Effect of precured degrees on morphology, thermal, and mechanical properties of BR/SBR/NR foams

Abstract

The ternary composites of 1,4‐cis polybutadiene rubbers (BR), styrene–butadiene rubber (SBR), and natural rubber (NR) foams containing chemical blowing agents Oxybis (benzene sulfonyl) hydrazide (OBSH) were prepared by two‐stage compression molding technique with various precured degrees. Foam force rheometer indicated that the cure rate was match with foaming rate at precured degree of 30%, which the time of the maximum foaming rate was earlier only 14 s than that of the maximum cure rate. SEM presented that the number of cell was denser at precured degree of 30% than those with other precured degrees. The average cell size declined, cell wall thickness became thicker, and cell distribution became narrower just as precured degree was increasing. The results of crosslinking density was measured by equilibrium swelling technique in good agreement with that of magnetism resonance crosslinking density spectrometer measurement, which crosslinking density was increased as precured degrees increased. Differential scanning calorimeter showed that each curve exhibits two steps in heat capacity for BR/SBR/NR foams. With further increase of precured degrees, the two groups of Tgs were all shift to the higher temperature, and the area of the melting peak decreased gradually between −20°C and −40°C. TGA results demonstrated that BR/SBR/NR foams with various precured degrees obtained better thermal stability than those of non‐precured foams. The high density of polymeric foams exhibits the high mechanical properties such as tensile strength, tear strength, and elongation at break. The inflection points of density, cell density, and hardness were all appeared at precured degree of 30%. POLYM. COMPOS., 34:849–859, 2013. © 2013 Society of Plastics Engineers