Non-Formaldehyde, Bio-Based Adhesives for Use in Wood-Based Panel Manufacturing Industry-A Review

Glued-bamboo composite based on a highly cross-linked cellulose-based adhesive and an epoxy functionalized bamboo surface

Bamboo, as a renewable bioresource, exhibits advantages of fast growth cycle and high strength. Bamboo-based composite materials are a promising alternative to load-bearing structural materials. It is urgent to develop high-performance glued-bamboo composite materials. This study focused on the chemical bonding interface to achieve high bonding strength and water resistance between bamboo and dialdehyde cellulose-polyamine (DAC-PA4N) adhesive by activating the bamboo surface. The bamboo surface was initially modified in a directional manner to create an epoxy-bamboo interface using GPTES. The epoxy groups on the interface were then chemically crosslinked with the amino groups of the DAC-PA4N adhesive, forming covalent bonds within the adhesive layer. The results demonstrated that the hot water strength of the modified bamboo was improved by 75.8 % (from 5.17 to 9.09 MPa), and the boiling water strength was enhanced by 232 % (from 2.10 to 6.99 MPa). The bonding and flexural properties of this work are comparable to those of commercial phenolic resin. The activation modification of the bamboo surface offers a novel approach to the development of low-carbon, environmentally friendly, and sustainable bamboo engineering composites.

Microcapsules of Poly(butylene adipate-co-terephthalate) (PBAT) Loaded with Aliphatic Isocyanates for Adhesive Applications

This work introduces the encapsulation of hexamethylene diisocyanate derivatives (HDI, TriHDI, and PHDI) with the biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) through a solvent evaporation method. These microcapsules (MCs) were then employed in adhesive formulations for footwear. Moreover, MCs containing PHDI were produced in a closed vessel, demonstrating the potential for recovering and reusing organic solvents for the first time. The MCs were achieved with an isocyanate payload reaching up to 68 wt %, displaying a spherical shape, a core-shell structure, and thin walls without holes or cracks. The application of MCs as cross-linking agents for adhesives was evaluated following industry standards. The adhesives' strength surpassed the minimum requirement by a significant margin. Creep tests demonstrated that the formulation with MCs exhibits superior thermostability. Furthermore, the formulation with MCs-PHDI presented the best results reported to date for this type of system, as no displacement was observed in the bonded substrates. Environmental assessment indicates that adhesives with MCs have higher global warming potential (+16.2%) and energy consumption (+10.8%) than the standard commercial adhesives, but under alternative realistic scenarios, the differences can be insignificant. Therefore, adhesive formulations incorporating MCs promise to be on par with traditional adhesive systems regarding environmental impacts while providing benefits such as improved and safe handling of isocyanates and excellent bonding effectiveness.

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.

The potential application of cellulose acetate membrane for CO2 adsorbent

Numerous countries have deployed significant efforts to reduce the amount of CO2 released into the atmosphere. Carbon capture and storage is widely regarded as a mitigation technique that can significantly reduce CO2 emissions. A crucial stage in carbon capture and storage is CO2 adsorption using a membrane. Cellulose acetate has demonstrated excellent properties as a membrane material. In this study, we examined the potential of cellulose acetate membrane (CAM) for CO2 gas capture. Two forms of CAM were developed for this study, with and without the addition of glycerol. Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR), and CO2 adsorption analyses were used to characterise CAM in numerous ways. The analysis revealed that the addition of glycerol improved the gas adsorption properties of the material. The incorporation of glycerol into the cellulose acetate matrix resulted in an observed augmentation in both the diameter and pore size. The adsorption properties of CO2 are significantly influenced by the microscopic structure of the cellulose acetate membrane. The CAM can be viewed as a possible material for CO2 adsorbers.

Structural Variations in Biobased Polyfurfuryl Alcohol Induced by Polymerization in Water

Poly(furfuryl alcohol) is a thermostable biobased thermoset. The polymerization of furfuryl alcohol (FA) is sensitive to a number of side reactions, mainly the opening of the furan ring into carbonyl species. Such carbonyls can be used to introduce new properties into the PFA materials through derivatization. Hence, better understanding of the furan ring opening is required to develop new applications for PFA. This article studies the structural discrepancies between a PFA prepared in neat conditions versus a PFA prepared in aqueous conditions, i.e., with more carbonyls, through NMR and MALDI ToF. Overall, the PFA prepared in water exhibited a structure more heterogeneous than the PFA prepared in neat conditions. The presence of ketonic derivatives such as enols and ketals were highlighted in the case of the aqueous PFA. In this line, the addition of water at the beginning of the polymerization stimulated the production of aldehydes by a factor two. Finally, the PFA prepared in neat conditions showed terminal lactones instead of aldehydes.

