Composite foaming material with excellent performance and preparation method thereof

Abstract

The invention belongs to the technical field of bio-based polymer composite materials, and particularly discloses a composite foam material with excellent performance and a preparation method thereof. The composite foaming material comprises 80-95 parts of polylactic acid; 5-20 parts of natural rubber; and 1-9 parts of epoxy natural rubber. According to the invention, the epoxy natural rubber is introduced as a reactive compatibilizer by a melt blending method, and an epoxy group of the epoxy natural rubber is mixed and entangled with a polylactic acid terminal hydroxyl group, and an isoprene main chain of the epoxy natural rubber can be mixed and entangled with a non-polar natural rubber chain to form a polylactic acid-epoxy natural rubber-natural rubber chemical bonding interface; by combining with a supercritical CO2 rapid heating foaming process, precise regulation and control of a foam structure are realized, and the green, light-weight, high-tensile-strength and equivalent-toughness composite foam material is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of bio-based polymer composite materials, and particularly relates to a composite foaming material with excellent performance and a preparation method thereof. Background Art

[0002] As a bio-based degradable material, polylactic acid is difficult to prepare a uniform microporous material with a high foaming ratio due to its low melt strength and narrow foaming window. In the prior art, the melt elasticity of polylactic acid can be improved by blending with an elastomer (such as natural rubber), but the significant polarity difference between polylactic acid and natural rubber leads to serious phase separation, resulting in micron-sized cavity defects (pore diameter > 50 μm) after foaming, and the tensile strength decreases by 60%-80%. A compatibilizer can be used to improve this drawback.

[0003] In the article "Research Progress on Compatibilization of Polylactic Acid-based Composites", the compatibilization problem of the polylactic acid and other polymer blending systems was discussed, and relevant information on the current commonly used compatibilization means was provided. However, due to the significant limitations of traditional compatibilizers, the following problems are caused: 1. Although the peroxide crosslinking agent (DCP) can strengthen the rubber phase through free radical crosslinking, the free radicals generated by the decomposition of DCP may cause the main chain of polylactic acid to break or crosslink excessively, resulting in a decrease in molecular weight, poor melt fluidity, and residual toxic by-products; 2. The maleic anhydride grafted product has limited compatibilization effect on the polylactic acid / natural rubber system with large polarity differences, and a complex grafting process is required; 3. Although the multi-epoxy chain extender (such as ADR-4368) can improve the compatibility between polylactic acid and polar polymers, its ability to disperse and control non-polar natural rubber is weak, the foaming performance deteriorates, and the cost is high.

[0004] Therefore, the development of a composite foaming material with low cost, green, lightweight, moderate strength and toughness, and certain hardness can broaden the application range of materials. Summary of the Invention

[0005] The present invention provides a composite foaming material with excellent performance and a preparation method thereof to overcome the problems of decreased molecular weight, poor melt fluidity, residual toxic by-products, complex preparation process, and high cost existing in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a composite foaming material with excellent performance and a preparation method thereof, including the following components and mass ratio:

[0007] Polylactic acid: 80-95 parts

[0008] Natural rubber: 5-20 parts

[0009] Epoxy natural rubber: 1-9 parts.

[0010] Furthermore, the epoxy degree of the above-mentioned epoxy natural rubber is 50%; the melt index of polylactic acid is 6 g / 10 min.

[0011] Furthermore, the above-mentioned includes the following steps:

[0012] Step 1: Dry polylactic acid, natural rubber, and epoxy natural rubber at 70-90 °C for 3-5 hours;

[0013] Step 2: High-temperature mixing of the dried polylactic acid and natural rubber in a mixer. After high-temperature mixing, add epoxy natural rubber and mix again at high temperature, then let it stand for later use; the rotation speed of the mixer is 30-50 rpm, and the time is 5-10 minutes;

[0014] Step 3: Vulcanize;

[0015] Step 4: Place the blend material in a supercritical CO2 foaming device, and keep it under pressure and thermally insulated and saturated for 1-2 hours;

[0016] Step 5: After quickly releasing the pressure, conduct foaming treatment for 10-90 seconds.

