Melting and crystallization of poly(vinylidene fluoride) blended with polyamide 6

Melting and crystallization of poly(vinylidene fluoride) (PVDF) blended with polyamide 6 (PA6) has been studied by differential scanning calorimetry. The melting of PVDF and PA6 is observed over a small temperature range, i.e. 174 to 181 degrees C and 220 to 230 degrees C, respectively, over the whole blend composition. This observation indicates that PVDF and PA6 are immiscible and do not co-crystallize, although evidence for intermolecular interactions between PVDF and PA6 has been previously reported. Crystallinity of PVDF seems to decrease on addition of the first 30 wt% PA6, although this effect is not so different from the experimental errors. Kinetics of non-isothermal crystallization of pure PVDF and PVDF blends containing 20 and 40 wt% PA6 has been investigated. The crystallization rate of PVDF is not influenced by PA6 in the temperature range 138.5-145 degrees C. At lower temperatures, it is, however, adversely affected by addition of PA6. The non-isothermal crystallization data for PVDF are fitted by the Ozawa equation in the temperature range 131-141 degrees C. The Ozawa index, or Avrami exponent, for pure PVDF decreases from 3 to 1 on decreasing temperature. This observation agrees with the nucleation of PVDF crystals which is heterogeneous, and a decrease from 3 to 1 in the growth dimension. The main effect of PA6 is to restrict the decrease of the Avrami exponent from 3 to 2 on decreasing temperature, more likely due to a slower decrease in the growth dimension. PA6 does not contribute to nucleation although it is phase separated.