A high-ratio foaming material and preparation method thereof

Abstract

The present invention relates to a high-ratio foaming material and a preparation method thereof, comprising the following raw material components by weight: 90-100 parts of polylactic acid resin, 1-3 parts of glyceryl monostearate, 5-15 parts of a novel anti-shrinkage agent and 10-20 parts of a physical foaming agent; the physical foaming agent comprises a mixture of carbon dioxide and alkanes, and the ratio of the weight of the alkanes to the total weight of the physical foaming agent is greater than or equal to 0.2. The present invention adopts a mixing method of carbon dioxide and alkanes to prepare a physical foaming agent, which greatly reduces the shrinkage rate of the foaming product while increasing the foaming ratio of the foaming product.

Description

Technical Field

[0001] The invention relates to the technical field of polymer foaming, and in particular to a high-ratio foaming material and a preparation method thereof. Background Art

[0002] In recent years, degradable plastics have attracted more and more attention from industrialists and researchers. Among them, polylactic acid (PLA) is a thermoplastic aliphatic polyester prepared by chemical synthesis using renewable plant resources through ring-opening polymerization and direct polycondensation. It can be completely converted into water and carbon dioxide by composting under the action of microorganisms, water, acid, alkali, etc., or degraded into lactic acid under the action of specific enzymes, without polluting the environment. And because of its biocompatibility and excellent mechanical processing properties, it is widely used in construction, transportation, automobiles, aerospace and other fields, and is considered to be the most environmentally friendly polymer material with the most industrial prospects.

[0003] Since PLA has good processing and mechanical properties, if it is prepared into a lightweight foam material, it will have good thermal insulation, sound absorption and cushioning properties, and is a potential substitute for traditional petroleum-based polymer foams (e.g., polystyrene foam, polyurethane foam).

[0004] At present, most PLA foaming technologies are committed to improving the foaming properties of PLA, including blending method, chain extension method, filling method, etc. For example, a Chinese patent document discloses a fully biodegradable heat-resistant polylactic acid foaming material and its preparation method (application number 201510728879.6), which is prepared by mixing polylactic acid with a chain extender, a nucleating agent and a foaming aid. This foaming material can realize continuous foaming technology and has the advantage of uniform cell size.

[0005] However, current PLA foaming materials often face the problem of foam shrinkage while achieving high magnification. The reason is that after the foaming of PLA is completed, it will undergo an aging process, that is, the exchange process between the foaming agent and the air in the pores. If the rate at which the foaming agent diffuses out of the foam is faster than the rate at which the air enters the foam, the pressure difference inside and outside the foam will cause the PLA foaming material to shrink and deform severely. For example, in the academic literature "Cellular Polymers, 2007 (26): 83-115)", CO2 was used as a foaming agent to prepare 50-60 times PLA foam, but the shape and size of the PLA foam shrank severely during the aging stage, and its volume shrank by more than 20% within 8 hours of aging. Although CO2 is currently the most promising green and environmentally friendly foaming agent, it is easy to prepare high-magnification PLA foam using CO2 as a physical foaming agent, but it is also accompanied by severe shrinkage of the foamed product. Summary of the invention

[0006] The technical problem to be solved by the present invention is: the present invention provides a high-ratio foaming material and a preparation method thereof, which can reduce the shrinkage rate of the foaming product while ensuring that the foaming agent has a high foaming rate.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] In a first aspect, an embodiment of the present invention provides a high-ratio foaming material, comprising the following raw material components in parts by weight:

[0009] 90-100 parts of polylactic acid resin, 1-3 parts of glyceryl monostearate, 5-15 parts of new anti-shrinkage agent and 10-20 parts of physical foaming agent;

[0010] The physical foaming agent comprises a mixture of carbon dioxide and alkanes, and the ratio of the weight of the alkanes to the total weight of the physical foaming agent is greater than or equal to 0.2.

[0011] The invention proposes a high-multiplication foaming material, which uses carbon dioxide and alkanes as physical foaming agents. After foaming, since the diffusion rate of CO2 out of the foam is much greater than the diffusion rate of alkanes out of the foam, the foaming agent fraction in the polylactic acid foam will change continuously, resulting in the gas in the foaming material being gradually dominated by alkanes; and as long as the weight proportion of alkanes in the physical foaming agent exceeds 20%, sufficient gas pressure can be guaranteed to maintain the dimensional stability of the foaming material.

[0012] Optionally, the ratio of the weight of the alkane to the total weight of the physical foaming agent is 0.2 to 0.4.

[0013] Optionally, the alkane is n-butane, isobutane or pentane.

[0014] Optionally, the novel anti-shrinkage agent is polybutylene succinate or linear low-density polyethylene.

