Fibres from semi-retted hemp bundles by steam explosion treatment

Hemp (Cannabis sativa), is an annual plant used in the pulp and paper industry. It consists of two main morphological regions, the fibre cells which are bound by the middle lamellae and arranged in bundles, themselves separated by the cortex parenchyma cells with pectic and hemicellulosic rich cell walls, and the woody core with lignified cells. Any industrial utilisation of hemp requires the separation of the fibres from the rest of the plant, which is traditionally achieved by undertaking a dew retting in the field followed by several mechanical treatments. Our objective was to substitute the slow and difficult to control retting process by a fast and well controlled process, i.e. steam explosion treatment (STEX) of semi-retted decorticated hemp bundles. During the STEX treatment the pectins and hemicelluloses are hydrolysed and rendered water- or alkali-soluble, the fibres being more easily degummed. We optimised the treatment parameters (temperature/pressure, time and pH of impregnation) and found that impregnation in alkali and steaming for 90 s at 200°C (1.5 MPa) were among the best conditions for the degumming and individualisation of the elementary fibres. After washing of the steamed material a carding mechanical treatment is necessary to separate the single fibres. The steam exploded samples were observed by scanning electron microscopy (SEM), and the morphological aspects of the steam exploded hemp fibres are discussed.