Antistatic easy-to-form polylactic acid foam material and preparation method thereof

Abstract

The invention provides an antistatic easy-to-form polylactic acid foam material and a preparation method thereof, the polylactic acid foam material is prepared from polylactic acid composite particles, each polylactic acid composite particle comprises a coating layer and an inner core, and according to mass percentage, the coating layer accounts for 3-20%, and the balance is the inner core; the coating layer is prepared from the following raw material components in parts by weight: 88 to 98 parts of biodegradable elastic polyester, 2 to 12 parts of an antistatic agent, 0.5 to 3 parts of a compatilizer and 0.5 to 2 parts of an anti-hydrolysis agent; the inner core is prepared from the following raw materials in parts by weight: 100 parts of polylactic acid, 1-3 parts of a nucleating agent, 0.5-2 parts of an antioxidant, 1-4 parts of an anti-hydrolysis agent and 5-10 parts of a chain extender. Compared with the prior art, the conductive filler is intensively and uniformly dispersed in the degradable elastic polyester coating layer, so that the problems that the conductive filler is easy to fall off and poor in cohesiveness in a mechanical coating-hot press molding method are solved, and the antistatic performance is improved through uniform dispersion of the conductive filler of the material; therefore, the material has a good application prospect in electronic packaging.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer foaming materials, and in particular relates to an antistatic and easily moldable polylactic acid foam material and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA), a bio-based polymer derived from renewable resources such as corn starch or cane sugar, has attracted much attention in the field of environmentally friendly materials due to its good biodegradability. The material is produced through a fermentation process and can be processed into a variety of forms of products, including but not limited to foam particles. PLA foam particles have the characteristics of light weight, heat insulation and shock absorption, making them an ideal choice for packaging materials, textiles, disposable tableware and medical devices.

[0003] However, in practical applications, polylactic acid foam materials face some challenges.

[0004] First, in the process of preparing polylactic acid foam particles, cell density and morphology are one of the key factors that determine material performance. Unstable cell density and uneven cell morphology may lead to changes in product physical properties, such as mechanical strength, thermal insulation and sound absorption. For example, in packaging applications, irregular cell structure may lead to unstable cushioning performance and affect the safety of the protected items.

[0005] Second, the sintering ability between beads is essential to form a strong and durable foam structure. Weak sintering ability will cause the foam material to easily break or delaminate when subjected to external forces, limiting its use in applications that require high strength.

[0006] Third, due to the special processing requirements of polylactic acid foam particles, including but not limited to the use of adhesives and coatings, the manufacturing cost of this type of product is relatively high. High cost has become an important factor hindering its widespread application.

[0007] Fourth, the high volume resistivity of polylactic acid foam makes it easy to accumulate static charge, especially in a dry environment. This static accumulation not only affects the operating performance of the product, such as causing dust adsorption or difficulty in material handling, but also in some cases, may cause discharge, thus posing a threat to the safety of production and use.

[0008] Patent application number CN201310206458.8 uses compression molding and foaming to prepare a modified conductive rigid cross-linked polyvinyl chloride flame retardant foam with good conductive properties. However, the above patent method has the problem that the conductive filler is easy to fall off and the adhesion is poor. At the same time, there is a risk of static electricity accumulation in a dry environment, and the pore density cannot be well controlled. Therefore, there are great limitations in practical applications.

[0009] In view of the above problems, there is an urgent need in the market for a polylactic acid foam particle and a preparation method thereof that can effectively control the pore density and morphology, enhance the sintering ability between beads, and have good antistatic properties and are economical. Summary of the invention

[0010] The technical purpose of the present invention is to provide an antistatic and easy-to-form polylactic acid foam material and a preparation method thereof, which has stable pore size, good particle resilience, and excellent antistatic and mechanical properties, and the formed device has good mechanical properties.

[0011] The present invention provides an antistatic and easily moldable polylactic acid foam material, wherein the polylactic acid foam material is made of polylactic acid composite particles, and the polylactic acid composite particles include a coating layer and an inner core, and in terms of mass percentage, the mass proportion of the coating layer is 3-20%, and the remainder is the inner core.

[0012] In some other embodiments, the raw materials of the coating layer include the following components in weight proportions: 88-98 parts of biodegradable elastic polyester, 2-12 parts of antistatic agent, 0.5-3 parts of compatibilizer, and 0.5-2 parts of anti-hydrolysis agent; the raw materials of the inner core include the following components in weight proportions: 100 parts of polylactic acid, 1-3 parts of nucleating agent, 0.5-2 parts of antioxidant, 1-4 parts of anti-hydrolysis agent, and 5-10 parts of chain extender.

