Upcycling of Waste Hop Stems into Cellulose Nanofibers: Isolation and Structural Characterization

Abstract

Hop (Humulus lupulus) is cultivated to harvest female flowers that lend a deep flavor, aroma, and bitter taste to beer. However, the rest of the plant is burned or land filled as agro-industrial waste. This work upcycles hop stems (HS), which contain 44% cellulose, and demonstrates their suitability as raw materials for the isolation of cellulose nanofibers (CNFs). The Wise method followed by alkaline pretreatment removed lignin and hemicellulose. 2,2,6,6-Tetramethylpiperidine-1-oxyl radical-mediated oxidation fibrillated CNFs from pretreated and non-pretreated HS. A uniform height distribution was inferred from atomic force microscopy, with a median of ∼2 nm for pretreated and non-pretreated HS-derived CNFs. Solid-state nuclear magnetic resonance and X-ray diffraction characterizations indicated that the pretreatment enhanced the purity and crystallinity of the CNFs, though traces of triacylglycerols and calcium oxalate monohydrate remained. The two CNF samples exhibited similar two-step thermal degradation at 255–260 and 300 °C, though less char residue was produced by the pretreated CNFs.

Preparation and Characterization of Cellulose Nanofibers from Banana Pseudostem by Acid Hydrolysis: Physico-Chemical and Thermal Properties

“…Lignin protects the plant against microorganism attack and conjointly influences the morphology, structural properties, bonding nature and wetness resistance of the fiber [ 44 ]. In this study, M. acuminata and M. balbisiana contain 0.73% and 1.08% lignin, respectively, in comparison to cellulose from hop stem ( Humulus lupulus ), which contains 44% cellulose, 13% hemicellulose, and 26% lignin [ 45 ].…”

Cellulose-reinforced poly(ethylene-co-vinyl acetate)-supported Ag nanoparticles with excellent catalytic properties: synthesis of thioamides using the Willgerodt–Kindler reaction

“…The obtained solid fraction was washed three times with distilled water, followed by drying. Cellulose was extracted using a literature-reported method, as follows: 40 the lignin and hemicellulose fractions of rice straw were removed, followed by alkaline treatment. A 150 mL aqueous solution comprising sodium chlorite (NaClO 2 ; 1.50 g) and acetic acid (CH 3 COOH; 0.3 mL) was added to the dried rice straw sample (4 g) in a 250 mL round-bottom flask.…”

Hop natural fiber-reinforced poly(butylene succinate-co-butylene adipate) (PBSA) biodegradable plastics: effect of fiber length on the performance of biocomposites

“…Hop products refer primarily to the inflorescences (seed cones) of the female plants of Humulus lupulus L.-belonging to the family of Cannabaceae-which are used in the beer's brewing to provide aroma and flavor; the rest of the plant (bines) are typically discarded. [1][2][3][4][5][6] However, hop bines are rich in lignocellulosic contents and can be used as a source of short fibers. 2,4,6 To date, there are limited reports related to the production or use of hop-derived fiber.…”