Thermal degradation behavior and kinetics of industrial hemp stalks and shives

Thermogravimetric curves are measured, at heating rates of 5, 10 and 20 K/min under a nitrogen flow, of industrial hemp and shives, a by-product of bast fiber production, after water retting and mechanical decortication of the plant stalk. To understand the influences of the pretreatments, measurements are also made for water-retted and water-washed hemp, and shives obtained from manual decortication. Beech wood is used for comparison. It is found that a five-component degradation scheme (in number of two, one and two, for the pseudo- hemicellulose, cellulose and lignin, in the order) provides an excellent description in all cases. The kinetic parameters are affected more by pretreatments (retting and decortication) than chemical composition (hemp stalks or shives). Moreover, in addition to the quantitative similarities between shives and beech wood, the differences between hemp and shives can be taken into account by slightly higher activation energies of the latter for the second and third component (177 and 195 kJ/mol versus 160 and 177 kJ/mol), thus describing its higher thermal stability. The performances of a standard three-component scheme are also evaluated.