine talc powder; the organic nucleating agent is at least one of sorbitol-based nucleating agents, amide-based nucleating agents, or hydrazide-based nucleating agents. Specifically, ultrafine talc powder (3000 mesh, K brand, produced in Guangxi), 1,3:2,4-di(3,4-dimethylbenzyl)-D-sorbitol (nucleating agent 3988), amide nucleating agent TMC-328 (Shanxi Provincial Chemical Research Institute), and diphenyldihydrazide adipic acid TMC-306 (Shanxi Provincial Chemical Research Institute) are used. PBS is a semi-crystalline thermoplastic polyester. By using a nucleating agent, rapid crystallization and grain refinement can be promoted during cooling. The finer grains increase grain boundaries, thereby achieving a stiffening effect.

[0015] The present invention also provides a method for preparing the above-mentioned rigid polybutylene succinate biodegradable sheet, comprising the following steps: S1. Starch and acid anhydride are modified by mechanical dry method to obtain modified starch; the modified starch and low molecular weight polybutylene succinate are chain extended by hot melt extrusion to form a shell-core structure composite material with polybutylene succinate as the shell and starch as the core. S2. Polybutylene succinate, core-shell composite material, polylactic acid, compatibilizer, lubricant, and nucleating agent are added to a high-speed mixer according to the formula in parts by weight and mixed. The mixture is then fed to a co-rotating twin-screw extruder. The temperatures of each section of the co-rotating twin-screw extruder are set as follows: Section 1 120-130℃, Section 2 140-150℃, Section 3 160-170℃, Section 4 160-170℃, Section 5 170-180℃, Section 6 160-170℃, Section 7 150-160℃, Section 8 140-150℃, Section 9 150-160℃, and Section 10 160-170℃. After melt extrusion, a sheet prototype is formed in the coat hanger die. The sheet is then calendered and shaped by a three-roll calender, cooled, trimmed, and wound to obtain a rigid polybutylene succinate biodegradable sheet.

[0016] Preferably, the mechanical dry modification involves refining starch under solvent-free, solid conditions through grinding or air jet milling, and promoting the esterification reaction between the hydroxyl groups on the starch particle surface and acid anhydrides. Starch particles have a dense, semi-crystalline structure, making it difficult for acid anhydrides to penetrate the dense crystalline region under dry mechanical force. The esterification reaction occurs only on the surface of the starch particles, preserving the rigidity of the starch. Furthermore, the esterification at the starch particle interface and the attachment of a certain amount of acid anhydride promote the chain extension and anchoring of low molecular weight polybutylene succinate on the starch particle surface.

[0017] More preferably, the grinding can be performed using conventional dry ball milling, without the need for deep esterification of starch granules; the air jet milling is performed using either an air jet mill or a vortex air jet mill. Air jet mills require high-pressure gas, placing higher demands on the equipment. The optimal choice is a vortex air jet mill, which uses a high-speed rotating turbine to shear and pulverize the material, and the fineness can be controlled by adjusting the turbine speed. It also makes it easier to control the degree of esterification, and does not require high-pressure airflow, resulting in high production efficiency and low energy consumption.

[0018] Preferably, when modified starch and low molecular weight polybutylene succinate are chain-extended via hot-melt extrusion, the hot-melt extrusion temperature is 160-180℃. The residence time of the material in the screw is extended by using low rotation speed and / or a reverse screw element to ensure sufficient hot-melt chain extension time. More suitablely, the residence time of the material in the screw is controlled at 240-360 seconds to achieve a high number-average molecular weight (Mn) of the chain-extended polybutylene succinate.

[0019] Preferably, the temperature distribution of the hanger mold head is 175-170-175℃.

[0020] Preferably, the speed difference ratio of the upper, middle, and lower rollers of the three-roll calender is 1:1.1:1.2; the temperature of the upper roller is 100-110℃, the temperature of the middle roller is 90-100℃, and the temperature of the lower roller is 80-90℃. Through speed difference and gradual cooling, the sheet is stretched in the longitudinal direction to increase the rigidity of the sheet.

