Influence of steam explosion pre-treatment conditions on binder-less boards from hemp shives and wheat straw

Abstract Non-catalysed steam explosion (SE) pre-treatment was used to valorise agricultural residues of hemp shives and wheat straw obtaining fibre bundles with self-bonding property. Three industrial hemp varieties of Futura75, Uso31 and Finola were used in the study. The crops were pre-treated at SE conditions temperature (℃)/time (min) of 200/1, 200/3, 220/2, 240/1 and 240/3. The influence of SE pre-treatment on the crops was evaluated by the particle size fractionation, scanning electron microscopy, cellulose content and its degree of polymerization (DP). Binder-less board samples with a thickness of 6 mm and a density of 900 kg/m3 were obtained from pre-treated crops at a temperature of 175 ℃. The influence of SE pre-treatment on the obtained binder-less boards was evaluated by the properties of thickness swelling (TS), water absorption (WA), modulus of elasticity (MOE), bending strength (MOR) and internal bonding strength (IB). The results show that increasing SE severity significantly decreased particle size and cellulose DP. Both factors of SE temperature and time significantly influence the obtained binder-less boards properties improving WA and IB up to SE240/3, and bending properties up to SE240/1. The best evaluation of binder-less boards was achieved by the crops pre-treated at SE conditions between 220/2 and 240/1 with the average property values of TS 9 %, WA 35 %, MOE 4482 N/mm2, MOR 22.1 N/mm2 and IB 0.54 N/mm2. The observed differences between the properties of the binder-less boards from pre-treated hemp shives indicate to the structural differences of the hemp varieties the most suitable being Uso31.