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Title: Co-extrusion of WPCs with a clear cap layer to improve color stability

Author: Stark, Nicole M.; Matuana, Laurent M.;

Date: 2009

Source: Proceedings: 4th Wood Fibre Polymer Composites International Symposium: March 30-31, 2009, Bordeaux, France: conferences and exhibition. [Paris?] : FCBA Institut Technologique, 2009: pages 1-13.

Publication Series: Miscellaneous Publication

Description: Wood-plastic composites (WPCs) have been gaining market share in residential construction applications such as lumber for decking, roof tiles, and siding. The durability of these materials in exterior environments is just beginning to be understood. Current research suggests that controlling moisture absorption by the composite is key to improving durability. Methods to improve moisture resistance of WPCs have met with limited success. Co-extrusion involves the simultaneous extrusion of two dissimilar materials as a single profile. A previous study demonstrated that co-extrusion of a base WPC with a clear cap layer positively enhanced water sorption characteristics initially, but weathering cracked the cap layer and caused delamination. Therefore, we investigated co-extruding a stabilized high-density polyethylene (HDPE) cap layer with a base WPC consisting of 50% juniper wood flour, 44% HDPE and 6% lubricant. The HDPE cap layer included combinations of a compatibilizer, nano-TiO2, and a photostabilizer package. A 2[superscript]3 full factorial design was used to determine the formulations of the cap layer. Composite color was monitored and changes were calculated after weathering for 1000 hours in a xenon-arc weathering apparatus. The results suggest that either nano-TiO2 or a photostabilizer package can be used to prevent cap layer cracking and aid in color retention after weathering. However, statistical models developed suggest that there is a negative interaction when using the two together.

Keywords: Wood-plastic composites, polyethylene, color fading, composite materials, deterioration, weathering, accelerated life testing, wood flour, extrusion process, injection molding of plastics, ultraviolet radiation, composite materials, moisture, adsorption, absorption, metallic oxides, titanium, juniper, discoloration, wood-plastic materials, accelerated testing, HDPE, photostabilizers, durability, surface properties, ultraviolet absorber, moisture content

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Stark, Nicole M.; Matuana, Laurent M. 2009. Co-Extrusion of WPCs with a clear cap layer to improve color stability. In: Proceedings of 4th wood fibre polymer composites international symposium. 30-31 March 2009. FCBA Institut Technologique. Bordeaux, FRANCE. (


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