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Crosslink Network Evolution and Stress Softening of Composite System of Butadiene Styrene Rubber and Metallic Methacrylate (Zinc、 Magnesium)

Author: HuangJing
Tutor: DingJianPing；SunGengLiang
School: South China University of Technology
Course: Materials Engineering
Keywords: styrene-butadiene rubber zinc methacrylate magnesium methacrylate crosslink network stress softening
CLC: TQ330.1
Type: Master's thesis
Year: 2011
Downloads: 58
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Abstract

The metallic methacrylate are an effective kind of modifying agent in rubber. They are used as not only a coagent for peroxide crosslinking but a reinforcing agent for many rubber systems. Because of the reactive groups, in situ polymerization of the metallic methacrylate in rubber matrix can reinforce rubber, producing metallic methacrylate /rubber composites in appropriate condition. The composites can impart the good mechanical properties including high modulus, high elasticity, high elongation at break and high thermal stability. In situ polymerization of the metallic methacrylate in rubber matrix contain covalent bonds and ionic bonds meanwhile that makes the crosslinking network of these composites are more complex than the composites filled with other common reinforcingfillers such as carbon black.In this dissertation, the reinforcement of zinc methacrylate (ZDMA) and magnesium methacrylate (MDMA) prepared in situ from zinc oxide (ZnO)/methacrylic acid (MAA) and magnesium hydroxide (MgO)/methacrylic acid (MAA) on non-polar styrene-butadiene rubber (SBR) vulcanizates were studied. The SBR/ZDMA and SBR/MDMA composites were produced during the curing process with dicumyl peroxide (DCP) curing agents. Chemical reaction structure and morphological characteristics of SBR vulcanizates were studied, the in situ formation and polymerization of the metallic methacrylate in rubber matrix was analysed, and the formation of the two crosslinking networks in the system was discussed by results of stress softening test, crosslink density determination, Fourier transform infrared (FTIR) spectroscopy and rubber processing analyzer (RPA).The results showed that polymerization of the ZDMA (or MDMA) and rubber chain were initiated by DCP, and the polymerization mostly happened at the beginning stage of curing at certain temperature. During this period, the covalent crosslinkings and ionic crosslinkings were increasing rapidly, the crosslinked network basically formed. With the curing process, the crosslinking rate became slower and the crosslink densities tended to saturation. When reduced the curing temperature and measured the crosslink density we found that the ionic crosslinkings, cooperating with some covalent crosslinkings and little physical adsorption crosslinkings, played an important role in supporting the crosslinked backbone of the composite to bear the external force in the initial curing time, but the crosslinkings were spread insteading of a whole network within the first minutes. Furthermore, the covalent crosslink density was much higher than ionic crosslink density in SBR system. The stress softening and Payne effect all increased with the addition of metallic methacrylate. The Payne effect can be caused by the construction and destruction of rubber networks (including graft-PZDMA or graft-PMDMA) and filler-filler networks which were formed by rigid organic particles of PZDMA (or PMDMA), the stress softening is supposed to be concerned with the high reinforcing filler. Thus the addition of metallic methacrylate could enhance the interaction between the fillers and rubber. The aging test indicates that there are some crosslinking reaction under the condition of hot oxygen, the specimen become so hard and brittle that its physical properities decrease rapidly.

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