[0021] The significant advantages of this invention compared to existing technologies are: (1) The present invention utilizes the mechanical modification of starch by acid anhydride under dry conditions to esterify the surface of starch microparticles and attach acid anhydride; by hot melt extrusion chain extension, low molecular weight polybutylene succinate is anchored on the surface of starch microparticles to form a firmly bonded core-shell structure, starch plays a significant role in stiffening, and the sheet prepared by dispersing in polybutylene succinate matrix resin has excellent rigidity.

[0022] (2) By pre-treating the starch with a core, the present invention has a firmly anchored core structure that is not only highly compatible with the polybutylene succinate matrix, but also avoids the exposure of starch particles. The prepared sheet will not swell and precipitate after boiling, and the mechanical properties will not be significantly reduced due to the addition of a large amount of starch.

[0023] (3) The biodegradable sheet of the present invention uses a nucleating agent to promote rapid crystallization and nucleation during the three-roll calendering and cooling process, making the crystals more uniform and dense, improving the rigidity and hardness of the sheet, reducing warping deformation, and forming a uniform sheet.

[0024] (4) The raw materials used in the production of this invention are simple, the hot melt extrusion equipment is suitable for large-scale continuous production, the starch addition is high, and the overall cost is low. Detailed Implementation

[0025] The present invention will be described in detail below with reference to specific embodiments, comparative examples, and reference examples. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0026] The following are the main raw materials for each embodiment and comparative example: Polybutylene succinate: sheet grade, MFR of 10g / 10min (190℃, 2.16kg), produced in Shandong.

[0027] Low molecular weight polybutylene succinate: number average molecular weight (Mn) is 3000-5000 Da.

[0028] Polylactic acid (PLA): REVODE110, Zhejiang Hisun Biomaterials Co., Ltd.

[0029] Inorganic nucleating agent: ultrafine talc powder, 3000 mesh, brand K, produced in Guangxi.

[0030] Sorbitol nucleating agent: 1,3:2,4-di(3,4-dimethylbenzyl)-D-sorbitol (nucleating agent 3988).

[0031] Amide nucleating agent: TMC-328, Shanxi Provincial Chemical Research Institute.

[0032] Acylhydrazide nucleating agent: Diphenyldihydrazide adipic acid, TMC-306, Shanxi Provincial Chemical Research Institute.

[0033] Example 1 S1. Corn starch and maleic anhydride are mixed at a mass ratio of 100:1.2. The mixture is then fed into a vortex airflow mill at a grinding disc speed of 1000 r / min and a classifying impeller speed of 1200 r / min. The high-speed rotation generates airflow that causes the starch to continuously collide and rub within the vortex-shaped airflow, achieving starch refinement and surface esterification, resulting in modified starch with a D50 particle size of less than 10 μm. The modified starch is then mixed with low molecular weight polybutylene succinate at a mass ratio of 100:35 and added to a co-rotating twin-screw extruder for hot melt extrusion. The temperatures of each section are: The screw has four temperature zones: 160℃ (second, third, fourth, fifth, sixth, seventh, eighth, and ninth). Each zone has a vacuum exhaust port at the eighth zone to promptly remove volatile water vapor and residual acid anhydride. The screw is designed with three sets of reverse threads. The screw speed is 120 r / min. Through color masterbatch tracking, the material residence time inside the screw is approximately 320 s. Through hot melt extrusion chain extension, a core-shell structure composite material with polybutylene succinate as the shell and starch as the core is formed. S2. Add 50kg of polybutylene succinate, 50kg of core-shell composite material, 3kg of polylactic acid, 1kg of compatibilizer PLA-g-GMA, 0.5kg of lubricant ethylene bis-stearamide, 0.5kg of nucleating agent ultrafine talc powder, and 0.2kg of nucleating agent 3988 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. The temperature settings for each section of the co-rotating twin-screw extruder are: Section 1 125℃, Section 2 140℃, Section 3 160℃, Section 4 170℃, Section 5 180℃, and Section 6 170℃. The temperature distribution of the sheet material is as follows: 0℃, 160℃ for seven sections, 150℃ for eight sections, 160℃ for nine sections, and 170℃ for ten sections. After melt extrusion, a sheet prototype is formed in the hanger die head, with a temperature distribution of 175-170-175℃. The sheet is then calendered and shaped using a three-roll calender, with the speed difference ratio of the upper, middle, and lower rolls being 1:1.1:1.2. The upper roll temperature is 110℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed, rolled up, and a rigid polybutylene succinate biodegradable sheet is obtained.

