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Lignin was successfully modified to prepare a bio-based wood adhesive by just two synthesis steps: demethylation and periodate oxidation. Fourier Transform Infrared Spectroscopy (FT-IR), Matrix Assisted Laser Desorption Ionization Time of Flight (MALDI-TOF) Mass Spectrometry and Thermomechanical Analysis (TMA) were combined to characterize the bio-based adhesives obtained. Furthermore, the adhesion performance of the bio-based lignin adhesive was measured by testing the tensile shear strength of the bonded joints. The results show that demethylated lignin gives to the wood joint acceptable dry shear strength, but no wet shear strength. Thus, sodium peroxide (NaIO4) oxidant was used to improve the bonding performance of lignin-based adhesives. The optimal formulation for oxidized demethylated lignin adhesives was found to be by 20% addition of NaIO4. The adhesive presented is a lignin-derived non- aldehyde addition, high biomass content, and its preparation is convenient, low-cost product and can be applied to wood bonding.

International audience; Soy-protein isolate (SPI) was used to prepare non-isocyanate polyurethane (NIPU) thermosetting adhesives for wood panels by reacting it with dimethyl carbonate (DMC) and hexamethylene diamine. Both linear as well as branched oligomers were obtained and identified, indicating how such oligomer structures could further cross-link to form a hardened network. Unusual structures were observed, namely carbamic acid-derived urethane linkages coupled with lactam structures. The curing of the adhesive was followed by thermomechanical analysis (TMA). It appeared to follow a two stages process: First, at a lower temperature (maximum 130°C), the growth of linear oligomers occurred, finally forming a physically entangled network. This appeared to collapse and disentangle, causing a decrease of MOE, as the temperature increases. This appears to be due to the ever more marked Brownian movements of the linear oligomer chains with the increase of the temperature. Second, chemi- cal cross-linking of the chains appeared to ensue, forming a hardened network. This was shown by the thermo- mechanical analysis (TMA) showing two distinct MOE maxima peaks, one around 130°C and the other around 220°C, with a very marked MOE decrease between the two. Plywood panels were prepared and bonded with the SPI-NIPU wood adhesive and the results obtained are presented. The adhesive appeared to pass comfortably the requirements for dry strength of relevant standards, showing to be suitable for interior grade plywood panels. It did not pass the requirements for wet tests. However, addition of 15% of glycerol diglycidyl ether improved the wet tests results but still not enough to satisfy the standards requirements.

International audience; Wheat gluten protein hydrolysate was used as a biomass feedstock to prepare environmentally friendly protein-based adhesives, with hydrolyzed wheat protein as control. Glutaraldehyde was used to modify it to obtain a glutaraldehyde-wheat protein (GP) adhesive. Polyethylenimine (PEI) was also used as a crosslinking agent. Plywood has been prepared and tested, and its performance was used to measure the wheat gluten protein hydrolysate adhesive bonding performance. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to analyze the adhesive thermal properties and the microstructures of the cured adhesives by scanning electron microscopy (SEM). The results show that modification by glutaraldehyde can effectively improve the bonding performance of wheat protein adhesives, the plywood bonded strength having been improved by its addition. The effect of PEI as a crosslinking agent became evident. It can greatly improve the bonding properties of glutaraldehyde-modified wheat protein adhesives. TMA analysis indicates that the glutaraldehydemodified GP adhesive has a higher storage modulus than the unmodified one. The modulus of the adhesive increased after adding the PEI cross-linking agent.

International audience

Glyoxal as a nonvolatile and nontoxic aldehyde, which can be used as a substitution of formaldehyde in wood industry to prepare novel melamine-glyoxal (MG) resins. However, for the reason of the lo...

Furfuryl alcohol, a biosourced material, is widely used in the foundry industry, and also as additive or modifier in the adhesives field. However, furanic resins have not been reported as being use...

Broussonetiapapyrifera leaf protein was used as a biomass feedstock to prepare wood adhesives, and the influence of cutting modes (cutting frequencies and cutting heights) on leaf protein content and reactivity was studied in this paper. Bonding performance of Broussonetiapapyrifera leaf protein-based adhesives were evaluated by shear strength of plywood. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetry (TG), and scanning electron microscope (SEM) were used to analyze them. The results indicated that: (1) the leaf protein content gradually increased as the cutting height increased, but it presented a decreasing trend as the cutting frequency increased. When the cutting frequency is two times per year and the cutting height is 30 cm, this leaf protein-based adhesive exhibited the best bonding strength with 0.75 MPa. (2) Cutting frequency and cutting height have no significant correlations to the reactivity of leaf protein with the crosslinker. (3) DSC and FTIR indicated that both leaf protein content and reactivity appeared to exert an influence on the bonding properties of the protein adhesives, and the latter is more pronounced. (4) TG and SEM analyses indicated that under different cutting modes, leaf protein content, especially protein reactivity, had a great effect on the thermal properties of the adhesives. (5) Contact angle analysis showed that Broussonetiapapyrifera leaf protein-based adhesives had good wettability on wood surfaces. Under different cutting modes with the difference of leaf protein content and reactivity, the crosslinking degree of the adhesives with crosslinker and compactness of the cured adhesives were different and thus affect their bonding strength and water resistance.

International audience

Soy protein isolate (SPI) and insoluble soy flour polymeric carbohydrates have been reacted with sodium periodate for the specific oxidation of vicinal &ndash, OH groups to investigate the reactions involved in this approach to soy flour adhesives. The reactions have been shown to generate carbohydrate oligomer fractions presenting one, two or multiple aldehyde groups. With the exception of the small molecular weight heptanedial, the smaller molecular weight aldehydes generated from mono- and disaccharides by the same reaction do not appear to form from the insoluble soy flour carbohydrates, or have already reacted. The reaction of periodate with soy protein isolate has been shown to generate some aldehydes too. When the mix of SPI and soy insoluble carbohydrates is treated with periodate, the majority of the observed aldehyde carrying species appear to be higher molecular weight carbohydrate oligomer fractions.

International audience

Sucrose-based non-isocyanate polyurethanes (S-NIPU) were synthesized by the already codified reaction of sucrose, dimethyl carbonate and hexamethylene diamine and used for the first time as adhesives for bonding particleboard. To decrease the NIPU adhesive curing temperature, a silane coupling agent was used as a crosslinking promoter. The performance of particleboards prepared at a press temperature of 230 °C, 200 °C and 180 °C and a press time of 8 min, 10 min and 12 min was tested and evaluated. The structure of the oligomers obtained was detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Thermomechanical analysis and differential scanning calorimetry were also used to analyze their behavior. The particleboards bonded with the S-NIPU adhesive at 230 °C showed excellent properties, which, however, decreased as the press time was reduced. The silane coupling agent used as a crosslinking promoter significantly reduced the curing temperature of the adhesive and allowed to obtain good bonding at a lower press temperature. The results obtained confirmed that coupling the S-NIPU adhesive with a silane used as a crosslinking promoter can yield sufficiently improved results to function as a suitable adhesive for particleboard, medium density fiberboard and other types of particulate wood panels. It was also the first time that a NIPU adhesive was used for wood bonding.

International audience