Valorization of Byproducts of Hemp Multipurpose Crop: Short Non-Aligned Bast Fibers as a Source of Nanocellulose

Abstract

Nanocellulose was extracted from short bast fibers, from hemp (Cannabis sativa L.) plants harvested at seed maturity, non-retted, and mechanically decorticated in a defibering apparatus, giving non-aligned fibers. A chemical pretreatment with NaOH and HCl allowed the removal of most of the non-cellulosic components of the fibers. No bleaching was performed. The chemically pretreated fibers were then refined in a beater and treated with a cellulase enzyme, followed by mechanical defibrillation in an ultrafine friction grinder. The fibers were characterized by microscopy, infrared spectroscopy, thermogravimetric analysis and X-ray diffraction after each step of the process to understand the evolution of their morphology and composition. The obtained nanocellulose suspension was composed of short nanofibrils with widths of 5–12 nm, stacks of nanofibrils with widths of 20–200 nm, and some larger fibers. The crystallinity index was found to increase from 74% for the raw fibers to 80% for the nanocellulose. The nanocellulose retained a yellowish color, indicating the presence of some residual lignin. The properties of the nanopaper prepared with the hemp nanocellulose were similar to those of nanopapers prepared with wood pulp-derived rod-like nanofibrils.

Hemp Stem Epidermis and Cuticle: From Waste to Starter in Bio-Based Material Development

“…In Figure 5 , representative FE-SEM images at 500× magnification are reported. As it can be seen, HC appeared as isolated fibrils with a rod-like structure and an average diameter of 15 µm, suggesting that cementing wax, hemicellulose, and lignin were almost removed during the extraction procedure [ 35 , 36 ]. TEM analysis images revealed a large crystalline region and small quantities of amorphous regions ( Figure 5 ).…”

Biobased Composites from Eugenol- and Coumarin-Derived Methacrylic Latex and Hemp Nanocellulose: Cross-Linking via [2 + 2] Photocycloaddition and Barrier Properties

“…An aqueous suspension of hemp nanocellulose (1.3 wt % solid content) was obtained from nonaligned bast fibers from hemp (Cannabis sativa L.) plants of the Carmagnola variety following a previously published procedure . The suspension was formed by nanofibrils with lengths of 100–300 nm and widths of 5–12 nm, together with stacks of nanofibrils and larger micron-sized fibers.…”

“…An aqueous suspension of hemp nanocellulose (1.3 wt % solid content) was obtained from nonaligned bast fibers from hemp (Cannabis sativa L.) plants of the Carmagnola variety following a previously published procedure. 7 The suspension was formed by nanofibrils with lengths of 100−300 nm and widths of 5−12 nm, together with stacks of nanofibrils and larger micron-sized fibers. A handsheet of hemp nanocellulose, indicated below as hemp nanopaper (HNP), with a thickness of 53 μm, was prepared 7 screening fabrics using a Rapid-Koẗhen standard sheet former (Frank-PTI, Germany) and was used as a reference.…”

“…A great effort is ongoing to enlarge the platform of available biobased raw materials, including those derived from waste biomass through different refining and extraction processes. Cellulose, the most abundant natural polymer, can be extracted in the form of nanocellulose, i.e., nanofibrils or nanocrystals, from a wide variety of lignocellulosic biomasses, including, besides wood, abundant agricultural residues such as rice husks, , corn stover, , or hemp stems. − Nanocellulose shows remarkable mechanical and gas barrier properties in dry conditions, which are however dramatically affected by humid environments . A well-recognized strategy to improve the water resistance of nanocellulose is to combine it with polymers .…”

“…Extending this preliminary study, in the present work, we synthesized an EDMA-based copolymer latex with a higher coumarin content, to allow for a higher cross-link density, performed its physicochemical characterization, and studied its cross-linking via [2 + 2] cycloaddition. We then prepared composite films with different weight fractions of hemp nanocellulose, prepared by our group to valorize an abundant local agricultural residue consisting of low-quality bast fibers separated from stalks discarded from plants harvested for oil and seeds . We cross-linked the composites by exposure to UV light to produce insoluble materials, and we finally investigated the properties of the cross-linked composites, with a particular focus on water vapor permeability.…”