| Sulfur is commonly used as a curing agent in tire and rubber products. However,because of the difference of sulfur’s solubility under different temperature, when a large amount of sulfur was used, parts of sulfur would migarate to rubber’s surface during storage, the so-called “blooming” in rubber industry usually caused decrease of rubber adhesion and products’ performance. Blooming needs to be addressed urgently because it not only degrades the performance of products but also caused resource waste and environmental pollution. Insoluble sulfur could solve the problem to some extent, but the problems exist in the production limits its deveolopment such as the corrosion of equipment under the high temperature and pressure during the synthesis, and damage to the environment by carbon disulfide and other toxic substances applied in the subsequent processing. Therefore, a new solution is badly needed in the market.This paper aims to solve the blooming problem with synthetic sulfur microcapsules when the shell materials coated on the sulfur surface make it easier to evenly dispersed into the rubber matrix. During the curing process, sulfur will release slowly through the softened or cracked shell materials to the rubber macromolecular chains, and a three-dimensional network structure with good properties was fomed under curing temperature. In this paper, a variety of inorganic and organic materials such as PUF, silica,GO, PMMA, PS and so on. A variety of analytical tools were used to understand microcapsules’ properties, such as FTIR, TGA, SEM, EDS and other characterization methods. The processing properties, mechanical properties and dynamic performance of the vulcanized rubber using sulfur microcapsules as vulcanizing agent were studied.Sulfur microcapsules could be successfully formed by coating PUF, silica, GO,PMMA, PS and other shell materials on sulfur through different methods. Compared withsublimed sulfur, The PUF resin coated sulfur microcapsule with SDS as surfactant was of regular morphology but rougher surface than sublimed sulfur while other surfactant was not available. Moreover, particle size could be uniformly controlled by mechanical stirring. With sulfur colloid as core material, the morphology of silica-coated sulfur microcapsules can be adjusted by controlling the reaction conditions through situ coating.It was found that when the sulfur/TEOS molar ratio was 2/1~3/2, alcohol/water ratio was85/15-80/20 and ammonia content was 2.5~3m L, composites exhibited most excellent morphology, and the bipyramid structure of sulfur crystals was well maintained after coating. Because of high specific surface area, GO can be easily coated on sulfur particles to form core-shell structure, it is also conducive for sulfur to effectively released from the porous structure of the sheet surface of GO at vulcanization temperature. By chaing the usage rate of GO/sulfur, a most suitable ratio of 10/90 was considered to improve the best performance. In addition, before post-treatment of GO encapsulated sulfur, a structure of reduced graphene oxide(r GO) loaded sulfur was obtained instead of r GO encapsulated sulfur by the addtion of reductant. Generally, sulfur could not be tightly coated for lack of active sites, but with stabilizer PVA, the coupling reaction of surface hydroxyl and KH570 can form active sites on suflur surface, and with AIBN as initiator, PMMA and PS was grafted and coated on sulfur crystal surface. The obtained PMMA/PS-coated sulfur microcapsules obtained were of uniform morphology and smooth surface with different sizes. In order to simplify the processing procedure, tactic sulfur microcapusle with polymer shell were obtained by one-step processing with stabilizer De TAB. The sulfur microcapsules with different shell materials were analysed through FTIR, TGA, SEM,EDS, etc. and the core-shell structure was demonstrated in all microcapsules, and better thermal stability was obtained which result from the delayed heat transfer by the shell.Except that, the core material content was more than 90%w which was higher than previous reports.The performance of rubber using microcapsules sulfur prepared as a vulcanizing agent was studied, the results showed that the processing properties such as scorching time and curing time were much the same while mechanical properties were significantly improved. The mechanical behavior of rubber was strengthed obviously. In particular, the tensile strength was increased from 16.37 MPa to 28.14 MPa with PS coated sulfur microcapsules, which mainly due to the better dispersion and good compatbility of curing agent with rubber matrix and bigger distribution probability of single-sulfur bonds after crosslinking. Referring to dynamic mechanics, r GO loaded sulfur vulcanized rubber wasof the best overall performance and and tanδ value at 60 ℃ was significantly reduced from 0.26 to 0.21.Compared with the vulcanized rubber made by various sulfur microcapsules, after one months’ s storage, blooming occurred in vucanized rubber made by sublimed sulfur,and precipitated sulfur crystals could be seen from the SEM image, while there was no blooming in sulfur microcapsules vulcanized rubber. |
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