Suitability of a lignin-derived mono-phenol mimic to replace phenol in phenol-formaldehyde resin for use in wood treatment

Abstract

The goal of this study was to assess the suitability of a single mono-aromatic for substitution of petroleum-based phenol for phenol-formaldehyde (PF) resin synthesis and the usage of a new resin for wood treatment. After proper thermal decomposition of wood-based lignin, pyrolysis oil can be obtained. Due to the heterogeneity of the lignin macromolecule, oil contains large variety of organic-based compounds, mainly mono-aromatics, which are proposed to be used for replacement of phenol during PF resin synthesis. Therefore, for this purpose, nine of the most abundant mono-aromatic compounds in bio-oil were selected: ortho-, meta-, para-cresol, guaiacol, catechol, 4-methylcatechol, resorcinol, syringol, 4-ethylphenol and resol-type resin from each mono-aromatic were synthesized. Relevant features of the resin such as pH, viscosity, average molecular weight and curing behavior of resins using differential scanning calorimetry (DSC) were analyzed. Scots pine (Pinus sylvestris L.) sapwood samples were used to evaluate the suitability of resin for wood treatment in terms of dimensional stability and were compared with the PF resin-treated wood. From all tested resins, those made of guaiacol or ortho-, or meta-, or para-cresol and/or 4-ethylphenol proved to be suitable for wood treatment, whereas resins made of catechol or 4-methylguaiacol and syringol did not. Suitability of mono-aromatics for synthesis of resol-type resin depends on chemical structure, where the reactivity of the mono-aromatic (derivative of hydroxybenzene) is defined by the type, location and number of substituents.

Lignin and Lignin-Derived Compounds for Wood Applications—A Review

“…Dier et al (2017) [82] tested the influence of model bio-oils with different ratios of monomers on the characteristics of the resols. As in the study by Biziks et al (2020), it was found that bio-oils that contain cresols have high potential to replace phenol in PF resins, while catechols negatively impacted the properties of the resin [82].…”

“…Methods for lignin cleavage to use lignin for such applications are underway. However, not all lignin cleavage products are suitable for the substitution of monomers commonly used in wood modification [ 80 , 81 ].…”

“…However, in most lignin depolymerization methods, the main products are phenolic compounds such as phenol, catechol, guaiacol, ortho-and para-cresol, etc. [80,81]. A screening of the combability of these monomers with PF-resols was done by Biziks et al (2020) [80].…”

“…[80,81]. A screening of the combability of these monomers with PF-resols was done by Biziks et al (2020) [80]. Herein, it was reported that guaiacol, o-, m-, p-cresol, and 4-ethylphenol were suitable for phenol replacement, whereas catechol, 4-methylguaiacol, and syringol had negative impacts on the performance of the resin.…”

“…Bio-oils obtained by cleaving lignin contain many compounds that are suitable for substitution of phenol in PF resins. However, due to the complex mixture it is often not possible to obtain a bio-oil that does not also contain molecules that worsen the resins' characteristics [80]. Dier et al (2017) [82] tested the influence of model bio-oils with different ratios of monomers on the characteristics of the resols.…”