[0013] Compared with the prior art, the present invention adopts biodegradable elastic polyester as the main component of the coating layer, which gives the coating layer excellent elasticity and flexibility, and helps to improve the rebound performance of the particles; and polylactic acid as the main component of the inner core provides good biodegradability and mechanical properties, and the nucleating agent can promote the rapid generation of crystal structure during the pore formation process, which helps to control the pore size and distribution, so that the foam material has more stable physical properties; combined with the role of other additives, by accurately adjusting the proportion of components, not only the problems existing in traditional polylactic acid foam materials are solved, but also the material has excellent antistatic properties, which makes the material have good application prospects in electronic packaging.

[0014] In some other embodiments, the melting point of the coating layer is lower than the melting point of the core.

[0015] In some other embodiments, the material of the biodegradable elastic polyester is selected from one or more of polybutylene adipate / terephthalate, polybutylene succinate, polybutylene succinate, and polybutylene adipate.

[0016] Among them, materials such as polybutylene adipate / terephthalate, polybutylene succinate, polybutylene succinate, and polybutylene adipate all have good elastic recovery properties, which help to improve the resilience of foam particles, ensure rapid recovery after being subjected to external force, and reduce the possibility of permanent deformation. These polyester materials provide excellent flexibility, allowing the coating layer to provide additional cushioning protection without affecting the inner core structure.

[0017] In some other embodiments, the antistatic agent is selected from one or more of polyethylene oxide, polyether ester amide, polyether ester imide, quaternary ammonium salt methacrylic acid copolymer, and sodium polystyrene sulfonate.

[0018] Compared with the prior art, the present invention uses the above antistatic agent to form a conductive channel inside the material or reduce the volume resistivity, thereby achieving an antistatic effect.

[0019] In some other embodiments, the compatibilizer is selected from one or more of methyl methacrylate glyceride grafts, ethylene methyl acrylate copolymers, ethylene methacrylic acid copolymers, ethylene acrylic acid copolymers, ethylene butyl acrylate copolymers, and ethylene glycidyl methacrylate copolymers.

[0020] Compared with the prior art, the present invention uses the above compatibilizer to increase the compatibility of the degradable polyester coating layer with the polylactic acid surface and prevent the polylactic acid core layer from separating due to foaming.

[0021] In some other embodiments, the polylactic acid is selected from one or more of an L-lactic acid homopolymer, a D-lactic acid homopolymer, and a copolymer of L-lactic acid and D-lactic acid.

[0022] Compared with existing technologies, these three types of PLA offer different crystallinity, melting points and degradation rates. PLLA has high crystallinity and good mechanical strength; PDLA is more flexible and easy to process; and PDLLA can balance the advantages of both by adjusting the ratio, providing better toughness, uniform cell structure and stable physical properties.

[0023] In some other embodiments, the nucleating agent is selected from one or two of talc, calcium carbonate, silica, mica, nanoclay, and kaolin.

[0024] Compared with existing technologies, these nucleating agents can promote the rapid formation of crystal structures during the cell formation process, control the cell size and distribution, and make the foam material have more stable physical properties. For example, nanoclay can not only act as an effective nucleating agent, but also enhance the mechanical properties and thermal stability of the material.

[0025] In some other embodiments, the antioxidant is selected from one or more of antioxidant 1010 and antioxidant 168.

[0026] Compared with existing technologies, these two antioxidants are common and highly effective antioxidant additives that can effectively delay the oxidation process, protect materials from the effects of thermal oxidative aging, and ensure that they can maintain excellent mechanical properties after long-term use. Antioxidant 1010 is mainly used to prevent the breakage of the polymer main chain, while antioxidant 168 helps to inhibit free radical reactions. The combination of the two can provide comprehensive antioxidant protection.

[0027] In some other embodiments, the anti-hydrolysis agent is selected from one or more of epoxy anti-hydrolysis agents, aromatic carbodiimide anti-hydrolysis agents, polycarbodiimide, glycidyl ether, diisopropylbenzene peroxide, and carbodiamine.

[0028] Compared with the prior art, the anti-hydrolysis agents used in the present invention can provide additional protection in a humid environment and prevent the polyester material from undergoing hydrolysis reactions that lead to performance degradation.

