<i>N</i>‑Alkylated Chitin Nanocrystals as a Collector in Malachite Flotation

The majority of reagents currently used in mineral flotation processes are fossil-based and potentially harmful to the environment. Therefore, it is necessary to find environmentally-friendly alternatives to reduce the impact of mineral processing activities. Chitin nanocrystals are a renewable resource that, due to the natural presence of amino groups on its surface, represents a promising collector for various minerals of economic relevance. This study examines the one-pot functionalization of chitin nanocrystals with aldehyde structures to obtain hydrophobized colloids suitable for mineral flotation. The chemical properties of these nano-colloids were investigated by nuclear magnetic resonance spectroscopy, their colloidal behavior and structure by electrophoretic light scattering and atomic force microscopy, and their wettability through water contact angle measurements. The functionalized N-alkylated chitin nanocrystals possessed a hydrophobic character, were able to dress mineral particles and featured a performance in the flotation of malachite similar to commercial collectors, which proves the high potential of chitin nanocrystals in this field of application

Superstable Wet Foams and Lightweight Solid Composites from Nanocellulose and Hydrophobic Particles

Colloids are suitable options to replace surfactants in the formation of multiphase systems while simultaneously achieving performance benefits. We introduce synergetic combination of colloids for the interfacial stabilization of complex fluids that can be converted into lightweight materials. The strong interactions between high aspect ratio and hydrophilic fibrillated cellulose (CNF) with low aspect ratio hydrophobic particles afford superstable Pickering foams. The foams were used as a scaffolding precursor of porous, solid materials. Compared to foams stabilized by the hydrophobic particles alone, the introduction of CNF significantly increased the foamability (by up to 350%) and foam lifetime. These effects are ascribed to the fibrillar network formed by CNF. The CNF solid fraction regulated the interparticle interactions in the wet foam, delaying or preventing drainage, coarsening, and bubble coalescence. Upon drying, such a complex fluid was transformed into lightweight and strong architectures, which displayed properties that depended on the surface energy of the CNF precursor. We show that CNF combined with hydrophobic particles universally forms superstable complex fluids that can be used as a processing route to synthesize strong composites and lightweight structures

Superstable Wet Foams and Lightweight Solid Composites from Nanocellulose and Hydrophobic Particles

Colloids are suitable options to replace surfactants in the formation of multiphase systems while simultaneously achieving performance benefits. We introduce synergetic combination of colloids for the interfacial stabilization of complex fluids that can be converted into lightweight materials. The strong interactions between high aspect ratio and hydrophilic fibrillated cellulose (CNF) with low aspect ratio hydrophobic particles afford superstable Pickering foams. The foams were used as a scaffolding precursor of porous, solid materials. Compared to foams stabilized by the hydrophobic particles alone, the introduction of CNF significantly increased the foamability (by up to 350%) and foam lifetime. These effects are ascribed to the fibrillar network formed by CNF. The CNF solid fraction regulated the interparticle interactions in the wet foam, delaying or preventing drainage, coarsening, and bubble coalescence. Upon drying, such a complex fluid was transformed into lightweight and strong architectures, which displayed properties that depended on the surface energy of the CNF precursor. We show that CNF combined with hydrophobic particles universally forms superstable complex fluids that can be used as a processing route to synthesize strong composites and lightweight structures

Superstable Wet Foams and Lightweight Solid Composites from Nanocellulose and Hydrophobic Particles

Colloids are suitable options to replace surfactants in the formation of multiphase systems while simultaneously achieving performance benefits. We introduce synergetic combination of colloids for the interfacial stabilization of complex fluids that can be converted into lightweight materials. The strong interactions between high aspect ratio and hydrophilic fibrillated cellulose (CNF) with low aspect ratio hydrophobic particles afford superstable Pickering foams. The foams were used as a scaffolding precursor of porous, solid materials. Compared to foams stabilized by the hydrophobic particles alone, the introduction of CNF significantly increased the foamability (by up to 350%) and foam lifetime. These effects are ascribed to the fibrillar network formed by CNF. The CNF solid fraction regulated the interparticle interactions in the wet foam, delaying or preventing drainage, coarsening, and bubble coalescence. Upon drying, such a complex fluid was transformed into lightweight and strong architectures, which displayed properties that depended on the surface energy of the CNF precursor. We show that CNF combined with hydrophobic particles universally forms superstable complex fluids that can be used as a processing route to synthesize strong composites and lightweight structures

