Surface cationized cellulose nanofibrils for the production of contact active antimicrobial surfaces (2023)

Dialdehyde cellulose nanofibrils (CNF) and nanocrystals (CNC) were prepared via periodate oxidation (CNF/CNC-ox) and subsequently functionalized with hexamethylenediamine (HMDA) via a Schiff-base reaction, resulting in partially crosslinked micro-sized (0.5–10μm) particles (CNF/CNC-ox-HMDA) with an aggregation and sedimentation tendency in an aqueous media, as assessed by Dynamic Light Scattering and Scanning Electron Microscopy. The antibacterial efficacy, aquatic in vivo (to Daphnia magna) and human in vitro (to A594 lung cells) toxicities, and degradation profiles in composting soil of all forms of CNF/CNC were assessed to define their safety profile. CNF/CNC-ox-HMDA exhibited higher antibacterial activity than CNF/CNC-ox and higher against Gram-positive S. aureus than Gram-negative E. coli, yielding a bacteria reduction of >90% after 24h of exposure at the minimum (≤2mg/mL), but potentially moderately/aquatic and low/human toxic concentrations (≥50mg/L). The presence of anionic, un/protonated amino-hydrophobized groups in addition to unconjugated aldehydes of hydrodynamically smaller (<1μm) CNC-ox-HMDA increased the reduction of both bacteria to log 9 at ≥4mg/mL and their bactericidal activity. While only CNF/CNC-ox can be considered as biosafe and up to >80% biodegradable within 24weeks, this process was inhibited for the CNF/CNC-ox-HMDA. This indicated their different stability, application and disposal after use (composting vs. recycling).

Masks proved to be necessary protective measure during the COVID-19 pandemic, but they provided a physical barrier rather than inactivating viruses, increasing the risk of cross-infection. In this study, high-molecular weight chitosan and cationised cellulose nanofibrils were screen-printed individually or as a mixture onto the inner surface of the first polypropylene (PP) layer. First, biopolymers were evaluated by various physicochemical methods for their suitability for screen-printing and antiviral activity. Second, the effect of the coatings was evaluated by analysing the morphology, surface chemistry, charge of the modified PP layer, air permeability, water-vapour retention, add-on, contact angle, antiviral activity against the model virus phi6 and cytotoxicity. Finally, the functional PP layers were integrated into face masks, and resulting masks were tested for wettability, air permeability, and viral filtration efficiency (VFE). Air permeability was reduced for modified PP layers (43% reduction for kat-CNF) and face masks (52% reduction of kat-CNF layer). The antiviral potential of the modified PP layers against phi6 showed inhibition of 0.08 to 0.97 log (pH7.5) and cytotoxicity assay showed cell viability above 70%. VFE of the masks remained the same (~99.9%), even after applying the biopolymers, confirming that these masks provided high level of protection against viruses.

Triboelectric nanogenerators (TENGs), as a new energy conversion device in self-powered sensing devices, have been used at extreme environmental conditions, which poses great challenges to the structural stability and chemical tolerance of triboelectric materials. However, the low tolerance characteristics of traditional triboelectric materials limit their expansion in emerging applications. Cellulose, with its unique multidimensional structure and, controlled surface chemistry regulation advantages, shows great potential in resisting extreme environmental conditions and is emerging as a new candidate. This review aims to design and fabricate cellulosic triboelectric materials with exceptional tolerance, providing a perspective on the emerging applications of TENGs at extreme environmental conditions. First, the performance advantages and design principles of action of cellulosic triboelectric materials at extreme environmental conditions are described. Second, the importance of physical and chemical regulation strategies is discussed through the multi-scale perspective from macroscopic fiber bundles to microscopic cellulose molecules. It also presents the latest applications of cellulosic triboelectric materials at extreme environmental conditions such as wide temperature, high humidity, high corrosion, and radiation. Finally, the idea of how cellulosic triboelectric materials can further expand the development of TENGs application areas is presented.

