Biodegradable polylactic acid-based polyester foamable particles and injection-molded low-density foamed products and preparation methods

Abstract

The present invention provides a biodegradable polylactic acid-based polyester foamable particles and an injection-molded low-density foamed product and a preparation method. The preparation method of the biodegradable polylactic acid-based polyester foamable particles comprises the following steps: mixing a biodegradable polymer, a biodegradable bead foaming agent and a nucleating agent, and then extruding and granulating to obtain completely biodegradable polylactic acid-based polyester foamable particles. The preparation method of the injection-molded low-density foamed product comprises the following steps: heating and melting the biodegradable polylactic acid-based polyester foamable particles and then injecting them into a mold, maintaining the pressure for a period of time after the injection is completed, and then opening the mold to obtain a polylactic acid-based polyester injection-molded low-density foamed product. The present invention solves the problem that biodegradable polyesters such as ordinary polylactic acid are not easy to foam due to low viscosity. The provided polylactic acid-based polyester injection-molded low-density foamed product is completely biodegradable and has good machinability and basic impact resistance.

Description

Technical Field

[0001] The invention relates to biodegradable polylactic acid-based polyester foamable particles and injection-molded low-density foamed products and a preparation method, belonging to the technical field of foaming materials. Background Art

[0002] Polymer foam materials have excellent properties such as low density, high toughness, good impact resistance, and high specific strength. Currently, the widely used polymer foam materials are based on traditional plastics such as polyolefins and polyurethanes, which put great pressure on the environment during the production process and after disposal.

[0003] Polylactic acid, as a biodegradable plastic with high mechanical strength and good biocompatibility, can be obtained by ring-opening polymerization of lactide, and its raw materials are derived from biomass. Polylactic acid is widely used in medical devices, packaging materials, daily necessities and other fields. However, due to the linear structure of its molecular chain, the melt exhibits shear-thinning properties. During the processing, as the temperature rises, the melt strength drops sharply. Conventional extrusion foaming processes are prone to cause cell collapse, making it difficult to obtain foamed products with high porosity and uniform cells. At the same time, due to the semi-rigid molecular chain structure and high glass transition temperature, the polylactic acid substrate exhibits low toughness and high hardness at room temperature. After injection molding, it is difficult to cut with a household pencil sharpener or the like.

[0004] CN113845689A, CN113980362A, and CN113736128A disclose supercritical CO 2 CN111410765A discloses a method for preparing biodegradable polyester foam beads and molded body materials, which uses polylactic acid and polybutylene terephthalate-adipate as the matrix, uses high-pressure water vapor as the foaming gas, and quickly releases the pressure after the fluid pressure reaches a predetermined pressure to perform a foaming process, and then places the fluid in a high-pressure container for heating to obtain subsequent foamed beads, and the density of the molded body is 0.03-0.15 g / cm 3 . This technology requires special high-pressure equipment, and the product cannot be processed by secondary foaming, especially injection molding. It is mainly used in the field of cushioning packaging. The addition of nucleating agents improves the foaming uniformity of the product. CN110591304A discloses a method for preparing a polyester foam material with uniform pores, high foaming ratio and biodegradability. The method irradiates the biodegradable polyester with electron beam or γ-ray to increase the melt strength, and then uses microwave oven foaming or microwave oven foaming to obtain an apparent density of 0.01 to 0.20 g / cm 3Polyester foaming materials, but this process is not convenient for large-scale production, and can only prepare sheets, not for injection molding. CN113736129A and CN113736128A respectively introduce lignin and polylactic acid stereocomplex crystals with a crystallinity greater than or equal to 15% to increase the average pore size of the foam and improve the foaming performance of biodegradable materials. CN110294923A made a self-made microsphere foaming agent containing low-boiling hydrocarbons, and blended it with polylactic acid, polybutylene terephthalate-adipate, corn starch, wood powder and other bio-based fillers to obtain a density of 0.52-0.81kg / m 3 The sheet is made of biodegradable materials, but the matrix material of its microsphere foaming agent is not biodegradable.