[0017] Furthermore, in the above-mentioned Step 2, the high temperature refers to 180-200 °C, the mixing time is 5-10 minutes, and the re-mixing time is 5-8 minutes.

[0018] Furthermore, in the above-mentioned Step 2 and Step 4, the pressure is 8-18 MPa, and the temperature is 35-45 °C.

[0019] Furthermore, in the above-mentioned Step 5, the temperature of the foaming treatment is 160-190 °C, and the time is 10-90 seconds.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] 1. The present invention provides a composite foaming material with excellent performance and its preparation method. Epoxy natural rubber is introduced on the basis of polylactic acid / natural rubber. By the method of melt blending, epoxy natural rubber is introduced as a reactive compatibilizer. Utilize the ring-opening reaction of its epoxy group with the terminal hydroxyl group of polylactic acid, and the isoprene main chain of epoxy natural rubber can entangle with the non-polar natural rubber chain to form a polylactic acid-epoxy natural rubber-natural rubber chemical bonding interface. Combined with the foaming method of supercritical CO2 and using the rapid heating method, precise control of the cell structure is achieved, and a composite foaming material is prepared at a lower pressure. A green, lightweight composite foaming material with high tensile strength and equivalent toughness is prepared. The provided preparation process is simple, has low cost, uniform molecular weight distribution, good melt fluidity, and no toxic by-products will remain.

[0022] 2. The present invention uses epoxidized natural rubber (ENR) with an epoxide degree of 50% as a reactive compatibilizer. Through the ring-opening reaction of its epoxy groups with the terminal hydroxyl groups of polylactic acid (PLA), chemical bonding is formed. At the same time, its isoprene main chain is physically entangled with non-polar natural rubber (NR) to construct a "PLA-ENR-NR" gradient interface, effectively solving the phase separation problem caused by the polarity difference between PLA and NR and significantly enhancing the interfacial bonding strength. A unique supercritical CO2 foaming process of "high-pressure low-temperature saturation - rapid pressure relief - gradient temperature rise" is developed to precisely control the cell size and cell density, breaking through the foaming ratio limit caused by the low melt strength of PLA and significantly reducing the foam density. Using ENR in-situ compatibilization to replace toxic peroxide crosslinking agents eliminates the risk of free radical degradation and does not require complex grafting processes, realizing the green preparation of materials. The composite foamed material prepared by the preparation method of the present invention has an average cell size increased from 2.3 μm to 6.2 μm, and the cell density decreased from 19×10 11 cells / cm 3 to 0.834×10 11 cells / cm 3 , with uniform size and thinner cell walls; the foam density is reduced to 0.432 g / cm 3 , the elongation at break is increased to 141.7±18%, and the hardness is reduced to 64 Shore A. The prepared material has excellent toughness and low density while maintaining relatively high strength.

[0023] 3. The composite foamed material provided by the present invention significantly improves the compatibility and cell structure of the polylactic acid / natural rubber system through the synergistic effect of interfacial chemical bonding and supercritical foaming process. The obtained material realizes lightweight while maintaining high rigidity and high toughness, achieving a balance of strength, toughness and density, and is suitable for fields with high requirements for lightweight, environmental protection and mechanical properties such as automotive interiors and medical packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a scanning electron microscope photograph of the epoxidized natural rubber compatibilized polylactic acid / natural rubber composite foamed material provided in Example 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0026] Among the raw materials used in the present invention, the epoxide degree of the epoxidized natural rubber is 50%; the melt index of the polylactic acid is 6 g / 10 min, 210 °C / 2.16 kg.

[0027] Example 1. A preparation method of a composite foamed material with excellent properties, including the following steps by mass fraction:

[0028] Step 1: Mix 90 parts of polylactic acid and 10 parts of natural rubber in a mixer at high temperature. After mixing for 7 minutes at 180 °C, add 1 part of epoxidized natural rubber, mix for another 5 minutes, and then let it stand for 24 hours for later use.

[0029] Step 2: Place the composite material from Step 1 in a 40 mm × 40 mm × 2 mm mold, and use a flat vulcanizer to hot-press it at 180 °C for 5 minutes to make a regular thin sheet for later use.

