Valorization of cannabis green waste to cellulose nanomaterials via phosphoric acid hydrolysis

Abstract

The recent increases in Cannabis sativa (cannabis) production, both in industrial hemp and recreational varieties, has highlighted the need for low-impact and sustainable practices for this expanding industry. Green waste of cannabis, consisting of the vegetative components like plant stalks, offers an unexplored opportunity for valorization through biomass optimization. Like hemp, recreational cannabis varieties contain two high cellulose fiber types: bast fiber (phloem tissue) and hurd fiber (xylem tissue). Using hemp as a model for recreational cultivars, this study demonstrates the ability to isolate cellulose nanomaterials from both bast and hurd fiber through phosphoric acid hydrolysis. Scanning electron microscopy (EM) shows that sodium hydroxide treatment is required for removing all non-cellulose surface components from hurd fiber. Comparison of the two fiber types with transmission EM reveals phosphoric acid-hydrolyzed bast fibers produce cellulose nanocrystals (CNC), while hurd fibers are more prone to producing a mixture of cellulose nanocrystals and nanofibril-like particles (CNF) without chemical pretreatment. Adding hydrogen peroxide to the sodium hydroxide pretreatment decreased the variation in CNC sizes resulting from both bast and hurd. The findings of this study provide several avenues for valorization of green waste, while aiming to minimize the techno-economic impact of pretreatments.