Changes in Crystal Structures of PVDF in PVDF/PMMA Blends Heat-treated in Several Ways

Hideo HORIBE* and Fumiaki BABA

Advanced Technology R & D Center, Mitsubishi Electric Corp.; 8-1-1, Tsukaguchi-honmachi, Amagasaki-shi 661-8661 Japan

It has been well known that PVDF/PMMA blends are compatible in the melt state. In the previous paper, UV transmittance of PVDF/PMMA blends was varied by blend ratio as well as cooling speed from the melt state.
In this study, we will report the relationship between crystal structures of PVDF and PVDF/PMMA blends heat-treated in several ways. We call PVDF/PMMA=x/(100-x)(wt%) as Fx. For example, PVDF/PMMA=70/30 is called F70. The wide angle X-ray diffraction(WAXD) shows that the quenched samples(Q) have amorphous(F0--F80) and PVDF(II) crystal structure(F90, F100). The slow cooled samples(S) have amorphous(F0--F30) and PVDF(II) crystal structure(F40--F100). The annealed samples(QA), heat treated Q samples, have amorphous(F0--F30), PVDF(II) crystal structure(F40, F50, F90, F100) and PVDF(I) crystal structure(F60--F80). The annealed samples(SA), heat-treated S samples, have amorphous(F0--F20) and PVDF(II) crystal structure(F30--F100).
The WAXD curves of F80 blends are very different in the cooling rate. It seems that QA sample has the crystal structure of PVDF(I). On the other hand, SA and S samples have PVDF(II) structure. Q sample is amorphous. It is known that different crystalline forms are obtained according to the crystallization speed. It is considered that the crystallization speed of F80 QA sample is comparatively slow and form the PVDF(I) structure.
PVDF has three forms of crystalline structure. PVDF(I) structure has piezoelectric and pyroelectric properties. But it is difficult to make PVDF(I) structure simply. We found that PVDF(I) structure can get simply when F70 or F80 is quenched from the melt and then annealed at 120 C.

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