The study of recovery behaviors of different types of Styrene Butadiene Rubber after aging using circular deformation

Recovery behaviors from circular deformation of styrene butadiene rubber were studied at different aging circumstances. SBR1502, VLS2525, NS116, were the material used to make different types of SBR. Circular deformation was done on all samples at different periods and temperatures. Recovery percent was measured and found that it was increased with deformation time and decreased with aging temperature increment and it was the highest for NS116 and the lowest for SBR1502. The study of recovery behaviors of different types of Styrene Butadiene ... 62 Also the apparent crosslink density was measured and found that it was increased with aging temperature for the three types rubber and the rate of its variation was the highest for SBR1502 and the lowest for NS116. Introduction Rubber is used in many products including tires, belts, tubes, sealant, wire, covering materials, and so on, depending on the advantage of its excellent elasticity, restorability and flexibility. Other properties like abrasion resistivity, oil resistivity, heat resistivity and electrical resistivity are also required of rubber depending on it application [1]. Styrene-butadiene rubber (SBR) is a copolymer of styrene and butadiene, the butadiene has three different microstructures of cis-1.4, trans-1.4, and 1,2-units. The 1,2-unit has one allylic carbon which is hindered by the vinyl group where as the cis-1,4and trans -1,4units have two allylic carbons (as in sketch-1). CH2=CH-CH=CH2 CH2=CH-CH-CH3 CH2-CH=CH-CH2 n-Butadiene 1,2-unit cis-1,4and trans-1,4-units Sketch-1: Chemical formulas of the butadiene types Fillers play an important role in changing the mechanical properties (Hardness, Toughness, etc.) due to the strong polymer-filler interaction, which leads to improve the wet-skid resistance [2, 3]. Carbon black and silica are the most popular reinforcing fillers in rubber compounds. Carbon black is added as the reinforcement agent to rubber for car tires that must have abrasion resistance, while silica is used as agent to increase the insulation of rubber[1]. Silica has a number of hydroxyl groups (silanol, Si-OH), which results in strong filler-filler interactions and adsorption of polar materials by hydrogen bonds [4]. Since intermolecular hydrogen bonds between silanol groups on silica surface are very strong, it can aggregate tightly [5, 6]. Deformation can be done permanently in rubber when they are deformed by any external stress for long time, especially in high temperature. One of principle reasons about permanent deformation is change of crosslink density [7]. Crosslink density of rubber is changed by thermal aging [8]. A rubber material has a recovery property to return to its original shape from deformation [9]. Degree of the instantaneous recovery is related with the sealing capability of sealant such as O-ring [10]. Many researches have been done on thermal aging to discover its effect on physical properties of rubber with different kind of fillers specially the sealing properties of sealant used rubber [8,11,12]. The aim of this work is to study the effect of aging on deformation recovery percent, instantaneous recovery percent and apparent crosslink density of different types of silica-reinforced styrene-butadiene rubber (SBR) at different times and temperatures.