Alkaline Swelling of Hemp Woody Core Chips

Abstract

Swelling of hemp woody core chips after alkaline (peroxide) impregnation at 70 °C, as is practised in alkaline peroxide mechanical pulping (APMP) processes is examined, in relation to pulp yield and chemical composition of the chips. In contrast to wood chips, maximum swelling is attained at elevated temperature (70 °C) without chemical treatment, possibly as the result of relatively high porosity of hemp woody core cell walls. Alkaline swelling at 70 °C correlates with the xylan:lignin ratio. Swelling at ambient temperature shows some correlation with acidic group content. Apparent pore size distributions were examined, using 1H NMR spin-spin relaxation. Several apparent pore size distributions could be distinguished within each sample. Elevated temperature, NaOH and peroxide addition are influencing apparent pore size distribution and total pore volume differently. Addition of peroxide results in remarkably enlarged apparent pore sizes, which emphasizes its importance (apart from bleaching) in APMP pulping, enhancing fiber flexibility and fibrillation.