Preparation method of self-repairing elastomer

Abstract

The invention belongs to the technical field of rubber macromolecules, and particularly relates to a preparation method of a self-repairing elastomer. The preparation method comprises the following steps: hydrolyzing vegetable oil to obtain unsaturated fatty acid, converting the unsaturated fatty acid into unsaturated fatty acid containing a polysulfide bond by adopting a common vulcanization system, then co-vulcanizing the unsaturated fatty acid containing the polysulfide bond and unsaturated rubber, and controlling the vulcanization degree to obtain the self-repairing elastomer. According to the preparation method, the raw materials are wide in source and low in cost, toxic and volatile solvents are not used, and the room-temperature self-repairing performance of the prepared self-repairing elastomer is excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of rubber polymers, and particularly relates to a preparation method of a self-healing elastomer. Background Art

[0002] Rubber has excellent resilience, insulation, cold resistance and chemical corrosion resistance, so it is widely used. Rubber must be chemically vulcanized before use, and chemical vulcanization ensures its dimensional stability and sufficient mechanical properties during use. However, once chemically vulcanized rubber is damaged, it is difficult to repair and has to be scrapped, resulting in waste. In recent years, self-healing elastomers have received more and more research and practical applications. A self-healing elastomer is a type of elastomeric material that can autonomously repair its structure and function through physical or chemical mechanisms after being damaged. This type of material combines the high elasticity of rubber with the self-healing property and has broad application prospects in the fields of flexible electronics, soft robotics, biomedicine, intelligent coatings, etc.

[0003] The repair mechanism of self-healing elastomers mainly achieves repair through dynamic reversible covalent bonds and / or supramolecular interactions inside the material. Dynamic covalent bonds such as Diels-Alder reaction, polysulfide bonds, imine bonds, borate ester bonds, etc. can trigger the reversible cleavage and recombination of bonds by applying pressure, heating, light irradiation or pH change. Supramolecular interactions mainly include hydrogen bonds, electrostatic interactions, metal coordination, chelation, etc., and rely on the reversible recombination of these non-covalent interactions to achieve the self-healing of the material. To sum up, the self-healing function is achieved through the reversible cleavage and reconstruction of weak bonds in the material, so self-healing materials will inevitably sacrifice some mechanical properties, such as a decrease in mechanical strength. Therefore, researchers usually combine multiple self-healing mechanisms together, hoping to achieve self-healing without sacrificing mechanical properties.

[0004] The electrostatic interaction and metal coordination / chelation of ionic groups are reversible and are important self-healing pathways. Unsaturated fatty acid molecules have both unsaturated bonds and ionizable groups. If the metal salt of unsaturated fatty acid is introduced into the rubber molecular chain, the electrostatic interaction and metal coordination / chelation of ionic groups can be generated between rubber chains, thereby generating self-healing function. However, the reaction probability of unsaturated fatty acid in the co-vulcanization reaction with rubber is very low.

[0005] The polysulfide bonds in the rubber crosslinking network are reversible weak bonds, which are an important way to achieve self-healing. The vulcanization process of rubber is very complex, forming various chemical bonds between rubber chains, and the relative proportions of these chemical bonds change significantly with the vulcanization process. In the first half of vulcanization, inter-chain polysulfide bonds predominate. However, as the vulcanization time prolongs, the polysulfide bonds become fewer and fewer, while the inter-chain carbon-carbon bonds and monosulfide bonds become more and more. Eventually, the polysulfide bonds disappear and all form carbon-carbon bonds and monosulfide bonds. Therefore, if the vulcanization time is controlled so that vulcanization is terminated at the stage when polysulfide bonds mainly exist in the system, then the crosslinking network of the resulting elastomer mainly consists of polysulfide bonds, and the self-healing function can be achieved by virtue of the reversible characteristics of polysulfide bonds while retaining good mechanical properties.

