Effects of Nanosilver-Impregnation and Heat Treatment on Coating Pulloff Adhesion Strength on Solid Wood

Effects of impregnation with a silver nano-suspension, as well as of heat-treatment, on pull-off adhesion strengths of the coating system on three commercial solid wood species were studied. The wood species included beech, poplar, and fi r. The size range of silver nanoparticles was 30 – 80 nm. The specimens were coated with an un-pigmented sealer and a clear fi nish on the basis of an organic solvent. The results showed that the highest and the lowest pull-off strengths were found in beech specimens heat-treated at 145 °C (5.7 MPa) and in nanosilver-impregnated poplar specimens heat-treated at 185 °C (2.5 MPa), respectively. Impregnation with nanosilver decreased pull-off strength in the case of all species as a result of formation of micro checks in the cell walls caused by the impregnation under high pressure in vessel. Heat-treatment at the temperature lower than 145 °C increased pull-off strength as to the irreversible hydrogen bonding in the course of water movements within the pore system of the cell walls, resulting in extra bonds among cell wall components and higher mechanical properties. However, heat treatment at the temperature higher than 185 °C significantly decreased the strength as the degradation of hemicellulose and cell wall wood components caused signifi cant decrease in mechanical strength and cell wall thinning. High thermal conductivity coefficient of silver intensified the impact of heat-treatment by rapid absorption of heat on the surface of the specimens.U radu su istraživani učinci impregnacije drva srebrnom nanosuspenzijom, kao i učinci toplinske obrade na čvrstoću prianjanja (adhezije) sustava premaza na tri komercijalne vrste masivnog drva. U istraživanjima je analiziran sustav premaza na drvu bukve, topole i jele. Raspon veličine srebrnih nanočestica bio je 30 – 80 nm. Uzorci su obrađeni nepigmentiranim punilom i završnim premazom na osnovi organskog otapala. Rezultati su pokazali da je najveća čvrstoća prianjanja izmjerena na uzorcima od toplinski obrađene bukovine pri 145 °C (5,7 MPa), a najmanja na uzorcima od drva topole impregniranima srebrnim nanočesticama i toplinski obrađenima pri 185 °C (2,5 MPa). Impregnacija srebrnim nanočesticama smanjila je čvrstoću adhezije na svim vrstama drva, što je posljedica stvaranja mikropukotina na staničnim stijenkama uzrokovanima impregnacijom pod visokim tlakom u posudi. Toplinska obrada na temperaturi nižoj od 145 °C povećala je čvrstoću adhezije s obzirom na ireverzibilne vodikove veze u toku kretanja vode u sustavu pora staničnih stijenki, što rezultira dodatnim vezama između komponenti stanične stijenke i boljim mehaničkim svojstvima. Međutim, toplinska obrada na temperaturi višoj od 185 °C bitno smanjuje čvrstoću adhezije jer propadanje hemiceluloze i komponenti stanične stijenke drva uzrokuje znatno smanjenje mehaničke čvrstoće i stanjivanje stanične stijenke. Visoki koeficijent toplinske vodljivosti srebra pojačava učinak toplinske obrade brzom apsorpcijom topline na površini uzorka