Preparation and characterization of tannin-based adhesives reinforced with cellulose nanofibrils for wood bonding

Abstract

Adhesives based on vegetable tannins are already a reality in the market. However, their use is still limited due to their low mechanical resistance and weak humidity resistance. Cellulose nanofibrils (CNFs) are being used as reinforcing materials in various composites, resulting in an improvement of mechanical proprieties in general. The objective of this work was to evaluate the incorporation of CNFs in adhesives made of tannins obtained from the Angico tree (Anadenanthera peregrine). Concentrations of nanofibrils at 1, 5, and 10% were added to the adhesives on a dry basis. Tests of viscosity, pH, solids content, and gel time were performed to determine the physical proprieties of the adhesives. The Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Raman spectra measurements were also determined to understand the interaction between tannins and CNFs. Thermogravimetric analyses (TGA) were carried out to determine the thermal resistance of the composite. The FTIR and Raman characterization identified some differences in the peaks in the chemical composition of the adhesives with different percentages of CNFs. The adhesives showed no different decomposition in the thermogravimetric analyses. The shear strength in the glue line of the adhesive with 5% of CNFs in Toona ciliata woods was determined. Among all the adhesives analyzed, the one with 5% of CNFs produced an improvement in the mechanical resistance and humidity resistance on the glue line.

Kraft Lignin/Tannin as a Potential Accelerator of Antioxidant and Antibacterial Properties in an Active Thermoplastic Polyester-Based Multifunctional Material

“…Considering the natural renewable reinforcements based on polyphenolic material, Kraft lignin (KL) and tannin (TANN) have great potential for the preparation of PLA composites to enhance functionality, especially toward bioactivity, whilst both phenolics act as free radical scavengers and thus as natural antioxidants that are UV resistant and bioactive [27,28]. In general, the incorporation of KL/TANN in polymer matrix exhibits several positive impacts as a compatibilizer, plasticizer, water repellent, flame retardant, and stabilizer; it also generates interest in the development of thermoplastic composites as adhesives and resins [29][30][31][32][33][34][35].…”

Tannin as a renewable raw material for adhesive applications: a review

“…Carbohydrates in tannin extracts are either monomers or oligomers, resulting from the hydrolysis of hemicellulose during tannin extraction. [61][62][63][64] These findings showed that the entire tannin extract, including polyphenolic components, can be used to prepare PUs. 194 Hydrolysable chestnut tannin possesses a small amount of hydroxyl group; after reacting with dimethyl carbonate, it reacts with hexamethylene di-amine later.…”

“…62 These non-tannin constituents are found to be responsible for weakening wood products and may also lead to decreased moisture resistance. 63 Pine-based tannin primarily confers two models: the first is unit-E, i.e., phloroglucinol 'I' ring and catechol 'II' ring structures, and the other one is unit 'F', i.e., phloroglucinol I-ring and phenol II-ring, represented in Fig. 3.…”

Valorization of Polyphenols from Stryphnodendron adstringens Bark for Use as a Sustainable Inhibitor of Nitrogen Volatilization in Soil

“…The phenolic bands with maximum intensities at 1606 (CO), 1440 (−CC−), 1340 (C−O−H), and 1031 cm −1 (C−H) are characteristic of aromatic rings from phenolic compounds. 42,43 The crude urease extract spectrum in Figure 3 shows the characteristic bands of enzymes: CO stretching in the amide I region with a maximum intensity at 1631 cm −1 (υ s (C O)) 44,45 and N−H bending in the amide II region with a maximum intensity at 1530 cm −1 (δ(N−H)). 46 Bands related to the amide I and amide II regions are characteristic of proteins.…”

“…The spectrum of the bark extract shown in Figure confirms the presence of phenolic groups. The phenolic bands with maximum intensities at 1606 (CO), 1440 (−CC−), 1340 (C–O–H), and 1031 cm –1 (C–H) are characteristic of aromatic rings from phenolic compounds. , …”