[0034] Example 2 S1. Cassava starch (from Guangxi) and succinic anhydride were mixed at a mass ratio of 100:1. The mixture was then processed in a vortex airflow mill at a grinding disc speed of 1100 r / min and a classifying impeller speed of 1200 r / min. The high-speed rotating airflow caused the starch to continuously collide and rub within the vortex, achieving starch refinement and surface esterification, resulting in modified starch with a D50 particle size of less than 10 μm. The modified starch was then mixed with low molecular weight polybutylene succinate at a mass ratio of 100:30 and hot-melt extruded using a co-rotating twin-screw extruder. The temperatures of each section were as follows: The temperature ranges from 160℃ in the first stage to 160℃ in the second, third, fourth, fifth, and sixth stages, all at 170℃, 170℃ in the seventh, eighth, and ninth stages, respectively. The eighth stage features a vacuum exhaust port to promptly remove volatile water vapor and residual acid anhydride. The screw is designed with three sets of reverse threads. The screw speed is 150 r / min. Through color masterbatch tracking, the material's residence time within the screw is approximately 292 seconds. Through hot-melt extrusion chain extension, a core-shell structure composite material with polybutylene succinate as the shell and starch as the core is formed. S2. Add 50 kg of polybutylene succinate, 50 kg of core-shell composite material, 4 kg of polylactic acid, 1 kg of compatibilizer PBS-g-GMA, 0.5 kg of lubricant stearic acid, 0.5 kg of nucleating agent ultrafine talc powder, and 0.3 kg of nucleating agent TMC-328 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. Set the temperatures of each section of the co-rotating twin-screw extruder as follows: Section 1 130℃, Section 2 140℃, Section 3 160℃, Section 4 160℃, Section 5 170℃, and Section 6 170℃. The temperature distribution of the sheet material is as follows: 175℃, 160℃ for seven sections, 150℃ for eight sections, 150℃ for nine sections, and 170℃ for ten sections. After melt extrusion, a sheet prototype is formed in the hanger die head, with the temperature distribution of the hanger die head being 175-170-175℃. The sheet material is then calendered and shaped by a three-roll calender, with the speed difference ratio of the upper, middle, and lower rolls of the three-roll calender being 1:1.1:1.2. The upper roll temperature is 100℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed, rolled up, and a rigid polybutylene succinate biodegradable sheet is obtained.

[0035] Example 3 S1. Corn starch and itaconic anhydride were mixed at a mass ratio of 100:1.5 and ground in a ball mill for 30 min to obtain modified starch with a D50 particle size of less than 10 μm; the modified starch was mixed with low molecular weight polybutylene succinate at a mass ratio of 100:35 and hot-melt extruded through a co-rotating twin-screw extruder, with the following temperatures for each stage: stage 1 160℃, stage 2 170℃, stage 3 180℃, stage 4 180℃, and stage 5 180℃. The temperature is set at 170℃ in six, seven, eight, nine, and ten sections; a vacuum exhaust port is located at section eight to promptly remove volatile water vapor and residual acid anhydride; the screw is designed with three sets of reverse threads; the screw speed is 100 r / min; the material residence time inside the screw is approximately 360 s via color masterbatch tracking; and a core-shell structure composite material with polybutylene succinate as the shell and starch as the core is formed through hot melt extrusion chain extension. S2. Add 40kg of polybutylene succinate, 50kg of core-shell composite material, 5kg of polylactic acid, 1.5kg of compatibilizer EVA, 0.3kg of lubricant pentaerythritol stearate, 0.5kg of nucleating agent ultrafine talc powder, and 0.5kg of nucleating agent TMC-306 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. The temperature settings for each section of the co-rotating twin-screw extruder are: section 1 120℃, section 2 140℃, section 3 160℃, section 4 160℃, section 5 170℃, section 6 170℃, section 7 160℃, section 8 150℃, section 9 160℃, and section 10 170℃. After melt extrusion, the temperature distribution of the hanger die head is 175-170-175℃. A sheet prototype is formed in the hanger die head and then calendered and shaped by a three-roll calender. The speed difference ratio of the upper, middle, and lower rolls of the three-roll calender is 1. : 1.1: 1.2; Upper roller temperature 110℃, middle roller temperature 100℃, lower roller temperature 90℃, cooled by cooling roller, trimmed, and wound to obtain a rigid polybutylene succinate biodegradable sheet.

