Effect of tie-layer thickness on the adhesion of ethylene-octene copolymers to polypropylene

The adhesion of some ethylene-octene copolymers to polypropylene (PP) and high density polyethylene (HDPE) was studied in order to evaluate their suitability as compatibilizers for PP/HDPE blends. A one-dimensional model of the compatibilized blend was fabricated by layer-multiplying coextrusion. The microlayered tapes consisted of many alternating layers of PP and HDPE with a thin tie-layer inserted at each interface. The thickness of the tie-layer varied from 0.1 to 15 mu m, which included thicknesses comparable to those of the interfacial layer in a compatibilized blend. The delamination toughness was measured in the T-peel test. Generally, delamination toughness decreased as the tie-layer became thinner with a stronger dependence for tie layers thinner than 2 mu m. Inspection of the crack-tip damage zone revealed a change from a continuous yielded zone in thicker tie layers to a highly fibrillated zone in thinner tie layers. By treating the damage zone as an Irwin plastic zone, it was demonstrated that a critical stress controlled the delamination toughness. The temperature dependence of the delamination toughness was also measured. A blocky copolymer (OBC) consistently exhibited better adhesion to PP than statistical copolymers (EO). A one-to-one correlation between the delamination toughness and the reported performance of the copolymers as compatibilizers for PP/HDPE blends confirmed the key role of interfacial adhesion in blend compatibilization. (C) 2009 Elsevier Ltd. All rights reserved.