Birch Wood Surface Characterization after Treatment with Modified Phenol-Formaldehyde Oligomers.

Juris Grinins,Guntis Sosins,Vladimirs Biziks,Mairis Iesalnieks,Ineta Gritane

doi:10.3390/polym14040671

Juris Grinins, Guntis Sosins + Show 3 more

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https://doi.org/10.3390/polym14040671

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Abstract

Phenol-formaldehyde (PF) resins with well-established molecular sizes are promising treatment agents for wood bulk protection. However, due to the presence of hydroxyl groups on the periphery, the PF oligomers tend to absorb the water, which can lead to water penetration into the wood. To overcome this drawback different PF pre-polymers have been chemically modified with different long-chain fatty acid chlorides (FAC) via esterification. To obtain the modified PF (M-PF) resins, the PF pre-polymers with average molecular weight (Mw) from 266 to 884 g/mol were esterified with decanoyl, lauroyl, myristoyl, palmitoyl, and stearoyl chloride in pyridine as the reaction medium. Silver birch (Betula pendula) wood specimens (15 × 70 × 150 mm3) were coated with M-PF pre-polymer 5% (w/w) solutions in tetrahydrofuran (THF), and hydrophobic properties of treated birch wood specimens were evaluated using surface contact angle (CA) measurements of water droplets. For all M-PF resin-treated specimens, CA was almost 2–2.5 times higher than for untreated wood (45°) and it remained 80–125° after 60 s. The aging properties of M-PF resin-coated birch wood were analyzed using artificial weathering with ultraviolet (UV) light and combination of both UV and water spray. Results clearly confirm, that the hydrophobic properties of M-PF-treated wood has short-term character and will gradually disappear during long-term application in outdoor conditions.

Highlights

Received: 17 December 2021The effect of UV irradiation and of the repeated wetting and re-drying of wood surfaces can be reduced to some extent by four approaches: 1. Using coatings
This study investigated a new approach of birch wood surface treatment with different molecular weight (Mw ) PF resins modified with different chain length fatty acid chlorides (FAC) to understand the effect on surface hydrophobicity, weathering performance, and color stability in accelerated laboratory conditions
Showed hydrophobic effect after exposure to UV light as contact angle (CA) was ~90◦. It seems that light caused splitting or destruction of long aliphatic chains in modified PF (M-PF) resin structure, and UV light caused splitting or destruction of long aliphatic chains in M-PF resin structure, hydrophilic destruction products were formed on the surface of wood

Summary

Introduction

Received: 17 December 2021The effect of UV irradiation and of the repeated wetting and re-drying of wood surfaces can be reduced to some extent by four approaches: 1. Using coatings. Wood surfaces are protected using opaque coatings with pigments These coatings considerably decelerate deterioration of the wood substrate, the natural appearance and texture of the wood are hidden (lost) under the pigments. To overcome this drawback, translucent coatings are used. The first one focuses on modifying coating formulations to adapt the properties of the coating systems and meet the requirements of the wood substrate. For this reason, coating flexibility has been in the focus of much research. Several clear and semi-transparent coatings on wood have been tested and it was found that formulations with a lower glass transition temperature (Tg) have lower rates of crack formation and longer service lives than formulations with a higher

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