[0029] In some other embodiments, the chain extender is selected from one or more of ADR-4468, ADR-4368, glyceryl methacrylate, and (3,4-epoxycycloethyl)methyl methacrylate.

[0030] Compared with the prior art, the present invention uses the above chain extender to significantly increase the molecular weight, melt strength and mechanical properties of the polymer, and improve its processing performance and thermal stability.

[0031] In some other embodiments, the dispersion medium is deionized water, the dispersant is selected from kaolin and / or dimethyl silicone oil, and the foaming agent is carbon dioxide.

[0032] The second object of the present invention is to provide a method for preparing a polylactic acid foam material, the preparation method specifically comprising the following steps: S1. Using a co-extrusion device, the dried biodegradable elastic polyester is mixed with an antistatic agent, an anti-hydrolysis agent, and a compatibilizer and put into an auxiliary extruder, and polylactic acid, a nucleating agent, an antioxidant, an anti-hydrolysis agent, and a chain extender are put into a main device, and co-extruded and pelletized to obtain polylactic acid composite particles; S2. Put the polylactic acid composite particles obtained in step S1 into a high-pressure reactor, add water, the amount of water added is 3 / 5 of the volume of the reactor, turn on stirring, then add a dispersant and a foaming agent, heat to 120-160°C, maintain the pressure at 2-5MPa, and release the pressure instantly after the reaction is completed to obtain an antistatic and easy-to-form polylactic acid foam material.

[0033] In some other embodiments, in step S2, the weight proportions of the raw materials are as follows: 100 parts of polylactic acid composite particles, 2-10 parts of dispersant, and 5-10 parts of foaming agent; the dispersant is kaolin and / or dimethyl silicone oil, and the foaming agent is carbon dioxide.

[0034] Furthermore, the present invention also provides an application method of the polylactic acid foam material: the polylactic acid foam material is matured for 5-10 days, placed in a pressure tank, the pressure of the pressure tank is 0.5-2MPa, the polylactic acid foam material is added to the cavity of a steam compression molding machine, and the mold is fully filled, and then saturated steam of a certain pressure is introduced into both sides of the mold, the saturated steam pressure is 0.5-4bar, and the saturated steam temperature is 120-195 degrees Celsius, so that the surface of the polylactic acid foam material is fused and sintered. Since the surface of the polylactic acid foam material is a low-melting-point polyester, it can be easier to form parts.

[0035] More specifically, the gas in the pressure tank is air or carbon dioxide.

[0036] Furthermore, when the required pressure in the pressure tank is 0.5-0.8 MPa, air is used, and when the required pressure in the pressure tank is 1.5-2 MPa, carbon dioxide is used.

[0037] Compared with the prior art, the present invention has the following advantages: 1. The present invention concentrates and evenly disperses the conductive filler in the degradable elastic polyester coating layer, which solves the problem of easy detachment and poor adhesion of the conductive filler in the mechanical coating-hot pressing molding method, and improves the antistatic performance through the uniform dispersion of the conductive filler of the material, so that the material has a good application prospect in electronic packaging; 2. The preparation process of the present invention has low requirements on equipment, and the preparation process is simple, convenient and easy to mass produce; 3. The antistatic and easily moldable polylactic acid foam material prepared by the present invention is easy to mold and consumes less energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a SEM image of a sample of the polylactic acid foam material after molding obtained in Example 1 of the present invention; Figure 2 This is a cross-sectional view of the polylactic acid composite foamed beads prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable changes derived therefrom are still within the scope of protection of the claims of the present invention.

[0040] It should be noted that the endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article.

[0041] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventionally understood meanings are defined herein for the purpose of clarification or ease of reference, and such definitions herein should not be construed as indicating significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents and instruments is carried out in accordance with the protocols and parameters given by the manufacturer.

[0042] The technical effects of the present invention are described below in conjunction with specific embodiments.

[0043] It is worth mentioning that in this specific implementation, the test method used is as follows: The closed-cell rate test standard of foam particles is mainly based on the national standard "GB / T 10799-2008 Determination of the volume percentage of open and closed cells of rigid foam plastics". The volume resistivity test is carried out in accordance with GB / T1410-2006 "Test method for volume resistivity and surface resistivity of solid insulating materials". The volume resistivity of the sample is tested using a 4339A / B high insulation resistance meter. The tensile strength test and elongation at break test are carried out in accordance with GB / T1040-1992 "Test method for tensile properties of plastics". The sample is cut into a dumbbell shape with a size of 4mm × 75mm × 2mm, using a microcomputer-controlled universal testing machine, the tensile speed is 50mm / min; the density test is carried out in accordance with GB / T533-2008 "Determination of density of vulcanized rubber or thermoplastic rubber"; the rebound resilience test is carried out in accordance with GB / T10652-2001C "Determination of elasticity of polymer porous elastic materials"; the above tests are repeated three times and the average value is taken.

