Effect of Cast Roll Temperature on Phase Transformations in Extruded PVDF film
Milind Mhalgi, Ashok Misra, Devang Khakhar
Indian Institute of Technology, Bombay
INDIA

Keywords: PVDF, Extrusion, Stretching

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Poly(vinylidene fluoride) (PVDF) exhibits complex crystalline polymorphism and has atleast four crystal
polymorphs namely alpha , beta , gamma and delta or forms II, I, III and IV respectively. The extraordinary electrical properties of this polymer are a direct consequence of its crystalline structure. The crystalline structures can be transformed to each other reversibly or irreversibly under suitable conditions. In the present work PVDF was extruded using the cast film extrusion technique. The films produced were cast at five different cast roll temperature namely 75 deg C, 91 deg C, 107 deg C, 120 deg C and 130 deg C. The film that was extruded at a cast roll temperature of 91 deg C was stretched at 80 deg C on a stretching unit and the stretch ratios employed were 2.6, 3.2, 3.5, 3.6 and 4.2. The film sample that was stretched at a stretch ratio of 4.2 showed maximum transformation from alpha phase to beta phase. The film samples that were cast at different cast roll temperatures were then stretched at a stretch ratio of 4.2. The stretched and unstretched film samples were characterized using birefringence, polarized FTIR and WAXD. The content of various phases in the sample found to be strongly dependent on the cast roll temperature. The content of beta phase found to vary depending on the stretch ratio as well as the cast roll temperature. The PVDF film sample that was cast at a cast roll temperature of 107 0 C showed the maximum transformation from alpha phase to beta phase. Thus the phase transformations in the PVDF film samples observed to be dependent also on the initial conditions of the film before stretching.