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Development of durable, solvent-free waterbased coatings for Wood-Polymer Composite (WPC) sidings

: Schirp, C.; Schirp, A.; Bellmann, C.; Calvimontes, A.

Facade coatings and plasters : European Coatings Conference, 29 - 30 October 2013, Düsseldorf, Germany
Hannover: Vincentz Network, 2013
European Coatings Conference on Facade Coatings and Plasters <2013, Hannover>
Conference Paper
Fraunhofer WKI ()

In this applied research project in cooperation with the Leibniz-Institute of Polymer Research Dresden and several industrial partners, we are aiming to develop solvent-free, water-based coatings for wood-polymer composite (WPC) sidings. Despite the fact that solvent-based coatings display good adhesion and surface wettability, they are more and more substituted by water-based solutions due to legal requirements such as the VOC (volatile organic compounds)-directive (1999) and the Decopaintdirective (2004). In general, to avoid or reduce changes in WPC caused by environmental factors, several options are available such as the use of pigments and UV-protective agents in the bulk WPC formulation, use of co-extrusion, covering with laminates or powder coating. Application of a liquid coating system represents a flexible, cost-efficient and technically feasible solution because only one WPC formulation needs to be extruded while pigmentation and UV protection are added as part of the coating system following extrusion. This way, small WPC batches with various colourations can be produced efficiently (no need for extrusion and storage of various WPC formulations). From an ecological point of view, it is advisable to formulate the primer as well as the top coat without addition of solvents and halogens. In addition, halogen-free products offer advantages pertaining to recycling. In this presentation, results will be shown which explain the relationship between surface composition of the WPC, surface energy, wettability and adhesion. WPC of know composition were extruded at Fraunhofer WKI with various base polymers and additives, and various concentrations of wood, polymer and additives. Specifically, we were interested in determining the location and disturbing of the additives (coupling agents, lubricants) and their influence on coatings adhesion. In addition, commercial WPC products were included in the experiments. Pretreatments such as plasma-treatment, flame treatment and brushing were also included. Finally, recommendations will be provided how different WPC substrates (variation in wood content, polymer and additive types and amount) can be effectively pre-treated and coated with water-based systems.