Preparation and characterization of vinyl silane crosslinked thermoplastic composites filled with natural fibres
Mokhena, Teboho Clement
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In this work sisal nanowhiskers (SNW) extracted from sisal fibres were used to reinforce polyethylene matrices, high-density polyethylene (HDPE) and low-density polyethylene (LDPE). The nanocomposites were prepared by solution casting from toluene and meltmixing, both followed by melt pressing. In the case of melt mixing, the surfaces of the SNW were also chemically modified with 1 phr of triethoxy vinyl silane (VTES) to improve their dispersibility and compatibility with the matrices. The nanocomposites and sisal nanowhiskers were characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and X-ray diffractometry (XRD). The sisal nanowhiskers, obtained through sulphuric acid hydrolysis treatment, had average lengths of 197 ± 75 nm and diameters of 12.2 ± 3.7 nm, and a crystallinity index of 89%. FTIR confirmed the surface chemical modification of the sisal nanowhiskers. The microscopic techniques demonstrated a fairly good dispersion of the whiskers in the matrices, regardless of the treatment or the preparation method. The storage modulus for the solution mixed nanocomposites was better than the untreated melt mixed nanocomposites. This behaviour was ascribed to the formation of a rigid cellulosic network during processing. For the treated melt mixed samples, the reinforcing effect was worse, suggesting the absence of a strong mechanical network because of the good interaction between the whiskers and the host polymer matrix. TGA revealed that there was no significant influence on the degradation behaviour of both polymers. The crystallization behaviour of the polymers was found to strongly depend on their morphologies. The melting and crystallization behaviour of the LDPE nanocomposites were almost unchanged, while an increase in crystallinity was observed for all the HDPE nanocomposites. The tensile properties depended on the type of polymer, the treatment, and the preparation method. Generally there was an improvement in tensile modulus, and a decrease in elongation at break, but the stress at break only improved for the HDPE nanocomposites.