An enhanced efficiency fertilizer (EEF) is essential for sustainable agriculture, and here, we evaluated cellulose nanofibrils (CNF) as a nutrient carrier dispersed in biodegradable polymeric matrices. CNF were functionalized with negative (CNF⁻) and positive (CNF⁺) charges to improve (i) the CNF-nutrient and (ii) the CNF-polymeric matrix interactions. The CNF encapsulated the KNO₃ nutrient by spray drying (microcapsules) and then inserted into a poly (hydroxybutyrate)/starch-based matrix by melt-compounding (tablets). These materials were morphologically, structurally, and thermally characterized before and after biodegradation. Nutrient release profiles showed the microcapsules released the nutrients for up to 1h, while the tablets did for 8h in water and over 80days in soil. Tablets with CNF⁻ released NO₃⁻ faster than K⁺, and those with CNF⁺ behaved inversely. Besides, the biodegradation efficiencies were up to 75% in 120days. The CNF charges affected nutrient release and the matrix biodegradation, ensuring the matrices were harmless to the environment.

The interest in nanocellulose has recently increased in many fields due to its natural abundance, exceptional mechanical/optical properties, and better biocompatibility. During the production of cellulose nanocrystals (CNCs) via sulfuric acid hydrolysis, sulfate groups are introduced, which decrease the thermal stability of CNCs and, thus, have a profound negative effect on the potential application of CNCs in nanocomposites. Also, mechanical methods exhibit poor morphological properties in CNCs with a reduced degree of crystallinity. Therefore, to improve the processability and performance of CNCs and extend their industrial applications and quality, nano-cellulose undergoes surface modifications by physical and chemical means. Surface modifications of CNCs lower the surface energy, increase hydrophobicity, improve interfacial adhesion, enhance their compatibility between nanocomposite components, and improve their dispersion and interaction. Surface-modified CNCs have wide applications in medicine, catalysis, optics, remediation processes, electronics, textiles, pulp, paper, etc. Other applications of CNCs are: supporting catalysts and sensors, as diaphragms in earphones; for tissue engineering, scaffolds, for toughened paper, as polymer nanocomposites for developing membranes, in flexible panels for flat panel displays, in the optical application and biomimetic foams, and as rheology modifiers. This review provides the latest advances in surface modification of CNCs and the relevant processes, properties, and applications.

Carbohydrate Polymers, Volume 152, 2016, pp. 170-180

Cationic cellulose hydrogels (CCGs) were prepared from quaternized celluloses with degrees of substitution (DS) of 0.56, 0.84, and 1.33, by the cross-linking reaction with poly(ethylene glycol) diglycidyl ether as a cross-linker. The CCGs exhibited swelling behavior in aqueous solutions, which was not affected by pH and temperature of the solution because of the presence of quaternary ammonium groups in their structures. The CCGs showed adsorption ability toward anionic dyes in aqueous solution, which increased with increasing DS. The dye adsorption was found to follow the pseudo-second order kinetic model and the equilibrium isotherm data can be described by the Langmuir adsorption model. In addition, the CCGs could be regenerated and proved to be recyclable adsorbents for wastewater treatment.

Carbohydrate Polymers, Volume 167, 2017, pp. 167-176

Here we demonstrate di-carboxylic acid hydrolysis for the integrated production of lignin containing cellulose nanocrystals (LCNC) and nanofibrils (LCNF) using two unbleached mixed hardwood chemical pulps of lignin contents of 3.9 and 17.2%. Acid hydrolysis experiments used maleic acid solution of 60wt% concentration at 120°C for 120min under ambient pressure. Yields of LCNC were low of less than 6% under this set of conditions. The higher lignin content sample produced LCNC with greater height (diameter) of 25nm but similar length of approximately 230nm to that from the lower lignin content fibers (height of 20nm). Interestingly, the higher lignin content sample resulted in LCNF with smaller height (diameter) of 7nm but longer length of >1μm, or greater aspect ratio than the LCNF from the lower lignin fibers of height 10nm and length <1μm. Lignin protected cellulose from esterification which resulted in LCNC and LCNF that was less carboxylated compared to those lignin-free CNC and CNF and therefore had lower charges. However, lignin is more hydrophobic and thermally stable than carbohydrates therefore LCNC and LCNF are favorable for composite applications.

