The thermal and crystallisation studies of short sisal fibre reinforced polypropylene composites

The thermal and crystallisation behaviour of sisal/PP composites was studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and polarising optical microscopy. Chemical modifications were made to sisal fibre using a urethane derivative of polypropylene glycol (PPG/TDI), maleic anhydride modified polypropylene (MAPP), and KMnO4 in order to improve the interfacial adhesion between the fibre and matrix. The thermal properties of the blends were analysed by TG analysis. The effects of fibre content and chemical treatments on the thermal properties were evaluated. It was found that treated fibre composites show superior properties compared to the untreated system. DSC measurements exhibited an increase in the crystallisation temperature and crystallinity, upon the addition of fibres to the PP matrix. This is attributed to the nucleating effects of the fibre surfaces, resulting in the formation of transcrystalline regions. On increasing the fibre content, the melting peak of the PP component was shifted to higher temperatures suggesting a constrained melting. The thickness of the transcrystalline layer formed depends on crystallisation temperature and time. The transcrystalline growth rate was slow in the quiescent state. On the other hand, upon the application of stress, transcrystallinity developed quickly. In fact, the shear stress at the polymer/fibre interface initiated the nucleation. Fibre surface modification by PPG/TDI increases the nucleating ability of sisal fibre to a very small extent.

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