[0015] According to the above description, the present invention also introduces low melt strength polymer as a novel antishrinkage agent. That is, polybutylene succinate or linear low density polyethylene is added in order to utilize its weak point of having poorer melt strength (the melt strength of PBS is usually at least one order of magnitude lower than that of PLA) compared to PLA. Therefore, in the present application, we add a small amount of novel antishrinkage agent polybutylene succinate or linear low density polyethylene in PLA, and the presence (low melt strength) of polybutylene succinate or linear low density polyethylene can make part of the cell wall form an open cell structure, so that the open cell ratio of the final foamed product is maintained at 10%-20%. By introducing a small amount of open cell structure in the foamed product, it can be conducive to the exchange of foaming agent and air, so that the foamed product has better dimensional stability.

[0016] Optionally, the physical foaming agent is 10-15 parts.

[0017] Optionally, the glyceryl monostearate is 1-2 parts.

[0018] Optionally, the novel anti-shrinkage agent is 5-15 parts.

[0019] In a second aspect, an embodiment of the present invention provides a method for preparing a high-ratio foaming material, comprising the following steps:

[0020] Polylactic acid resin, glyceryl monostearate, a novel anti-shrinkage agent and a physical foaming agent are melted and mixed to form a homogeneous solution, and the homogeneous solution is sequentially extruded, cooled, stretched and curled to obtain a high-ratio foaming material.

[0021] The polylactic acid resin, glyceryl monostearate, novel anti-shrinkage agent and physical foaming agent are melted and mixed in an extrusion foaming machine.

[0022] Among them, the technical effect corresponding to the preparation method of a high-ratio foaming material provided in the second aspect refers to the relevant description of a high-ratio foaming material provided in the first aspect. DETAILED DESCRIPTION

[0023] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods.

[0024] In order to better understand the above technical scheme, exemplary embodiments of the present invention will be described in more detail below. It should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a clearer and more thorough understanding of the present invention, and to be able to fully convey the scope of the present invention to those skilled in the art.

[0025] A high-ratio foaming material in the present invention comprises the following raw material components in parts by weight:

[0026] 90-100 parts of polylactic acid resin, 1-3 parts of glyceryl monostearate, 5-15 parts of polybutylene succinate or linear low-density polyethylene and 10-20 parts of physical foaming agent;

[0027] The physical foaming agent comprises a mixture of carbon dioxide and alkanes, wherein the ratio of the weight of the alkanes to the total weight of the physical foaming agent is greater than or equal to 0.2. Optionally, the alkanes are n-butane, isobutane or pentane.

[0028] The specific preparation method of the above-mentioned high-ratio foaming material comprises the following steps:

[0029] After polylactic acid resin, glyceryl monostearate, a new anti-shrinkage agent and a physical foaming agent are melted and mixed in an extrusion foaming machine to form a homogeneous solution, the homogeneous solution is sequentially extruded, cooled, stretched and curled to obtain a high-ratio foaming material.

[0030] Example 1

[0031] A polylactic acid foam material comprises the following raw material components in parts by weight:

[0032] 100 parts of polylactic acid resin, 2 parts of glyceryl monostearate, 10 parts of polybutylene succinate and 10 parts of physical foaming agent; wherein the physical foaming agent is a mixture of 8 parts of carbon dioxide and 2 parts of isobutane, and the ratio of the weight of the alkane to the total weight of the physical foaming agent is 0.2.

[0033] It is prepared by the following method:

[0034] Polylactic acid resin, glyceryl monostearate, a new anti-shrinkage agent and a physical foaming agent are added to an extrusion foaming machine. After melt mixing, the foaming agent dissolves and diffuses, a polymer / foaming agent homogeneous solution is formed, and the homogeneous solution is sequentially extruded, cooled, stretched and curled to obtain a high-ratio foaming material.

[0035] Example 2

[0036] The difference between this embodiment and the first embodiment is that the addition amount of each component is different.

[0037] A polylactic acid foam material, comprising the following components in parts by weight:

[0038] 100 parts of polylactic acid resin, 1.5 parts of glyceryl monostearate, 12 parts of polybutylene succinate and 12 parts of physical foaming agent; wherein the physical foaming agent is a mixture of 9 parts of carbon dioxide, 1 part of normal butane and 2 parts of isobutane, and the ratio of the weight of the alkane to the total weight of the physical foaming agent is 0.25.

[0039] Example 3

[0040] The difference between this embodiment and the first embodiment is that the addition amount of each component is different.

