Effects of Kraft lignin and corn cob agro-residue on the properties of injected-moulded biocomposites

Lignocellulosic by-products are frequently disposed by means of combustion. This study investigates an alternative route for corn cob and Kraft lignin resources in order to support circular economy. The respective plantbased fibres and filler were compounded for the first time together with a poly(lactic acid) (PLA) matrix. Consecutively, seven different biocomposites were processed by injection-moulding and further characterized. The biocomposite containing a mixture of Kraft lignin and corn cob (12 wt% in total) exhibited the highest flexural strength (84 MPa). A proper wetting of PLA onto the corn cob particles demonstrated a good compatibility at matrix/fibre interface. PLA molecular structure changed in presence of 20 wt% lignin filler, with effect on the glass transition temperature and on the composite mechanical strength. The fibres moderately influenced composites surface tension, while Kraft lignin contributed to a slight increase of surface hydrophobicity. Surface energy (sigma sTotal) of composites have been estimated at 27.6, 28.7 and 27.8 mN/m for PLA/KL-20, PLA/CC-10 and PLA/KL-15/CC-5 respectively. While the polar component (sigma sPolar) have been estimated at 17.8, 20.0 and 18.7 mN/m for PLA/KL-20, PLA/CC-10 and PLA/KL-15/CC-5 respectively. Unlike the PLA/corn cob composite, those containing Kraft lignin were entirely biodegraded within 2 months in industrial composting conditions study. The materials could be utilized for end-use products thanks to their good mechanical and thermal properties. By adding wood-lignin and corn by-products, materials cost and carbon footprint shall decrease in comparison to pure PLA, while being a biodegradable and sustainable replacement of polyolefins.