Weathering and biodegradation effects in wood-plastic composites (WPC) made with zinc borate

Abstract

The effects of zinc borate (ZB) on physical and mechanical properties of wood plastic composites (WPCs) were assessed. WPCs were elaborated with 0, 1, 3, y 5 % ZB concentrations, wood flour, mesh 60 and polypropylene in 50/48, 50/47, 50/45 y 50/43 proportions as a function of ZB concentration. 2 % of maleic anhydride of polypropylene (MAPP) was included in all WPCS. Specimens were exposed to natural weathering for 6 months. Bioassays with the fungi Gleophyllum trabeum (brown rot) and Trametes versicolor (white rot) were conducted by means of agar (EN 350-1) and soil block (ASTM D 2017-05) tests. Moreover, water absorption and swelling as well as static bending, tensile strength and impact strength were evaluated. Other properties like surface brightness and morphological characterization by means of scanning electron microscopy (SEM) were also considered. Zinc borate has no effect on mechanical properties of the untreated WPCS. After weathering, ZB had no effect on static bending and impact strength. However, a positive effect on tensile strength was observed. ZB had a positive influence on impact strength of WPCS exposed to biodegradation by fungi. Regardless of the low decay rates, ZB proved effective against fungal decay; weight losses suffered by WPC specimens exposed in agar and soil block tests showed no significant differences.