The Impact of a CO2 Laser on the Adhesion and Mold Resistance of a Synthetic Polymer Layer on a Wood Surface

Ladislav Reinprecht,Zuzana Vidholdová

doi:10.3390/f12020242

Abstract

In the wood industry, laser technologies are commonly applied for the sawing, engraving, or perforation of solid wood and wood composites, but less knowledge exists about their effect on the joining and painting of wood materials with synthetic polymer adhesives and coatings. In this work, a CO2 laser with irradiation doses from 2.1 to 18.8 J·cm−2 was used for the modification of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies /L./ Karst) wood surfaces—either in the native state or after covering them with a layer of polyvinyl acetate (PVAc) or polyurethane (PUR) polymer. The adhesion strength of the phase interface “synthetic polymer—wood”, evaluated by the standard EN ISO 4624, decreased significantly and proportionately in all the laser modification modes, with higher irradiation doses leading to a more apparent degradation and carbonization of the wood adherent or the synthetic polymer layer. The mold resistance of the polymers, evaluated by the standard EN 15457, increased significantly for the less mold-resistant PVAc polymer after its irradiation on the wood adherent. However, the more mold-resistant PUR polymer was able to better resist the microscopic fungi Aspergillus niger Tiegh. and Penicillium purpurogenum Stoll. when irradiation doses of higher intensity acted firstly on the wood adherent.

Highlights

The bubbles in the synthetic polymer layers probably arose as a result of thermal decomposition reactions in their macromolecules, together with the creation of lower-molecular gasses which inflated a layer of thermoplastic polyvinyl acetate (PVAc) polymer or a layer of the completely non-crosslinked PUR polymer
The increased doses H of CO2 laser from 2.1 to 18.8 J·cm−2 acting on the native beech and spruce wood surfaces or on the layers of synthetic PVAc and PUR polymers present on wood surfaces caused the decomposition and carbonization of wood components or synthetic polymers—visible by their darkening until blacking and the creation of air bubbles in synthetic polymers
Due to the laser irradiation, the adhesion strength decreased more for the beech wood versus the spruce wood adherent, for the PUR polymer versus the PVAc polymer layer, and for the laser beam focusing on the native wood versus the synthetic polymer

Summary

Introduction

The intentional processing or modification of wood surfaces can be performed by various mechanical, physical, chemical, and biological methods. Their aim is to improve or optimize (1) the final characteristics of wood surfaces—e.g., their shape, roughness, hardness, color, gloss, and resistance (to water, sun, fire, fungi and other biological agents) [1,2,3,4];. (2) the inter-operational characteristics of wood surfaces—e.g., the wettability, free surface energy, and density—which are important before wood gluing/painting with natural and synthetic polymer adhesives/coatings [5,6,7].

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Conclusion