Improving Optical Clarity of Polyethylene Blown Films

摘要

Although it has been known in the industry that blending LDPE into LLDPE improves the optical clarity of the latter, the mechanism is still not fully understood. We have examined the haze arising from internal and external structures (internal haze and external haze) of blown films made of different LLDPE/LDPE blends. The results indicated that the internal haze contributed relatively small, compared to the external haze, to the total haze of blown films. While the internal haze is controlled by the bulk crystallization kinetics and bulk crystallite orientation, the overall optical clarity of the films is predominantly controlled by the surface morphology - roughness and surface orientation. Both the relaxation and crystallization behavior of polymer melt are found to be very important in controlling the surface morphology and thereby the optical properties of the films. This observation was made possible by combining two analytical methods - atomic force microscopy and surface orientation by ATR-FTIR coupled with polarizer.