The effect of compatibilizers on the crystallisation, melting and polymorphic composition of β-nucleated isotactic polypropylene and polyamide 6 blends

Non-compatibilized and compatibilized blends of isotactic polypropylene (iPP) and polyamide 6 (iPP/PA6) as well as their beta-nucleated versions were prepared using maleic anhydride functionalized iPP (MAPP) with different anhydride contents as compatibilizer. Ca-suberate, a highly efficient and selective beta-nucleating agent was added to the blends in order to promote the formation of the beta-modification of W. The melting and crystallisation characteristics, as well as the polymorphic composition of the blends were studied by differential scanning calorimetry (DSC). The supermolecular and phase structure of the blends were studied by polarised light microscopy (PLM). iPP and PA6 form blends with heterogeneous phase structure; the PA6 component is dispersed in the iPP matrix in the concentration range studied. The compatibilizer promotes the dispersion of PA6 resulting in smaller particles than without MAPP. In the non-compatibilized beta-nucleated blends, art iPP matrix consisting mainly of the alpha-modification was formed already at low PA6 content. On the contrary, predominantly beta-iPP matrix developed in the presence of MAPP compatibilizers. The formation of alpha-iPP matrix in the absence of compatibilizer is related to the selective encapsulation of the nucleating agent in the polar PA6 phase. The influence of the blending technique on the polymorphic composition of the matrix supports the hypothesis of selective encapsulation. Compatibilizers, besides their traditional benefits assist the distribution of the beta-nucleating agent between both phases of the blends and promote the formation of a matrix rich in beta-iPP. In the presence of beta-nucleating agent MAPP with low anhydride content and blends of iPP containing maleated polypropylene crystallise predominantly in the beta-form. (c) 2006 Published by Elsevier Ltd.