Surface and thermal characterization of natural fibres treated with enzymes

• Enzymatic treatments produced a homogeneous cellulose surface for subsequent activation.
• Removal of thermally labile pectic and hemicellulosic content resulted in improved thermal stability.
• The ultra structure of flax fibres (versus hemp) renders it more susceptible to enzymatic degradation.

Natural fibres are a potential replacement for glass fibre in composite materials. Inherent advantages such as low density, biodegradability and comparable specific mechanical properties (relative to glass fibre composites) make natural fibres an attractive option. However, limitations such as poor thermal stability, moisture absorption and poor compatibility with polymeric matrices are challenges that need to be resolved. The primary objective of this research was to study the effect of five enzymatic systems on the surface chemical, morphological and thermal properties of natural fibres. Flax and hemp fibres were treated with hemicellulases, pectinases and oxidoreductase. Surface and thermal properties were measured using X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and force tensiometry. Each treatment rendered the surface topography of both fibres free of contaminants and exposed the individual fibre bundles. Treatment with hemicellulase and pectinase improved the thermal properties for both fibres. XPS measurements confirmed reduction of the hemicellulosic content of both fibres for xylanase and pectinases (polygalacturonase and pectinmethylesterase). Removal of amorphous hemicellulosic material from the fibre surface and consequent exposure of the crystalline cellulose network resulted in a lower contact angle for all the treated samples. This work demonstrated that enzymes offer an inexpensive and environmentally attractive option to improve the surfaces of natural fibres for composite applications.