Crystallinity and β Phase Fraction of PVDF in Biaxially Stretched PVDF/PMMA Films

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 beta phase fraction of PVDF in blend films were investigated. The distributions of crystallinity and beta phase fraction on variable locations were also studied. The results of FTIR and XRD showed that beta phase appeared in PVDF/PMMA blends after extrusion and casting procedures. Although beta phase fraction decreased after preheating, there was still an increasing trend during following biaxial stretching. More importantly, the increase in PMMA content improved beta phase fraction, and the highest beta phase fraction of 93% was achieved at PMMA content of 30 wt% and stretching ratio of 2x2. 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 beta 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 beta phase and crystallinity of PVDF.

Automated summary

PVDF/PMMA blend films were prepared by biaxial stretching, and the effects of PMMA content and stretching ratio on the crystallinity and beta phase fraction of PVDF in blend films were investigated. Results showed that increasing PMMA content and stretching ratio improved the beta phase fraction and crystallinity of PVDF, with a continuous increasing trend observed even after preheating.