Investigation of chitosan-phenolics systems as wood adhesives

Optimization of Chitosan Properties with the Aim of a Water Resistant Adhesive Development

Chitosan is a bio-sourced polysaccharide widely used in different fields from health to wastewater treatment through food supplements. Another important use of this polymer is adhesion. Indeed, the current demand to replace non-natural and hazardous polymers by greener ones is well present in the adhesive field and open good opportunities for chitosan and its derivatives. However, chitosan is water soluble and exhibits a poor water-resistance in the field of adhesion which reduces the possibilities of its utilization within the paste field. This review focuses on exploration of different ways available to modify the chitosan and transform it into a water-resistant adhesive. The first part concerns the chitosan itself and gives important information from the discovery of chitin to the pure chitosan ready to use. The second part reviews the background information relative to adhesion theories, ideal properties of adhesives and the characteristics of chitosan as an adhesive. The last part focuses on exploration of the possible modification of chitosan to make it a water-resistant chemical adhesive.

Microbial demethylation of lignin: Evidence of enzymes participating in the removal of methyl/methoxyl groups

Lignin is an abundant natural plant aromatic biopolymer containing various functional groups that can be exploited for activating lignin for potential commercial applications. Applications are hindered due to the presence of a high content of methyl/methoxyl groups that affects reactiveness. Various chemical and enzymatic approaches have been investigated to increase the functionality in transforming lignin. Among these is demethylation/demethoxylation, which increases the potential numbers of vicinal hydroxyl groups for applications as phenol-formaldehyde resins. Although the chemical route to lignin demethylation is well-studied, the biological route is still poorly explored. Bacteria and fungi have the ability to demethylate lignin and lignin-related compounds. Considering that appropriate microorganisms possess the biochemical machinery to demethylate lignin by cleaving O-methyl groups liberating methanol, and modify lignin by increasing the vicinal diol content that allows lignin to substitute for phenol in organic polymer syntheses. Certain bacteria through the actions of specific O-demethylases can modify various lignin-related compounds generating vicinal diols and liberating methanol or formaldehyde as end-products. The enzymes include: cytochrome P₄₅₀-aryl-O-demethylase, monooxygenase, veratrate 3-O-demethylase, DDVA O-demethylase (LigX; lignin-related biphenyl 5,5'-dehydrodivanillate (DDVA)), vanillate O-demethylase, syringate O-demethylase, and tetrahydrofolate-dependent-O-demethylase. Although, the fungal counterparts have not been investigated in depth as in bacteria, O-demethylases, nevertheless, have been reported in demethylating various lignin substrates providing evidence of a fungal enzyme system. Few fungi appear to have the ability to secrete O-demethylases. The fungi can mediate lignin demethylation enzymatically (laccase, lignin peroxidase, manganese peroxidase, O-demethylase), or non-enzymatically in brown-rot fungi through the Fenton reaction. This review discusses details on the aspects of microbial (bacterial and fungal) demethylation of lignins and lignin-model compounds and provides evidence of enzymes identified as specific O-demethylases involved in demethylation.

Review on Adhesives and Surface Treatments for Structural Applications: Recent Developments on Sustainability and Implementation for Metal and Composite Substrates

Using adhesives for connection technology has many benefits. It is cost-efficient, fast, and allows homogeneous stress distribution between the bonded surfaces. This paper gives an overview on the current state of knowledge regarding the technologically important area of adhesive materials, as well as on emergent related technologies. It is expected to fill some of the technological gaps between the existing literature and industrial reality, by focusing at opportunities and challenges in the adhesives sector, on sustainable and eco-friendly chemistries that enable bio-derived adhesives, recycling and debonding, as well as giving a brief overview on the surface treatment approaches involved in the adhesive application process, with major focus on metal and polymer matrix composites. Finally, some thoughts on the connection between research and development (R&D) efforts, industry standards and regulatory aspects are given. It contributes to bridge the gap between industry and research institutes/academy. Examples from the aeronautics industry are often used since many technological advances in this industry are innovation precursors for other industries. This paper is mainly addressed to chemists, materials scientists, materials engineers, and decision-makers.

Lignocellulose-Chitosan-Multiwalled Carbon Nanotube Composites with Improved Mechanical Strength, Dimensional Stability and Fire Retardancy

A novel composite composed of lignocellulose (LC), glutaraldehyde crosslinked chitosan (GC) and multiwalled carbon nanotube (MWCNT) was fabricated by the hot-pressing process. The effect of the additional GC and MWCNT on the mechanical strength, dimensional stability and fire retardancy of lignocellulose composites was investigated. The results showed that LC/GC/MWCNT composite exhibited the maximum modulus of rupture (MOR) of 35.3 MPa, modulus of elasticity (MOE) of 2789.1 MPa and internal bonding (IB) strength of 1.2 MPa. Meanwhile, the LC/GC/MWCNT composite displayed improved dimensional stability with a thickness swelling (TS) value of 22.4%. Besides, the LC/GC/MWCNT composite exhibited improved fire retardancy with a limiting oxygen index of 29.0%. The peak heat release rate, the total heat release, the total smoke production and the maximum smoke production ratio of LC/GC/MWCNT composite decreased by 15.9%, 10.7%, 45.5% and 20.7% compared with those of LC composite, respectively. Therefore, the LC/GC/MWCNT composite may be a promising candidate for green wood based composites.

