Crystallisation and miscibility of poly(ethylene oxide)/poly(vinyl chloride) blends

Isothermal crystallisation of blends of Poly(ethylene oxide) and Poly(vinyl chloride), PEO/PVC, was analysed by differential scanning calorimetry (DSC). The influence of the amorphous polymer, PVC, on crystallisation rate of PEO was investigated using pure PEO as reference. Pure PEO and PEO/PVC blends were submitted to different crystallisation temperatures (from 40 to 58°C) and crystallisation times (from 1 to 72 h). Using the Hoffman-Weeks plot procedure, the equilibrium melting temperature, Tm°, was determined for pure PEO and for PEO/PVC blends with compositions (in wt%): 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80. The lamellar thickness factor of PEO crystals for pure PEO and for the blends showed a strong decrease when the PVC content was higher than 60 wt%. A small depression in Tm° was verified as the composition of PVC was increased. From the depression in Tm° the polymer-polymer interaction parameter, χ12, was evaluated using the Nishi-Wang equation. The results indicate that the miscibility between PEO and PVC in the molten state depends on the blend composition. The crystallisation rate also depends on the blend composition: the richer in PVC is the blend, the slower the crystallisation process.