A thermoplastic elastomer with shape memory properties and its preparation method

Abstract

This invention provides a thermoplastic elastomer with shape memory properties and its preparation method, belonging to the field of polymer materials technology. This invention utilizes a diunsaturated carboxylic acid and a metal additive. One molecule of maleic acid contains two carboxylic acid molecules that can react in situ with the metal additive to generate an unsaturated carboxylate. After graft polymerization, the resulting unsaturated carboxylate polymer exhibits stronger intermolecular ionic interactions, improving material performance. Under the action of a vulcanizing agent, the unsaturated carboxylate undergoes polymerization and grafting reactions between the molecular chains of EPDM rubber and polypropylene. The decomposition of the vulcanizing agent generates free radicals that initiate the polymerization of the unsaturated carboxylate. Simultaneously, these free radicals abstract hydrogen from the molecular chains of EPDM rubber and polypropylene, generating high-molecular-weight free radicals. This allows the unsaturated carboxylate to graft onto the molecular chains of EPDM rubber and polypropylene, enhancing the shape memory properties of the thermoplastic elastomer.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a thermoplastic elastomer with shape memory properties and its preparation method. Background Technology

[0002] Shape memory materials are materials that can respond to external stimuli, changing their shape when one or more external stimuli are applied. These stimuli include heat, light, electricity, magnetic fields, and solvents, and the corresponding materials are called thermotropic, phototropic, and electrotropic shape memory materials, respectively. In the deformation process, the material first deforms under external force and is fixed in a temporary shape. Subsequently, the material recovers its permanent shape under external stimulation. Shape memory materials include metallic materials, ceramic materials, and polymer materials, among which shape memory polymer materials have advantages such as low density, low cost, excellent deformability, and deformation recovery ability. Currently, shape memory polymer materials are widely used in heat shrink tubing in the cable industry, heat shrink film or labels in the packaging industry, and heat shrink toys. Shape memory polymer materials are expected to be applied in a wider range of fields such as biomedicine, aerospace components, and soft robotics.

[0003] There are various methods for preparing shape memory materials using polymers, including block copolymers, interpenetrating polymer networks, cross-linked polymers, and supramolecular polymer networks. Most of the materials listed above have fully cross-linked structures, limiting their reprocessing and reuse properties. Thermoplastic elastomers prepared by dynamic vulcanization generally possess a "sea-island" microstructure, exhibiting reprocessing potential; however, unmodified dynamically vulcanized thermoplastic elastomers exhibit poor shape memory properties.

[0004] Existing technologies disclose the in-situ reaction of adding methacrylic acid, acrylic acid and metal oxides to generate unsaturated carboxylates. The product of unsaturated carboxylates under the action of vulcanizing agents can improve the shape memory properties of thermoplastic elastomers, but the problem of poor shape memory properties of the resulting thermoplastic elastomers still exists. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a thermoplastic elastomer with shape memory properties and a method for preparing the same. The thermoplastic elastomer provided by the present invention has excellent shape memory properties.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a thermoplastic elastomer with shape memory properties, which is made from raw materials comprising the following parts by weight:

[0008] EPDM rubber: 40-80 parts, polypropylene: 20-60 parts, vulcanizing agent: 0.2-2.5 parts, diunsaturated carboxylic acid: 1.2-20 parts, metal additives: 0.4-8 parts, wherein the metal additives include metal oxides and / or metal hydroxides.

[0009] Preferably, the diunsaturated carboxylic acid is maleic acid.

[0010] Preferably, the metal element in the metal additive includes magnesium or zinc.

[0011] Preferably, the vulcanizing agent comprises dicumyl peroxide.

[0012] Preferably, the thermoplastic elastomer with shape memory properties is made from raw materials comprising the following parts by weight:

[0013] EPDM rubber: 50-70 parts, polypropylene: 30-50 parts, vulcanizing agent: 0.5-1.8 parts, diunsaturated carboxylic acid: 1.855-11.13 parts, metal additives: 0.645-3.87 parts.