Carbohydrate Polymers, Volume 199, 2018, pp. 219-227

Deep eutectic solvents (DESs) are potential green systems that can be used as reagents, extraction agents and reaction media. DESs are often biodegradable, easy to prepare and have low toxicity. In this work, a recyclable DES formed from aminoguanidine hydrochloride and glycerol (AhG) was used as a reaction medium and reagent (aminoguanidine hydrochloride) for the production of cationic nanocelluloses. Under mild conditions (i.e., a reaction time of 10 min at 70 °C), dialdehyde celluloses (DACs) with two different aldehyde contents (2.18 and 3.79 mmol g⁻¹) were cationized by AhG DES to form cationic dialdehyde celluloses (CDACs). Both CDACs achieved a similar high charge density of approximately 1.1 mmol g⁻¹. At 80 °C (for 10 min), a very high cationic charge density of 2.48 mmol g⁻¹ was obtained. The recyclability of AhG DES was demonstrated by reusing it five times without decreasing the reaction efficiency. In particular, due to the low consumption of amoniguanidine hydrochloride, high recycling efficiency could be achieved without the use of any additional chemicals. The cationized celluloses, CDACs, were further mechanically disintegrated to obtain cationic nanocelluloses. According to the initial aldehyde content of DACs, the morphology of the nanocellulose could be tailored to produce highly cationic cellulose nanofibrils (CNFs) or cellulose nanocrystals (CNCs). Transmission electron microscopy confirmed that individual CNFs and CNCs with an average width of 4.6 ± 1.1 nm and 5.7 ± 1.3 nm, respectively, were obtained. Thus, the results presented here indicate that the AhG DES is a promising green and recyclable way of producing cationized CNFs and CNCs.

Carbohydrate Polymers, Volume 103, 2014, pp. 187-192

The aqueous pre-treatment of cellulose with periodate and Girard’ reagent T was employed as a novel and promising method to promote nanofibrillation of wood pulp and to obtain cellulosic nanofibrils with cationic functionality (CNFC). To demonstrate the feasibility of CNFCs in particle aggregation, a kaolin clay model suspension was aggregated by the CNFCs. Direct high-pressure homogenization of cationized cellulose resulted in nanofibrils exhibiting typical widths of 10–50nm and cationic charge densities ranging from 1.10 to 2.13mequiv.g⁻¹. The nanofibril suspensions existed in the form of highly transparent gels and possessed cellulose I crystalline structures. All of the CNFCs promoted strong aggregation of kaolin and produced voluminous kaolin-CNFC aggregates with lateral dimensions of several millimeters. Moreover, the CNFCs maintained good aggregation performance through wide pH (3–9) and temperature (25–60°C) ranges. Thus, CNFCs were shown to be highly potential candidates for replacement of present synthetic soluble flocculation and coagulation aids.

Carbohydrate Polymers, Volume 132, 2015, pp. 598-605

In this work, Micro-fibrillated Cellulose (MFC) was cationically modified by quaternary ammonium groups with different chemical structures aiming to improve the sorption capacity to bile acid. The in-vitro bile acid sorption was performed by investigating various factors, such as quaternary ammonium group content and length of its alkyl substituent of the modified cationic MFC (CMFC), ionic strength, initial concentration and hydrophobicity of bile acid. The results showed that the sorption behavior of the modified CMFC was strongly influenced by the quaternary ammonium group content and the lengths of its alkyl substituent, the sorption capacity for the modified CMFC with a C₁₈ alkyl substituent, was approximately 50% of that of Cholestyramine. The experimental isotherm results were well fitted into the Temkin model. The effect of salts in the solution was smaller for the bile acid sorption onto the hydrophobic CMFC than the CMFC. It was also found that the binding capacity of CMFC was higher for more hydrophobic deoxycholate in comparison with cholate.

Carbohydrate Polymers, Volume 133, 2015, pp. 80-89

Cellulose nanofibrils (CNF) grafted with glycidyltrimethylammonium chloride (GTMAC), containing quaternary ammonium contents of 0.44 (QCNF-1), 1.47 (QCNF-2), and 2.28 (QCNF-3) meqg⁻¹, were evaluated as flocculants for the removal of Reactive Orange 16, an anionic azo dye, from aqueous solution. A rotatable and orthogonal central composite design was used to examine the performance of QCNFs under a range of experimental conditions. Removal efficiencies at the centre point of the design space were found to be 236.9±7.8, 254.2±3.8, and 264.6±2.8mgg⁻¹ for QCNF-1, QCNF-2 and QCNF-3, respectively. The highest removal efficiency, 295.1mgg⁻¹, was observed when using QCNF-3 at a low monovalent salt concentration. The QCNF reported herein provides a sustainable and biodegradable alternative to traditional synthetic flocculants for the decolorization of dye-containing effluents.