Morphological and rheological properties of cellulose nanofibrils prepared by post-fibrillation endoglucanase treatment

Development of high-barrier composite films for sustainable reduction of non-biodegradable materials in food packaging application

Widely employed petroleum-based food packaging materials have inflicted irreparable harm on ecosystems, primarily stemming from their non-biodegradable attributes and recycling complexities. Inspired by natural nacre with a layered aragonite platelet/nanofiber/protein multi-structure, we prepared high-barrier composite films by self-assembly of cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), montmorillonite (MMT), polyvinyl alcohol (PVA) and alkyl ketene dimer (AKD). The composite films demonstrated outstanding barrier properties with oxygen vapor transmission of 0.193 g·mm·m-2·day-1 and water vapor transmission rates of 0.062 cm3·mm·m-2·day-1·0.1 MPa-1, which were significantly lower than those of most biomass-degradable packaging materials. Additionally, the impacts of mixing nanocellulose with various aspect ratios on the tensile strength and folding cycles of the films were examined. The exceptional resistance of the composite films to oil and water provides a novel and sustainable approach to reduce non-biodegradable plastic packaging.

Producing Cellulose Microfibrils at a High Solid Content with and without Mechanical or Enzymatic Pretreatment

This study conducted a detailed evaluation of the feasibility of producing cellulose microfibrils (CMF) from a kraft-bleached hardwood pulp at high solid contents with and without pretreatments. CMFs produced by planetary ball milling at solid contents 17 and 28% were compared with those from 1 to 5% under the same milling conditions. Fiber pretreatments using a commercial endoglucanase and mechanical refining using a laboratory PFI mill were also applied before ball milling at a solid content of 28%. Two mechanisms of fiber fibrillation were identified from the results obtained: (i) ball and fiber/fibril interactions─the primary mechanism and (ii) interfiber/fibril frictional and tensional interactions─the secondary mechanism. The secondary mechanism plays an important role only in early-stage fibrillation and became less important as fibrillation proceeded in the later stage toward nanofibrillation. Improving fiber dispersion at lower solid content facilitated fibrillation. Endoglucanase pretreatment substantially shortened fibers to result in a "pulverized-like" CMF with short fibrils at an extended milling time. Mechanical refining of fibers facilitated fibrillation to result in CMFs with a morphology similar to that from runs without any fiber pretreatment but for a much shorter milling time. Both CMF water retention value (WRV) measurements and CMF suspension sedimentation experiments showed results consistent with imaging observations. The insights gained through this study provide relevant information with commercial significance regarding CMF production at high solids, which is not currently available in the literature.

Determination of carbohydrate content in kenaf degumming wastewater and converting them to carbon dots

The traditional textile degumming process produces abundant wastewater, which contains a lot of monosaccharides and oligosaccharides. It is of great economic and environmental significance to utilize these carbohydrates in high value. In this study, high performance liquid chromatography (HPLC) was used to analyze the carbohydrate components in kenaf degumming wastewater, and then the production of C-dots using the wastewater was explored. The results showed that the types and content in the degumming wastewater were monosaccharides (glucose, xylose and arabinose) and oligosaccharides (dextran, xylan and araban). The carbohydrate (mainly glucan and xylan) content in wastewater accounted for 91.16 % of the total carbohydrates weight loss in kenaf degumming process. By using hydrolysis and hydrothermal reaction on kenaf degumming wastewater, blue-green carbon dots (C-dots) with good performance were prepared and successfully applied to anti-counterfeiting printing. In particular, the as-prepared C-dots prepared from kenaf degumming wastewater with urea added (WUC-dots) showed an excitation-dependent photoluminescence (PL) spectrum and quantum yield (QY) of 2.4 % in aqueous solution. The fluorescent code exhibited a clear outline, excitation-tunable color and good stability, showing a great potential for anti-counterfeiting system.

Tailoring Hydrogel Structures: Investigating the Effects of Multistep Cellulose Defibrillation on Polyvinyl Alcohol Composites

Defibrillating cellulose through various grinding steps and incorporating it into hydrogels introduces unique properties that warrant thorough exploration. This study investigates cellulose defibrillation at different steps (15-120) using an ultra-fine friction grinder, blended with high-molecular-weight polyvinyl alcohol (PVA), and crosslinked via freeze-thawing. A critical discovery is the influence of defibrillation on the hydrogel structure, as evidenced by reduced crystallinity, thermal degradation, and the enhanced swelling of PVA chains. Despite an increased elastic modulus of up to 120 steps, the synthesized material maintains remarkable strength under hydrated conditions, holding significant promise in biomaterial applications.

Formulation and stabilization of high internal phase emulsions via mechanical cellulose nanofibrils/ethyl lauroyl arginate complexes

Motivated by the quest for biocompatibility, we report on oil-in-water (O/W), high-internal-phase Pickering emulsions stabilized via complexes of mechanical cellulose nanofibrils (CNF) and food-grade cationic surfactant ethyl lauroyl arginate (LAE). The complexation of oppositely charged CNF and LAE can be held together by electrostatic interaction. Their effect on suspensions electrostatic stabilization, heteroaggregation state, and emulsifying ability was studied and related to properties of resultant interfacial tension between oil and water and 3D printing of emulsions. The Pickering system with adjustable droplet diameter and stability against creaming and oiling-off during storage was achieved resting with LAE loading. Complexes formed by LAE adjustment act as Pickering stabilizers and three-dimensional networks in emulsion system, forming a scaffold with elastoplastic rheological properties that flows above critical stress while, without any additional treatment, exhibiting the required self-standing properties for 3D printing. By understanding the properties of CNF/LAE behavior in bulk and on interfaces, printing edible functional foods of CNF/LAE-based emulgel inks has been demonstrated to enable regulation of oil release.

