New Eucalyptus tar-derived polyurethane coatings

Varying proportions of Eucalyptus tar derivatives (biopitch and heavy oil), along with castor oil, have been used to synthesize polyurethane coatings. Two-compound polyurethanes have been obtained using MDI (4,4'-methane diphenyl diisocyanate) and DBTDL (dibutyl tin dilaurate) as catalyst, and an NCO/OH ratio of 1.0. Two coatings systems have been obtained - a varnish based on tar oil and a black paint based on biopitch. Both systems were characterized by FTIR, thermogravimetry (TGA) under air and nitrogen atmospheres, viscosity by Ford viscosity cup, thickness, hiding power, adhesion, gloss and hardness. Weathering assays were carried out in salt spray chamber for 72 h, weather-ometer (WO) (192 h) and QUV (192 h). New physical assays were carried out after the weather-ometer and QUV (gloss and hardness), the WO test being the harshest one, mainly on varnish. The biopitch black paint showed good results to salt spray assay, presenting anticorrosive properties. (C) 2004 Elsevier B.V. All rights reserved.