Hybrid composites consisting of soft rubber (carboxyl-terminated butadiene acrylonitrile, CTBN) and silica nanoparticles with average particle size of 20 nm were studied for improving toughness of epoxy resins (diglycidyl ether of bisphenol A, DGEBA). The hybrid carboxyl-terminated butadiene acrylonitrile /silica nanoparticles epoxy systems exhibited improvements in the Young’s modulus, and more importantly, fracture toughness (KIC), which can be explained by synergistic impact from the inherent characteristics of each filler. In this study, the highest KIC was reached with addition of small amounts of silica nanoparticles (5 vol.%) to the epoxy containing 15 vol.% carboxyl-terminated butadiene acrylonitrile, where the KIC was distinctly higher than with the epoxy containing carboxyl-terminated butadiene acrylonitrile or silica nanoparticles alone. Cavitation of rubber particles with matrix dilation and particle debonding with subsequent void growth were determined as the toughening mechanisms responsible for the toughness improvements for epoxy. The evidence indicates that debonding of the silica nanoparticles causes a weakening of the matrix–particle interface. The toughness enhancement in hybrid nanocomposites involves an increase in silica nanoparticles particle debonding an increase in plastic zone size, which allows the epoxy matrix to dissipate more fracture energy.

The effect of vulcanization processes and surface treatment of cellulose were investigated on tensile strength, degradation temperature, and morphological properties of cellulose/natural rubber composites. Cellulose was surface-treated with Si-69 silane coupling agent and used as reinforcing filler in natural rubber (NR). Different vulcanization processes including electron beam irradiation (EB-Cured) and sulphur vulcanization (S-Cured) were used to crosslink NR. The incorporation of both untreated and treated cellulose at various concentrations (5, 10, 15 and 20 phr) into NR was found to significantly improve the tensile strength and modulus. Notably, with addition of treated cellulose in NR, the tensile strength and modulus were considerably higher than that of the untreated cellulose for all curing system. SEM morphological analysis revealed a well dispersion of cellulose particles in NR matrix. Addition of cellulose slightly decreased the onset of degradation temperature of NR, however, the degradable temperature was found to be unchanged. The curing systems had shown an impact on tensile property of NR. S-Cured NR exhibited highest modulus of 2.23 MPa comparing to the EB-Cured NR (1.69 MPa) for the same amount of cellulose (20 phr), due to a stronger crosslink network. However, the curing system had no significant impact on degradation temperature of NR.