Structural and physico-chemical characterization of industrial hemp hurd: Impacts of chemical pretreatments and mechanical refining

Abstract

Effective utilization of agricultural and industrial wastes has attracted increasing attention due to the promotion of sustainability and circular economy in our society. In this study, we investigated an economical and environmentally friendly decortication method using metal oxide-assisted hydrogen peroxide oxidization to separate hemp bast and hurd from wasted industrial hemp (Cannabis sativa) stalk. With various chemical pretreatments and mechanical refining, the compositional, structural, and physico-chemical properties of the resulting hemp hurd were comprehensively characterized and analyzed. Chemical composition analysis revealed that decorticated hemp hurd contained 45.66 % cellulose, 24.57 % hemicellulose, and 21.67 % lignin as its major components. The harsher milling conditions led to significantly reduced particle size and destroyed the crystalline structure of hemp hurd bio-aggregates, as indicated by X-ray diffraction and dynamic light scattering results. Chemical pretreatments disintegrated the native cell wall structure, broke covalent or hydrogen-bonded linkages between cell wall components, digested cell wall components, and fractionated hemp hurd into lignocellulosic bio-aggregates with differentiated chemical compositions, morphology, crystalline structure, and thermal stability. Compared to single-step chemical pretreatment, sequential alkaline and bleaching pretreatments removed most of the non-cellulosic components (32.4 wt% reduction) and rendered the resulting hemp hurd fibers with high crystalline structure (70.4 %) and sufficient thermal stability (maximum degradation temperature ∼355 °C). The current study may highlight the importance of chemical pretreatments and particle size for the upscaling of wasted industrial hemp hurd for papermaking, biorefinery, or bioplastic composites industry.