Tannin-based extracts of Mimosa tenuiflora bark: features and prospecting as wood adhesives

Abstract

Mimosa tenuiflora (Willd.) Poir. (MT) is an underutilized plant specie since its wood is mostly used for energy production. Nonetheless, the bark from this forest plant has a high amount of tannins and other valuable compounds. Tannins have high worldwide importance and, because of that, there is an increasing number of researches on biorefinery systems aiming at maximizing their exploitation. The present study evaluated tannins extracted from the MT bark and their use for producing wood adhesives. Three types of powdered tannins were extracted using different solvents: a pure aqueous solution, a 5% sodium hydroxide (NaOH) aqueous solution, and a 5% sodium bisulfite (NaHSO3) aqueous solution. Distilled water, wheat flour, and formaldehyde were also used as a solvent, a glue extender, and a catalyst, respectively. These adhesives were applied for bonding pine wood joints and their shear strengths were determined. All the MT-based adhesives showed high viscosities and, yielded glue lines with similar shear strengths and similar shear deformations if compared to each other. That tannin-based glue incorporated with the tannin extracted using NaOH or NaHSO3 stood out and yielded similar bonding performances if compared to a commercial adhesive applied as a positive control.

Polyurethane Adhesives for Wood Based on a Simple Mixture of Castor Oil and Crude Glycerin

“…The detection of unreacted NCO groups in the 2:1 and 3:1 adhesives with higher CG content suggests that achieving complete chemical conversion may be more challenging under these conditions. The peak around 2370 cm −1 , related to the presence of unreacted NCO groups [45][46][47][48][49][50][51][52][53], was only detected in the 2:1 and 3:1 adhesives, where the content of CG was higher. This again indicates that the addition of CG hindered the consumption of hydroxyls by the NCO groups of p-MDI, even considering that a stoichiometric NCO/OH ratio of 1.3 was maintained in all cases.…”

“…The consequences and practical implications of the behavior where NCO (isocyanate) groups are completely consumed in the context of polyurethane adhesives can vary depending on the intended application and the properties required for that specific use. In general, cross-linking usually leads to stronger adhesive bonds, enhancing the overall strength and durability of the adhesive The peak around 2370 cm −1 , related to the presence of unreacted NCO groups [45][46][47][48][49][50][51][52][53], was only detected in the 2:1 and 3:1 adhesives, where the content of CG was higher. This again indicates that the addition of CG hindered the consumption of hydroxyls by the NCO groups of p-MDI, even considering that a stoichiometric NCO/OH ratio of 1.3 was maintained in all cases.…”

“…The FTIR spectra of the cured adhesives are shown in Figure 4. The peak at 1030 cm −1 is related to the C-H bonding vibrations, while the prominent bands at 1220 cm −1 and 1660 cm −1 are attributed to the asymmetric stretching vibrations of the C-O bonds and the C=O stretching vibrations of the urethane groups, respectively, and the peak at 1400 cm −1 is attributed to the C-H bonding vibrations [38,48,49]. The coexistence of both 1030 cm −1 and 1400 cm −1 peaks indicates the presence of multiple types of C-H bonds in the adhesive, each contributing to its molecular structure.…”

Mechanical and Microstructural Characterization of Rammed Earth Stabilized with Five Biopolymers

“…Tannins are extracted from different plants and are mainly composed of phenols. Tannins are principally commercialized as natural antioxidants to enhance the properties of wines and as natural stabilization aid for beer production, but is also used as antifungal, anticorrosion, and antibacterial agents, as well as a base agent for natural glue production [36][37][38]. The use of tannins for earthen construction and soil stabilization presents some interesting results.…”

An Eco-Friendly Wood Adhesive Consisting of Soybean Protein and Cardanol-Based Epoxy for Wood Based Composites

“…Potential biomass including starch, protein, lignin, tannin, etc., are investigated for wood adhesives [ 4 , 9 , 10 ]. Among them, vegetable proteins are emerging as raw material for the preparation of biomass adhesives due to their numerous functional groups such as amino groups, carboxylic acid groups, and hydroxyl groups [ 11 , 12 ].…”