[0014] Preferably, the thermoplastic elastomer with shape memory properties is made from raw materials comprising the following parts by weight:

[0015] EPDM rubber: 40-60 parts, polypropylene: 40-60 parts, vulcanizing agent: 0.6-0.7 parts, diunsaturated carboxylic acid: 2.597-8.904 parts, metal additives: 0.774-3.096 parts.

[0016] This invention also provides a method for preparing the thermoplastic elastomer with shape memory properties described in the above technical solution, comprising the following steps:

[0017] EPDM rubber, diunsaturated carboxylic acid and metal additives are mixed and reacted in situ to obtain EPDM rubber-unsaturated carboxylic acid mixture.

[0018] The EPDM-unsaturated carboxylate mixture, polypropylene, and vulcanizing agent are mixed and dynamically vulcanized to obtain the thermoplastic elastomer with shape memory properties.

[0019] Preferably, the in-situ reaction is carried out at a temperature of 130–140°C for a time of 10–30 min.

[0020] Preferably, the dynamic vulcanization temperature is 160–175°C and the time is 3–10 min.

[0021] Preferably, the dynamic vulcanization is carried out in an internal mixer at a speed of 60-70 rpm.

[0022] This invention provides a thermoplastic elastomer with shape memory properties, which is made from raw materials comprising the following parts by weight: ethylene propylene diene monomer (EPDM) rubber: 40-80 parts, polypropylene: 20-60 parts, vulcanizing agent: 0.2-2.5 parts, diunsaturated carboxylic acid: 1.2-20 parts, and metal additives: 0.4-8 parts, wherein the metal additives include metal oxides and / or metal hydroxides.

[0023] This invention utilizes diunsaturated carboxylic acids and metal additives. One molecule of maleic acid contains two carboxylic acid molecules that can react in situ with the metal additive to form unsaturated carboxylates. After graft polymerization, the resulting unsaturated carboxylate polymer exhibits stronger intermolecular ionic interactions, further improving material performance. Under the action of a vulcanizing agent, the unsaturated carboxylates undergo polymerization and grafting reactions between the molecular chains of EPDM rubber and polypropylene. The decomposition of the vulcanizing agent generates free radicals that initiate the polymerization of the unsaturated carboxylates. Simultaneously, these free radicals abstract hydrogen from the molecular chains of EPDM rubber and polypropylene, producing… The generation of high molecular free radicals allows unsaturated carboxylates to be grafted onto the molecular chains of EPDM rubber and polypropylene, improving the interfacial bonding force and stress transfer efficiency between the rubber and plastic phases, thereby enhancing the shape memory properties of thermoplastic elastomers. Furthermore, maleic acid can not only react with metal additives to generate unsaturated carboxylates, but excess maleic acid can also be dehydrated to generate maleic anhydride. Under the action of vulcanizing agents, maleic anhydride can also be grafted onto the molecular chains of EPDM rubber and polypropylene, further enhancing the interfacial bonding force between the rubber and plastic phases, thereby further improving the shape memory properties of the material.

[0024] Furthermore, the raw materials used in this invention are safe and environmentally friendly, avoiding the problems of severe burns and poor operational safety caused by the use of corrosive substances such as methacrylic acid and acrylic acid. It also avoids the environmental hazards caused by the use of acrylic acid and prevents adverse effects on aquatic organisms.

[0025] Furthermore, the diunsaturated carboxylic acid maleic acid used in this invention has low hazard and toxicity, is more environmentally friendly, and has high operational safety. Moreover, it is a solid particle at room temperature, which makes it more conducive to uniform mixing with EPDM rubber, simplifying the processing technology and improving production efficiency. Attached Figure Description

[0026] Figure 1 This is a scanning electron microscope image of the thermoplastic elastomer prepared in Example 2 after being etched with xylene. Detailed Implementation

[0027] This invention provides a thermoplastic elastomer with shape memory properties, which is made from raw materials comprising the following parts by weight:

[0028] EPDM rubber: 40-80 parts, polypropylene: 20-60 parts, vulcanizing agent: 0.2-2.5 parts, diunsaturated carboxylic acid: 1.2-20 parts, metal additives: 0.4-8 parts, wherein the metal additives include metal oxides and / or metal hydroxides.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0030] The preferred mass fraction of ethylene propylene diene monomer (EPDM) rubber in the raw materials for preparing the thermoplastic elastomer provided by this invention is 50-70 parts, more preferably 40-60 parts. The use of EPDM rubber in this invention can provide the elastic recovery force required for shape memory materials and also improve the elastic properties of the material.

