Improving the accessibility of hemp fibres using caustic to swell the macrostructure for enzymatic enhancement

• Mercerization prior to enzymatic treatment results in better enzyme penetration.
• Effectiveness of mercerization prior to enzyme depends on enzyme type.
• Effectiveness of mercerization prior to enzyme depends location of component targeted.
• Use of caustic + enzyme resulted in hemp fibres that were less hydrophilic.
• Caustic + enzymatic treatment resulted in increased thermal stability.

The main aim of this study was to investigate the effect of mercerization prior to enzymatic treatments on the surface, on the thermal and morphological properties of hemp fibres. Hemp fibres were treated with sodium hydroxide (5%, w/v) and five different enzyme systems. The enzymes studied were xylanase, xylanase + 10% cellulase, pectinmethylesterase, polygalacturonase and laccase. A previous report utilizing enzymes alone (George et al., 2014) was used as a baseline to determine the impact of caustic swelling of the hemp fibres coupled to enzymatic treatment. Thermal gravimetric analysis (TGA) was used to study the effect of each system on thermal properties of the hemp fibres. Scanning electron microscopy (SEM) was used to monitor the changes in the morphological features of the hemp fibres, while X-ray photoelectron spectroscopy (XPS) was used to study the influence of each treatment of the surface chemical composition. Force tensiometry was used to investigate the effect of the different systems on the surface polarity of the treated fibres. The additional treatment with NaOH + hemicellulases was found to result in enhanced thermal properties when compared to previous systems. SEM micrographs confirmed greater fibre bundle rupture and increase in surface roughness of the base + enzyme treated samples. This work demonstrates that mercerization prior to enzymes, depending on the mode of action and arrangement of chemical components of the fibre, can be an effective method for improving the thermal and surface properties of fibres for composite applications.