ABSTRACT: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°C. T-peel and tensile tests in combination with SEM were used to characterize the heat seals. A minimum seal initiation temperature of 120°C was identified for OPP/CPP laminate heat sealing. Peel strength increased sharply from zero at 110°C to maximum at 120°C, after which a gradual decrease was observed. Tensile strength initially increased until 120°C, after which it gradually decreased until 170°C and assumed a constant value beyond that. The initial rise has been associated to cold crystallization, while the reduction between 120°C and 170°C was due to relaxation in molecular orientation. Beyond 170°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 tempera-

ABSTRACT:A previous study has shown that the adhesion between the film and substrate of film-insert injectionmolded poly(propylene) (PP) film/PP substrate was evident with the increases in barrel temperature and injection holding pressure. In this second part of the research work, the crystallinity at the interfacial region (i.e., region between the film and the injected substrate) was extensively studied using FTIR imaging, polarized light microscopy, and DSC in an attempt to determine the level of influence that crystallinity has on the interface and bulk mechanical properties. Consequently, a more thorough and clearer picture of the influence of the inserted film on the interfacial crystallinity and subsequently the substrate mechanical properties, such as peel strength and impact strength, has been revealed. The initial proposition that crystallinity could enhance film-substrate interfacial bonding has been confirmed, judging from the higher peel strength with increasing crystallinity at the interfacial region. Nevertheless, the change in crystallinity was not only confined to the interfacial region. With the film acting as heat-transfer inhibitor between the injected resin and the mold wall, the total crystal structure of the substrate was substantially altered, which subsequently affected the bulk mechanical properties. The lower impact strength of film-insert injection-molded samples compared to that of samples without film inserts provided evidence of how the film could impart inferior properties to the substrate. The difference in cooling rate between the substrate and film might also cause other defects such as warpage and/or residual stress build-up within the product.

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An extensive study on the peel strength between a polypropylene (PP) film and PP substrate fabricated using film insert injection molding technique was carried out through a 180°peel test. Injection molding conditions such as barrel temperature, injection speed and holding pressure were varied to gauge their effects on the mechanical and morphological properties. Morphological observations were made at the filmsubstrate interfacial regions by means of transmission electron microscopy (TEM). The injection molded products, with the films still attached, were subjected to bending and impact tests to determine if there is any relationship between film-substrate adhesion and bulk properties. Observation of the load-displacement curves during the peel test revealed three unique and interesting curves, corresponding to different peeling and film fracture mechanisms. Increases in injection speed, barrel temperature and holding pressure lead to increased bonding between the film and substrate surfaces. The enhancement of bonding between these two polymer surfaces could be attributed to polymer-polymer interdiffusion. Substantiating evidence from TEM, which shows the fading of the interface as the bond strengthens, further boosts the accuracy of this assumption. The hope that the films could contribute to enhancing bulk properties has been diminished since the bending properties appeared to be similar with or without the film attached.

This paper describes highly oriented films prepared by the evaporation of poly(dimethyl silane). The specimens are prepared at various evaporation speeds and substrate temperatures. The polymer is divided into species of about 2 nm length on the evaporation heater, and the species recrystallize on the substrate. The structure and orientation of the films are investigated using wide-angle X-ray diffraction and ultraviolet absorption methods. The substrates used are single-crystal silicon (100) for the X-ray diffraction measurement and fused silica for the ultraviolet absorption measurement. The polymer exhibits the same orientation on both substrates. It is found that most of the silicon chains are perpendicular to the substrate surface in the film prepared under the condition whose growth rate is lower than 20 nm min-1. On increasing the substrate temperature, the number of silicon chains whose orientation is normal to the substrate surface increases.