Contribution of coalescence to microfibril formation in polymer blends during cold drawing

Abstract

The main goal of this study is to obtain a morphological confirmation of the contribution of coalescence to the fibril formation mechanism in microfibril reinforced composites (MFC) and in this way to explain the large differences in sizes of the starting spheres and the resulting long microfibrils, at rather modest draw ratios (between 6 and 12). For this purpose, the peculiar property of compatibilisers has been exploited, namely coating the dispersed particles and thus preventing them from eventual coalescing after coming in contact. Using scanning electron microscopy on samples at various stages of the cold drawing of polypropylene/poly(ethylene terephthalate) blends with and without a compatibiliser, the assumed mechanism has been established: the MFC from compatibilised blends show much shorter microfibrils since the compatibiliser inhibits the coalescence process. A qualitative model illustrating the transformation of the dispersed spheres into microfibrils due to coalescence during the cold drawing is also discussed.