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Abstract
Polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA) blend films were prepared using biaxial stretching. The effects of PMMA content and stretching ratio on the crystallinity and β phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and β phase fraction on variable locations were also studied. The results of FTIR and XRD showed that β phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although β phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved β phase fraction, and the highest β phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2×2. Besides, the reduction in PMMA content and the increase in stretching ratio improved the crystallinity of PVDF. The mechanical properties of the stretched films were significantly improved by increasing the stretching ratio as well. The uniform stress distribution on different regions of biaxial stretching films contributed to the uniform distribution of β phase fraction and crystallinity of PVDF with the aid of simulation. This work confirmed that biaxial stretching can be a candidate method to prepare PVDF/PMMA blend films with uniform distributions of comparable β phase and crystallinity of PVDF.
Highlights
Polyvinylidene fluoride (PVDF) as one of piezoelectric polymers is widely used in flexible sensors, actuators, and self-powering devices [1,2,3,4], etc
Independent of processing conditions, the fraction of β phase of PVDF was increased via the addition of poly(methyl methacrylate) (PMMA), i.e., the fraction was increased from 50% to 54% and 64% for PVDF/PMMA = 80/20 and 60/40 in a low shear mixer (100 rpm), respectively
When the casting films that went through both extrusion and casting stages were concerned, β phase was observed compared with the melt samples without mechanical field
Summary
Polyvinylidene fluoride (PVDF) as one of piezoelectric polymers is widely used in flexible sensors, actuators, and self-powering devices [1,2,3,4], etc. A low temperature and a high stretching ratio increased the crystallinity and the fraction of β phase, both of which are lower than that prepared by uniaxial stretching at the same temperature [34]. There is few reports on the β phase fraction and crystallization of PVDF in biaxially stretched PVDF blends films. We investigated the crystallinity and β phase fraction of PVDF in biaxially stretched PVDF/PMMA films. The effects of mass ratio and stretching ratio on crystallinity and β phase fraction of PVDF were studied Their distributions on different regions of the stretched films were studied via experiments and simulations. The thickness of these sheets was controlled as 350–400 μm by changing the speed of rotating rollers and the width of the die mouth. When the film thickness was less than 20 μm, the stretch fracture often occurred
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