Facile and eco-friendly extraction of cellulose nanocrystals via electron beam irradiation followed by high-pressure homogenization†
An innovative system for extracting cellulose nanocrystals (CNCs) was proposed that uses a two-step process that combines short-time pretreatment by electron-beam irradiation (EBI) in the solid state and disintegration using high pressure homogenization (HPH) and was compared with the classic production by tedious acid hydrolysis. EBI caused cellulose pulp to obviously degrade with a reduction of the degree of polymerization (DP) from 998 (raw) to 156 at 100 kGy, whereas the carboxylate content was significantly increased by oxidative activation from 0.04 to 0.84 mmol g−1 in the dose range of 200–3000 kGy. Subsequent alkaline treatment for facile HPH isolated high-purity dissociated cellulose pulp for CNC production. The EBI-induced CNCs in the suspensions displayed stable dispersion and background transparency, which was substantially obtained via HPH (10 passes at 25 000 psi and 25 °C) and centrifugation, had a uniform width and a tunable length of 23–31 nm and 128–747 nm, respectively, with a rod-like shape, a high crystallinity index of 71–81%, and a reasonable negative charge density similar to those of conventional CNCs. A higher yield of 35–67% and increased thermal stability (Td onset = 229–249 °C and Td max = 318–324 °C) could also be achieved. For re-dispersion after spray drying or additional chargeability, the irradiated cellulose pulp was further oxidized or cationized with sodium hypochlorite or glycidyltrimethylammonium chloride to increase or reverse charge on the surface, respectively, followed by HPH disintegration for CNC preparation. The combined EBI and HPH method offers a promising and efficient approach with a low environmental impact for CNC industry sustainability.