Abstract:

The aim of this research project was to investigate the mercerisation process of natural rapeseed straw used to manufacture composites with thermoplastic polymers. Alkali treatment of the native cellulose causes polymorphic transition to cellulose II and, consequently, improvement of mechanical properties of natural lignocellulosic materials. Different concentrations of alkali solutions were employed in the course of the rape (Brassica napus) mercerisation of Kaszub and Californium varieties: 5, 10, 12.5, 15, 17.5, 20, & 25%, and the process lasted for 1, 2, 3 4, 5, 7.5, 10, 15, 30, 60, 90 and 120 minutes, respectively. The structural transformation from cellulose I to cellulose II for rapeseed straw after alkali treatment with sodium hydroxide was investigated by means of the wide-angle X-ray scattering (WAXS) method. The X-ray diffraction pattern was recorded within the angle range of 5 - 30° 2Θ. The polymorphic transition was calculated on the basis of the individual areas under the peaks of both cellulosic forms. It was found that the amount of cellulose II in wooden parts of rapeseed straw depended on the concentration of alkali solution as well as on the time of chemical treatment. It was further found that the great efficiency of Cellulose I → Cellulose II transition (over 50%) was observed for both experimental varieties at a wide range of the concentrations applied, from 12.5 to 20%, when the process was conducted for at least 5 minutes. This result indicates a different behaviour of rapeseed straw in comparison with such other lignocellulosic materials as wood or natural fibres. There were no structural differences found between various rapeseed straw varieties in the mercerisation process. On the basis of the degree of cellulose crystallinity in rapeseed straw after alkali treatment, no degradation of lignocellulosic material was found to occur in the above-mentioned conditions.