Interfacial morphologies in carbon fibre-reinforced polypropylene microcomposites

Abstract

Formation and build-up of interfacial morphologies along a high-modulus carbon fibre (HMCF), produced by isothermal crystallization in quiescent and sheared melts of isotactic polypropylene (PP), were studied by thermo-optical methods. It was established that in the quiescent melt, the HMCF generates α-transerystallization due to its strong α-nucleation ability. In the isothermally crystallized sheared melt, achieved by pulling the HMCF slightly above the crystallization temperature, a transcrystalline-like supermolecular structure developed. It was evidenced that this shear-induced supermolecular structure is composed of two crystalline phases: α and β. The α-layer, generated by melt-shearing along the CF surface (α-row nuclei), triggered the growth of the β-modification of PP under the crystallization conditions selected. This shear-induced polymorphous interfacial morphology should be correctly termed ‘cylindrite’. The basic difference between transcrystallization and cylindritic crystallization is related to the fact that transcrystallization is induced by heterogeneous nucleation, whereas cylindritic growth is induced by self (homogeneous) nucleation.