Improving Properties of Starch-Based Adhesives with Carboxylic Acids and Enzymatically Polymerized Lignosulfonates

Effect of Salts on Laccase-Catalyzed Polymerization of Lignosulfonate

Enzymatic polymerization of lignosulfonate (LS) has a high potential for various applications ranging from coatings to adhesives. Here, the effect of different ions in low concentrations on enzymatic polymerization of LS was investigated, including salt solutions consisting of mono- and dicarboxylic acids, sulfate, phosphate and chloride with sodium as counter ion. LS polymerization was followed by viscometry and size exclusion (SEC) chromatography. Interestingly, there was only a small effect of ions on the activity of the laccase on standard substrate ABTS, while the effect on polymerization of LS was substantially different. The presence of acetate led to a 39 % higher degree of polymerization (DP) for LS. Small angle X-ray scattering (SAXS) revealed that the structure of the enzyme was largely unaffected by the ions, while the determination of the zeta potential showed that those ions conveying higher negative surface charges onto LS particles showed lower DPs, than those not affecting the surface charge. Further, electron paramagnetic resonance (EPR) spectroscopy showed 5-times higher intensity in phenoxyl radicals for the monovalent ions compared to the divalent ones. It was concluded that the DPs of LS could be tuned in the presence of certain ions, by facilitating the interaction between the laccase substrate-binding site and the LS molecules.

A Novel Bio-Adhesive Based on Chitosan-Polydopamine-Xanthan Gum for Glass, Cardboard and Textile Commodities

The escalating environmental concerns associated with petroleum-based adhesives have spurred an urgent need for sustainable alternatives. Chitosan, a natural polysaccharide, is a promising candidate; however, its limited water resistance hinders broader application. The aim of this study is to develop a new chitosan-based adhesive with improved properties. The polydopamine association with chitosan presents a significant increase in adhesiveness compared to pure chitosan. Polydopamine is synthesized by the enzymatic action of laccase from Trametes versicolor at pH = 4.5, in the absence or presence of chitosan. This pH facilitates chitosan's solubility and the occurrence of catechol in its reduced form (pH < 5.5), thereby increasing the final adhesive properties. To further enhance the adhesive properties, various crosslinking agents were tested. A multi-technique approach was used for the characterization of formulations. The formulation based on 3% chitosan, 50% polydopamine, and 3% xanthan gum showed a spectacular increase in adhesive properties when tested on glass, cardboard and textile. This formulation increased water resistance, maintaining the adhesion of a sample soaked in water for up to 10 h. For cardboard and textile, material rapture occurred, in mechanical tests, prior to adhesive bond failure. Furthermore, all the samples showed antiflame properties, expanding the benefits of their use. Comparison with commercial glues confirms the remarkable adhesive properties of the new formulation.

Production of Chemically Modified Bio-Based Wood Adhesive from Camote and Cassava Peels

Adhesives are significant for manufacturing competent, light, and sturdy goods in various industries. Adhesives are an important part of the modern manufacturing landscape because of their versatility, cost-effectiveness, and ability to enhance product performance. Formaldehyde and polymeric diphenylmethane diisocyanate (PMDI) are conventional adhesives utilized in wood applications and have been classified as carcinogenic, toxic, and unsustainable. Given the adverse environmental and health effects associated with synthetic adhesives, there is a growing research interest aimed at developing environmentally friendly bio-based wood adhesives derived from renewable resources. This study aimed to extract starch from camote and cassava peels and focuses on the oxidization of starch derived from camote and cassava peels using sodium hypochlorite to create bio-based adhesives. The mean yield of starch extracted from camote and cassava peels was 13.19 ± 0.48% and 18.92 ± 0.15%, respectively, while the mean weight of the oxidized starches was 34.80 g and 45.34 g for camote and cassava, respectively. Various starch ratios sourced from camote and cassava peels were examined in the production of bio-based adhesives. The results indicate that the 40:60 camote to cassava ratio yielded the highest solid content, while the 80:20 ratio resulted in the best viscosity. Furthermore, the 40:60 ratio produced the most favorable particle board in terms of mechanical properties, density, thickness, swelling, and water absorption. Consequently, the starch extracted from camote and cassava peels holds promise as a potential source for bio-based adhesives following appropriate chemical modification.

Enhancing Hydrophobicity and Oxygen Barrier of Xylan/PVOH Composite Film by 1,2,3,4-Butane Tetracarboxylic Acid Crosslinking

Hemicellulose has potential advantages in food packaging because of its abundant reserves, degradability and regeneration. However, compared with fossil-derived plastic films, hemicellulose-based films show inferior hydrophobicity and barrier properties because of their low degree of polymerization and strong hydrophilicity. Focusing on such issues, this work covers the modification of a xylan/polyvinyl alcohol (PVOH) film using 1,2,3,4-butane tetracarboxylic acid (BTCA) as esterifying agent. The thus prepared composite film was more compact owing to the esterification reaction with xylan and PVOH forming a crosslinked network structure and reducing the distance between molecular chains. The results showed that BTCA had a positive effect on the oxygen barrier, hydrophobicity and mechanical properties of the composite film. The tensile strength of the xylan/PVOH composite film with 10% BTCA content increased from 11.19 MPa to 13.99 MPa. A 20% BTCA loading resulted in an increase in the contact angle of the composite film from 87.1° to 108.2°, and a decrease in the oxygen permeability from 2.11 to 0.43 (cm³·µm)/(m²·d·kPa), corresponding to increase in the contact angle by 24% and a decrease in oxygen permeability by 80%. The overall performance enhancement indicates the potential application of such composites as food packaging.

Effect of Mat Moisture Content, Adhesive Amount and Press Time on the Performance of Particleboards Bonded with Fructose-Based Adhesives

The study evaluates the performance of laboratory, single-layered particleboards made out of fructose-hydroxymethylfurfural-bishexamethylenetriamine (SusB) adhesive as a sustainable alternative. Several production parameters such as mat moisture content (MMC), adhesive amount and press time were varied and their effect on the bonding efficiency investigated. The internal bond strength (IB) and thickness swelling after 24 h of water immersion (TS) were taken as evaluation criteria for the bonding efficiency. pMDI-bonded particleboards were produced as fossil-based, formaldehyde-free reference. Particleboard testing was complemented by tensile shear strength measurements and thermal analysis. It was found that the MMC has the highest impact on the internal bond strength of SusB-bonded particleboards. In the presence of water, the reaction enthalpy of the main curing reaction (occurring at 117.7 °C) drops from 371.9 J/mol to 270.5 J/mol, leading to side reactions. By reducing the MMC from 8.7%, the IB increases to 0.61 N/mm², thus surpassing P2 requirements of the European standard EN312. At a press factor of 10 s/mm, SusB-bonded particleboards have a similar IB strength as pMDI-bonded ones, with 0.59 ± 0.12 N/mm² compared to 0.59 ± 0.09 N/mm². Further research on the improvement of the dimensional stabilization of SusB-bonded PBs is needed, as the TS ranges from 30-40%.