Improving Bond Performance and Reducing Cross-Linker Dosage of Soy Protein Adhesive via Hyper-Branched and Organic-Inorganic Hybrid Structures

Eco-friendly soybean protein adhesives could be an ideal substitute for replacing traditional formaldehyde-based adhesives in wood industry. However, a large number of cross-linking agents are required in soy protein adhesive formulations to obtain sufficiently performing properties. Inspired by the high performance of nacre and branched structures, a hyper-branched amine (HBPA) was synthesized and grafted to graphene oxide (GO), generating a hyper-branched amine-functionalized GO (FGO). A novel soy protein-based adhesive was developed by mixing FGO with soy protein (SPI) and a low dose polyamidoamine-epichlorohydrin (PAE). Results showed that the addition of only 0.4 wt% FGO and 0.75 wt% PAE to the SPI adhesive formulation enhanced the wet shear strength of plywood to 1.18 MPa, which was 181% higher than that of the adhesive without enhancement. The enhanced performance is attributed to the denser cross-linking structure and improved toughness of the adhesive layer. Using FGO in the adhesive formulation also greatly reduced the concentration of the additive cross-linker by up to 78.6% when compared with values reported in the literature. Thus, using a hyper-branched functionalized nano-material to form an organic-inorganic hybrid structure is an effective and efficient strategy to reinforce the composites and polymers. It significantly reduces the chemical additive levels, and is a practical way to develop a sustainable product.

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%.

Formaldehyde-Free Resins for the Wood-Based Panel Industry: Alternatives to Formaldehyde and Novel Hardeners

Due to its carcinogenic properties, the presence of formaldehyde in resins and other industrial products has been a subject of great concern in recent years. The presented review focuses on modern alternatives for the production of wood-based panels; i.e., substitutes for formaldehyde in the production of amino and phenolic resins, as well as novel hardeners for formaldehyde-free wood adhesives. Solutions in which formaldehyde in completely replaced are presented in this review. Recent advances indicate that it is possible to develop new formaldehyde-free systems of resins with compatible hardeners. The formaldehyde substitutes that have primarily been tested are glyoxal, glutaraldehyde, furfural, 5-hydroxymethylfurfural, and dimethoxyethanal. The use of such substitutes eliminates the problem of free formaldehyde emission originating from the resin used in the production of wood-based panels. However, these alternatives are mostly characterized by worse reactivity, and, as a result, the use of formaldehyde-free resins may affect the mechanical and strength properties of wood-based panels. Nonetheless, there are still many substantial challenges for the complete replacement of formaldehyde and further research is needed, especially in the field of transferring the technology to industrial practice.

Preparation and characterization of wet adhesives based on (poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate)/castor oil/styrene butadiene rubber) using gamma irradiation for trapping of reptiles and rodents

Wet adhesives from poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate), castor oil, and styrene butadiene rubber were prepared at variable compositions. These components were exposed to a certain range of irradiation dose for γ-rays. Wet adhesives were characterized by adhesion force, Fourier transform infrared, thermogravimetric analysis and derivative thermal gravimetric, gel permeation chromatography, proton nuclear magnetic resonance spectroscopy and scan electron microscopy. Results declared that dose and composition have significant effect on features of wet adhesives. Further, the adhesion force and thermal stability of wet adhesives improved by increasing the irradiation dose. Moreover, the adhesion force reached ~ 690 (kPa). The analysis of gel permeation chromatography showed that molecular weight of wet adhesive 48,921 (g/mol). The wet adhesives were exploited to trap reptiles and rodents. Through the results, it can be observed that the wet adhesives had good efficiency for trapping the reptiles and rodents. The results showed that the best sample of wet adhesive was from 98% of [poly (vinyl butyral-co-vinyl alcohol-co-vinyl (10%)/castor oil (90%))] to [2% of styrene butadiene rubber] at 30 kGy In conclusion, this study referred that this type of wet adhesive has an excellent ability to adhere and trap of reptiles and rodents such as geckos and mice respectively. Consequently, these wet adhesives could be utilized in pilot scale.

Understanding the PLA–Wood Adhesion Interface for the Development of PLA-Bonded Softwood Laminates

With polylactic acid (PLA) usage projected to increase in wood-based composite materials, a study comparing composite processing parameters with resulting PLA−wood adhesion and panel performance is warranted. In this study, PLA-softwood veneer laminates have been prepared and spatial chemical imaging via FTIR analysis was applied to identify PLA bondlines characterizing bondline thickness and the extent of PLA migration into the wood matrix. These PLA–wood adhesion interface characteristics have been compared with the performance of panels varying in pressing temperature, pressing time and PLA grades. For amorphous PLA, bondline thicknesses (60–120 μm) were similar, pressing at 140 °C or 160 °C, whereas with semi-crystalline PLA, the bondline thickness (340 μm) significantly reduced (155–240 μm) only when internal panel temperatures exceeded 140 °C during pressing. Internal temperatures also impacted PLA penetration, with greater PLA migration from bondlines evident with higher pressing temperatures and times with distinctions between PLA grades and bondline position. Performance testing revealed thinner PLA bondlines were associated with greater dry strength for both PLA grades. Cold-water soaking revealed laminated panels exhibit a range of wet-strength performance related to panel-pressing regimes with the semi-crystalline PLA pressed at 180 °C having similar tensile strength in dry and wet states. Moreover, an excellent correlation between wet-strength performance and bondline thickness and penetration values was evident for this PLA grade. Overall, study findings demonstrate PLA wood composite performance can be tuned through a combination of the PLA grade and the pressing regime employed.