Crystallinity in the polypropylene/cellulose system. I. Nucleation and crystalline morphology

The amount of research on lignocellulosic/thermoplastic composites has increased dramatically. Little attention, however, has been directed towards the subject of crystallinity at the interface (interphase). Optical microscopy and differential scanning calorimetry were used in this work to study crystallinity in the cellulose/polypropylene system. The results verify that cellulose acts as a nucleating agent for polypropylene, producing a transcrystalline region around the fiber. Treatment of the fibers with alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), or stearic acid, inactivates the surface features responsible for transcrystallinity. These treatments also affect the overall degree of crystallinity of the sample. Morphological features, resulting from a transcrystalline or nontranscrystalline interphase, may have a significant effect on mechanical properties. A possible mechanism for the appearance of transcrystallinity involving crystal structure matching is also proposed.