Cationic cellulose nano-fibers (CCNF) as versatile flocculants of wood pulp for high wet web performance

Hierarchical Assembly of Cellulose Fibrils and Tannin in Biocomposite Foam: Scalable Production via Oven Drying and Customizable Metal Ions Release for Antimicrobial Activity

Advanced cellulose-based foams are urgently needed as sustainable packaging materials in an era of prioritizing environmental consciousness. However, transferring the mechanical properties of cellulose fibers into porous structures is always limited by gas entrapment during foaming and irreversible structural collapse upon liquid evaporation. Herein, a hierarchical assembly strategy combines cationic cellulose nanofibrils (CCNF) with a dynamic covalent tannin/borate (T/B) complex to fabricate 3D continuous foams with distinct lamellar structure via oven drying is proposed for scalable production. CCNF assembles the T/B complex onto cellulose fibers by electrostatic attraction and hydrogen bonding, while the reversible covalent bonds among T/B complex impart shear-thinning and self-healing properties, thereby ensuring foamability (exceeding 300%) and structural stability. Moreover, the T/B foam offers a versatile platform for customization with metal ions (Fe3+, Cu2+, and Ag+), allowing the tailoring of physical and mechanical properties. At an optimized tannin addition of 10%, the 10T/5B-Fe foam exhibits the highest normalized strength above 410 Pa/density, while maintaining an ultralow density of 9.2 mg cm- 3. Additionally, the pH-responsiveness of T/B complexes enables the release of metal ions for long-term antimicrobial activity. This study demonstrates a green and scalable strategy for functional foam production, offering new possibilities for next-generation antimicrobial packaging materials.

High-consistency modification of cellulose fibers: Resource-efficient introduction of cationic charges, and their effect on fiber and nanofibril properties

Quaternized cellulose fibers and cellulose nanofibrils (CNFs) are attractive candidates for the development of new renewable and biodegradable materials. However, the etherification reaction, through which functionalization is commonly achieved, provides low efficiencies, limiting industrial interest in the modification. This work primarily aims to increase the efficiency for the quaternization of cellulosic fibers while keeping the fiber-structure intact. This was achieved using high-consistency kneading to mix and modify the fibers at far higher solids contents than previously reported, efficiently limiting the alkaline hydrolysis of the reagent. Increasing the solids content from 5 to 45 wt% improved the reaction efficiency from 2 % to unprecedented 38 %. Characterization of the fibers showed that high-consistency quaternization affected the wet dimensions of the fibers, with enhanced swelling and fibrillation being obtained. Based on the tensile testing of handsheets made, it was concluded that quaternizing the fibers enhanced the strainability of the material, from 1.8 to 6.7 %, and that kneading achieved a concomitant increase in stress-at-break, from 15 to 103 MPa. CNFs produced from fluidized high-consistency-quaternized fibers had dimensions comparable to those produced from hand-mixed fibers, having aspect ratios above 200, the CNF films produced were transparent, tough, and with a high propensity to sorb water.

Homogeneous synthesis of cationic celluloses with broad-spectrum antibacterial activities for the treatment of vaginitis in mice

Microbial infection is a significant health issue for humans. Despite the development of numerous antibiotics, the continuous rise of drug-resistant bacteria highlights the urgent need for new materials to combat these problems. In this study, four water-soluble quaternized cellulose (QC) derivatives with degrees of substitution (DS) ranging from 0.23 to 0.45 were synthesized homogeneously from cellulose carbamate (CC) in NaOH/ZnO aqueous solution. The QC derivatives exhibited broad-spectrum antibacterial activity against gram-negative/positive bacteria, fungi and drug-resistance bacteria. Models of bacterial vaginitis (BV) and vulvovaginal candidiasis (VVC) were used to evaluate the application of QC derivatives visually. Secretion smears and tissue section staining revealed that treatment with QC derivatives led to a reduction in mycelia and spores in the vagina and secretions in the VVC model, along with improved inflammation. In the BV model, vaginal secretions were reduced, clue cells in smears significantly decreased, and inflammation markedly improved. Additionally, cell experiments and staining of mouse organ tissue sections demonstrated that QC derivatives exhibited good biocompatibility. Therefore, using QC derivatives in flushing douches represents a novel approach for treating vaginitis and could serve as a benchmark for addressing other infectious diseases.

