COMPATIBILIZING EFFECTS OF BLOCK-COPOLYMERS IN LOW-DENSITY POLYETHYLENE POLYSTYRENE BLENDS/

The phase and mechanical properties of a low-density polyethylene/poly styrene 70/30 (LDPE/PS 70/30) blend has been determined after compatib ilization with various styrene-ethylene, styrene-ethylene/butene and s tyrene-ethylene/propylene type block copolymers. It is shown that high interfacial activity, as reflected in the reduction of the dispersed phase size, does not necessarily bring about an improvement in the mec hanical properties of the blend. Although the diblock copolymers were more efficient in reducing the phase size, the triblock copolymers wer e more effective in improving the mechanical properties. The effect of a poly(styrene-b-ethylene) (S-E) block copolymer on the particle coal escence and rheological properties of the LDPE/PS 70/30 blend has been investigated. It is shown that small amounts of the block copolymer c an significantly retard or actually suppress the coalescence of the di spersed phases, and thus stabilize the morphology of the blend. The ad dition of the S-E copolymer increases the elastic modulus and dynamic viscosity of the blend, and the samples become more non-Newtonian as t he block copolymer concentration increases. (C) 1998 Published by Else vier Science Ltd. All rights reserved.