Quantitative evaluation of iPP nucleation in the presence of carbon fibers: induction time approach

Crystallization and nucleation behavior in model composites based on iPP and differently sized carbon fibres have been analyzed in this work. The investigations were performed in the isothermal regime (120-127 ºC) using PLM and DSC. The results were analyzed by applying the Avrami and Muchova-Lednicky methods. It was shown that the carbon fibre surface acts as a nucleating agent during the crystallization of the iPP matrix. The highest effect was obtained with the fibres of PP-compatible size (C-T) related to unsized carbon fibres (C-U). The induction time, ti, and half-time of crystallization decreased with increasing carbon fibre content. The energy effect on the thickness of the critical nucleus decreased in the presence of C-fibres, a fact confirmed by a decrease in the nucleation parameter Q and the difference energy parameter ?? (Q decreased from - 4.96 for iPP to -21.32 for C/iPP model composites, and ?? decreased from 6.14x10-7 J/cm2 for iPP to 1.63x10-7 J/cm2 for model composites). The results of the model composites and their comparison with published data confirmed that the Muchova-Lednicky method could be successfully applied for the quantitative evaluation of the nucleation parameters not only in the temperature range previously suggested (130-138ºC), but also at lower crystallization temperatures (Tc=121-127ºC).