The structural changes during three-step synthesis of low-molar ratio urea–formaldehyde (UF) resin were tracked by quantitative ¹³C nuclear magnetic resonance (¹³C NMR) analysis and electrospray ionization-mass spectrometry (ESI–MS). Condensations that produced polymers were found to be linked by ether bonds in addition to hydroxymethylation reactions at the first alkaline stage with a formaldehyde to urea ratio of 2:1. Considerable formation of branched methylene linkages, with the highest content among all the condensed structures, was the key feature of the acidic stage. Notable changes were observed for the chemical structures and molecular masses of the resin components after the formaldehyde to urea molar ratio was lowered to 1.2 by adding post-urea at the final alkaline stage. Specifically, most of the branched hydroxymethyl groups on the polymers were cleaved, resulting in a significant decrease in the branching degree of the polymers. The performance degradation of the UF resin was attributed to this debranching effect and the production of components with low molecular masses. Based on the observations, the curing pattern of low molar ratio UF resin was postulated and branched polymeric formaldehyde catcher bearing urea-reactivity was proposed.

Urea-formaldehyde (UF) resins based on different formaldehyde/urea (F/U) mole ratio were synthesized with oxidized cassava starch added at the final stage of the resin synthesis process. The basic characteristics of resins including solid content, viscosity, and curing time were studied, and the dry and wet bond strengths were evaluated by producing a three layer plywood. Additionally, the curing characteristics of different resins were investigated via differential scanning calorimetry (DSC). Structural distributions between UF and oxidized cassava starch were examined via FT-IR and 13C NMR analysis. The results indicated that the addition of oxidized starch not only improved resin bond strength but also notably reduced the curing start temperature of modified resins. Furthermore, a negative relationship between F/U mole ratio and the extent of reduction was identified. The structural distribution of UF resins changed dramatically because of oxidation cassava starch addition, but the changes varied due to different F/U mole ratios.

Soybean meal (SM) adhesive is widely acknowledged as a viable substitute for traditional formaldehyde-based adhesives, given its ability to be easily modified, the utilization of renewable sources, and its eco-friendly characteristics. However, the application of SM adhesive in manufacturing has been impeded due to its restricted bonding capacity and inadequate water resistance. Researchers in the wood industry have recognized the significance of creating an SM-based adhesive, which possesses remarkable adhesive strength and resistance to water. This study endeavors to tackle the issue of inadequate water resistance in SM adhesives. Sodium lignosulfonate (L) was oxidized using hydrogen peroxide (HP) to oxidized lignin (OL) with a quinone structure. OL was then used as a modifier, being blended with SM to prepare SM-based biomass (OLS) adhesives with good water resistance, which was found practically through its utilization in the production of plywood. The influence of the HP dosage and OL addition on plywood properties was examined. The changes in the lignin structure before and after oxidation were confirmed using gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The curing behavior and thermal stability of OLS adhesives were analyzed using dynamic mechanical analysis (DMA) and thermogravimetric (TG) analysis. The reaction mechanism was also investigated using FT-IR and XPS. The outcomes indicated a decrease in the molecular weight of L after oxidation using HP, and, at the same time, quinone and aldehyde functionalized structures were produced. As a result of the reaction between the quinone and aldehyde groups in OL with the amino groups in SM, a dense network structure formed, enhancing the water resistance of the adhesive significantly. The adhesive displayed exceptional resistance to water when the HP dosage was set at 10% of L and the OL addition was 10% based on the mass of SM. These specific conditions led to a notable enhancement in the wet bonding strength (63 °C, 3 h) of the plywood prepared using the adhesive, reaching 0.88 ± 0.14 MPa. This value represents a remarkable 125.6% increase when compared to the pure SM adhesive (0.39 ± 0.02 MPa). The findings from this study introduce a novel approach for developing adhesives that exhibit exceptional water resistance.

Energy storage materials to modulate indoor microclimates are needed to improve energy efficiency and for human comfort. Of these, phase-change material (PCM) is considered a very useful material because of its excellent latent heat energy storage. For application, some synthetic porous materials for supporting PCM are usually not friendly enough for people and housing environments due to their non-degradation characteristics. Hence, to develop an eco-friendly porous material is needed in order to encapsulate PCM composites that are always expected in indoor applications. In this work, heat-treated bamboo bricks were delignified to provide a delignified bamboo (DB) matrix. A phase-change composite was then fabricated by impregnating DB with polyethylene glycol (PEG) polymer. Impregnation was carried out under wet conditions to ensure the regular arrangement of the DB structure so as to achieve dimensional stability. The final DB/PEG composite was investigated for dimensional stability, load rate, latent heat, and phase-change temperature. Results showed that the DB matrix could be easily impregnated with PEG polymer under wet conditions, and the DB/PEG composite was found to have high enthalpy and a large phase-change temperature interval. Moreover, the composite was found to be a good regulator of indoor temperature and a stable dimension with a snow-white appearance. In summary, this DB/PEG composite is an energy storage material with the potential to modulate ambient indoor temperature and reduce building energy consumption.

Developing bio-based plastic has become an important strategy for solving environmental pollution. In this study, konjac flour (KF) and poly-vinyl alcohol (PVA) as main film-forming substances with added citric acid (CA), glutaraldehyde (GA) and glycerin, were used to prepare bio-based composite films via solution casting. How the PVA polymer amount affected the composite films including mechanical performance, structural properties and morphology was investigated. The results revealed that PVA polymer could obviously improve the mechanical property of the films, and the addition of 25% PVA based on KF mass when CA, GA and glycerin were fixed, was demonstrated as the optimal amount, maintaining an excellent tensile strength (TB) and elongation at break (EAB). Fourier transform infrared spectra (FT-IR) and X-ray diffraction (XRD) results indicated the successful cross-linking reaction between PVA and KF, and some further proofs could be confirmed from scanning electron microscopy (SEM) and thermogravimetry (TG). After modification with PVA, the cross section of the KF/PVA composite film was more dense and uniform, implying that PVA was well fused with KF system. Meanwhile, the films modified with PVA presented a good thermal resistance ability. This work provided an effective pathway for preparing KF/PVA composite films with improved mechanical properties, which may be an alternative way for using konjac flour.