Abstract
This work reports on an experimental study of the stretching of ultra-high molecular weight polyethylene (UHMWPE) film in various uniaxial/biaxial stretching modes at various temperatures and stretching speeds. We examined the stress-birefringence relationship as a stress-optical rule (SOR) under uniaxial stretching and evaluated the stress-optical coefficient (SOC). Wide-angle X-ray diffraction (WAXD) measurements were applied to evaluate the contribution to birefringence of the crystalline and amorphous phases and to characterize stretching modes. In simultaneous biaxial stretching, the melting temperature (Tm) proved critical to structural formation. We applied thermal analysis techniques and tensile testing to evaluate higher order structures after each stretching mode.
Highlights
Long-chain structures of semi-crystalline polymers have been used to create films with advanced properties
In our previous study [14], we investigated stress-optical coefficient (SOC) of cyclic olefin copolymer films stretched at temperatures above Tg, SOC values were found to approach the photo-elastic coefficient (PEC) under fast stretching speed
While retardation shows distribution of a certain degree, we focused on multiplied by 130 nm
Summary
Long-chain structures of semi-crystalline polymers have been used to create films with advanced properties. An understanding of the structural evolution of polymer film during stretching is essential to establishing ideal processing conditions, including temperature, stretching speed, draw ratio and stretching mode. Stretching of polymer film changes the crystallinity and the structure of crystalline polymers; these changes are more complex than for amorphous polymers. Film stretching speed in industrial process nowadays reaches 400 m/min for polymers such as polypropylene (PP) and polyethylene terephthalate (PET) which can provide high production rate. It is an important task to make it compatible with the required properties of stretched film. Insight into different types of stretching modes helps in controlling processing window and understanding the nature of the film. On-line structure evaluations during film stretching have been studied to understand higher order structures in addition to off-line evaluation
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