[0036] Comparative Example 1 50 kg of polybutylene succinate, 50 kg of thermoplastic starch (glycerol-plasticized TPS), 3 kg of polylactic acid, 1 kg of compatibilizer PLA-g-GMA, 0.5 kg of lubricant ethylene bis-stearamide, 0.5 kg of nucleating agent ultrafine talc, and 0.2 kg of nucleating agent 3988 were added to a high-speed mixer and mixed. The mixture was then fed into a co-rotating twin-screw extruder. The temperatures of each section of the co-rotating twin-screw extruder were set as follows: Section 1 125℃, Section 2 140℃, Section 3 160℃, Section 4 170℃, Section 5 180℃, and Section 6 180℃. The sheet is formed by melt extrusion at 70℃, 160℃ for seven sections, 150℃ for eight sections, 160℃ for nine sections, and 170℃ for ten sections. The temperature distribution of the sheet at the die head is 175-170-175℃. The sheet is then calendered and shaped by a three-roll calender with a speed difference ratio of 1:1.1:1.2 between the upper, middle, and lower rolls. The upper roll temperature is 110℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed and rolled up to obtain a rigid polybutylene succinate biodegradable sheet.

[0037] This comparative example uses glycerol-plasticized thermoplastic starch (TPS) to replace the core-shell composite material in the preparation of PBS sheets. The sheets have low rigidity and swell and release sticky substances after absorbing water.

[0038] Comparative Example 2 S1. Corn starch and aluminate coupling agent are mixed at a mass ratio of 100:1.5. In a vortex airflow pulverizer, the pulverizing disc rotates at 1000 r / min and the classifying impeller rotates at 1200 r / min. The high-speed rotating airflow generates a strong centrifugal force, causing the material to continuously collide and rub in the vortex airflow to achieve starch refinement and surface coupling modification, thus obtaining modified starch. S2. Add 62kg of polybutylene succinate, 37kg of modified starch, 3kg of polylactic acid, 1kg of compatibilizer PLA-g-GMA, 0.5kg of lubricant ethylene bis-stearamide, 0.5kg of nucleating agent ultrafine talc, and 0.2kg of nucleating agent 3988 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. The temperature settings for each section of the co-rotating twin-screw extruder are: Section 1 125℃, Section 2 1... The sheet is formed by melt extrusion at 40℃, three sections at 160℃, four sections at 170℃, five sections at 180℃, six sections at 170℃, seven sections at 160℃, eight sections at 150℃, nine sections at 160℃, and ten sections at 170℃. It is then calendered and shaped using a three-roll calender with a speed difference ratio of 1:1.1:1.2 between the upper, middle, and lower rolls. The upper roll temperature is 110℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed, wound, and obtained as a rigid polybutylene succinate biodegradable sheet.

[0039] In this comparative example, starch was modified with a coupling agent and then added to PBS to prepare sheets. The resulting sheets had good rigidity, but the starch absorbed water significantly after boiling, and sticky substances were released.

