Blends of polypropylene with poly(vinyl butyral)

The thermal stability, crystallization behaviour, and morphology of poly-(vinyl butyral) (PVB) with differing compositions of vinyl alcohol and butyral units were investigated. It was found that the glass-transition temperature of PVB decreases with increasing concentration of butyral units, mainly because of the reduced number of hydrogen bonds between hydroxyl groups of the chains. PVB samples with high vinyl alcohol content (>=63.3% by weight) are crystallizable and present an endothermic melting peak in the range 170-220°C. The thermal stability of PVB is also influenced by composition and increases with the number of butyral units. The thermal and crystallization characteristics of PVB were compared with those of neat polyvinyl alcohol (PVA), and the differences explained in terms of molecular structure. Two amorphous PVB samples, containing 31 and 14 wt % of vinyl alcohol units, respectively, were blended with isotactic polypropylene grafted with maleic anhydride (PP-MA), the latter of which was present to favour compatibilization of the components through chemical reaction or dipolar interactions involving the anhydride groups of the PP-MA and the hydroxyl groups of PVB. Properties of PP-MA/PVB 90/10 blends, prepared by melt extrusion, were compared to those of neat PP-MA. Both the PVBs used were immiscible with PP-MA, as indicated by the invariance of glass-transition temperatures with the composition of the blends. However, a high level of compatibility between the components was achieved because the blends showed good mechanical properties that were comparable to, or even superior to, those of neat PP-MA. The analysis of the crystallization kinetics, performed both in isothermal and nonisothermal modes, showed that crystallization of polypropylene is only slightly influenced by the presence of the PVB phase.