[0031] Based on the mass fraction of EPDM rubber, the mass fraction of polypropylene in the raw materials for preparing the thermoplastic elastomer provided by the present invention is preferably 30-50 parts, more preferably 40-60 parts. The polypropylene used in the present invention can provide the shape retention force required for shape memory materials, improve the rigidity of the material, and the compatibility between polypropylene and EPDM rubber is superior to other resins.

[0032] Based on the mass fraction of the EPDM rubber, the mass fraction of the vulcanizing agent in the raw materials for preparing the thermoplastic elastomer provided by the present invention is preferably 0.5 to 1.8 parts, more preferably 0.6 to 0.7 parts. The vulcanizing agent used in the present invention can cause crosslinking of the EPDM rubber, providing sufficient elastic recovery force for the material's shape recovery. In addition, the vulcanizing agent can initiate polymerization reactions, grafting reactions, and maleic anhydride grafting reactions of unsaturated carboxylates. If too much vulcanizing agent is added, it may cause chain scission of polypropylene under high temperature and high shear, leading to a decrease in the mechanical strength of the material; if too little is added, the degree of crosslinking of the rubber phase will be too low, resulting in a decrease in mechanical properties and shape recovery rate.

[0033] In this invention, the vulcanizing agent preferably includes dicumyl peroxide (DCP).

[0034] Based on the mass fraction of the EPDM rubber, the preferred mass fraction of the diunsaturated carboxylic acid in the raw material for preparing the thermoplastic elastomer provided by this invention is 1.855–11.13 parts, more preferably 2.597–8.904 parts, and most preferably 4.452–6.678 parts. The diunsaturated carboxylic acid used in this invention can react with metal additives to form unsaturated carboxylate salts and undergo a dehydration reaction.

[0035] In this invention, the diunsaturated carboxylic acid is preferably maleic acid.

[0036] Based on the mass fraction of the EPDM rubber, the preferred mass fraction of the metal additive in the raw material for preparing the thermoplastic elastomer provided by this invention is 0.645–3.87 parts, more preferably 0.774–3.096 parts, and most preferably 1.02–2.322 parts. The metal additive used in this invention can react with diunsaturated carboxylic acids to generate unsaturated carboxylates, thereby undergoing polymerization and grafting reactions under the action of a vulcanizing agent.

[0037] In this invention, the metal element in the metal oxide and metal hydroxide preferably includes magnesium or zinc.

[0038] In this invention, the thermoplastic elastomer with shape memory properties is preferably made from raw materials comprising the following parts by weight:

[0039] EPDM rubber: 50-70 parts, polypropylene: 30-50 parts, vulcanizing agent: 0.5-1.8 parts, diunsaturated carboxylic acid: 1.855-11.13 parts, metal additive: 0.645-3.87 parts, more preferably made from raw materials comprising the following parts by weight:

[0040] EPDM rubber: 40-60 parts, polypropylene: 40-60 parts, vulcanizing agent: 0.6-0.7 parts, diunsaturated carboxylic acid: 2.597-8.904 parts, metal additives: 0.774-3.096 parts.

[0041] This invention also provides a method for preparing the thermoplastic elastomer with shape memory properties described in the above technical solution, comprising the following steps:

[0042] EPDM rubber, diunsaturated carboxylic acid and metal additives are mixed and reacted in situ to obtain EPDM rubber-unsaturated carboxylic acid mixture.

[0043] The EPDM-unsaturated carboxylate mixture, polypropylene, and vulcanizing agent are mixed and dynamically vulcanized to obtain the thermoplastic elastomer with shape memory properties.