Nanostructured Cellulose II Gel Consisting of Spherical Particles

Cellulose nanofibrils (CNF) are usually obtained by breaking down the lignocellulosic structure of pulp, i.e., as cellulose I allomorph and according to rather energy-intensive pathways. In contrast to those approaches, TENCEL gel is obtained from a nonfibrous cellulose II precursor directly out of the Lyocell process in a deceptively energy-efficient way: After enzymatic treatment and only one cycle in a high-pressure homogenizer (comparing to up to 20 cycles for CNF manufacture) the final gel is obtained. The utilization of a starting material from an already existing industrial process is another distinct advantage. This novel cellulose II gel possesses a particle-like, homogeneous morphology and is composed of individual particles with a size of less than one micron, featuring the rheological behavior of a soft solid. The course of the gel production process was studied with respect to changes in crystallinity, appearance and molecular weight, whereas the morphology and size of the final gel particles were assessed comprehensively by light-microscopy, dynamic light scattering and electron microscopy. In water, the individual particles form aggregates with a mean size of 11 μm. The viscoelastic gel forms highly porous cryogels with a surface area of 298 m2/g and a well-defined nanostructure. These features were studied in depth by SAXS, nitrogen sorption experiments and SEM. The economic production in combination with the highly accessible surface offers unique properties, and applications are envisioned as tailored, high performance materials

Assessment of Electrothermal Pretreatment of Rambutan (Nephelium lappaceum L.) Peels for Producing Cellulose Fibers

Agroindustrial wastes are renewable sources and the most promising sustainable alternative to lignocellulosic biomass for cellulose production. This study assessed the electrothermal pretreatment of rambutan peel (RP) for producing cellulose fibers. The pretreatment was carried out by Ohmic heating at a solid-to-liquid ratio of 1:10 (w/v) in a water/ethanol (1:1, v/v) mixture as the electrical transmission medium at 60 ± 1 °C for different holding times (15, 30, and 60 min). Ohmic heating did not significantly influence the total fiber yield for the various holding times. However, the compositions of the samples in terms of extractives, lignin, hemicellulose, and α-cellulose content were significantly influenced. In addition, the electrothermal pretreatment method reduced the bleaching time of RP by 25%. The pretreated fibers were thermally stable up to 240 °C. Ohmic heating pretreatment times of 15 and 30 min were found most promising, reducing the required bleaching chemicals and increasing the α-cellulose yield. The pretreated bleached cellulose fibers had similar properties to nontreated bleached fibers and could be efficiently processed into stable gels of strong shear-thinning behavior with potential application as rheology modifiers in food products. Our results demonstrate that rambutan peel could serve as a promising sustainable alternative to woody biomass for cellulose production. Ohmic heating meets the requirements for industrial applications as it is eco-friendly, improves the efficiency and energy consumption in fiber processing, and could as well be included in the processing of similar food wastes

Upcycling Byproducts from Insect (Fly Larvae and Mealworm) Farming into Chitin Nanofibers and Films

Nowadays, environmental concerns make us rethink the way that we live and eat. In this regard, alternative protein sources are emerging; among them, insects are some of the most promising alternatives. Insect farming is still an infant industry, and to improve its profitability and environmental footprint, valorization of the byproducts will be a key step. Chitin as the main polysaccharide in the exoskeleton of insects has a great potential in this regard and can be processed into high value-added materials. In this study, we extracted and fibrillated chitin fibers from fly larvae (Hermetia illucens) and compared them with commercial chitin from shrimp shells. A mix of chitin and cellulose fibers was also extracted from mealworm farming waste. The purified chitinous fibers from different sources had similar chemical structures as shown by Fourier transform infrared and nuclear magnetic resonance spectroscopies. After mechanical fibrillation, the nanostructures of the different nanofibers were similar with heights between 9 and 11 nm. Chitin nanofibers (ChNFs) from fly larvae presented less nonfibrillated fiber bundles than the shrimp-derived analogue, pointing toward a lower recalcitrance of the fly larvae. ChNF suspensions underwent different film-forming protocols leading to films with tensile strengths of 83 ± 7 and 71 ± 4 MPa for ChNFs from shrimp and fly, respectively. While the effect of the chitin source on the mechanical properties of the films was demonstrated to be negligible, the presence of cellulose nanofibers closely mixed with ChNFs in the case of mealworm led to films twice as tough. Our results show for the first time the feasibility of producing ChNFs from insect industry byproducts with high potential for valorization and integral use of biomass