[0044] Example 1 The present embodiment first provides an antistatic and easy-to-form polylactic acid foam material, which is prepared by the following preparation method: using a co-extrusion device, 100 parts of polylactic acid, 1 part of talcum powder, 1 part of glycidyl ether, and 5 parts of ADR4468 are added to a main extruder; 100 parts of polybutylene adipate / butylene terephthalate copolymer, 0.5 parts of methyl methacrylate graft, and 5 parts of sodium polystyrene sulfonate are mixed and put into a secondary extruder; wherein the temperatures of the main extruder are set to 140, 150, and 180° C., respectively, and the temperatures of the secondary extruder are set to 120, 140, and 170° C., respectively, and after cooling and pelletizing, polylactic acid composite particles with antistatic properties are obtained; Put the above polylactic acid composite particles into a 500L reactor, add 300L water, put in 700g kaolin, add 2.5kg carbon dioxide gas, stir at 200r, heat to 150℃, pressure to 5MPa, keep warm for 20 minutes, release pressure and discharge to obtain antistatic and easy-to-form polylactic acid foam particles. Screen the material.

[0045] Furthermore, in this embodiment, the polylactic acid foam particles are matured for 7 days to keep the carbon dioxide gas and air inside the particles stable, and are placed in a pressure tank with air pressure of 0.5 MPa for more than 24 hours. They are then injected into a steam compression molding machine, and the surfaces of the polylactic acid composite foam beads are melted and bonded by steam heating, while the inside of the composite foam beads are kept unmelted. The particles are cooled and demolded to obtain an antistatic polylactic acid composite foam product.

[0046] Example 2 This embodiment provides an antistatic and easy-to-form polylactic acid foam material. The only difference from Example 1 is that in this embodiment, during the polylactic acid composite bead foaming step, 2.0 kg of carbon dioxide gas is added to the reactor. The rest is the same as Example 1 and will not be repeated here.

[0047] Example 3 This embodiment provides an antistatic and easy-to-form polylactic acid foam material. The only difference from Example 1 is that in the polylactic acid composite bead foaming step, the stirring speed of this embodiment is 250r. The rest is the same as Example 1 and will not be repeated here.

[0048] Example 4 This embodiment provides an antistatic and easy-to-form polylactic acid foam material. The only difference from Example 1 is that in the polylactic acid composite bead foaming step, the insulation time is 30 minutes. The rest is the same as Example 1 and will not be repeated here.

[0049] Example 5 This embodiment provides an antistatic and easily moldable polylactic acid foam material, which is different from Embodiment 1 only in that 2 parts of talc are used in the preparation process of this embodiment, and the rest is the same as Embodiment 1, which will not be described again.

[0050] Example 6 This embodiment provides an antistatic and easily moldable polylactic acid foam material. The only difference from Embodiment 1 is that kaolin is not added during the preparation process of this embodiment. The rest is the same as Embodiment 1 and will not be described again.

[0051] Comparative Example 1 This comparative example provides a polylactic acid foam material, which is different from Example 1 only in that ADR4468 is not added in this comparative example, and the rest is the same as Example 1, which will not be repeated here.

[0052] Comparative Example 2 This comparative example provides a polylactic acid foam material, which is different from Example 1 only in that sodium polystyrene sulfonate is not added in this comparative example, and the rest is the same as Example 1, which will not be repeated here.

[0053] Comparative Example 3 This comparative example provides a polylactic acid foam material, which is different from Example 1 only in that no compatibilizer is added in this comparative example, and the rest is the same as Example 1, which will not be described again.

[0054] Comparative Example 4 This comparative example provides a polylactic acid foam material, which is different from Example 1 only in that in the polylactic acid composite bead foaming step, the heat preservation time is 10 minutes, and the rest is the same as Example 1, which will not be repeated here.

[0055] The inventors tested the properties of the polylactic acid foam materials obtained in Example 1, Example 2, Example 5 and Comparative Examples 1-3. The test results are shown in Table 1: Furthermore, the inventor observed the polylactic acid foam material obtained in Example 1, and the results were as follows: Figure 1 and Figure 2 As shown, Figure 1 This is a SEM image of a sample of the polylactic acid foam material after molding obtained in Example 1 of the present invention; Figure 2 This is a cross-sectional view of the polylactic acid composite foamed beads prepared in Example 1 of the present invention.

