Polymer Degradation and Stability 89 (2005) 327e335 www.elsevier.com/locate/polydegstab
Composition, structure and thermal degradation of hemp cellulose after chemical treatments S. Ouajai, R.A. Shanks* Applied Chemistry Department, RMIT University, GPO Box 2476V, Melbourne 3001, Australia Received 23 November 2004; received in revised form 13 January 2005; accepted 18 January 2005 Available online 11 March 2005
Abstract The thermal degradation behaviour of hemp (Cannabis sativa L.) fibres under a nitrogen atmosphere was investigated by using thermogravimetry (TGA). The kinetic activation energy of treated fibres was calculated from TGA data by using a varied heating rate from 2.5 to 30 ! C/min. The greater activation energy of treated hemp fibre compared with untreated fibre represented an increase of purity and improvement in structural order. A hydrophobic solvent affected the degree of non-cellulosic removal. Mercerisation and enzyme scouring removed non-cellulosic components from the fibre; however, structural disruption was observed after higher alkaline concentration, 20 %wt/v and longer scouring time, respectively. Structural disruption was observed by X-ray measurement. The FTIR results indicated an elimination of the non-cellulosic components by the mercerisation treatment and a specific removal of low methoxy pectin by use of pectate lyase enzyme (EC 4.2.2.2). An increase of temperature at the maximum rate of degradation and the rate of weight loss was characteristic of the purity and structure of treated hemp fibre. ! 2005 Elsevier Ltd. All rights reserved. Keywords: Cellulose fibre; Thermal degradation; Kinetics; Scouring; Crystallinity
1. Introduction Composites derived from natural and sustainable resources, especially cellulose are increasing in importance due to their numerous applications and advantages. The composites require a strong fibre with good adhesion between matrix and fibre to enhance their final properties. The bast fibres from hemp (Cannabis sativa L.) were selected for pre-treatment. As a natural product, the complex fibre composite was created via biosynthesis. The bast fibres in hemp are bound by a central lamella and arranged in bundles, separated by the cortex parenchyma cell with pectic- and hemicellulosic-rich cell wall [1,2]. The particular species, time of cultivation and weather
* Corresponding author. Tel.: C61 3 9925 2122; fax: C61 3 9639 1321. E-mail address:
[email protected] (R.A. Shanks). 0141-3910/$ - see front matter ! 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2005.01.016
produce differences in non-cellulosic composition [3,4]. The hemp bundle bast fibres were found to contain a large amount of pectins (18%), hemicelluloses (16%) and a small amount of lignin (4%) [1,2]. These chemicals are not thermally stable and tend to degrade at an early stage of heating. Further processing of a composite requires thermal stability information for materials selection and process operation. Removal of non-cellulosics from fibre surfaces was suggested to achieve this purpose. Various degrees of purity are required for different applications. Therefore, several methods have been applied to hemp cellulose. Firstly, solvent extraction is an important method conducted to remove the extractable fraction from cellulosic fibres [3,4]. This procedure may cause slight damage to the fibre structure and results in a more exposed cellulosic surface. Secondly, the chemical process of mercerisation is widely used to modify many types of cellulosic fibres. It is a well-known treatment for fibres
