Effect of a tie layer on the delamination toughness of polypropylene and polyamide-66 microlayers

The effect of a thin tie layer on the adhesion of polypropylene (PP) and po lyamide-66 (PA) was studied by delamination of microlayers. The microlayers consisted of many alternating layers of PP and PA separated by a thin laye r of a maleated PP. The peel toughness and delamination failure mode were d etermined using the T-peel test. Without a tie layer, there was no adhesion between PP and PA. A tie layer with 0.2% MA provided some adhesion; howeve r, delamination occurred by interfacial failure. Increasing the maleic anhy dride (MA) content of the tie layer increased the interfacial toughness. Wi th 0.5% MA, the interfacial toughness exceeded the craze condition of PP, a nd a transition from interfacial delamination to craze delamination occurre d. Crazing ahead of the crack tip effectively reduced the stress concentrat ion at the interface and dramatically increased the delamination toughness. (C) 1999 John Wiley & Sons, Inc.