PEELING OF LAMINATED FILMS COMPRISING HIGH-DENSITY POLYETHYLENE AND POLYPROPYLENE LOW-DENSITY POLYETHYLENE BLENDS

The peel strength of laminated films comprising high-density polyethylene (HDPE) and blends of isotactic polypropylene (PP)/low-density polyethylene (LDPE) was studied as a function of the heat-treatment temperature, T-H the cooling condition, and the blend composition of the substrate films, where HDPE is the peel, i.e. the film to be peeled or the flexible adherend, and the blend is the substrate (the rigid adherend). The peel strength was strongly dependent on T-H and the cooling rate. In the case of quenched films, the peel strength increased drastically for the films with T-H higher than the melting temperature of PP, T-m,T-pp. For slowly cooled films, however, the peel strength had a maximum for films with T-H nearly equal to T-m,T-pp. By varying LDPE composition in the substrate, a systematic decrease in the peel strength was observed, indicating the important role of LDPE in the PP matrix in controlling the peel strength between HDPE and PP. The adhesion mechanism and the role of LDPE are discussed from the viewpoints of (1) partial miscibility and interdiffusion among PP, HDPE and LDPE, and (2) crystallization kinetics of the component polymers.