[0006] In the existing technologies for preparing self-healing elastomers, in some methods, volatile organic solvents with certain toxicity or raw materials with certain toxicity are used, which does not conform to the concept of green synthesis. Summary of the Invention

[0007] The present invention provides a method for preparing a self-healing elastomer. First, polysulfide bonds are introduced into unsaturated fatty acid molecules derived from vegetable oil to obtain unsaturated fatty acids containing polysulfide bonds. Then, the unsaturated fatty acids containing polysulfide bonds are mixed and co-vulcanized with unsaturated rubber and a vulcanization system to obtain a self-healing elastomer. The polysulfide bonds and ionic groups on the network of the resulting self-healing elastomer both have dynamic reversible destruction-reconstruction functions, enabling the resulting self-healing elastomer to have excellent self-healing functions.

[0008] To achieve the above invention objectives, the present invention adopts the following technical solutions:

[0009] A method for preparing a self-healing elastomer, characterized in that the preparation method comprises the following steps:

[0010] S1: Mix vegetable oil and concentrated NaOH aqueous solution in a reactor, stir at 80 °C for 4 h to completely hydrolyze the vegetable oil; then pour an HCl aqueous solution with an amount 10% in excess of the equivalent of the used NaOH into the reactor, and stir vigorously at 50 °C for 1 h to ensure that the oil phase is fully acidified; then pour the product into a separatory funnel, let it stand for stratification, drain the lower aqueous phase, and retain the oil phase; then wash the oil phase with a large amount of deionized water multiple times to completely remove the excess HCl, electrolytes, and other impurities in the oil phase to obtain unsaturated fatty acids;

[0011] S2: Put the unsaturated fatty acids obtained in S1, sulfur, ZnO, and tetramethylthiuram disulfide into the reactor, protect with nitrogen, continuously stir, and react at 100-150 °C for 1-6 h to obtain unsaturated fatty acids containing polysulfide bonds;

[0012] S3: Knead the matrix rubber on a kneader at room temperature, successively add sulfur, ZnO, tetramethylthiuram disulfide, and unsaturated fatty acids containing polysulfide bonds, thin pass six times and then make a triangular package and cut into sheets to obtain a mixed rubber; vulcanize and shape the mixed rubber, vulcanize at 110-150 °C, and the vulcanization time is 1 / 2 of the optimum vulcanization time determined by a vulcameter to obtain a self-healing elastomer.

[0013] Further, according to the preparation method of a self-healing elastomer described in claim 1, it is characterized in that, in step S1, the vegetable oil is one or more of sunflower oil, corn oil, olive oil, soybean oil, and peanut oil.

[0014] Further, according to the preparation method of a self-healing elastomer described in claim 1, it is characterized in that, in step S2, the mass ratio of ZnO to the unsaturated fatty acid is 1:50-1:25; the mass ratio of tetramethylthiuram disulfide to the unsaturated fatty acid is 1:50-1:25; the mass ratio of sulfur to the unsaturated fatty acid is 1:50-1:25.

[0015] Further, according to the preparation method of a self-healing elastomer described in claim 1, it is characterized in that, in step S3, the matrix rubber is one or more of natural rubber, isoprene rubber, cis-butadiene rubber, styrene-butadiene rubber, and nitrile rubber.

[0016] Further, according to the preparation method of a self-healing elastomer described in claim 1, it is characterized in that, in step S3, the mass ratio of the unsaturated fatty acid containing polysulfide bonds to the matrix rubber is 1:8-1:3; the mass ratio of ZnO to the matrix rubber is 1:50-1:30; the mass ratio of tetramethylthiuram disulfide to the matrix rubber is 1:50-1:30; the mass ratio of sulfur to the matrix rubber is 1:50-1:25.

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) In the technical solution of the present invention, the unsaturated fatty acid containing polysulfide bonds is co-vulcanized with the unsaturated rubber, introducing carboxylate anion groups into the rubber crosslinking network, forming ionic bonds with the Zn 2+ cations brought by the accelerator in the system, playing a crosslinking role. This ionic bond also has the ability of dynamic reversible destruction-reconstruction, endowing the elastomer with self-healing function; furthermore, by controlling the degree of vulcanization, the network mainly contains polysulfide bonds, and polysulfide bonds also have the ability of dynamic reversible destruction-reconstruction, endowing the elastomer with self-healing function. In summary, the ionic bond and polysulfide bond form a dual dynamic reversible crosslinking network, which not only improves the mechanical properties of the elastomer but also has excellent self-healing ability.