[0041] A polylactic acid foam material comprises the following raw material components in parts by weight:

[0042] 100 parts of polylactic acid resin, 2 parts of glyceryl monostearate, 10 parts of polybutylene succinate and 10 parts of physical foaming agent; wherein the physical foaming agent is a mixture of 9 parts of carbon dioxide and 1 part of isobutane, and the ratio of the weight of the alkane to the total weight of the physical foaming agent is 0.1.

[0043] Although the polylactic acid foam material obtained in Example 3 is prepared using a (CO2+alkane) physical foaming agent, due to the small proportion of alkanes, the foamed product will encounter a shrinkage problem (ie, the ratio continues to decrease over time).

[0044] Comparative Example 1

[0045] A polylactic acid foam material comprises the following raw material components in parts by weight:

[0046] 100 parts of polylactic acid resin, 2 parts of glyceryl monostearate, 10 parts of polybutylene succinate and 10 parts of CO2 foaming agent.

[0047] The preparation method is the same as that of Example 1.

[0048] Ratio test method: Density of foamed sample (ρ f ) is obtained through the density component test provided by Mettler-Toledo, and the test standard is ASTM D792-00. The foaming ratio of the foamed product (R v ) is the density of the unfoamed sample (ρ0) and the density of the foamed product (ρ f ), that is, R v =ρ0 / ρ f .

[0049] The foaming ratios of the polylactic acid foam materials of Examples 1-3 and Comparative Example 1 at different placement times are shown in Table 1.

[0050] Table 1

[0051]

[0052] From the results in Table 1, it can be seen that with the increase in the weight proportion of alkanes, the foaming ratio of the polylactic acid foam material is improved. When the weight proportion of alkanes reaches 10%, the foaming ratio can reach 58 times in 10 minutes, but with the increase of time, the foaming volume of the polylactic acid foam material shrinks; when the weight proportion of alkanes reaches 20%, the foaming ratio reaches more than 57 times, and the foaming volume of the polylactic acid foam material does not shrink; when the weight proportion of alkanes reaches 25%, the foaming ratio reaches more than 60 times, and the foaming volume of the polylactic acid foam material does not shrink. When the foaming agent only does not contain alkanes, the foaming ratio can reach 56 times in 10 minutes, but with the increase of time, the foaming volume of the polylactic acid foam material shrinks significantly.

[0053] Therefore, according to the above experimental results, when alkanes are added to the physical foaming agent, the foaming ratio of the polylactic acid foam material can be increased and the shrinkage rate can be reduced. As the proportion of alkanes increases, the foaming ratio of the polylactic acid foam material is further increased, while the shrinkage decreases or even does not exist.

[0054] The present invention adopts the introduction of alkane to replace a part of CO2, and prepares a polylactic acid foam product with good dimensional stability by using a CO2+alkane mixed foaming agent. Due to the addition of polybutylene succinate, a small amount of open-cell structure is introduced into the polylactic acid foam material, the exchange process of the CO2+alkane mixed foaming agent and air can be more rapid, the foaming agent and air can freely pass through the open-cell part, and the diffusion rate is good, thereby more significantly improving the dimensional stability of the polylactic acid foam material. For the closed-cell part in the polylactic acid foam material, only a small amount of alkane is needed to maintain the pressure in the foam, ensuring that the product has excellent dimensional stability, that is, the ratio of the weight of the alkane to the total weight of the physical foaming agent only needs to reach 0.2, so that the shrinkage problem of the polylactic acid foam material can be avoided.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-ratio foaming material, characterized in that: It includes the following raw material components by weight: 90-100 parts of polylactic acid resin, 1-3 parts of glyceryl monostearate, 5-15 parts of new anti-shrinkage agent and 10-20 parts of physical foaming agent; The physical foaming agent comprises a mixture of carbon dioxide and alkanes, wherein the weight ratio of the alkanes to the total weight of the physical foaming agent is 0.2 to 0.4; The alkane is n-butane, isobutane or pentane; The novel anti-shrinkage agent is polybutylene succinate or linear low-density polyethylene.

2. A high-ratio foaming material according to claim 1, characterized in that: The physical foaming agent is 10-15 parts.

3. A high-ratio foaming material according to claim 1, characterized in that: The glyceryl monostearate is 1-2 parts.

4. A method for preparing a high-ratio foaming material as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Polylactic acid resin, glyceryl monostearate, a novel anti-shrinkage agent and a physical foaming agent are melted and mixed to form a homogeneous solution, and the homogeneous solution is sequentially extruded, cooled, stretched and curled to obtain a high-ratio foaming material.

5. The method for preparing a high-ratio foaming material according to claim 4, characterized in that: The polylactic acid resin, glyceryl monostearate, novel anti-shrinkage agent and physical foaming agent are melted and mixed in an extrusion foaming machine.

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