On the determination of charge and nitrogen content in cellulose fibres modified to contain quaternary amine functionality

Research interest in quaternization of cellulose fibres has increased considerably over the past decades. However, there is little or no consensus regarding how to characterize the material in terms of degree of substitution (DS), and the literature suggests a range of different methods focusing on charge determination as well as nitrogen content quantification. This work aims to fill the knowledge gap regarding how the different methods perform in relation to each other, and for what cellulosic systems each method has advantages, disadvantages and even potential pitfalls. FT-IR and NMR measurements are used to establish successful modification and determine the relative number of substituent groups. Another six methods are compared for the determination of the DS of cellulosic fibres and nanofibrils. The methods include Kjeldahl measurements, nitrogen determination by chemiluminescence, determination of molecular nitrogen by the Dumas method, colloidal titration, conductometric titration and polyelectrolyte adsorption. It can be concluded that most techniques investigated are reliable within certain ranges of DS and/or when using appropriate post-treatment of the quaternized material and suitable sample preparation techniques. The results from the present work hence provide recommendations to make an educated choice of method, and experimental protocol, based on the technique at hand.

Study on the enhancement of paper tensile strength and hydrophobicity by adding PEI-KH560 in pulp suspension

Novel eco-friendly strength agent has inspired much attention of researchers. Herein, the PEI-KH560 prepared by PEI (polyethyleneimine) and KH560 (γ-glycidyl ether propyl trimethoxysilane) was added in the pulp suspension to enhance the paper performance. The results showed that the m(PEI):m(KH560) ratio and PEI's molecular weight were closely related with the paper strength and hydrophobicity. The SEM morphology of paper surface showed that the fiber-fiber crosslinking reached the tightest, at the optimal m(PEI):m(KH560) ratio and PEI's molecular weight. The results showed that when the Mw (molecular weight) of PEI was 10,000 and the m(PEI):m(KH560) ratio was 1:2, the PEI-KH560 presented the best strengthening performance on the paper strength and hydrophobicity. Dry tensile index and wet tensile index could reach 29.9 N·m/g and 1.37 N·m/g after adding the PEI10000-KH560 in pulp suspension before the paper formation. Further, the effect of process conditions (temperature, time, the addition amount, and pulp concentration) on the strength and hydrophobicity of paper network structure was investigated, after adding PEI-KH560 into the pulp suspension. It was of great significance for studying the mechanism between the chemical structures of PEI-KH560 and paper performance, which provided valuable theoretical practice on the preparation of novel strength agent.

Cellulose-Templated Nanomaterials for Nanogenerators and Self-Powered Sensors

Energy crisis inspires the development of renewable and clean energy sources, along with related applications such as nanogenerators and self-powered devices. Balancing high performance and environmental sustainability in advanced material innovation is a challenging task. Addressing the global challenges of sustainable development and carbon neutrality lead to increased interest in biopolymer research. Nanocellulose materials, derived from biopolymers, demonstrate potential as template candidates for advanced materials, due to their unique properties, including high strength, high surface area, controllable pore structures and high-water retention. In recent years, cellulose-templated nanomaterials enable delicate nano-/microscale structural construction, thus promoting developments in the field of nanogenerators and self-powered sensors. However, there is still a limited number of reviews focused on cellulose-templated nanomaterials for applications in nanogenerators and self-powered sensors. This review aims to fill this research gap by introducing various cellulose-templated nanomaterials and providing a detailed analysis of their fashionable applications in nanogenerators and self-powered sensors. The goal is to present cellulose-templated nanomaterials as highly promising template and guest materials for templating technologies, offering sustainable nano-/microscale control over advanced materials for the foreseeable future. This potential is promising for new applications in the fields of nanogenerators and self-powered sensors.

Effect of molecular weight of PEI on the strength and hydrophobic performance of fiber-based papers via PEI-KH560 surface sizing

In recent years, researchers have put much attention on the improvements and upgrades of novel wet strength agent in the papermaking fields, especially in the usage of household paper. Herein, PEIM-KH560 by polyethyleneimine (PEI) and γ-glycidyl ether propyl trimethoxysilane (KH560) was synthesized with five molecular weights (Mw) of PEI at 600, 1800, 10,000, 70,000 and 750,000. Results showed that the molecular weight greatly influenced the physicochemical properties of PEI-KH560, such as the size and thermal stability. The intrinsic cationic charge of PEI-KH560 provided the bonding sites with the paper fibers, forming strengthened fiber-fiber joints. It was shown that the dry, wet strength and hydrophobicity of cellulosic paper sheets were obviously improved. When the m (PEI):m(KH560) is 1:2, the strength of papers after sizing by Mw of PEI at 600 and 1800 is the most obvious, with the dry strength increased by 227.9 % and 187.5 %, and the wet strength increased by 183.8 % and 207.8 %, respectively. The maximum hydrophobicity was found at the PEI1800-KH560 with the contact angle value of 130.6°. The resultant environmental-friendly agent (PEI-KH560) obtained in this work provides valuable significance for the preparation of household and food packaging paper.