[0005] It can be seen from this that the current polylactic acid-based polyester foaming process mainly has the following technical problems: First, the use of supercritical CO 2 Or water vapor as a foaming agent, which has high requirements for production equipment and complex processes, and is only suitable for the production of extremely low-density foamed bead molded bodies, with pore diameters mostly above 100μm; secondly, in order to stabilize the bubbles, many existing technologies require radiation cross-linking, or introduce stereocomplex crystals, lignin crystals and other processing steps, which improve the melt strength while improving the material's fracture strength and elastic modulus, but are not suitable for the production of easy-to-cut polylactic acid-based polyester foam products. Due to the linear structure and low melt strength of biodegradable polyester, it is difficult to use conventional processes for foaming and molding. At present, there are few technologies that do not require complex methods or special raw materials to increase the melt strength of the base material, use general low-viscosity biodegradable polyester and ordinary injection molding processes, and are suitable for the production of low-density polylactic acid-based polyester injection molding profiles. In particular, a microporous foaming process that can control the hardness of the product, ensure that the product is completely biodegradable, does not produce microplastic pollution, and makes the product have good machinability and basic impact resistance needs to be developed urgently. Summary of the invention

[0006] In order to solve the above technical problems, the object of the present invention is to provide a biodegradable polylactic acid-based polyester foamable particle and a preparation method thereof. Another object of the present invention is to provide a polylactic acid-based polyester injection-molded low-density foamed product and a preparation method thereof. The polylactic acid-based polyester injection-molded low-density foamed product provided by the present invention is completely biodegradable and has good machinability and basic impact resistance.

[0007] In order to achieve the above object, the first aspect of the present invention provides a method for preparing biodegradable polylactic acid-based polyester foamable particles, which comprises the following steps:

[0008] S1, mixing: mixing a biodegradable polymer, a biodegradable bead foaming agent and a nucleating agent to obtain a mixed material; wherein, in parts by mass, the biodegradable polymer includes 50 to 100 parts of polylactic acid (PLA), 50 to 0 parts of polybutylene terephthalate-adipate (PBAT), and 40 to 0 parts of polybutylene succinate-adipate (PBSA);

[0009] S2, extrusion granulation: the mixed material is extruded and granulated to obtain the biodegradable polylactic acid-based polyester foamable particles.

[0010] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, in parts by mass, based on 100 parts of the biodegradable polymer, the amount of the biodegradable bead foaming agent used is 0.5 to 10 parts. More preferably, in parts by mass, based on 100 parts of the biodegradable polymer, the amount of the biodegradable bead foaming agent used is 3 to 8 parts.

[0011] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, in parts by mass, based on 100 parts of the biodegradable polymer, the amount of the nucleating agent is 0.1 to 0.7 parts.

[0012] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, the particle size of the biodegradable bead foaming agent is 20-50 μm, the foaming temperature is 190-200° C., and the optimal foaming temperature is 220-260° C.

[0013] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, the biodegradable bead foaming agent is prepared by the following steps: reacting the biodegradable polyester with an isocyanate chain extender, then mixing with an azo foaming agent and / or a hydrazide foaming agent, and then molding to obtain the biodegradable bead foaming agent.

[0014] The process of reacting the biodegradable polyester with the isocyanate chain extender and then mixing with the azo foaming agent can be carried out using conventional mixing equipment in the art, such as but not limited to internal mixers, open mixers, etc. The molding process can also be carried out in a conventional manner using conventional molding equipment in the art, as long as the above-mentioned particle size requirements (20 to 50 μm) are met.

[0015] More preferably, the biodegradable polyester includes polybutylene succinate-adipate (PBSA) and the like.

[0016] More preferably, the isocyanate chain extender includes one or a combination of hexamethylene diisocyanate, isophorone diisocyanate and 4,4'-diphenylmethane diisocyanate, etc. The isocyanate chain extender used in the present invention effectively improves the melt strength of the biodegradable bead foaming agent.

[0017] More preferably, the azo foaming agent and / or hydrazide foaming agent includes azodicarbonamide and / or 4,4'-oxybisbenzenesulfonylhydrazide.

