The effect of combining and baling on canola stem, fibre extraction, and properties
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Abstract
Canola is the third largest source of vegetable oil globally and a potential lignocellulosic bast fibre source. This study investigates the impact of harvest machinery, operations on the fibre properties of canola. Collected stems came from three stages of harvest: pre-combine (control), post-combining (PC), and post-baling (PB). Visual inspection of canola stems revealed no stem breakage during the pre-combine stage, whereas severe mechanical damage was observed in stems from the combined and baled stages. This damage included splitting, sharp cuts, fibrillation, fractures, and stem compression. Scanning electron microscope (SEM) analysis of fibres extracted from these damaged sections revealed defects such as longitudinal cracks, axial cracks, cracks (approximately 45° angle), cut fibres, and kinks. In contrast, no such cracks were observed in fibres from the pre-combine stage, and the severity of defects was significantly greater in fibres from stems subjected to baling. However, fibres from visually whole canola stems were extracted after 42 hours of treatment at 40oC in a closed-loop retting machine with two different water application rates: 225 ml/min (Zone 1) and 400 ml/min (Zone 2). The tension measured to extract fibres from the retted stems was significantly lower for the post-baling stage (0.211N) when compared with pre- and post-combine (0.341 and 0.314N). Analysis of stems from different harvest stages retted in different Zones confirmed that only post-baling significantly differed from the other stages and Zone was not a significant factor in extraction force. Fibre yield (%) was lowest for the baling stage, while the highest fibre yield was obtained from the pre-combine stage. Finally, individual fibres were tested for elastic modulus and tensile strength. In each test the first sign of break was used to evaluate the Young’s modulus and the tensile strength of the fibre. Each stage of harvest was equivalent in these fibre properties. The results of this study could be used to modify either baling practice or retting of baled stems to supply defect-free stems for the downstream canola fibre industry.