Current progress in functionalization of cellulose nanofibers (CNFs) for active food packaging

There is a growing interest in utilizing renewable biomass resources to manufacture environmentally friendly active food packaging, against the petroleum-based polymers. Cellulose nanofibers (CNFs) have received significant attention recently due to their sustainability, biodegradability, and widely available sources. CNFs are generally obtained through chemical or physical treatment, wherein the original surface chemistry and interfacial interactions can be changed if the functionalization process is applied. This review focuses on promising and sustainable methods of functionalization to broaden the potential uses of CNFs in active food packaging. Novel aspects, including functionalization before, during and after cellulose isolation, and functionalization during and after material processing are addressed. The CNF-involved structural construction including films, membranes, hydrogels, aerogels, foams, and microcapsules, is illustrated, which enables to explore the correlations between structure and performance in active food packaging. Additionally, the enhancement of CNFs on multiple properties of active food packaging are discussed, in which the interaction between active packaging systems and encapsulated food or the internal environment are highlighted. This review emphasizes novel approaches and emerging trends that have the potential to revolutionize the field, paving the way for advancements in the properties and applications of CNF-involved active food packaging.

Cationic cellulose nanofibers/chitosan auxiliary-dominated win-win strategy for paper yarn with superior color and physical performances

The colored and high-saline effluents during the traditional dyeing process poses serious environmental challenge. In our study, an eco-friendly cationic cellulose nano-fiber/chitosan (CCNF/CS) binary versatile auxiliary was designed for the neutral salt-free dyeing and physical enhancement of paper by mixing with pulp simply. Profiting from the rich cationic binding sites of CCNF/CS (Charge density: 3749.67 μmol/g), under near neutral conditions (pH = 6.2), the maximum adsorption capacity of anionic GL (Direct fast turquoise blue GL) on paper with 0.5 % CCNF/CS reached 1865.06 mg/g with a desirable evenness (45.5 % and 92.1 % higher than that of CCNF and NaCl group, respectively), and the dye uptake was up to 97 %. The spontaneous adsorption behavior was aligned with the pseudo-second-order and Langmuir models, with a primary physical mechanism enhanced by chemical forces. The combination of strong electronic attraction, hydrogen bonding, and n-π stacking effects granted CCNF/CS an enhanced proficiency in anionic dye adsorption. In addition, the tensile strength of the resulting paper yarn with 0.5 % CCNF/CS increased to 52.47 MPa under the optimal parameters, deriving from the CCNF/CS-induced inter-fiber cohesion. Overall, our research provided a green promising approach for the innovative neutral salt-free dyeing and mechanical enhancement of paper.

Effect of cationization pretreatment on the properties of cationic Eucalyptus micro/nanofibrillated cellulose

Micro/nanofibrillated celluloses (M/NFCs) have attracted considerable research interest over the past few decades, with various pretreatments being used to reduce energy consumption and/or increase fibrillation. To date, few studies have considered cationization as a pretreatment for their preparation. In this work, quaternary ammonium groups were attached to cellulose fibers by a direct reaction with 2,3-epoxypropyltrimethylammonium chloride or by a two-step method (periodate oxidation + Girard's reagent T). The cationic fibers with degrees of substitution (DS) between 0.02 and 0.36, were subjected to homogenization treatment. The morphological properties, chemical composition, and rheological behavior were evaluated to assess the effect of DS and the effect of the cationization method (for samples with similar DS). The two-step cationization resulted in significant degradation of the cellulose structure, leading to the formation of short fibrils and solubilization of the material, ranging from 6% to almost complete solubilization at a DS of 0.36. Direct cationization resulted in longer fibrils with an average diameter of 1 μm, and no significant cellulose degradation was observed, leading to a more cohesive gel-like material (at 1 wt%). These observations clearly show the strong influence of the cationization method on the final properties of the cationic cellulosic materials.

Impacts of degree of substitution of quaternary cellulose on the strength improvement of fiber networks

The degree of substitution (DS) of cellulose derivative is significantly associated with its properties. In this paper, a series of quaternary cellulose (QC) samples with different DS (ranging from 0.16 to 0.51) were synthesized with assistance of microwave and their relationship with strength improvement of fiber networks was investigated systematically. QCs were characterized by elemental analysis, FT-IR, ¹H NMR, and TGA, etc. The results showed that the cationic quaternary ammonium salt group was successfully grafted onto the backbones of cellulose chains and the thermal stability was associated inversely with the DS of QCs. However, the results of strength test for the fiber networks from secondary fiber of old corrugated containers showed that the tensile and burst strength was enhanced by addition of QCs, and their performance was positively correlated their DS. The best result achieved in this investigation was in the case of QC with DS of 0.51, with increments of tensile and burst strength 6.17% and 11.68%, respectively, at a dosage of 1.0 wt% based on oven-dry pulp. This investigation highlights the importance of DS of QC to its application in strength improvement for fiber networks.

