A new method, namely two-step crosslinking, is developed to compatibilize the blends of polystyrene (PS), polyethylene (PE) and styrene-butadiene- styrene (SBS). It was found that when the PE was first mixed with dicumyl peroxide (DCP) at 160°C and then blended with the PS and finally SBS, the mechanical properties of the blend increased dramatically. The impact strength of the blend was 197 J/m, which is about 13 times higher than that of the PS/PE blend. The role of DCP in the processing was investigated by measuring the concentration of the PE radicals in each of the mixing steps using electron spin resonance spectroscopy (ESR). From the ESR spectrum, the PE radicals were detected in the PE/DCP and PE/DCP/PS blends. The PE radicals were found completely consumed after the PE/DCP/PS w...[ Read more ]

A new method, namely two-step crosslinking, is developed to compatibilize the blends of polystyrene (PS), polyethylene (PE) and styrene-butadiene- styrene (SBS). It was found that when the PE was first mixed with dicumyl peroxide (DCP) at 160°C and then blended with the PS and finally SBS, the mechanical properties of the blend increased dramatically. The impact strength of the blend was 197 J/m, which is about 13 times higher than that of the PS/PE blend. The role of DCP in the processing was investigated by measuring the concentration of the PE radicals in each of the mixing steps using electron spin resonance spectroscopy (ESR). From the ESR spectrum, the PE radicals were detected in the PE/DCP and PE/DCP/PS blends. The PE radicals were found completely consumed after the PE/DCP/PS was further blended with the SBS. We therefore proposed that the PE radicals reacted with the butadiene groups of the SBS, leading to a crosslinked PE-SBS interface, which enhanced the interfacial strengths and improved the tensile and impact strengths of the PS/PE/SBS blends. The success of this method can also be visualized by studying the fracture surface using Scanning Electron Microscopy (SEM). Large plastic deformation was observed on the fracture surface of the blends. The major source of toughness was attributed to the shear deformation at the crack tip. The pullout process of the fiber-like PE phase stopped the growth of crazed formed in the PS matrix. Based on the experimental observation, a fracture model was proposed to explain the high fracture toughness of the compatibilized PS/PE/SBS ternary blends.