[0040] Comparative Example 3 S1. Mix corn starch and maleic anhydride at a mass ratio of 100:1. In a vortex airflow pulverizer, the pulverizing disc rotates at 1000 r / min and the classifying impeller rotates at 1200 r / min. The high-speed rotating airflow generates a strong centrifugal force, causing the material to continuously collide and rub in the vortex airflow to achieve starch refinement and surface esterification, thus obtaining modified starch. S2. Add 62kg of polybutylene succinate, 37kg of modified starch, 3kg of polylactic acid, 1kg of compatibilizer PLA-g-GMA, 0.5kg of lubricant ethylene bis-stearamide, 0.5kg of nucleating agent ultrafine talc, and 0.2kg of nucleating agent 3988 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. The temperature settings for each section of the co-rotating twin-screw extruder are: Section 1 125℃, Section 2 1... The sheet is formed by melt extrusion at 40℃, three sections at 160℃, four sections at 170℃, five sections at 180℃, six sections at 170℃, seven sections at 160℃, eight sections at 150℃, nine sections at 160℃, and ten sections at 170℃. It is then calendered and shaped using a three-roll calender with a speed difference ratio of 1:1.1:1.2 between the upper, middle, and lower rolls. The upper roll temperature is 110℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed, wound, and obtained as a rigid polybutylene succinate biodegradable sheet.

[0041] In this comparative example, starch was directly esterified with maleic anhydride and then added to PBS to prepare sheets. The resulting sheets had good rigidity, but the starch absorbed water significantly after boiling, and a sticky substance was precipitated.

[0042] Comparative Example 4 S1. Corn starch and maleic anhydride are mixed at a mass ratio of 100:1.2, and then mixed with low molecular weight polybutylene succinate at a mass ratio of 100:35. The mixture is then hot-melt extruded through a co-rotating twin-screw extruder. The temperatures of each section are: Section 1 160℃, Section 2 170℃, Section 3 180℃, Section 4 180℃, Section 5 180℃, Section 6 170℃, Section 7 170℃, Section 8 160℃, Section 9 160℃, and Section 10 160℃. A vacuum exhaust port is located at Section 8 to promptly remove volatile water vapor and residual anhydride. The screw assembly has three sets of reverse threads. The screw speed is 110 r / min. Using a color masterbatch tracking indicator, the material residence time within the screw is approximately 320 s. Through hot-melt extrusion and chain extension, a core-shell structure composite material is formed. S2. Add 50kg of polybutylene succinate, 50kg of core-shell composite material, 3kg of polylactic acid, 1kg of compatibilizer PLA-g-GMA, 0.5kg of lubricant ethylene bis-stearamide, 0.5kg of nucleating agent ultrafine talc powder, and 0.2kg of nucleating agent 3988 to a high-speed mixer and mix. Feed the mixture to a co-rotating twin-screw extruder. The temperature settings for each section of the co-rotating twin-screw extruder are: Section 1 125℃, Section 2... The sheet is formed by melt extrusion at temperatures of 140℃ for three sections, 160℃ for three sections, 170℃ for four sections, 180℃ for five sections, 170℃ for six sections, 160℃ for seven sections, 150℃ for eight sections, 160℃ for nine sections, and 170℃ for ten sections. The sheet is then formed in a 175-170-175℃ temperature distribution at the hanger die head after melt extrusion. It is then calendered and shaped using a three-roll calender with a speed difference ratio of 1:1.1:1.2 between the upper, middle, and lower rolls. The upper roll temperature is 110℃, the middle roll temperature is 90℃, and the lower roll temperature is 80℃. After cooling by a cooling roller, the sheet is trimmed, wound, and obtained as a rigid polybutylene succinate biodegradable sheet.

[0043] In this comparative example, starch and maleic anhydride were not pre-treated with mechanical esterification. Instead, starch, maleic anhydride, and low molecular weight polybutylene succinate were directly hot-melt extruded and chain-extended. The anchoring effect of the core-shell structure formed by the chain-extended polybutylene succinate and starch was significantly weakened, and starch was exposed. Although there were no obvious exudates in the sheet after boiling, it was obvious to absorb water and swell.

