Abstract
The mechanical properties of coatings strongly influence wood coatings’ performance, as coatings may be stressed by dimensional variations of wood when exposed outdoors. Within the European project SERVOWOOD (2014–2016), the influence of coating formulation on mechanical properties and cracking resistance has been studied. Several acrylic and alkyd formulations with different pigment volume concentrations (PVCs), with and without UV protection have been applied on pine samples and exposed to artificial weathering (EN 927-6) for 12 weeks. Persoz hardness of coatings applied on wood was assessed before and after weathering. Tensile tests on free films have been carried out at −10 °C, 20 °C, and 45 °C. For each formulation, elastic modulus, tensile strength, and strain at break have been determined for the three test temperatures. For each test temperature, there was no correlation between the elastic modulus and strain at break, nor between tensile strength and strain at break. The results showed a relation between Persoz hardness and elastic modulus. The best performing formulation had a mean elastic modulus at room temperature lower than 400 MPa and a mean strain at break higher than 30%.
Highlights
Improving the durability of exterior coatings is essential for the use and development of wood as a building material
The study of coatings made from a broader range of alkyd resins for exterior wood coatings would be useful to refine this analysis, as the relation found between Persoz hardness and elastic modulus of acrylic coatings was already shown [9]
The study has shown that making tensile tests both at negative and positive temperatures was useful to understand the mechanical behavior of the different formulations and the resistance to cracking
Summary
Improving the durability of exterior coatings is essential for the use and development of wood as a building material. Mechanical properties of coatings strongly influence wood coatings’ performance when exposed outdoors, as coatings may be stressed by dimensional variations of wood [2,3]. Despite their significant influence on performance, a prior control of the tensile properties of coating formulations has not yet been systematically assessed. The European Standard EN 927-2 [4] regarding performance specification for exterior wood coating does not include any mechanical properties in the performance criteria. The work content of this European project and some preliminary results have been recently presented [6] Within this project, the influence of coating formulation on mechanical performance and resistance to cracking. Tensile strength, and strain at break have been determined and analyzed in terms of cracking resistance after exposure to artificial weathering according to the standard EN 927-6 [7]
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