Microstructural and Micromechanical Characterization of Modified Urea-Formaldehyde Resin Penetration into Wood

Abstract

Characterization of the adhesive penetration behavior in wood is highly desired for optimizing the manufacturing processes and product properties. In this study, modified urea-formaldehyde (UF) adhesive was used to prepare glued laminated timber (Cryptomeria fortunei Hooibrenk). The depth of gross penetration was measured by fluorescence microscopy (FM), which showed the UF passed through 1.5 to 3.5 earlywood tracheids (with an average penetration depth of 88.95 ± 27.49 μm) or 0.5 to 4.0 latewood tracheids (with an average penetration depth of 36.39 ± 15.14 μm). In addition, the distribution of cell wall penetration was observed clearly by confocal laser scanning microscopy (CLSM). The adhesive was found to diffuse into the cell walls of surface tissues embedded in the UF. To verify the results from CLSM, the mechanical properties of cell walls with and without adhesive penetration were measured through nanoindentation (NI). The reduced elastic modulus of exposed cell walls (18.10 GPa) was roughly equal to that of fully filled cell walls (17.68 GPa) but significantly greater than that of reference ones (15.71 GPa). The hardness showed a similar variation trend for these three types of cell walls. Combining the three techniques, both the microstructure and micromechanics of the adhesive penetration behavior can be quantitatively identified in a complementary manner.

Review of Existing Methods for Evaluating Adhesive Bonds in Timber Products

“…The anatomical structure of samples, its wood type, adhesive type and their properties (viscosity for example) could all affect the penetration measurement and its replicability for various studies and products. (Left) Imaging of effective penetration (EP) and maximum penetration (MP) of gross penetration of into structure [8] and (right) penetration of urea formaldehyde (UF) into wood cell walls shown in green colour [9].…”

“…The comparison with light microscopic imaging showed the advantages of using CLSM in showing the details of penetration into cell lumina and fine surface cracks [61]. The separation between urea formaldehyde (UF) resin and wood cells is not usually easy with common microscopic methods; Figure 26-right show images of UF resin using CLSM [9]. has capabilities in enhancing the contrast between the wood and coating or adhesive materials to improve the image quality and clarity.…”

“…Figure 2. (Left) Imaging of effective penetration (EP) and maximum penetration (MP) of gross penetration of into structure[8] and (right) penetration of urea formaldehyde (UF) into wood cell walls shown in green colour[9].…”

Bonding performance of plywood with pig blood adhesives prepared by a novel method

“…The microscopy images were processed with graphics processing software (ImageJ, National Institutes of Health, v1.8.0, Bethesda, America) to calculate the average penetration depth (AP), effective penetration depth (EP), and permeation area (A) of the adhesive layer. The AP was obtained by taking the average of the five maximum penetration depth values of the adhesive layer, A is the area of the adhesive on the entire fluorescent image, and A divided by the length of the adhesive line is the EP (Gavrilovic-Grmusa et al 2016;Qin et al 2016).…”

Improvement of Mechanical, Hydrophobicity and Thermal Properties of Chinese Fir Wood by Impregnation of Nano Silica Sol

“…However, some inherent inferior properties, e.g., lower strength and dimension changes over the exposing environments and easy to lose mechanical strength under attack by insects, have prevented efficient uses and exploitation of its full potential. To improve the strength and hardness, dimensional stability, and antiseptic properties, modifications with suitable chemicals have been employed and proven to be an attractive way [ 1 , 2 ]. In order to improve the physical and mechanical properties and weather resistance of wood, different scholars use various inorganic or organic modifiers to treat the wood [ 2 , 3 , 4 ].…”