Effect of calcium rich and alkaline solutions on the chemical behaviour of hemp fibres

Chemical reactivity of hemp fibres placed into a cimentitous matrix was studied by using a lime solution as a simplified cement solution. The hemp fibres contain 56.1 wt.% of cellulose, 20.1 wt.% of pectin, 10.9 wt.% of hemicellulose and 6 wt.% of lignin. These compounds are not solubilised in a basic medium rich in calcium but a part located at the fibre surface should be degraded. This treatment leads also to the decrease of the cristallinity index of the cellulose. Calcium ions adsorb in a large quantity onto the fibre surface due to the high concentration of pectin. The structure of the homogalacturonic part of pectin forms with Ca2+ a stable chelate called “egg-box”, supporting cation adsorption. The fibres are then covered by Ca(OH)2 nodules after immersion in a lime solution.