[0019] (2) The raw materials are inexpensive and widely available, the preparation method is simple, and volatile toxic organic solvents are not used during the preparation process, realizing green preparation. Detailed implementation mode

[0020] The technical solution of the present invention will be specifically described below in conjunction with embodiments.

[0021] Example 1

[0022] Dissolve 21.6 g of NaOH in 50 g of deionized water to obtain an aqueous NaOH solution; add 150 g of corn oil and the aqueous NaOH solution to a three-necked flask, start vigorous stirring, and react in an 80 °C oil bath for 4 h; cool the product to 50 °C, and pour 590 mL of 1 M HCl aqueous solution into the product in several portions, stir vigorously for 15 min, let it stand for phase separation, and wash the oil phase with a large amount of deionized water multiple times to obtain unsaturated fatty acids;

[0023] Add 100 g of unsaturated fatty acids, 3 g of sulfur, 2 g of ZnO, and 3 g of tetramethylthiuram disulfide to a three-necked flask in sequence, and react at 100 °C for 6 h to obtain unsaturated fatty acids containing polysulfide bonds;

[0024] First, knead 150 g of natural rubber on a two-roll mill at room temperature, and then add 3 g of sulfur, 2 g of ZnO, 3 g of tetramethylthiuram disulfide, and 50 g of unsaturated fatty acids containing polysulfide bonds in sequence. After passing through six thin passes, make a triangular package and cut it into sheets to obtain a mixed rubber; vulcanize and shape the mixed rubber, vulcanize at 110 °C, and the vulcanization time is 1 / 2 of the optimum vulcanization time determined by a vulcameter to obtain a self-healing elastomer.

[0025] Example 2

[0026] Dissolve 21.6 g of NaOH in 50 g of deionized water to obtain an aqueous NaOH solution; add 150 g of corn oil and the aqueous NaOH solution to a three-necked flask, start vigorous stirring, and react in an 80 °C oil bath for 4 h; cool the product to 50 °C, and pour 590 mL of 1 M HCl aqueous solution into the product in several portions, stir vigorously for 15 min, let it stand for phase separation, and wash the oil phase with a large amount of deionized water multiple times to obtain unsaturated fatty acids;

[0027] Add 100 g of unsaturated fatty acids, 2 g of sulfur, 4 g of ZnO, and 4 g of tetramethylthiuram disulfide to a three-necked flask in sequence, and react at 140 °C for 2 h to obtain unsaturated fatty acids containing polysulfide bonds;

[0028] At room temperature, 150 g of natural rubber was first kneaded on an open mill, and then 3 g of sulfur, 3 g of ZnO, 4 g of tetramethylthiuram disulfide, and 20 g of unsaturated fatty acid containing polysulfide bonds were added in sequence. After passing through the mill six times thinly and making a triangular package and cutting into sheets, a mixed rubber was obtained; the mixed rubber was vulcanized and shaped, and vulcanized at 150 °C. The vulcanization time was 1 / 2 of the optimum vulcanization time determined by a vulcameter to obtain a self-healing elastomer.

[0029] Comparative Example 1

[0030] Repeat the steps described in Example 1, except that the vulcanization time was the optimum vulcanization time determined by a vulcameter.

[0031] Comparative Example 2

[0032] Repeat the steps described in Example 2, except that the vulcanization time was the optimum vulcanization time determined by a vulcameter.

[0033] Example 3

[0034] The self-healing elastomer prepared in the example was subjected to a tensile test in accordance with the national standard GB / T528-2009. The test tensile rate was 50 mm / min and it was carried out at room temperature.