[0018] More preferably, the mass ratio of the biodegradable polyester, the isocyanate chain extender and the azo foaming agent and / or hydrazide foaming agent is 100:(0.1-0.3):100.

[0019] More preferably, the reaction temperature of the biodegradable polyester and the isocyanate chain extender is 120-150° C., and the reaction time is 3-10 min.

[0020] More preferably, the temperature for mixing with the azo foaming agent and / or hydrazide foaming agent is 120-140° C., and the mixing time is 3-5 min.

[0021] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester expandable particles, in the biodegradable bead foaming agent, an azo foaming agent and / or a hydrazide foaming agent is dispersed in a high-viscosity chain-extended modified PBSA matrix.

[0022] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, the nucleating agent includes polybutylene fumarate and / or nano hexagonal boron nitride and the like.

[0023] In the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles, preferably, the mixing and extrusion granulation methods include but are not limited to using a single-screw extruder or a twin-screw extruder, etc.; more preferably, the heating temperature of the single-screw extruder or the twin-screw extruder can be 160-210°C, and the screw speed can be 10-200rpm.

[0024] According to a specific embodiment of the present invention, preferably, the method for preparing the above-mentioned biodegradable polylactic acid-based polyester foamable particles further includes before step S1: step S0, drying: drying the biodegradable polymer, the drying is vacuum drying, the vacuum drying temperature can be 50-100°C, and the vacuum drying time can be 2-16h.

[0025] The second aspect of the present invention provides biodegradable polylactic acid-based polyester foamable particles, which are prepared by the above-mentioned method for preparing biodegradable polylactic acid-based polyester foamable particles.

[0026] The present invention has no special requirements on the size of the biodegradable polylactic acid-based polyester foamable particles. According to a specific embodiment of the present invention, generally speaking, the biodegradable polylactic acid-based polyester foamable particles obtained by extrusion granulation can be columnar particles with a diameter of about 3 mm and a height of about 5 mm.

[0027] The third aspect of the present invention provides a method for preparing a polylactic acid-based polyester injection-molded low-density foamed product, which comprises the following steps:

[0028] (1) Preheating the materials: heating and melting the above-mentioned biodegradable polylactic acid-based polyester foamable particles to obtain a biodegradable polylactic acid-based polyester foamable particle melt;

[0029] (2) Injection molding: The biodegradable polylactic acid-based polyester foamable particle melt is injected into a mold, and after the injection is completed, the pressure is maintained for a period of time, and then the mold is opened to obtain the polylactic acid-based polyester injection-molded low-density foamed product.

[0030] In the above-mentioned method for preparing the polylactic acid-based polyester injection-molded low-density foamed product, preferably, the temperature of the melt of the biodegradable polylactic acid-based polyester foamable particles is 210-240° C. (ie, the foaming temperature).

[0031] In the above-mentioned method for preparing the polylactic acid-based polyester injection-molded low-density foamed product, preferably, the injection pressure of injecting the biodegradable polylactic acid-based polyester foamable particle melt into the mold is 10 to 40 MPa.

[0032] In the above-mentioned method for preparing the polylactic acid-based polyester injection-molded low-density foamed product, preferably, the temperature of the mold is 20-130°C.

[0033] In the above-mentioned method for preparing the polylactic acid-based polyester injection-molded low-density foamed product, preferably, the holding pressure after injection is 0 to 30 MPa, and the holding time is 10 to 120 seconds.

[0034] The fourth aspect of the present invention provides a polylactic acid based polyester injection molded low-density foamed product, which is prepared by the above-mentioned method for preparing the polylactic acid based polyester injection molded low-density foamed product.

[0035] According to a specific embodiment of the present invention, preferably, the diameter of the pores of the polylactic acid-based polyester injection-molded low-density foamed product is 20 to 100 μm.

[0036] According to a specific embodiment of the present invention, preferably, the porosity of the polylactic acid-based polyester injection-molded low-density foamed product is 5%-60%, more preferably 10%-60%.