[0044] This invention involves mixing EPDM rubber, diunsaturated carboxylic acid, and metal additives and reacting them in situ to obtain an EPDM rubber-unsaturated carboxylic acid mixture.

[0045] In this invention, the mixing is preferably carried out in an open mill.

[0046] In this invention, the temperature of the in-situ reaction is preferably 130-140°C, and the time is preferably 10-30 min. During the in-situ reaction, the diunsaturated carboxylic acid and the metal additive react to obtain an unsaturated carboxylate.

[0047] After obtaining the EPDM rubber-unsaturated carboxylate mixture, the present invention mixes the EPDM rubber-unsaturated carboxylate mixture, polypropylene and vulcanizing agent and performs dynamic vulcanization to obtain the thermoplastic elastomer with shape memory properties.

[0048] The present invention preferably involves adding the polypropylene in a mixer, melting it, adding the EPDM-unsaturated carboxylate mixture, and then adding the vulcanizing agent for dynamic vulcanization to obtain the thermoplastic elastomer.

[0049] In this invention, the temperature of the dynamic vulcanization is preferably 160-175°C, more preferably 165°C, and the time is 3-10 min, more preferably 5 min.

[0050] In this invention, the rotational speed of the internal mixer is preferably 60-70 rpm.

[0051] To further illustrate the present invention, the thermoplastic elastomer with shape memory properties and its preparation method provided by the present invention are described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.

[0052] The formulations of the examples and comparative examples are shown in Table 1.

[0053] The preparation methods of Examples 1-10 are as follows:

[0054] (1) Weigh the raw materials according to the amount in Table 1, set the temperature of the open mill to 50°C, mix the EPDM rubber, magnesium oxide and maleic acid evenly on the open mill by cutting the left and right sides and making triangular bags, and then mix at 135°C until the magnesium oxide and maleic acid react completely to prepare a uniform EPDM rubber-unsaturated carboxylate mixture for later use.

[0055] (2) The speed of the internal mixer is set to 60 rpm and the temperature is set to 165℃. After adding the metered polypropylene for 3 minutes, it is completely melted. Then, the EPDM-unsaturated carboxylate mixture is added. After mixing evenly, the vulcanizing agent is added and the mixture is dynamically vulcanized at 165℃ for 5 minutes. The thermoplastic elastomer material is then discharged.

[0056] Comparative Example 1

[0057] (1) Weigh the raw materials according to the amount in Table 1, set the temperature of the open mill to 50°C, mix the EPDM rubber and magnesium oxide evenly on the open mill by cutting the left and right sides and making triangular bags, then add methacrylic acid slowly and mix evenly, then mix until the magnesium oxide and methacrylic acid react completely to form a uniform mixture of EPDM rubber and unsaturated carboxylates for later use.

[0058] (2) The speed of the internal mixer is set to 60 rpm and the temperature is set to 165℃. After adding the metered polypropylene for 3 minutes, it is completely melted. Then, the mixture of EPDM rubber and unsaturated carboxylate is added. After mixing evenly, the vulcanizing agent is added and the mixture is dynamically vulcanized for 5 minutes. The thermoplastic elastomer material is then discharged.

[0059] Comparative Example 2

[0060] (1) Weigh the raw materials according to the amount in Table 1, set the temperature of the open mill to 50°C, mix the EPDM rubber and magnesium oxide evenly on the open mill by cutting the left and right sides and making triangular bags, then add acrylic acid slowly and mix evenly, and then mix until the magnesium oxide and acrylic acid react completely to make a uniform mixture of EPDM rubber and unsaturated carboxylates for later use.

[0061] (2) The speed of the internal mixer is set to 60 rpm and the temperature is set to 165℃. After adding the metered polypropylene for 3 minutes, it is completely melted. Then, the mixture of EPDM rubber and unsaturated carboxylate is added. After mixing evenly, the vulcanizing agent is added and the mixture is dynamically vulcanized for 5 minutes. The thermoplastic elastomer material is then discharged.

