Investigations on biocomposites from oat hull and biodegradable polymers

Abstract

Oat hull is an abundantly available form of biomass in Canada, which is mostly used as low-value feed material. With high fibre content, it can be used in the production of industrial products by providing opportunity as an additive in the replacement of petroleum-based products. Moreover, bio-based plastics/ biodegradable polymers are gaining popularity, as reinforced matrices into natural fibres to produce biodegradable composites. Therefore, the objectives of this investigation were to develop biocomposite materials from cellulose and lignin which were post-hydrolysis products of oat hull using biodegradable polymers (polylactic acid (PLA) and polycaprolactone (PCL)) and to compare the physical and mechanical properties of formulated biocomposites with polypropylene (PP) biocomposites so that a low-cost and eco-friendly biomaterial can be produced. Further, the effect of an impact modifier was investigated to improve the impact properties of such biocomposites. The oat hull biomass was cleaned and chemically pretreated to produce different kinds of fibres by dilute acid hydrolysis followed by delignification at different temperature conditions. The fibres resulting from pretreatment processes were AHB (acid-catalyzed hydrolysis by-product), CRB-30 and CRB-65 (cellulose-rich biofibre). Chemical analysis of fibres showed a reduction in hemi-cellulose and lignin content, with increased cellulose content. Formulations with rates of at 15% and 30% AHB or CRB fibres of the total mass of biocomposites were tested. The effect of impact modifier at 15% inclusion rate was also investigated with polylactic acid- and polycaprolactone-based composites. A twin screw extruder and a compression molding machine were respectively used for compounding the formulations and product molding/fabrication. The performance of the composites in all formulations was finally assessed by measuring their physical and mechanical properties such as density, color measurement, water absorption, tensile strength, flexural strength and tensile-impact energy. Fibre loading from 15% to 30% significantly affected the density and water absorption of the manufactured composites. The density of composites increased with addition of fibres; water absorption also increased with fibre addition in all formulations. Color analysis showed that products appeared darker in color because of addition of fibres. The results for the mechanical properties of PLA-based composites indicated that tensile and flexural strength of biocomposites generally decreased when compared to those of virgin polymers, while Young’s modulus and flexural modulus increased with corresponding increase in fibre content from 15% to 30%. On the other hand, PCL-based biocomposites with 30% fibre loading offered higher flexural strength than that of composites loaded with 15% fibres; similarly, tensile modulus and flexural modulus increased with an increase in fibre content. The most significant result is that tensile-impact strength of PLA- and PCL-based composites increased with addition of an impact modifier. Therefore, eco-friendly composites were successfully developed from an oat hull biomass by-product in combination with biodegradable polymers.