[0037] According to a specific embodiment of the present invention, preferably, the apparent density of the polylactic acid-based polyester injection-molded low-density foamed product is 0.5 to 1.2 g / cm 3 More preferably, the apparent density of the polylactic acid-based polyester injection-molded low-density foamed product is 0.5 to 1.0 g / cm 3 , Shore hardness is 30-70HD.

[0038] The invention provides a biodegradable polylactic acid-based polyester foamable particles and injection-molded low-density foamed products and their preparation methods. The invention first mixes polylactic acid, optional polybutylene terephthalate-adipate, optional polybutylene succinate-adipate, a biodegradable bead foaming agent and a nucleating agent, and obtains foamable particles after extrusion granulation, and the biodegradable bead foaming agent does not foam during the extrusion process; then the foamable particles are fully melted, injected into a mold, and foamed to obtain a polylactic acid-based polyester foamed product with low density and adjustable density, uniform pores, a microporous structure (less than 100 μm) and a closed-cell structure, and high porosity.

[0039] The technical solution of the present invention selectively introduces polybutylene terephthalate-adipate and / or polybutylene succinate-adipate into polylactic acid-based polyester on the one hand, which can regulate its toughness, strength and hardness; on the other hand, a biodegradable bead foaming agent is introduced to form micron-sized pores (pore diameter is 20-100 μm), and a nucleating agent is introduced to accelerate the molding cycle of the product and ensure the dimensional stability of the product. In addition, in the process of preparing foamable particles by extrusion, the present invention controls the biodegradable bead foaming agent not to foam, and performs micro-foaming in the subsequent injection molding process to obtain the injection-molded low-density foamed product of the present invention. The biodegradable bead foaming agent of the present invention is composed of a biodegradable polyester shell and a foaming agent core. The unique foaming mechanism reduces the requirements for the viscosity of the polymer melt, and the injection-molded low-density foamed product finally prepared has a microporous structure and greatly improved machinability.

[0040] Compared with the existing polylactic acid-based polyester foaming material and its preparation process, the preparation method of the present invention is safe and convenient, does not rely on special high temperature and high pressure equipment, can prepare pellets that are easy to form and process, solves the problem that ordinary polylactic acid and other biodegradable polyesters are not easy to foam due to low viscosity, and the injection-molded product has a microporous structure (below 100 μm), and the foam cells are uniform, have a closed-cell structure, and have a high porosity. The apparent density is reduced by 20% to 60% compared with polylactic acid, and has excellent properties such as light weight, good impact resistance, and easy cutting, and can be completely biodegradable. The polylactic acid-based polyester injection-molded low-density foamed product of the present invention can be applied to products that need to be cut, such as cosmetic pen holders, to prevent plastic and microplastic pollution caused by cutting fragments of non-degradable plastic products. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a SEM image of the cross section of the liquid nitrogen brittle fracture specimen of the product provided in Example 1.

[0042] Figure 2 This is a SEM image of the cross section of the liquid nitrogen brittle fracture specimen of the product provided in Comparative Example 2. DETAILED DESCRIPTION

[0043] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0044] The raw materials used in the following examples and comparative examples, such as polylactic acid, polybutylene terephthalate-adipate, polybutylene succinate-adipate, polybutylene fumarate, nano hexagonal boron nitride, hexamethylene diisocyanate, and azodicarbonamide, can all be obtained commercially.

[0045] Example 1

[0046] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0047] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 60°C and dried for 12 h;

[0048] After cooling, 85g of polylactic acid, 10g of polybutylene terephthalate-adipate, 5g of polybutylene succinate-adipate, 4g of biodegradable bead foaming agent, and 0.3g of polybutylene fumarate were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 50rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and finally the die temperature was 180°C;

[0049] The biodegradable bead foaming agent is prepared by the following steps: by weight, 100 parts of polybutylene succinate-adipate and 0.1-0.3 parts of hexamethylene diisocyanate are added into an internal mixer, reacted at 130° C. for 5 minutes, chain extended to improve melt strength, then 100 parts of azodicarbonamide are added, kneaded for 3 minutes, taken out and powdered to obtain the biodegradable bead foaming agent, the particle size of which is 20-50 μm;

[0050] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C, preheated for 120 seconds, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.83g / cm 3 The Shore hardness is 57HD. The mechanical properties of the product are shown in Table 1. The SEM image of the cross section of the liquid nitrogen brittle fracture specimen of the product is shown in Table 1. Figure 1 The pore diameter of the product is 20-100 μm, and the pore size distribution is uniform, and the porosity is 34%.