Cytotoxicity and metal ions removal using antibacterial biodegradable hydrogels based on N-quaternized chitosan/poly(acrylic acid)

Physically crosslinked hydrogels resulted from interaction between N,N,N-trimethyl chitosan chloride (N-Quaternized Chitosan) (NQC) and poly(acrylic acid) (PAA) were synthesized in different weight ratios (3:1), (1:1) and (1:3) taking the following codes Q3P1, Q1P1 and Q1P3, respectively. Characterization of the mentioned hydrogels was done using several analysis tools including; FTIR, XRD, SEM, TGA, biodegradation in simulated body fluid (SBF) and cytotoxicity against HepG-2 liver cancer cells. FTIR results proved that the prepared hydrogels were formed via electrostatic and H-bonding interactions, while XRD patterns proved that the prepared hydrogels -irrespective to their ratios- were more crystalline than both matrices NQC and PAA. TGA results, on the other hand, revealed that Q1P3 hydrogel was the most thermally stable compared to the other two hydrogels (Q3P1 and Q1P1). Biodegradation tests in SBF proved that these hydrogels were more biodegradable than the native chitosan. Examination of the prepared hydrogels for their potency in heavy metal ions removal revealed that they adsorbed Fe (III) and Cd (II) ions more than chitosan, while they adsorbed Cr (III), Ni (II) and Cu (II) ions less than chitosan. Moreover, testing the prepared hydrogels as antibacterial agents towards several Gram positive and Gram negative bacteria revealed their higher antibacterial activity as compared with NQC when used alone. Evaluating the cytotoxic effect of these hydrogels on an in vitro human liver cancer cell model (HepG-2) showed their good cytotoxic activity towards HepG-2. Moreover, the inhibition rate increased with increasing the hydrogels concentration in the culture medium.

Development of sustainable bio-adhesives for engineered wood panels – A Review

Stricter legislation on formaldehyde emissions as well as growing consumer interest in sustainable raw materials and products are the main driving factors behind research on bio-based adhesives, as alternatives to amino-based ones, for wood panels.

Aiding alternatives assessment with an uncertainty-tolerant hazard scoring method

This research developed a single-score system to simplify and clarify decision-making in chemical alternatives assessment, accounting for uncertainty. Today, assessing alternatives to hazardous constituent chemicals is a difficult task-rather than comparing alternatives by a single definitive score, many independent toxicological variables must be considered at once, and data gaps are rampant. Thus, most hazard assessments are only comprehensible to toxicologists, but business leaders and politicians need simple scores to make decisions. In addition, they must balance hazard against other considerations, such as product functionality, and they must be aware of the high degrees of uncertainty in chemical hazard data. This research proposes a transparent, reproducible method to translate eighteen hazard endpoints into a simple numeric score with quantified uncertainty, alongside a similar product functionality score, to aid decisions between alternative products. The scoring method uses Clean Production Action's GreenScreen as a guide, but with a different method of score aggregation. It provides finer differentiation between scores than GreenScreen's four-point scale, and it displays uncertainty quantitatively in the final score. Displaying uncertainty also illustrates which alternatives are early in product development versus well-defined commercial products. This paper tested the proposed assessment method through a case study in the building industry, assessing alternatives to spray polyurethane foam insulation containing methylene diphenyl diisocyanate (MDI). The new hazard scoring method successfully identified trade-offs between different alternatives, showing finer resolution than GreenScreen Benchmarking. Sensitivity analysis showed that different weighting schemes in hazard scores had almost no effect on alternatives ranking, compared to uncertainty from data gaps.

Comparison of sensory and compositions of five selected persimmon cultivars (Diospyros kaki L.) and correlations between chemical components and processing characteristics

Persimmon is one of the most popular and valuable fruits in markets because of its distinguished flavor as well as its significant benefits to health. The present study systematically compared the sensory characteristics and chemical compositions of five commercial persimmon fruits, and the correlations between chemical components and processing characteristics were also included. Our results showed that obvious differences in aroma and taste were found among the cultivars. Likewise, the contents of chemical components including sugar, total phenol, β-carotene and ascorbic acid, varied significantly (p < 0.05) across different persimmon cultivars. The processing characteristics of persimmon fruit closely correlated with the chemical compositions. Pectin (r = 0.76, p < 0.01) and total phenol (r = 0.576, p < 0.05) were found to enhance the viscosity of persimmon pulp, and the colour of persimmon powder was greatly influenced by β-carotene, ascorbic acid and sugar contents (r = 0.823, -0.729 and -0.685, p < 0.01, respectively). Powder recovery of persimmon was positively correlated with pectin content (r = 0.503, p < 0.05) and negatively related to total sugar content (r = -0.668, p < 0.01). Pectin content exerted positive effect (r = 0.719, p < 0.01) on hygroscopicity of persimmon powder, and the powder solubility showed a positive correlation to sugar and a negative relationship to pectin contents (r = 0.662 and -0.716, p < 0.01, respectively). In addition, a positive correlation (r = 0.642, p < 0.01) of the content of ascorbic acid to phenolic retention was also observed.

In situ–forming quercetin-conjugated heparin hydrogels for blood compatible and antiproliferative metal coating

In this study, in situ–forming quercetin-conjugated heparin hydrogels to be used to coat metal surfaces for blood compatibility were developed and characterized. Four units of quercetin and poly(ethylene glycol)–tyramine were conjugated per heparin for blood compatibility and hydrogel formation, respectively. The product, quercetin-conjugated heparin–poly(ethylene glycol)–tyramine, was cross-linked in situ via an enzymatic reaction using horseradish peroxidase and hydrogen peroxide to form a hydrogel. The physicochemical properties, such as the gelation time and swelling/degradation time as well as the release kinetics of quercetin, were controlled by changing the catalytic concentrations. The quercetin-conjugated heparin hydrogel, when adhered to a metal surface, enhanced blood compatibility and reduced platelet adhesion by 77%. The release of quercetin inhibited the proliferation of smooth muscle cells. The quercetin-conjugated heparin–poly(ethylene glycol)–tyramine hydrogel is a promising biomaterial with a stable-coated metal surface, with enhanced blood compatibility and antiproliferation effects.