[0030] Step 3: Cut the thin sheet prepared in Step 2 into 40 mm × 10 mm × 2 mm splines with a cutter.

[0031] Step 4: Place the splines prepared in Step 3 in a supercritical foaming autoclave, evacuate the air in the autoclave, set the temperature to 40 °C, fill the autoclave with carbon dioxide gas to the specified pressure of 16 MPa, and hold the pressure for 1 h.

[0032] Step 5: Quickly release the pressure in the autoclave at the specified time, and immediately transfer it to an oven at 180 °C, place it for 10 seconds and then take it out to obtain the composite foamed material.

[0033] Example 2, different from Example 1 in that: the amount of epoxidized natural rubber added in Step 1 is 5 parts.

[0034] Example 3, different from Example 1 in that: in Step 1, it is 80 parts of polylactic acid, 20 parts of natural rubber and 3 parts of epoxidized natural rubber.

[0035] The average cell size of the polylactic acid - ENR - natural rubber composite foamed material prepared in Example 3 increased from 2.3 μm to 4.3 μm, the cell density decreased from 19×10 11 cells / cm 3 to 13×10 11 cel ls / cm 3 , the size is uniform, and the cell wall becomes thinner; the foam density drops to 0.493 g / cm 3 , the elongation at break increases to 112.7 ± 18%, and the hardness drops to 66 Shore A.

[0036] Example 4, different from Example 1 in that: in Step 1, it is 95 parts of polylactic acid, 5 parts of natural rubber and 1 part of epoxidized natural rubber.

[0037] Example 5, different from Example 1 in that: in Step 1, it is 85 parts of polylactic acid, 15 parts of natural rubber and 9 parts of epoxidized natural rubber.

[0038] Examples 1-5 were tested. The test plan was to observe the cell microstructure using a scanning electron microscope (SEM) to measure the cell size and evaluate the size uniformity and cell wall thickness. The cell density was calculated using a formula, the foam density was measured using the Archimedes drainage method, the elongation at break was tested using a universal material testing machine, and the hardness was determined using a Shore hardness tester. The results showed that Example 2 was the best example, with an average cell size of 6.2 μm, a cell density of 0.834×10 cells / cm 3 , and at the same time, the size was uniform and the cell wall was thin; the foam density was 0.432 g / cm 3 , the elongation at break was 141.7±18%, and the hardness was 64 Shore A.

[0039] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A composite foam material with excellent performance, characterized in that: It includes the following components and mass proportions: Polylactic acid: 80-95 parts Natural rubber: 5-20 parts Epoxy natural rubber: 1-9 parts.

2. The composite foam material with excellent performance according to claim 1, characterized in that: The epoxy degree of the epoxy natural rubber is 50%; The melt index of the polylactic acid is 6 g / 10 min, 210° C. / 2.16 kg.

3. The method for preparing a composite foam material with excellent performance according to claim 1, characterized in that: The following steps are involved: Step 1, drying the polylactic acid, natural rubber and epoxy natural rubber at 70-90° C. for 3-5 hours; Step 2, the dried polylactic acid and natural rubber are mixed at high temperature in an internal mixer, and after mixing at high temperature, epoxy natural rubber is added, mixed again at high temperature, and allowed to stand for use; the speed of the internal mixer is 30-50 rpm, and the time is 5-10 minutes; Step 3: vulcanization; Step 4: Place the blended material in a supercritical CO2 foaming device and soak it for 1-2 hours under pressure and heat preservation; Step 5: After rapid pressure relief, perform foaming treatment for 10-90 seconds.

4. The method for preparing a composite foam material with excellent performance according to claim 3, characterized in that: In the step 2, the high temperature refers to 180-200° C., the mixing time is 5-10 minutes, and the re-mixing time is 5-8 minutes.

5. The method for preparing a composite foam material with excellent performance according to claim 3, characterized in that: In the step 2 and step 4, the pressure is 8-18 MPa and the temperature is 35-45°C.

6. The method for preparing a composite foam material with excellent performance according to claim 3, characterized in that: In the step 5, the temperature of the foaming treatment is 160-190° C., and the time is 10-90 seconds.

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