[0062] Figure 1 This is a scanning electron microscope image of the thermoplastic elastomer prepared in Example 2 after being etched with xylene.

[0063] Table 1. Examples and Comparative Formulas (parts by mass)

[0064]

[0065] In this invention, the tensile tests in the comparative examples and embodiments were conducted in accordance with GB / T 528-2009. Shape memory performance was measured by the shape retention rate and shape recovery rate of the tested material after the specimen was stretched to 100% deformation. The results are shown in Table 2. The shape retention rate and shape recovery rate are affected by the rubber-to-plastic ratio and the amount of DCP used. In comparative examples 1 and 2, compared to example 2 with the same rubber-to-plastic ratio and DCP amount, the shape retention rate and shape recovery rate are improved. Comparative examples and embodiments are comparable only when the amount of DCP or the rubber-to-plastic ratio is the same. By comparing the embodiments with the comparative examples, it can be concluded that the thermoplastic elastomer material prepared by the present invention has good physical and mechanical properties and shape memory properties. The rubber-to-plastic ratio of Comparative Example 1, Comparative Example 2 and Embodiment 2 is 60 / 40. Under the same rubber-to-plastic ratio, the physical and mechanical properties and shape memory properties of Embodiment 2 are better than those of Comparative Example 1 and Comparative Example 2. It can be seen from the scanning electron microscope image of Embodiment 2 that the microstructure of the thermoplastic elastomer material prepared by the present invention is a "sea-island" structure, and the interfacial contact area between the rubber and plastic phases is increased, reflecting that the rubber and plastic phases have good compatibility, thereby resulting in better material performance.

[0066] Table 2 Performance test results for comparative examples and embodiments

[0067]

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A thermoplastic elastomer with shape memory properties, characterized in that, It is made from raw materials comprising the following parts by weight: EPDM rubber: 50-70 parts, polypropylene: 30-50 parts, vulcanizing agent: 0.5-1.8 parts, diunsaturated carboxylic acid: 1.855-11.13 parts, metal additive: 0.645-3.87 parts, wherein the metal additive is magnesium oxide; The diunsaturated carboxylic acid is maleic acid; The molar ratio of magnesium oxide to maleic acid is 1:1 or 1.48:1; The method for preparing the thermoplastic elastomer with shape memory properties includes the following steps: EPDM rubber, diunsaturated carboxylic acid and metal additives are mixed and reacted in situ to obtain EPDM rubber-unsaturated carboxylic acid mixture. The EPDM-unsaturated carboxylate mixture, polypropylene, and vulcanizing agent are mixed and dynamically vulcanized to obtain the thermoplastic elastomer with shape memory properties.

2. The thermoplastic elastomer with shape memory properties according to claim 1, characterized in that, The vulcanizing agent includes dicumyl peroxide.

3. The thermoplastic elastomer with shape memory properties according to claim 1 or 2, characterized in that, It is made from raw materials comprising the following parts by weight: EPDM rubber: 50-70 parts, polypropylene: 30-50 parts, vulcanizing agent: 0.6-0.7 parts, diunsaturated carboxylic acid: 2.597-8.904 parts, metal additives: 0.774-3.096 parts.

4. The method for preparing the thermoplastic elastomer with shape memory properties according to any one of claims 1 to 3, characterized in that, Includes the following steps: EPDM rubber, diunsaturated carboxylic acid and metal additives are mixed and reacted in situ to obtain EPDM rubber-unsaturated carboxylic acid mixture. The EPDM-unsaturated carboxylate mixture, polypropylene, and vulcanizing agent are mixed and dynamically vulcanized to obtain the thermoplastic elastomer with shape memory properties.

5. The preparation method according to claim 4, characterized in that, The in-situ reaction is carried out at a temperature of 130-140°C for a time of 10-30 minutes.

6. The preparation method according to claim 4, characterized in that, The dynamic vulcanization temperature is 160~175℃, and the time is 3~10min.

7. The preparation method according to claim 4 or 6, characterized in that, The dynamic vulcanization is carried out in an internal mixer at a speed of 60-70 rpm.

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