[0035] The self-healing elastomers prepared in Examples 1-2 and Comparative Examples 1-2 were cut into standard splines. For the splines of each example or comparative example, half of the number of splines were directly subjected to a tensile test to obtain the average breaking strength σ0 and elongation at break ε0. The other half of the number of splines were cut in the middle along the direction perpendicular to the tensile axis, and after standing for 1 h, the cut splines were closely contacted together with a mechanical force of 25 kPa. Self-healing could be achieved after contacting at room temperature for 8 h. The self-healed splines were subjected to a tensile test to obtain the average breaking strength σ1 and elongation at break ε1. The self-healing efficiency R was:

[0036]

[0037] Table 1. Test results of the self-healing elastomers prepared in Examples 1-2 and Comparative Examples 1-2

[0038]

[0039] According to the above test results, the self-healing elastomer prepared by the present invention has good mechanical properties and excellent room temperature self-healing efficiency. In addition, the differences between Comparative Examples 1-2 and Examples 1-2 are only the differences in vulcanization time. Comparative Examples 1-2 adopted the optimum vulcanization time, while Examples 1-2 adopted half of the optimum vulcanization time. Therefore, in Comparative Examples 1-2, there are mainly monosulfide bonds, etc., which do not have the self-healing characteristics of reversible fracture-reconstruction; while the vulcanization time of Examples 1-2 is only half of the optimum vulcanization time, so the vulcanization reaction is terminated when polysulfide bonds are formed in the vulcanization reaction, so that a large number of polysulfide bonds with self-healing functions are retained in the obtained vulcanizate, thus realizing excellent self-healing function at room temperature. A large number of ionic bonds in the vulcanizate are also an important factor for realizing the self-healing function.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, for those of ordinary skill in the art, it is still possible to modify the technical solutions described in the foregoing embodiments, or to equivalently replace some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions required to be protected by the present invention.

Claims

1. A method for preparing a self-healing elastomer, characterized in that, The preparation method comprises the following steps: S1: Mix vegetable oil and concentrated NaOH aqueous solution in a reactor, stir at 80 °C for 4 h to completely hydrolyze the vegetable oil; then pour HCl aqueous solution with an amount 10% in excess of the equivalent amount of NaOH used into the reactor, stir vigorously at 50 °C for 1 h to ensure that the oil phase is fully acidified; then pour the product into a separatory funnel, let it stand for layering, drain the lower aqueous phase, and retain the oil phase; then wash the oil phase with a large amount of deionized water multiple times to completely remove the excess HCl, electrolytes and other impurities in the oil phase to obtain unsaturated fatty acids; S2: Put the unsaturated fatty acids obtained in S1, sulfur, ZnO, and tetramethylthiuram disulfide into the reactor, protect with nitrogen, continuously stir, and react at 100 - 150 °C for 1 - 6 h to obtain unsaturated fatty acids containing polysulfide bonds; S3: Knead the matrix rubber on a two-roll mill at room temperature, sequentially add sulfur, ZnO, tetramethylthiuram disulfide, and unsaturated fatty acids containing polysulfide bonds, pass through the mill six times thinly and then make a triangle package and take off the sheet to obtain a mixed rubber; vulcanize and shape the mixed rubber, vulcanize at 110 - 150 °C, and the vulcanization time is 1 / 2 of the optimum vulcanization time determined by a vulcameter to obtain a self-healing elastomer.

2. The preparation method of a self-healing elastomer according to claim 1, characterized in that, The vegetable oil described in step S1 is one or more of sunflower oil, corn oil, olive oil, soybean oil, and peanut oil.

3. The preparation method of a self-healing elastomer according to claim 1, characterized in that, In step S2, the mass ratio of ZnO to the unsaturated fatty acids is 1:50 - 1:25; the mass ratio of tetramethylthiuram disulfide to the unsaturated fatty acids is 1:50 - 1:25; the mass ratio of sulfur to the unsaturated fatty acids is 1:50 - 1:

25.

4. The preparation method of a self-healing elastomer according to claim 1, characterized in that, In step S3, the matrix rubber is one or more of natural rubber, isoprene rubber, cis-1,4-polybutadiene rubber, styrene-butadiene rubber, and nitrile rubber.

5. The preparation method of a self-healing elastomer according to claim 1, characterized in that In step S3, the mass ratio of the unsaturated fatty acids containing polysulfide bonds to the matrix rubber is 1:8 - 1:3; the mass ratio of ZnO to the matrix rubber is 1:50 - 1:30; the mass ratio of tetramethylthiuram disulfide to the matrix rubber is 1:50 - 1:30; the mass ratio of sulfur to the matrix rubber is 1:50 - 1:25.

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