[0056] It can be seen from the above results that the polylactic acid foam material prepared by the raw materials and preparation process of the present invention has a stable pore size, good particle resilience, and excellent antistatic and mechanical properties, and the molded device has good mechanical properties.

[0057] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. An antistatic and easily moldable polylactic acid foam material, characterized in that: The polylactic acid foam material is made of polylactic acid composite particles, and the polylactic acid composite particles include a coating layer and an inner core. In terms of mass percentage, the mass proportion of the coating layer is 3-20%, and the remainder is the inner core.

2. The polylactic acid foam material according to claim 1, characterized in that: The raw materials of the coating layer include the following components in parts by weight: 88-98 parts of biodegradable elastic polyester, 2-12 parts of antistatic agent, 0.5-3 parts of compatibilizer, and 0.5-2 parts of anti-hydrolysis agent; the raw materials of the inner core include the following components in parts by weight: 100 parts of polylactic acid, 1-3 parts of nucleating agent, 0.5-2 parts of antioxidant, 1-4 parts of anti-hydrolysis agent, and 5-10 parts of chain extender.

3. The polylactic acid foam material according to claim 1, characterized in that: The melting point of the cladding layer is lower than the melting point of the inner core.

4. The polylactic acid foam material according to claim 2, characterized in that: The material of the biodegradable elastic polyester is selected from one or more of polybutylene adipate / terephthalate, polybutylene succinate, polybutylene succinate, and polybutylene adipate; And / or, the antistatic agent is selected from one or more of polyethylene oxide, polyether ester amide, polyether ester imide, quaternary ammonium salt methacrylic acid copolymer, and sodium polystyrene sulfonate.

5. The polylactic acid foam material according to claim 2, characterized in that: The compatibilizer is selected from one or more of methyl methacrylate glycerol grafts, ethylene methyl acrylate copolymers, ethylene methacrylic acid copolymers, ethylene acrylic acid copolymers, ethylene butyl acrylate copolymers, and ethylene glycidyl methacrylate copolymers.

6. The polylactic acid foam material according to claim 2, characterized in that: The polylactic acid is selected from one or more of an L-lactic acid homopolymer, a D-lactic acid homopolymer, and a copolymer of L-lactic acid and D-lactic acid.

7. The polylactic acid foam material according to claim 2, characterized in that: The nucleating agent is selected from one or two of talc, calcium carbonate, silicon dioxide, mica, nanoclay, and kaolin; And / or, the antioxidant is selected from one or more of antioxidant 1010 and antioxidant 168.

8. The polylactic acid foam material according to claim 2, characterized in that: The anti-hydrolysis agent is selected from one or more of epoxy anti-hydrolysis agents, aromatic carbodiimide anti-hydrolysis agents, polycarbodiimide, glycidyl ether, diisopropylbenzene peroxide, and carbodiamine; And / or, the chain extender is selected from one or more of ADR-4468, ADR-4368, glyceryl methacrylate, and (3,4-epoxycycloethyl)methyl methacrylate.

9. A method for preparing a polylactic acid foam material according to any one of claims 1 to 8, characterized in that: The preparation method specifically comprises the following steps: S1. Using a co-extrusion device, the dried biodegradable elastic polyester is mixed with an antistatic agent, an anti-hydrolysis agent, and a compatibilizer and put into an auxiliary extruder, and polylactic acid, a nucleating agent, an antioxidant, an anti-hydrolysis agent, and a chain extender are put into a main device, and co-extruded and pelletized to obtain polylactic acid composite particles; S2. Put the polylactic acid composite particles obtained in step S1 into a high-pressure reactor, add water, the amount of water added is 3 / 5 of the volume of the reactor, turn on stirring, then add a dispersant and a foaming agent, heat to 120-160°C, maintain the pressure at 2-5MPa, and release the pressure instantly after the reaction is completed to obtain an antistatic and easy-to-form polylactic acid foam material.

10. The preparation method according to claim 9, characterized in that: In step S2, the weight proportions of the raw materials are as follows: 100 parts of polylactic acid composite microparticles, 2-10 parts of dispersant, and 5-10 parts of foaming agent; the dispersant is kaolin and / or dimethyl silicone oil, and the foaming agent is carbon dioxide.

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