Melting and crystallization behaviour of poly(vinylidene fluoride) samples in its blends with some polyacrylates, poly(vinyl esters) and poly(aryl ether ether ketone)

Abstract

The melting and crystallization behaviour of poly(vinylidene fluoride) (PVF₂) blends with each of poly(phenyl acrylate) (PPA), poly(methyl acrylate) (PMA), poly(vinyl benzoate) (PVBz), poly(vinyl acetate) (PVAc) and poly(aryl ether ether ketone) (PEEK) has been studied. Two PVF₂ samples with different amounts of head-to-head defect structure were used. The compatibility of PVF₂ with each of PPA, PVBz and PEEK has been tested by glass transition temperature measurements. The results indicate immiscibility in each case, which is attributed to steric hindrance of the phenyl group. The melting-point depression of PVF₂ in incompatible pairs of the above is less than in compatible pairs. Also, the initial slopes of the melting-point depression curves for lower-defect-content blends (compatible or incompatible) are lower compared with those of higher-defect-content samples. The crystallization kinetics of pure PVF₂, PVF₂ in incompatible blends and PVF₂ in compatible blends at weight fraction W_PVF = 0.8 were measured at 147°C. The rate of crystallization of PVF₂ varies as: pure PVF2 > incompatible blend > compatible blend. Analysis of the Avrami exponent indicates that the nucleation mechanism is the same for all cases, though the growth becomes diffusion-controlled for higher-defect-content PVF₂ samples and for its blends. Comparison of crystallization rate between lower- and higher-defect-content PVF₂ blends again indicates greater miscibility for higher-defect-content samples. The results have been explained qualitatively by homopolymer-copolymer miscibility theory.