Penetration process of polyurethane adhesive into the wood ultrastructure

• Published in: AIP Conference Proceedings 2022-11, Vol.2611 (1)
• Main Authors: Vaněrek, Jan, Böhm, Martin, Běťák, Adam, Kulich, Pavel, Mašek, Josef
• Format: Article
• Language: English
• Subjects: Adhesives; Calcium carbonate; Dimethylformamide; Dispersion; Energy dispersive X ray analysis; Fluorescence; Iodine; Lumens; Microscopy; Nanoparticles; Penetration; Polyurethane resins; Rhodamine; X ray analysis
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0119524

The main goal of this paper was to ascertain the exact distribution of one-component polyurethane adhesive in the structure of spruce wood. The used polyurethane (PUR) adhesive meets the requirements set out by EN 301 for bonding structural timber. Fluorochrome Rhodamine B showed sufficient fluorescence when mixed with the PUR adhesive in the amount of 2.5% (diluted in N,N-Dimethylformamide) and subsequent fluorescence microscopy showed the distribution of adhesive in the lumen and in the medullary rays of spruce wood. The adhesive penetration in the transverse direction made its way to the 4th row of wood cells from the bondline. The existence of the adhesive in lumens that were further away was caused by adhesive penetration in medullary rays. Using transmission electron microscopy, the CaCO3 nanoparticles that were deagglomerated in the adhesive using ultrasound were only observed in the lumens of wood cells. The energy dispersive X-ray analysis of the bondline area only detected iodine (dispersed in an amount of 10% and 20% by weight in PUR) in the lumens of the wood cell, and in much higher amounts than in the cell wall. All of the experimental techniques used show that the one-component polyurethane adhesive is not able to penetrate the cell wall structure.