[0051] Example 2

[0052] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0053] Place polylactic acid and polybutylene terephthalate-adipate in a vacuum oven at 60°C and dry for 12 h;

[0054] After cooling, 70g of polylactic acid, 30g of polybutylene terephthalate-adipate, 1g of biodegradable bead foaming agent, and 0.5g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 60rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0055] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C. After preheating for 120 seconds, the melt is injected into the mold at a temperature of 20°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 1.12g / cm 3 The Shore hardness is 77HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 11%.

[0056] Example 3

[0057] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0058] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 60°C and dried for 12 h;

[0059] After cooling, 70g of polylactic acid, 20g of polybutylene terephthalate-adipate, 10g of polybutylene succinate-adipate, 3g of biodegradable bead foaming agent, and 0.5g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 50rpm, the screw heating section was subjected to a gradient heating of 160 to 190°C, a gradient cooling of 190 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0060] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C, preheated for 120s, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 15MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.87g / cm 3 The Shore hardness is 60HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 31%.

[0061] Example 4

[0062] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0063] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 100°C and dried for 2 h;

[0064] After cooling, 50g of polylactic acid, 40g of polybutylene terephthalate-adipate, 10g of polybutylene succinate-adipate, 4g of biodegradable bead foaming agent, and 0.2g of nano hexagonal boron nitride are blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed is set to 40rpm, the screw heating section undergoes a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and finally the die temperature is 180°C; wherein the preparation steps of the biodegradable bead foaming agent are the same as those in Example 1;

[0065] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 230°C, preheated for 120 seconds, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 12MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.90g / cm 3 The Shore hardness is 62HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 29%.

[0066] Example 5

[0067] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0068] Polylactic acid and polybutylene terephthalate-adipate were placed in a vacuum oven at 80°C and dried for 4 h;

[0069] After cooling, 50g of polylactic acid, 50g of polybutylene terephthalate-adipate, 3g of biodegradable bead foaming agent, and 0.3g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 40rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0070] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 230°C, preheated for 120s, and then injected into the mold at a temperature of 20°C. The injection pressure is 30MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.92g / cm 3 The Shore hardness is 63HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 27%.

[0071] Example 6

[0072] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0073] Polylactic acid and polybutylene terephthalate-adipate were placed in a vacuum oven at 80°C and dried for 4 h;

[0074] After cooling, 50g of polylactic acid, 50g of polybutylene terephthalate-adipate, 4g of biodegradable bead foaming agent, and 0.3g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 40rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0075] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C, preheated for 120s, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 20MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.98g / cm 3 The Shore hardness is 70HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 22%.

[0076] Example 7

[0077] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0078] The polylactic acid was placed in a vacuum oven at 60°C and dried for 12 h;

[0079] After cooling, 100g of polylactic acid, 7g of biodegradable bead foaming agent, and 0.5g of nano hexagonal boron nitride were mixed and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 60rpm, the screw heating section was subjected to a gradient heating of 160 to 190°C, a gradient cooling of 190 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0080] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C. After preheating for 120 seconds, the melt is injected into the mold at a temperature of 20°C. The injection pressure is 20MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.65g / cm 3 , Shore hardness is 36HD. The mechanical properties of the product are shown in Table 1. The pore diameter of the product is 20-100 μm, and the pore size distribution is uniform, and the porosity is 48%.