Extraction of super high-yield lignin-carbohydrate complexes from rice straw without compromising cellulose hydrolysis

Lignin-carbohydrate complexes (LCC) that exhibit both structural advantages of lignin and carbohydrates are promising amphiphilic biopolymers, but the extraction is challenged by its liable chemical bond cleavage between lignin and carbohydrates. This work proposed a facile chemical route to integrating the production of water-insoluble (WIS LCC) and water-soluble LCC (WS LCC) into the emerging deep eutectic solvent (DES) biorefinery at mild conditions. The tailored mechanochemical fractionation process of ball milling assisted aqueous alkaline DES could extract 24.2 % LCC in total, with the co-production of a highly hydrolysable cellulose fraction (98.7 % glucose conversion). The resulting LCC exhibited considerably high contents of β-O-4, phenyl glycoside, and ferulic acid linkage bonds. When 100 g starting straw was subjected to this technique route, 9.1 g WIS LCC, 15.1 g WS LCC and 45.5 g glucose were cascaded produced. It was proposed that the selective disruption of hydrogen bonding entangled network and the quasi-state dissolution of the whole biomass allowed the subsequent cascade fractionation of WIS LCC, WS LCC and highly hydrolysable cellulose through solution property adjustment. This work showed a promising approach for LCC production with high yield without compromising cellulose conversion potential, which has been challenging in the current lignocellulose biorefinery.

High-strength hydrophilic N-halamines chitosan and cellulose nanofibers membranes with repeated bactericidal properties

Direct addition of disinfectants and membrane separation techniques have been common methods to address microbial contamination in water. However, disinfectants may generate toxic by-products, and even minor damage or biofilm formation on filtration membranes can lead to a heightened risk of microbial contamination. Consequently, how to quickly and safely disinfect microbial contaminated water sources remains a huge challenge. In this study, the high-strength broad-spectrum antibacterial CNF/CS composite membrane was fabricated by utilizing cellulose nanofibers (CNF) to reinforce the structure of chitosan (CS). The resulting CNF/CS composite membrane exhibits an impressive tensile strength of 148 MPa and boasts an active chlorine content of 5.29 %. Notably, even after undergoing 50 washing cycles and 10 repeated chlorination procedures, the structural integrity and high active chlorine content of the composite membrane remain preserved, validating its exceptional strength, stability, and chlorine rechargeability. Additionally, the CNF/CS antibacterial materials demonstrate remarkable attributes in terms of rapid sterilization, sustained and consistent release of active chlorine, and efficient inhibition of biofilm formation, demonstrating great potential in efficient, green, and safe sterilization.

Integrated enzyme hydrolysis assisted cellulose nanofibril (CNF) fabrication: A sustainable approach to paper mill sludge (PMS) management

The landfilling of paper mill sludge (PMS) has been restricted or even banned in many countries due to the raised concern about greenhouse gas (GHG) emissions and contamination of the soil and water, calling for a sustainable PMS management approach. The potential valorization of PMS to nanomaterials combined with traditional biorefinery was examined in this work. Three types of PMS-derived cellulose nanofibrils (CNFs) were prepared and evaluated: enzymatically assisted CNF (AU: with in-house produced enzyme and CT: with commercial enzyme), mechanically pretreated CNF (BT), and chemically pretreated CNF by TEMPO oxidation (TEMPO). It was found that enzyme-assisted mechanical fibrillation-derived CNFs had a comparable average diameter (27.9 nm for AU and 22.7 nm for CT) with that produced from mechanical pretreatment (26.5 nm for BT) and TEMPO oxidation pretreatment (20.0 nm for TEMPO), and they showed the best drainage properties among the three types of CNF. The CNFs resulting from enzymatic pretreatment reduced 15% of energy consumption compared to the mechanical method and had better thermostability than TEMPO oxidation method. In addition, the on-site produced enzyme showed similar performance to the commercial enzymes towards the CNF properties. These findings provide new insights into a promising integrated strategy in engineering CNF from PMS with on-site enzyme production as a novel and sustainable approach for PMS management and valorization.

Mechanically strong nanopapers based on lignin containing cellulose micro- and nano-hybrid fibrils: Lignin content-fibrils morphology-strengthening mechanism

Lignin-containing cellulose nanopapers are emerging multifunctional materials in the fields of coatings, films, and packaging. However, the forming mechanism and properties of nanopapers with various lignin content have not been thoroughly studied. In this work, a mechanically strong nanopaper was fabricated based on lignin-containing cellulose micro- and nano-hybrid fibrils (LCNFs). The influence of lignin content and fibrils morphology on the formation process of nanopapers was investigated to understand the strengthening mechanism of nanopapers. LCNFs with high lignin content provided nanopapers with intertwined micro- and nano-hybrid fibrils layers with small layer spacing, while LCNFs with low lignin content offered nanopapers interlaced nanofibrils layers with large layer spacing. Although lignin was expected to interfere with hydrogen bonds between fibrils, the uniformly distributed lignin contributed to the stress transfer between fibrils. Due to the good coordination between microfibrils, nanofibrils and lignin (as network skeleton, filler and natural binder, respectively), the well-designed LCNFs nanopapers with lignin content of 14.5 % showed excellent mechanical properties, including tensile strength (183.8 MPa), Young's modulus (5.6 GPa) and elongation (9.2 %). This work deeply reveals the relationship between lignin content, morphology and strengthening mechanism of nanopapers, and providing theoretical guidance for employing LCNFs as structural and reinforcing materials to design robust composites.