Utjecaj pripreme površine na hrapavost, kvašenje i adheziju premaza na nemodificiranome i toplinski modificiranom drvu

In this research, the influence of face milling, sanding and UV irradiation of the hornbeam and ash wood sample on the wetting and adhesion strength of solvent-based and water-borne coating was studied. The adhesion of coatings to substrates is one of the most important parameters for finishing quality and service life of wood coatings, while wetting properties are usually used to assess the quality of surfacing process and could also provide important information on the adhesion ability of coatings. Surface roughness, contact angle of coatings and water as well as adhesion strength of coatings were tested on differently prepared (face milled, sanded and UV irradiated) samples of unmodified and thermally modified ash and hornbeam wood. Surface roughness was measured with stylus-type profilometer over the traverse of 12.5 mm and with a cut-off value of 2.5. Contact angle was measured using the sessile drop method 2 s, 10 s and 30 s after the application of the liquid drop on the sample surface, and adhesion strength was measured according to ASTM D4541. Results showed that sanding of hornbeam and ash wood resulted in the least rough surface compared to the face milled and UV irradiated surface. Contact angles of the water-borne coating were on average three times higher than the contact angles of the solvent-based coating. Sanding the surface of hornbeam and ash samples increased the adhesive strength in relation to the face milled surface, while UV irradiation of the sanded surface decreased the adhesive strength of most samples coated with solvent-based coating.U radu je istraživan utjecaj čeonog blanjanja, brušenja i UV zračenja grabovine i jasenovine na kvašenje i adhezivnu čvrstoću premaza na bazi organskih otapala i vodenog premaza. Adhezija premaza jedan je od najvažnijih parametara za kvalitetu površinske obrade i trajnost premaza za drvo, dok svojstva kvašenja obično služe za ocjenu kvalitete nanošenja i adhezije premaza. Na različito pripremljenim uzorcima (obrađenim čeonim blanjanjem, brušenjem ili UV zračenjem) nemodificirane i toplinski modificirane grabovine i jasenovine ispitivana je hrapavost, kontaktni kut premaza i vode te adhezivna čvrstoća premaza. Hrapavost površine mjerena je profilometrom na duljini vrednovanja 12,5 mm, uz referentnu duljinu od 2,5 mm. Kontaktni kut mjeren je metodom s kapljicom, i to 2 s, 10 s i 30 s nakon nanošenja kapljice na površinu uzorka, a adhezivna čvrstoća određivana je prema normi ASTM D4541. Rezultati su pokazali da je brušenje grabovine i jasenovine rezultiralo najmanje hrapavom površinom u usporedbi s čeono blanjanom i UV zračenom površinom. Kontaktni kutovi vodenog premaza bili su u prosjeku tri puta veći od kontaktnih kutova premaza na bazi organskih otapala. Brušenjem površine uzoraka grabovine i jasenovine adhezivna je čvrstoća postala veća od čvrstoće čeono blanjanih površina, dok je UV zračenjem na brušenim površinama većine uzoraka smanjena adhezivna čvrstoća premaza na bazi organskih otapala