[0044] Reference example 100 kg of polybutylene succinate, 0.5 kg of lubricant ethylene bis-stearamide, 0.5 kg of nucleating agent ultrafine talc powder, and 0.2 kg of nucleating agent 3988 were added to a high-speed mixer and mixed. The mixture was then fed into a co-rotating twin-screw extruder. The temperatures of each section of the co-rotating twin-screw extruder were set as follows: Section 1 125℃, Section 2 140℃, Section 3 160℃, Section 4 170℃, Section 5 180℃, Section 6 170℃, Section 7 160℃, Section 8 150℃, Section 9 160℃, and Section 10 170℃. After melt extrusion, a sheet prototype was formed in the hanger die head, with a temperature distribution of 175-170-175℃. The sheet was then calendered and shaped using a three-roll calender, with the speed difference ratio of the upper, middle, and lower rolls of the three-roll calender being 1:1.1. 1.2; The upper roller temperature is 110℃, the middle roller temperature is 90℃, the lower roller temperature is 80℃, the material is cooled by a cooling roller, trimmed, and wound up to obtain a rigid polybutylene succinate biodegradable sheet.

[0045] The reference example is pure PBS sheet, which has extremely low rigidity and good strength and water resistance.

[0046] The tensile strength, tensile modulus of elasticity, flexural stiffness, and water resistance of the biodegradable sheets (thickness of 0.5 mm) prepared in Examples 1-3, Comparative Examples 1-4, and Reference Examples were tested.

[0047] Tensile strength: Tested according to GB / T 1040.1-2025 (Determination of tensile properties of plastics - Part 1: General) at a tensile rate of 5 mm / min. The test results are shown in Table 1.

[0048] Tensile modulus of elasticity: Tested according to GB / T 1040.1-2025 (Determination of tensile properties of plastics - Part 1: General). The higher the tensile modulus of elasticity, the better the rigidity and load-bearing capacity of the material. The test results are shown in Table 1.

[0049] Bending stiffness: The Taber stiffness of the sheet material was determined according to GB / T 22364-2018 to measure its rigidity and resistance to bending deformation. Longitudinal and transverse samples were cut, with a standard sample size of 70 mm × 38 mm and a clamping distance of 50 mm. The Taber stiffness (mN·m) was tested at a bending angle of 15°. The higher the stiffness value, the stronger the material's rigidity and the better its resistance to bending deformation. The test results are shown in Table 1.

[0050] Table 1: As shown in Table 1, compared to the reference example (pure PBS sheet), the tensile modulus of elasticity and flexural stiffness of the biodegradable sheet of this invention are significantly increased, indicating enhanced supporting rigidity and resistance to bending deformation. This solves the problem of severe sagging during heating and poor tray fixation when using PBS sheets for blister packaging. In production practice, reducing the sheet thickness from 1mm to 0.5mm still maintains rigidity, bending strength, and resistance to deformation, significantly reducing costs. Compared to pure PBS, the biodegradable sheet of this invention contains more starch, resulting in a significant cost reduction, but without a significant decrease in tensile strength, fully meeting the usage requirements.

[0051] Hot water resistance: Referring to GB / T1034-2008 "Determination of Water Absorption of Plastics", the water absorption rate was measured after immersion in boiling water for 30 minutes. The presence of exudates, bubbling, or swelling was observed, and the flexural stiffness retention rate after immersion in boiling water was tested to evaluate the supporting rigidity of the sheet when filled with liquid. Test results are shown in Table 2.

[0052] Table 2: As shown in Table 2, the biodegradable sheet of the present invention exhibits excellent hot water resistance, showing no precipitates or swelling / bubbling after boiling in water for 30 minutes. A comparison of the examples with Comparative Examples 1-4 and the reference example confirms that: using currently available thermoplastic starch (Comparative Example 1) offers extremely limited improvement in the rigidity of PBS, and the plasticized thermoplastic starch has extremely high water absorption, resulting in starch precipitation and stickiness, making it unsuitable for packaging sheets; simple surface modification of starch (Comparative Examples 2 and 3) significantly improves the rigidity of the PBS sheet, but starch granule exposure remains severe, and water absorption is high; direct hot-melt extrusion chain extension of starch and low molecular weight PBS under anhydride assistance (Comparative Example 4) results in better rigidity of the sheet, with no precipitates after boiling, but some swelling still occurs.

[0053] Therefore, this invention esterifies the surface of starch microparticles and attaches acid anhydrides. Through hot-melt extrusion chain extension, low molecular weight polybutylene succinate is anchored to the surface of the starch microparticles, forming a firmly bonded core-shell structure. When used in the preparation of sheets from polybutylene succinate matrix resin, starch exhibits a significant stiffening effect, and the starch is protected by a robust shell, making it less prone to water immersion and degradation of the sheet's water resistance. It has low water absorption and high flexural stiffness retention, making it ideal for disposable hot food containers.

