Effect of the heat treatment on the adhesion strength of water based wood varnishes

Abstract

Effects of heat treatment on the adhesion strength of water based wood varnish were studied using four tree species woods [Anatolian black pine (Pinus nigra J.F. Arnold subsp. nigra var. caramenica (Loudon) Rehder), Calabrian pine (Pinus brutia Ten.), Sessile oak (Quercus petraea Liebl.) and Sweet chestnut (Castanea sativa Mill.)] and two components water based varnish (one-component semi-matte and two-component glossy water-based varnish). Those tree species' woods were selected randomly from timber merchants as test materials because of their wide use in industry. Under atmospheric pressure, the wood samples were subjected to three different temperatures (130, 180 and 230°C) at two different time intervals (2 and 8 h). After that, the wood samples were coated with two components water-based varnish. Adhesion strength of varnish film was then measured with a pull-off test according to the ASTM-D 4541 (1995). The coatings presented the highest adhesion strength (3.33 MPa) on oak wood, followed of the adhesion strength on chestnut (2.1 MPa) and on pine species (black pine 1.78 and Calabrian pine 1.65 MPa) Sessile oak wood showed the highest adhesion strength (3.33) followed by Sweet chestnut (2.19) and pine species (Anatolian black pine 1.78 and Calabrian pine 1.65 MPa). The adhesion strength of all wood types decreased increasing temperature and time.