[0081] Example 8

[0082] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0083] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 60°C and dried for 12 h;

[0084] After cooling, 70g of polylactic acid, 15g of polybutylene terephthalate-adipate, 15g of polybutylene succinate-adipate, 6g of biodegradable bead foaming agent, and 0.5g of polybutylene fumarate are blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed is set to 50rpm, the screw heating section undergoes a gradient temperature increase of 180 to 210°C, a gradient temperature decrease of 210 to 180°C, and finally the die temperature is 180°C; wherein the preparation steps of the biodegradable bead foaming agent are the same as those in Example 1;

[0085] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C, preheated for 120 seconds, and then the melt is injected into the mold at a temperature of 100°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 60s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.73g / cm 3 The Shore hardness is 38HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 42%.

[0086] Example 9

[0087] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0088] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 60°C and dried for 12 h;

[0089] After cooling, 75g of polylactic acid, 15g of polybutylene terephthalate-adipate, 10g of polybutylene succinate-adipate, 4g of biodegradable bead foaming agent, 0.5g of polybutylene fumarate, and 0.2g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 50rpm, the screw heating section was subjected to a gradient heating of 160 to 190°C, a gradient cooling of 190 to 180°C, and finally the die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0090] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C. After preheating for 120 seconds, the melt is injected into the mold at a temperature of 70°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 60s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.78g / cm 3 The Shore hardness is 42HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 38%.

[0091] Example 10

[0092] This embodiment provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0093] Polylactic acid, polybutylene terephthalate-adipate, and polybutylene succinate-adipate were placed in a vacuum oven at 60°C and dried for 12 h;

[0094] After cooling, 70g of polylactic acid, 15g of polybutylene terephthalate-adipate, 15g of polybutylene succinate-adipate, 8g of biodegradable bead foaming agent, and 0.5g of polybutylene fumarate are blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed is set to 50rpm, the screw heating section undergoes a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 190 to 180°C, and finally the die temperature is 180°C; wherein the preparation steps of the biodegradable bead foaming agent are the same as those in Example 1;

[0095] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 240°C. After preheating for 120 seconds, the melt is injected into the mold at a temperature of 50°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 60s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.55g / cm 3 The Shore hardness is 32HD. The pore diameter of the product is 20-100μm, and the pore size distribution is uniform, and the porosity is 56%.

[0096] Comparative Example 1

[0097] This comparative example provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0098] Place polylactic acid and polybutylene terephthalate-adipate in a vacuum oven at 60°C and dry for 12 h;

[0099] After cooling, 85g of polylactic acid, 15g of polybutylene terephthalate-adipate, and 4g of biodegradable bead foaming agent were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 50rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 210 to 180°C, and the final die temperature was 180°C; wherein the preparation steps of the biodegradable bead foaming agent were the same as those in Example 1;

[0100] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C, preheated for 120s, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 60MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 30MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 0.95g / cm 3 , Shore hardness is 61HD. In this comparative example, no nucleating agent is used, and a higher injection pressure is selected, the foamed product prepared has uneven cells, has large bubbles with a cell diameter exceeding 100 μm, and has a decreased foaming rate.

[0101] Comparative Example 2

[0102] This comparative example provides a biodegradable polylactic acid-based polyester injection-molded product, which is prepared by the following method:

[0103] Place polylactic acid and polybutylene terephthalate-adipate in a vacuum oven at 60°C and dry for 12 h;

[0104] After cooling, 85 g of polylactic acid and 15 g of polybutylene terephthalate-adipate were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester particles; wherein the screw speed was set to 50 rpm, the screw heating section was subjected to a gradient temperature increase of 180 to 210° C., a gradient temperature decrease of 210 to 180° C., and the final die temperature was 180° C.;

[0105] The polylactic acid-based polyester particles are added to the injection molding machine barrel preset at 220°C, preheated for 120 seconds, and then the melt is injected into the mold at a temperature of 20°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection molded product is obtained. The apparent density of the product is 1.28g / cm 3 The Shore hardness is 82HD. The SEM image of the cross section of the liquid nitrogen brittle fracture specimen of the product is as follows Figure 2It can be seen that this comparative example does not use the biodegradable bead foaming agent of the present invention, nor does it use a nucleating agent, and no foamed product is prepared.

