Characterization of suberinic acids from birch outer bark as bio-based adhesive in wood composites
International Journal of Adhesion and Adhesives 112 (2022) 102989
Janis Rizhikovs, Prans Brazdausks, Aigars Paze, Ramunas Tupciauskas, Juris Grinins, Maris Puke, Ance Plavniece, Martins Andzs, Daniela Godina, Raimonds Makars
Keywords
Suberinic acids
Adhesives for wood
Novel adhesives
Wood and wood composites
Health and safety
A suberinic acids-based adhesive from birch outer bark as an alternative to replace synthetic adhesives for particleboard production was obtained and characterized. The adhesive prepared in the water solution and precipitated together with LCC significantly improved the moisture resistance and mechanical properties of the resulting particleboards. KOH and the raw material fraction of 1–4 mm showed most favorable preliminary results to be selected for the further investigation using DOE.
The DOE results have shown that, with increasing the concentration of KOH up to 4% and the reaction time up to 1.5 h, suberin is depolymerized to a higher extent and thus there is a higher amount of monomeric sberinic acids, monosaccharides, polyphenolic compounds and KNO3 salts in the resulting adhesive, which positively affects the physico-mechanical properties of the obtained particleboard. The Epoxy is directly proportional to the pH of the acidification, and in a higher amount (up to 5.25% at pH 3) decreases the mechanical properties of the particleboards (MOR 10.6 N mm−2). The chemical composition and FTIR analysis of the raw material and adhesives confirmed the above-mentioned assumptions about the impact of each compound on the properties of particleboards.
The optimal depolymerization conditions were as follows: KOH concentration 4%, acidification to pH 3 and the reaction time 0.5 h. Thus, particleboards with superior mechanical properties and moisture resistance were obtained, i.e. TS 14.3%, MOR 19.0 N mm−2, MOE 2604 N mm−2 and IB 2.25 N mm−2. In the frame of formaldehyde-free adhesives, the obtained results are promising, and they comply with the particleboard standard EN 312 type P3. The most important achievement of the study is that the suberinic acids-based adhesive cures without any additives or modifiers, being a completely ecological product.
