Native wood celluloses can be converted to individual nanofibers 3–4 nm wide that are at least several microns in length, i.e. with aspect ratios >100, by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidation and successive mild disintegration in water. Preparation methods and fundamental characteristics of TEMPO-oxidized cellulose nanofibers (TOCN) are reviewed in this paper. Significant amounts of C6 carboxylate groups are selectively formed on each cellulose microfibril surface by TEMPO-mediated oxidation without any changes to the original crystallinity (∼74%) or crystal width of wood celluloses. Electrostatic repulsion and/or osmotic effects working between anionically-charged cellulose microfibrils, the ζ-potentials of which are approximately −75 mV in water, cause the formation of completely individualized TOCN dispersed in water by gentle mechanical disintegration treatment of TEMPO-oxidized wood cellulose fibers. Self-standing TOCN films are transparent and flexible, with high tensile strengths of 200–300 MPa and elastic moduli of 6–7 GPa. Moreover, TOCN-coated poly(lactic acid) films have extremely low oxygen permeability. The new cellulose-based nanofibers formed by size reduction process of native cellulose fibers by TEMPO-mediated oxidation have potential application as environmentally friendly and new bio-based nanomaterials in high-tech fields.

TEMPO-oxidized cellulose nanofibers

Chitosan, a versatile hydrophilic polysaccharide derived from chitin, has a broad antimicrobial spectrum to which gram-negative, gram-positive bacteria and fungi are highly susceptible. In the current review, three possible and accepted antimicrobial mechanisms for chitosan are presented and briefly discussed. The activity dependence on polymeric molecular weight (MW) and degree of acetylation (DA) are described. The chitosan minimum inhibitory concentrations (MIC) are summarized according to recent data found in the literature. The potential to improve inhibitory growth of bacteria by using water soluble chitosan derivatives is also discussed. The data indicate that the effectiveness of chitosan varies and is dependent on species of target microorganisms.

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A Review of the Antimicrobial Activity of Chitosan

Grafting: a versatile means to modify polymers Techniques, factors and applications

Of late, the most bountiful natural biopolymer chitin and chitosan have become cynosure of all party because of an unusual combination of biological activities plus mechanical and physical properties. However applications of chitin are limited due to its inherent insoluble and intractable nature. Chitosan, alkaline hydrolytic derivative of chitin has better solubility profile, less crystallinity and is amenable to chemical modifications due to presence of functional groups as hydroxyl, acetamido, and amine. The chemical modification of chitosan is of interest because the modification would not change the fundamental skeleton of chitosan, would keep the original physicochemical and biochemical properties and finally would bring new or improved properties. In view of rapidly growing interest in chitosan its chemical aspects and chemical modification studies is reviewed. The several chemical modifications such as oligomerization, alkylation, acylation, quternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization along with many assorted modifications have been carried out. The chemical modification affords a wide range of derivatives with modified properties for specific end use applications in diversified areas mainly of pharmaceutical, biomedical and biotechnological fields. Assorted modifications including chitosan hybrids with sugars, cyclodextrin, dendrimers, and crown ethers have also emerged as interesting multifunctional macromolecules. The versatility in possible modifications and applications of chitosan derivatives presents a great challenge to scientific community and to industry. The successful acceptance of this challenge will change the role of chitosan from being a molecule in waiting to a lead player.

Chitosan-modifications and applications: Opportunities galore

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

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Application of Spectroscopic Methods for Structural Analysis of Chitin and Chitosan

Preparation and antibacterial activity of a water-soluble chitosan derivative

One-step preparation (3D/2D/2D) BiVO4/FeVO4@rGO heterojunction composite photocatalyst for the removal of tetracycline and hexavalent chromium ions in water

Fabrication of BiVO4/BiPO4/GO composite photocatalytic material for the visible light-driven degradation

The two-parameter Weibull distribution does not always adequately describe the experimental bast fibre strength at different gauge lengths. For this reason, it was modified by incorporating the diameter variation of jute fibres in this paper. The fibre diameter was measured with an optical microscope. The three-parameter Weibull model was also used to compare with the modified model. It was found that as the fibre diameter variation increased the tensile strength of the jute fibre decreased. The strength predicted by modified Weibull distribution was more accurate than that of the two conventional models. In addition, the breaking strength of jute fibre was less sensitive to gauge length than that of cotton fibre because the breaking of jute filament involves ultimate cells breaking repeatedly and matrix cracking.

Study on the breaking strength of jute fibres using modified Weibull distribution

Enhanced photocatalytic degradation performance of organic contaminants by heterojunction photocatalyst BiVO4/TiO2/RGO and its compatibility on four different tetracycline antibiotics

Wei Wang

Papers

Preparation and antibacterial activity of a water-soluble chitosan derivative

One-step preparation (3D/2D/2D) BiVO4/FeVO4@rGO heterojunction composite photocatalyst for the removal of tetracycline and hexavalent chromium ions in water

Fabrication of BiVO4/BiPO4/GO composite photocatalytic material for the visible light-driven degradation

Study on the breaking strength of jute fibres using modified Weibull distribution

Enhanced photocatalytic degradation performance of organic contaminants by heterojunction photocatalyst BiVO4/TiO2/RGO and its compatibility on four different tetracycline antibiotics