[0106] Comparative Example 3

[0107] This comparative example provides a biodegradable polylactic acid-based polyester injection-molded low-density foamed product, which is prepared by the following method:

[0108] Place polylactic acid and polybutylene terephthalate-adipate in a vacuum oven at 60°C and dry for 12 h;

[0109] After cooling, 85g of polylactic acid, 15g of polybutylene terephthalate-adipate, 2g of azodicarbonamide, and 0.5g of nano hexagonal boron nitride were blended and extruded in a twin-screw extruder to obtain polylactic acid-based polyester foamable particles; wherein the screw speed was set to 50rpm, the screw heating section was subjected to a gradient temperature increase of 160 to 190°C, a gradient temperature decrease of 210 to 180°C, and the final die temperature was 180°C;

[0110] The polylactic acid-based polyester foamable particles are added to the injection molding machine barrel preset at 220°C. After preheating for 120 seconds, the melt is injected into the mold at a temperature of 20°C. The injection pressure is 18MPa. After the injection is completed, the pressure is maintained for a period of time. The pressure is set to 10MPa and the pressure holding time is 40s. After cooling and opening the mold, the biodegradable polylactic acid-based polyester injection-molded low-density foamed product is obtained. The apparent density of the product is 1.18g / cm 3 , Shore hardness is 78HD. This comparative example does not use the biodegradable bead foaming agent of the present invention, but uses a conventional azo foaming agent, and only a small amount of large bubbles exist in the product, the foaming rate is very low, the cell diameter of the foamed product is greater than 200μm, and the porosity is 7%.

[0111] Table 1 Mechanical properties of Example 1 and Example 7

[0112] project Example 1 Example 7 Elastic modulus (MPa) 1008.30±26.05 1166.60±164.90 Yield stress (MPa) 15.14±0.72 15.90±2.04 Yield elongation (%) 4.84±3.33 2.67±0.27 Fracture stress (MPa) 1.65±0.42 0.82±0.37 Elongation at break (%) 10.58±1.10 8.58±2.19 Tensile strength(MPa) 15.35±0.66 16.02±2.13 Maximum stress elongation (%) 8.47±1.44 6.23±3.08 <![CDATA[Izod impact strength of cantilever beam notched (kJ / m 2 )]]> 12.64±2.25 9.48±0.31

[0113] From the above, it can be seen that the preparation method of the present invention is safe and convenient, does not rely on special high temperature and high pressure equipment, can prepare pellets that are convenient for subsequent molding and processing, and the products obtained by injection molding have a microporous structure (less than 100 μm), and the bubbles are uniform, have a closed-cell structure, high porosity, low density, and have excellent properties such as light weight, good impact resistance, and easy cutting, and are completely biodegradable.

Claims

1. A method for preparing biodegradable polylactic acid-based polyester foamable particles, The following steps are involved: S1, mixing: mixing a biodegradable polymer, a biodegradable bead foaming agent and a nucleating agent to obtain a mixed material; wherein, in parts by mass, the biodegradable polymer comprises 50 to 100 parts of polylactic acid, 50 to 0 parts of polybutylene terephthalate-adipate and 40 to 0 parts of polybutylene succinate-adipate; S2, extrusion granulation: extruding and granulating the mixture to obtain the biodegradable polylactic acid-based polyester foamable particles; The biodegradable bead foaming agent is prepared by the following steps: reacting a biodegradable polyester with an isocyanate chain extender, then mixing with an azo foaming agent and / or a hydrazide foaming agent, and then molding to obtain the biodegradable bead foaming agent; wherein the biodegradable polyester comprises polybutylene succinate-adipate; The nucleating agent includes polybutylene fumarate and / or nano hexagonal boron nitride.

2. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In parts by mass, based on 100 parts of the biodegradable polymer, the amount of the biodegradable bead foaming agent is 0.5 to 10 parts.

3. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 2, in, In parts by mass, based on 100 parts of the biodegradable polymer, the amount of the biodegradable bead foaming agent is 3 to 8 parts.

4. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In parts by mass, based on 100 parts of the biodegradable polymer, the amount of the nucleating agent is 0.1 to 0.7 parts.

5. The method for preparing biodegradable polylactic acid-based polyester foamable particles according to claim 1, wherein the particle size of the biodegradable bead foaming agent is 20-50 μm, the foaming temperature is 190-200°C, and the optimal foaming temperature is 220-260°C.

6. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In the step of preparing the biodegradable bead foaming agent, the isocyanate chain extender includes one or a combination of hexamethylene diisocyanate, isophorone diisocyanate and 4,4'-diphenylmethane diisocyanate.

7. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In the step of preparing the biodegradable bead foaming agent, the azo foaming agent and / or hydrazide foaming agent includes azodicarbonamide and / or 4,4'-oxybisbenzenesulfonylhydrazide.

8. The method for preparing biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In the step of preparing the biodegradable bead foaming agent, the mass ratio of the biodegradable polyester, the isocyanate chain extender and the azo foaming agent and / or the hydrazide foaming agent is 100:(0.1-0.3):

100.

9. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In the step of preparing the biodegradable bead foaming agent, the reaction temperature of the biodegradable polyester and the isocyanate chain extender is 120-150° C., and the reaction time is 3-10 min.

10. The method for preparing biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, In the step of preparing the biodegradable bead foaming agent, the temperature for mixing with the azo foaming agent and / or hydrazide foaming agent is 120-140° C., and the mixing time is 3-5 minutes.

11. The method for preparing the biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, The mixing in step S1 and the extrusion granulation in step S2 include using a single-screw extruder or a twin-screw extruder; the heating temperature of the single-screw extruder or the twin-screw extruder is 160-210° C., and the screw speed is 10-200 rpm.

12. The method for preparing biodegradable polylactic acid-based polyester foamable particles according to claim 1, in, The method for preparing the biodegradable polylactic acid-based polyester foamable particles further comprises, before step S1: step S0, drying: drying the biodegradable polymer, wherein the drying is vacuum drying, the vacuum drying temperature is 50-100° C., and the vacuum drying time is 2-16 hours.

13. Biodegradable polylactic acid-based polyester foamable particles, which are prepared by the method for preparing biodegradable polylactic acid-based polyester foamable particles according to any one of claims 1 to 12.

14. A method for preparing a polylactic acid-based polyester injection-molded low-density foamed product, wherein The following steps are involved: (1) Preheating the materials: heating and melting the biodegradable polylactic acid-based polyester foamable particles according to claim 13 to obtain a biodegradable polylactic acid-based polyester foamable particle melt; (2) Injection molding: The biodegradable polylactic acid-based polyester foamable particle melt is injected into a mold, and after the injection is completed, the pressure is maintained for a period of time, and then the mold is opened to obtain the polylactic acid-based polyester injection-molded low-density foamed product.

15. The method for preparing the polylactic acid-based polyester injection-molded low-density foamed product according to claim 14, in, The temperature of the biodegradable polylactic acid-based polyester foamable particle melt is 210-240°C.

16. The method for preparing the polylactic acid-based polyester injection-molded low-density foamed product according to claim 14, in, The injection pressure of injecting the biodegradable polylactic acid-based polyester foamable particle melt into the mold is 10-40 MPa; the temperature of the mold is 20-130° C.; the holding pressure after injection is 0-30 MPa, and the holding time is 10-120 s.

17. A polylactic acid based polyester injection molded low-density foamed product, which is prepared by the method for preparing a polylactic acid based polyester injection molded low-density foamed product according to any one of claims 14 to 16.

18. The polylactic acid-based polyester injection-molded low-density foamed product according to claim 17, in, The diameter of the pores of the polylactic acid-based polyester injection-molded low-density foamed product is 20 to 100 μm.

19. The polylactic acid-based polyester injection-molded low-density foamed product according to claim 17, in, The apparent density of the polylactic acid-based polyester injection-molded low-density foamed product is 0.5 to 1.2 g / cm 3 , Shore hardness is 30~78HD.

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