Industrial Crops and Products 53 (2014) 365–373 Contents lists available at ScienceDirect Industrial Crops and Products journal h om epage: www.elsevier.com/locate/indcrop Surface and thermal characterization of natural fibres treated with enzymes Michael George, Paolo G. Mussone, David C. Bressler ∗ Biorefining Conversions and Fermentations Laboratory, Department of Agricultural, Food and Nutritional Science, University of Alberta, T6E 2P5 Edmonton, Canada a r t i c l e i n f o Article history: Received 19 September 2013 Received in revised form 25 November 2013 Accepted 23 December 2013 Keywords: Enzymes Surface Thermal characterization Natural fibres a b s t r a c t 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 pectin- methylesterase). 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 sam- ples. This work demonstrated that enzymes offer an inexpensive and environmentally attractive option to improve the surfaces of natural fibres for composite applications. © 2014 Elsevier B.V. All rights reserved. 1. Introduction High-performance composite materials require a dispersed phase with elevated surface wettability and elevated cohesion with the polymeric matrix in order to attain efficient transfer of stress within the structure. While natural fibres constitute an attractive alternative to glass fibres owing, their limited thermal stability and incompatibility with synthetic polymer matrices constitute a significant challenge toward industrial implementation of these materials platforms (Mohanty et al., 2002; Milanese et al., 2012; Fei et al., 2009). Several stategies have been investigated to address these deficiencies. For examples, mercerization (Mwaikambo and Ansell, 2002), acetylation (Bledzki et al., 2008) and silane treat- ment (Anyakora and Abubakre, 2011) are known either to reduce hydrogen bonding within the complex structure or by reacting with the many hydroxyl groups on the surface (Gonzalez et al., 1999; Tserki et al., 2005). Physical methods have also been ∗ Corresponding author. Tel.: +1 780 492 4986; fax: +1 780 492 4265. E-mail addresses: Mngeorge@Ualberta.Ca (M. George), david.bressler@ualberta.ca (D.C. Bressler). studied and a comprehensive review was compiled by Mukhopadhay and Fangueiro (2009). Methods such as steam explosion (Kalia et al., 2009), plasma treatment (Yuan et al., 2004) and corona discharge (Gassan and Gutowski, 2000) promote separation of fibre bundles into more homogenous structures that can be evenly deposited in one direction in the matrix materials. An alternative to chemical and physical methods is repre- sented by the rapidly expanding use of biological agents such as fungi (Pickering et al., 2007; Gulati and Sain, 2006) and enzymes (Gustavsson et al., 2005; Kharazipour et al., 1997 and Pietak et al., 2007). Biological modifications offer several advantages over chem- ical and physical methods. They can selectively remove hydrophilic pectic and hemicellulosic material and require lower energy input. Enzymatic systems, in addition, can be recycled after each use (Li and Pickering, 2008). Li and Pickering (2008) used chelators and enzymes to separate hemp fibres into individual bundles. They found that the crystallinity (X-ray diffraction) and thermal prop- erties (thermal gravimetric analysis) improved after separating the bundles. In another study, Pietak et al. (2007) investigated the sur- face wettability of natural fibres using atomic force microscopy and contact angle measurements. They measured an increase in adhe- sion force for treated samples because enzymatic and chemical 0926-6690/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.indcrop.2013.12.037