COMPATIBILIZATION OF POLYSTYRENE AND LOW-DENSITY POLYETHYLENE BLENDS BY A 2-STEP CROSS-LINKING PROCESS

A new method has been developed to compatibilize the blends of polysty rene (PS) and polyethylene (PE). Polyethylene is first crosslinked par tially by using a small amount of dicumyl peroxide (DCP) in a mixer at 165 degrees C. Then the crosslinked PE is melt-blended with PS for an other 5 min. Finally, a styrene-butadiene-styrene block copolymer (SBS ) is added to the melt and mixed for another 5 min. We refer to this s pecial procedure as the two-step crosslinking process. During the fina l mixing step of this process, the residual free radicals in the PE re act with SBS. The crosslinking that occurs between PE and SBS has a si gnificant impact on the mechanical properties of the blends including the impact strength, the tensile modulus, and the elongation-at-break. Scanning electron microscopy (SEM) results indicate that the interfac ial adhesion is increased significantly, even though the domain sizes have not changed significantly in comparison with the non-crosslinked system. Transmission electron microscopy (TEM) results indicate that a thin SBS interfacial layer fully encapsulates the PE particles. This method could also be applied to other blend systems containing at leas t one component and a compatibilizer that are crosslinkable. (C) 1998 Elsevier Science Ltd. All rights reserved.