FTIR studies of the effects of outdoor exposure on varnish-coated wood pretreated with CCB or water repellents

Abstract

Scots pine (Pinus sylvestris L.)and chestnut (Castanea sativa Mill.) panels were coated with a polyurethane or an alkyd-based synthetic varnish. Some of the panels were impregnated with chromium-copper-boron (CCB) or the varnishes themselves before coating, as preservative-coating or water repellent (WR)-coating combination treatments, respectively. Earlier drastic changes in the intensity of the bands assigned to lignin and their shifts to some other stretching points were mostly attributed to chemical modification of lignin with the chromium in CCB, as well as the previously reported high color stability of CCB-impregnated wood. IR spectra of the nine months of weathering indicated that the synthetic varnish coating of non-impregnated or CCB-impregnated wood limited the reactions in lignin compared with polyurethane coating. Wood density and structural difference also seemed to play an important role since changes in lignin were mostly observed after six months of exposure for chestnut wood. Therefore, chemical reactions of CCB-wood cell wall components on the surface appeared likely to be affected from varnish type (their relative absorbency and distribution of sunlight), wood species (density and extractive substances), and exposure time and conditions.