Nanocellulose Removes the Need for Chemical Crosslinking in Tannin-Based Rigid Foams and Enhances Their Strength and Fire Retardancy

Thermal insulation and fire protection are two of the most critical features affecting energy efficiency and safety in built environments. Together with the associated environmental footprint, there is a strong need to consider new insulation materials. Tannin rigid foams have been proposed as viable and sustainable alternatives to expanded polyurethanes, traditionally used in building enveloping. Tannin foams structure result from polymerization with furfuryl alcohol via self-expanding. We further introduce cellulose nanofibrils (CNFs) as a reinforcing agent that eliminates the need for chemical crosslinking during foam formation. CNF forms highly entangled and interconnected nanonetworks, at solid fractions as low as 0.1 wt %, enabling the formation of foams that are ca. 30% stronger and ca. 25% lighter compared to those produced with formaldehyde, currently known as one of the best performers in chemically coupling tannin and furfuryl alcohol. Compared to the those chemically crosslinked, our CNF-reinforced tannin foams display higher thermal degradation temperature (peak shifted upward, by 30–50 °C) and fire resistance (40% decrease in mass loss). Furthermore, we demonstrate partially hydrophobized CNF to tailor the foam microstructure and derived physical–mechanical properties. In sum, green and sustainable foams, stronger, lighter, and more resistant to fire are demonstrated compared to those produced by formaldehyde crosslinking

3D-Printed Collagen–Nanocellulose Hybrid Bioscaffolds with Tailored Properties for Tissue Engineering Applications

Hybrid collagen (Coll) bioscaffolds have emerged as a promising solution for tissue engineering (TE) and regenerative medicine. These innovative bioscaffolds combine the beneficial properties of Coll, an important structural protein of the extracellular matrix, with various other biomaterials to create platforms for long-term cell growth and tissue formation. The integration or cross-linking of Coll with other biomaterials increases mechanical strength and stability and introduces tailored biochemical and physical factors that mimic the natural tissue microenvironment. This work reports on the fabrication of chemically cross-linked hybrid bioscaffolds with enhanced properties from the combination of Coll, nanofibrillated cellulose (NFC), carboxymethylcellulose (CMC), and citric acid (CA). The bioscaffolds were prepared by 3D printing ink containing Coll-NFC-CMC-CA followed by freeze-drying, dehydrothermal treatment, and neutralization. Cross-linking through the formation of ester bonds between the polymers and CA in the bioscaffolds was achieved by exposing the bioscaffolds to elevated temperatures in the dry state. The morphology, pores/porosity, chemical composition, structure, thermal behavior, swelling, degradation, and mechanical properties of the bioscaffolds in the dry and wet states were investigated as a function of Coll concentration. The bioscaffolds showed no cytotoxicity to MG-63 human bone osteosarcoma cells as tested by different assays measuring different end points. Overall, the presented hybrid Coll bioscaffolds offer a unique combination of biocompatibility, stability, and structural support, making them valuable tools for TE

Assembling Native Elementary Cellulose Nanofibrils via a Reversible and Regioselective Surface Functionalization

Selective surface modification of biobased fibers affords effective individualization and functionalization into nanomaterials, as exemplified by the TEMPO-mediated oxidation. However, such a route leads to changes of the native surface chemistry, affecting interparticle interactions and limiting the development of potential supermaterials. Here we introduce a methodology to extract elementary cellulose fibrils by treatment of biomass with N-succinylimidazole, achieving regioselective surface modification of C6-OH, which can be reverted using mild post-treatments. No polymer degradation, cross-linking, nor changes in crystallinity occur under the mild processing conditions, yielding cellulose nanofibrils bearing carboxyl moieties, which can be removed by saponification. The latter offers a significant opportunity in the reconstitution of the chemical and structural interfaces associated with the native states. Consequently, 3D structuring of native elementary cellulose nanofibrils is made possible with the same supramolecular features as the biosynthesized fibers, which is required to unlock the full potential of cellulose as a sustainable building block