The effect of heat sealing temperature on the mechanical properties and morphology of OPP/CPP laminate films was investigated. The laminated films were placed in an impulse type heat sealing machine with both CPP sides facing each other. The temperatures investigated ranged from 100 to 250 degrees C. T-peel and tensile tests in combination with SEM were used to characterize the heat seats. A minimum seal initiation temperature of 120 degrees C was identified for OPP/CPP laminate heat sealing. Peel strength increased sharply from zero at 110 degrees C to maximum at 120 degrees C, after which a gradual decrease was observed. Tensile strength initially increased until 120 degrees C, after which it gradually decreased until 170 degrees C and assumed a constant value beyond that. The initial rise has been associated to cold crystalization, while the reduction between 120 degrees C and 170 degrees C was due to relaxation in molecular orientation. Beyond 170 degrees C, all the orientation in the laminate has been lost so orientation effects are nullified. Morphological studies with SEM revealed that seals were partially formed at lower temperatures, while the laminates were totally fused together at high temperatures, with intermediate temperatures showing properties that lie in between. (c) 2005 Wiley Periodicals, Inc.