Cellulose-based dispersants and flocculants

Natural dispersants and flocculants, often referred to as dispersion stabilizers and liquid-solid separators, respectively, have secured a promising role in the bioprocessing community. They have various applications, including in biomedicine and in environmental remediation. A large fraction of existing dispersants and flocculants are synthesized from non-safe chemical compounds such as polyacrylamide and surfactants. Despite numerous advantages of synthetic dispersants and flocculants, issues such as renewability, sustainability, biocompatibility, and cost efficiency have shifted attention towards natural homologues, in particular, cellulose-based ones. Within the past decade, cellulose derivatives, obtained via chemical and mechanical treatments of cellulose fibrils, have successfully been used for these purposes. In this review article, by dividing the functional cellulosic compounds into "polymeric" and "nanoscale" categories, we provide insight into the engineering pathways, the structural frameworks, and surface chemistry of these "green" types of dispersants and flocculants. A summary of their efficiency and the controlling parameters is also accompanied by recent advances in their applications in each section. We are confident that the emergence of cellulose-based dispersing and flocculating agents will extend the boundaries of sustainable green technology.

Cellulose nanofibrils (CNFs) produced by different mechanical methods to improve mechanical properties of recycled paper

In current study, CNFs produced by different mechanical methods, were used to improve the mechanical properties of recycled paper. The result showed the morphology of CNFs had great impact on reinforced effect and the length of fibrils determined their contribution in recycled paper strength. For different CNFs with similar diameter, the higher aspect ratio resulted in better reinforced effect. The CNFs produced by microfluidic homogenization and suitable PFI milling conditions (RM-CNF1) got best reinforced effect which improved tensile index and burst index by 35.5 % and 49.4 % at 5.0 wt% addition, respectively, due to their high aspect ratio. Although the CNFs produced by ball milling and ultrasonication (BU-CNF2) still had many bundles that were not fibrillated completely, their reinforced effect just below RM-CNF1 due to their special morphology and high retention rate. This work aims to study the influence of CNFs on recycled fibers reinforcement.

Recent Achievements in Polymer Bio-Based Flocculants for Water Treatment

Polymer flocculants are used to promote solid-liquid separation processes in potable water and wastewater treatment. Recently, bio-based flocculants have received a lot of attention due to their superior advantages over conventional synthetic polymers or inorganic agents. Among natural polymers, polysaccharides show many benefits such as biodegradability, non-toxicity, ability to undergo different chemical modifications, and wide accessibility from renewable sources. The following article provides an overview of bio-based flocculants and their potential application in water treatment, which may be an indication to look for safer alternatives compared to synthetic polymers. Based on the recent literature, a new approach in searching for biopolymer flocculants sources, flocculation mechanisms, test methods, and factors affecting this process are presented. Particular attention is paid to flocculants based on starch, cellulose, chitosan, and their derivatives because they are low-cost and ecological materials, accepted in industrial practice. New trends in water treatment technology, including biosynthetic polymers, nanobioflocculants, and stimulant-responsive flocculants are also considered.

Industrial Application of Nanocelluloses in Papermaking: A Review of Challenges, Technical Solutions, and Market Perspectives

Nanocelluloses (NC) increase mechanical and barrier paper properties allowing the use of paper in applications actually covered by other materials. Despite the exponential increase of information, NC have not been fully implemented in papermaking yet, due to the challenges of using NC. This paper provides a review of the main new findings and emerging possibilities in this field by focusing mainly on: (i) Decoupling the effects of NC on wet-end and paper properties by using synergies with retention aids, chemical modification, or filler preflocculation; (ii) challenges and solutions related to the incorporation of NC in the pulp suspension and its effects on barrier properties; and (iii) characterization needs of NC at an industrial scale. The paper also includes the market perspectives. It is concluded that to solve these challenges specific solutions are required for each paper product and process, being the wet-end optimization the key to decouple NC effects on drainage and paper properties. Furthermore, the effect of NC on recyclability must also be taken into account to reach a compromise solution. This review helps readers find upscale options for using NC in papermaking and identify further research needs within this field.