Improving weathering performance of wood by borates impregnation and liquid glass coating

Abstract

Poor weathering performance of impregnated and coated wood products is an important issue that infl uences their appearance as well as their service life after outdoor or indoor exposure. A novel procedure to improve the weathering performance of Scots pine wood (Pinus sylvestris L.) is proposed in this study. Wood samples were impregnated with ammonium tetrafl uoroborate (ATFB), ammonium pentaborate (APB) and boric acid (BA), and afterward coated with a layer of liquid glass (LG). Surface hardness, color changes, and surface roughness of wood samples were investigated after 250 h and 500 h of exposure to artifi cial weathering. The results revealed that, except for untreated (control), all other treatment groups caused an increase in surface hardness of Scots pine after weathering. A decrease in the CIE L* value corresponds to the darkening of samples after weathering. Borates-impregnated and LG-coated Scots pine samples possessed the highest color stability. However, all treatment combinations resulted in reddish and yellowish tones after weathering. Exposure to weathering increased surface roughness of wood samples. The surface roughness of the untreated (control) group was higher than that of impregnated and coated samples.

Slaba otpornost impregniranoga i premazanog drva pri izlaganju vremenskim utjecajima velik je problem koji utječe na izgled i vijek trajanja drva nakon izlaganja u eksterijeru ili interijeru. U ovom je istraživanju predložen novi postupak poboljšanja otpornosti borovine (Pinus sylvestris L.) izložene vremenskim utjecajima. Uzorci drva impregnirani su amonijevim tetrafl uoroboratom (ATFB), amonijevim pentaboratom (APB) i bornom kiselinom (BA), nakon čega su premazani tekućim staklom (LG). Ispitivana je tvrdoća površine, promjena boje i hrapavost površine uzoraka drva nakon 250 i 500 sati umjetnog izlaganja vremenskim utjecajima. Rezultati su pokazali da se na svim površinski obrađenim uzorcima borovine povećala tvrdoća njezine površine nakon izlaganja vremenskim utjecajima. Smanjenje vrijednosti CIE L* upućuje na tamnjenje uzoraka nakon izlaganja vremenskim utjecajima. Najbolju stabilnost boje pokazali su uzorci borovine impregnirani boratima i premazani tekućim staklom. Međutim, sve kombinacije površinske obrade rezultirale su povećanjem crvenoga i žutog tona nakon izlaganja uzoraka vremenskim utjecajima. Izlaganjem vremenskim utjecajima povećala se hrapavost površine uzoraka drva. No hrapavost površine kontrolnih uzoraka (površinski neobrađenih) bila je veća nego hrapavost površine impregniranih i premazanih uzoraka.