Claims

1. A rigid polybutylene succinate biodegradable sheet, characterized in that, It is made from the following raw materials in parts by weight: 40-55 parts polybutylene succinate, 40-50 parts core-shell composite material, 3-5 parts polylactic acid, 1-2 parts compatibilizer, 0.3-0.5 parts lubricant, and 0.5-1.0 parts nucleating agent; The core-shell composite material is prepared by the following method: starch and acid anhydride are mechanically and dryly modified to obtain modified starch; the modified starch and low molecular weight polybutylene succinate are chain extended by hot melt extrusion to form a core-shell composite material with polybutylene succinate as the shell and starch as the core.

2. The rigid polybutylene succinate biodegradable sheet according to claim 1, characterized in that, The mass ratio of starch to acid anhydride is 100:(1-1.5); the starch is at least one of corn starch and tapioca starch; the acid anhydride is at least one of maleic anhydride, itaconic anhydride, and succinic anhydride.

3. The rigid polybutylene succinate biodegradable sheet according to claim 1, characterized in that, The mass ratio of the modified starch to low molecular weight polybutylene succinate is 100:(30-35); the number average molecular weight of the low molecular weight polybutylene succinate is 3000-8000 Da.

4. The rigid polybutylene succinate biodegradable sheet according to claim 1, characterized in that, The compatibilizer is at least one of ethylene-acrylic acid copolymer, ethylene-vinyl acetate copolymer, PLA grafted glycidyl methacrylate, and PBS grafted glycidyl methacrylate.

5. The rigid polybutylene succinate biodegradable sheet according to claim 1, characterized in that, The lubricant is at least one of glyceryl tristearate, ethylene bis-stearamide, stearic acid, and pentaerythritol stearate.

6. The rigid polybutylene succinate biodegradable sheet according to claim 1, characterized in that, The nucleating agent is an ultrafine inorganic powder nucleating agent and / or an organic nucleating agent.

7. A method for preparing a rigid polybutylene succinate biodegradable sheet according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Starch and acid anhydride are modified by mechanical dry method to obtain modified starch; the modified starch and low molecular weight polybutylene succinate are chain extended by hot melt extrusion to form a shell-core structure composite material with polybutylene succinate as the shell and starch as the core. S2. Polybutylene succinate, core-shell composite material, polylactic acid, compatibilizer, lubricant, and nucleating agent are added to a high-speed mixer according to the formula in parts by weight and mixed. The mixture is then fed to a co-rotating twin-screw extruder. The temperatures of each section of the co-rotating twin-screw extruder are set as follows: Section 1 120-130℃, Section 2 140-150℃, Section 3 160-170℃, Section 4 160-170℃, Section 5 170-180℃, Section 6 160-170℃, Section 7 150-160℃, Section 8 140-150℃, Section 9 150-160℃, and Section 10 160-170℃. After melt extrusion, a sheet prototype is formed in the coat hanger die. The sheet is then calendered and shaped by a three-roll calender, cooled, trimmed, and wound to obtain a rigid polybutylene succinate biodegradable sheet.

8. The method for preparing a rigid polybutylene succinate biodegradable sheet according to claim 7, characterized in that, The mechanical dry modification involves micronizing and esterifying starch through grinding or air jet milling under solvent-free, solid conditions.

9. The method for preparing a rigid polybutylene succinate biodegradable sheet according to claim 7, characterized in that, In step S1, the hot melt extrusion temperature is 160-180℃; the residence time of the material on the screw is controlled to be 240-360 seconds by using low speed and / or reverse screw elements.

10. The method for preparing a rigid polybutylene succinate biodegradable sheet according to claim 7, characterized in that, In step S2, the speed difference ratio of the upper, middle, and lower rollers of the three-roll calender is 1:1.1:1.2; the temperature of the upper roller is 100-110℃, the temperature of the middle roller is 90-100℃, and the temperature of the lower roller is 80-90℃.

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