© Faculty of Mechanical Engineering, Belgrade. All rights reserved FME Transactions (2017) 45, 405-411 405 Received: October 2016, Accepted: December 2016 Correspondence to: Dr. Franco Bulian CATAS S.p.a, Via Antica, 24/3, 33048 San Giovanni al Natisone (UD), Italy E-mail: bulian@catas.com doi:10.5937/fmet1703405B Franco Bulian R&D Director CATAS S.p.A. Italy Flaviano Collavini Senior Researcher CATAS S.p.A. Italy Alessia Matellon Senior Researcher CATAS S.p.A. Italy Investigating the Effects of Weathering on Wood Coatings The aim of this study is to elucidate the effects of weathering on wood coatings for exterior use. By means of analytical techniques as DSC, DMA, tensile test, UV/Vis and FTIR-ATR spectroscopies, it is possible to identify and measure the degree of damage, and so the chemical, physical and mechanical changes caused by degradation phenomena. The results can improve the predictive capability on coatings’ performance (glass transition, elasticity, light transmission) and help the assessment of the protective ability of light-stabilizing additives, in order to satisfy the requirements of coating producers and users. Keywords: wood, coatings, weathering, UV absorber, HALS 1. INTRODUCTION It is well known that wood coatings are susceptible to degradation when exposed outdoors in consequence to various weathering, phenomena mainly promoted by light, heat, water and oxygen. The evidence of such negative evolution during a weathering trial is the development of various defects like cracking, flaking and loss of adhesion whose initiation and progress mainly depend on coating formulation [1-6]. This risk is evident, in particular, when advanced manufacturing processes [7-8] or materials are used [9-10]. The lifetime prediction of outdoor exposure on the basis of accelerated weathering data would be of great importance, since the duration of the natural weathering tests is usually much too long to be practical [11-12]. Moreover, the evaluation criteria currently included in the standards EN 927-3 and EN 927-6 (respectively natural and artificial weathering for paints and varnishes for exterior wood coatings) are based on visual assessments of the exposed samples, which are not often exempt from subjective interpretation which lead to a scarce repeatability and reproducibility of the two methods. In this study various analytical techniques have been investigated in order to identify physical, mechanical and chemical changes in free coating films that indicate the initiation and progress of the degradation phenomena associated to a weathering process. The execution of real measurements of crucial parameters for the coating performance could be extremely helpful not only to improve the reliability and the predictive capability of the above mentioned test methods, but it would also represent a objective and unquestionable support for coating formulators. 2. MATERIALS AND METHODS The study has been carried out on four clear water- based coating materials (Table 1) expressly formulated and constituted by an aqueous emulsion of an acrylic binder with two different additives: an ultraviolet radiation absorber (UVa) and a hindered amine light stabilizer (HALS). The first additive is composed of an aqueous dispersion of a red shifted 2-hydroxyphenyl-s- triazine, while the second is a dispersion of an aminoether-substituted tetramethyl piperidine deriva– tive. A general overview of emissions related to wood products is available in [13]. Table 1. Composition of the coating materials analysed Coating material Binder UVa (wt%) HALS (wt%) A Acrylic - - B Acrylic 3% 1,5% C Acrylic 3% - D Acrylic - 1,5% Each coating material was exposed to artificial weathering in accordance with the European standard EN 927-6 in a proper device, both as coated wood samples and free films (Figure 1). The coatings were applied by brush to the front and side faces of wood panels (the back was left uncoated) with three coats corresponding to a total spreading rate of (150 ± 30) g/m 2 . After application, the wood specimens were dried for one week in a conditioned room at 23°C and 50% RH. Free coating films were also prepared using glass plates. The films were applied with a wet film thickness of 250 μm using a bar film applicator. After natural drying for 72 hours in a climatic room at 23°C and 50% RH, the solid films were peeled off from the glass plates by a mild vaporization on a thermostatic bath at (43 ± 1)°C. The dry film thickness was about 100 μm for all samples. Specimens for the artificial weathering were produced by cutting the free coating films in the dimension of 230 x 78 mm and clamping them on specimen holders by a proper sealant. All the samples were weathered up to six weeks. The degradation effects on wood panels (blistering, flaking, cracking, chalking, loss of adhesion) were estimated by visual assessments according to ISO 4628.