Transcrystallinity in maize tissues/polypropylene composites: First focus of the heterogeneous nucleation and growth stages versus tissue type

The improvement of cellulosic biomass-polymer composites needs to evaluate what occurs at the biomass-matrix interface during crystallization. Different well-defined maize tissues were obtained by original dry fractionation processes, without chemical treatment. Their morphological features were identified by optical and scanning electron microscopies. For each type of tissue, a small fragment was sandwiched between two films of isotactic polypropylene. The composite was subjected to quiescent isothermal conditions, followed in-situ by polarized optical microscopy. Focus of the heterogeneous nucleation at the surface of maize tissues showed that in all cases, more or less numerous semi-crystalline entities originated from the tissue surface, indicating a moderate nucleating activity. Different crystallization behaviors were observed as a function of the tissue. Growth rates of surface layers were generally higher that the growth rates of bulk spherulites. The differences were small, but significant. They were discussed within the frame of kinetic theory of growth.