Fibre surface modifications through different treatments with the help of design expert software for natural fibre-based biocomposites

Composites of untreated and treated kenaf fibres with recycled polypropylene were fabricated by melt-cast technique with and without using maleic anhydride-grafted polypropylene. To improve interfacial bonding between kenaf fibres and recycled polypropylene, surface modifications of fibres were performed through ultrasound, enzyme and alkali pre-treatments. Klason lignin test, Fourier-transform infrared spectroscopy and scanning electron microscopy were used for the characterization of fibres. For characterization of composites, the samples were examined by density measurements, mechanical tests, field-emission scanning electron microscopy, X-ray diffraction study, differential scanning calorimetry and thermogravimetric analysis. Results revealed that ultrasound was able to remove the highest amount of lignin (32%). Tensile strength of the composites was increased by 57%, 58% and 40% due to the treatment with alkali, ultrasound and enzyme, respectively. Optimization of treatment parameters was carried out by means of the design expert software. The optimum treatment parameters, such as alkali concentration, soaking time in alkali, sonication power, temperature, enzyme concentration and soaking time in enzyme were found to be 4.6 wt%, 4.95 h, 99.96%, 94.46 degrees C, 1.26 wt% and 3.89 h, respectively, which are reasonably close to the experimental ones. The preferential b-axis orientation in recycled polypropylene crystal was found to be more apparent due to treated kenaf fibres with maleic anhydride-grafted polypropylene than untreated kenaf fibres with maleic anhydride-grafted polypropylene. A correlation among crystallinity, surface morphology, and tensile and thermal properties of composites with the fibre-matrix interactions has been established.