Plasma Treatment Reduced the Discoloration of an Acrylic Coating on Hot-Oil Modified Wood Exposed to Natural Weathering

Arash Jamali,Philip D Evans

doi:10.3390/coatings10030248

Abstract

We test the hypothesis that plasma-treatment will remove oil from the surface of hot-oil modified blue-stained pine wood, and improve the adhesion and outdoor performance of a white acrylic coating on the modified wood. Modified wood was treated with water-vapour plasma, and microstructural changes at wood surfaces were examined. Plasma treatment removed oil from the surface of modified wood and etched bordered pits. The contact angle of water droplets on modified wood was 91.8°, but plasma-treatment for only 33 s reduced contact angle to less than that of the unmodified control (48.6°). The adhesion of the acrylic paint to modified wood was unaffected by plasma-treatment, but the adhesion rating of coated samples tested wet was slightly lower (3.1) than that of the coating on samples tested dry (3.5). The lightness value (CIE-L) of the acrylic coating on hot-oil modified wood samples exposed outdoors for 18 months was significantly lower (darker, 65.5) than that of the coating on similarly modified and exposed samples pre-treated with plasma (75.8). We conclude that plasma-treatment shows promise as a way of removing oil from the surface of hot-oil modified wood and reducing the discolouration of an acrylic coating on modified wood exposed to natural weathering.

Highlights

The performance of coatings on hydrophobic materials such as plastics can be improved by treating the surface of the material with plasma, a reactive mixture of charged particles [1,2]
Oil at the surface of wood is reported to reduce coating adhesion [15], but we found that removal of oil from the surface of hot-oil modified blue-stained lodgepole pine wood by plasma did not alter the adhesion of an acrylic primer to the modified wood
A water-vapor plasma pre-treatment reduced the discolouration of a water-borne acrylic latex coating on hot-oil modified, blue-stained lodgepole pine wood exposed to natural weathering for

Summary

Introduction

The performance of coatings on hydrophobic materials such as plastics can be improved by treating the surface of the material with plasma, a reactive mixture of charged particles [1,2]. Plasma treatment of thermally modified wood has positive effects on both wettability [7,8,9,10,11], and coating adhesion [11]. These findings were obtained using wood that was thermally modified in air/steam or nitrogen [7,8,9,10,11]. There have been no studies of the effects of plasma treatment on wood that has been thermally modified in hot-oil.

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