Combined ultraviolet and water exposure as a preconditioning method in laboratory fungal durability testing

During outdoor exposure, woodfiber-plastic composites (WPC) are subject to biological, moisture, and ultraviolet (UV) degradation. The purpose of laboratory evaluations is to simulate outdoor conditions and accelerate the testing for quicker results. Traditionally, biological, moisture, and W laboratory tests are done separately, and only combined in outdoor field exposure. This research evaluates WPCs exposed to a combination of UV, moisture, and fungal degradations. Due to the slow moisture sorption of WPCs, the ASTM D 1413 standard laboratory soil block test was modified to include preconditioning by W and water. WPCs consisting of 50 percent western pine wood flour and 50 percent high-density polyethylene (HDPE) were extruded into 30 by 140 mm (1.2 by 5.5 in.) radius edge deck boards. Four blends were extruded containing the following additives by weight percentages: 1. control; 2. 1 percent zinc borate; 3. 1.5 percent W stabilizer package; and 4. 1 percent zinc borate + 1.5 percent UV package Specimens (3 by 13 by 89 mm) were cut from the boards and exposed to one of two preconditioning methods: 1. 2-week water soak or 2. 1,000 hours in a weatherometer plus a 2-week water soak. After the 2-week water soak the autoclaved “wet” specimens were placed in a modified soil block test against the brown-rot fungus Gloeophyllum trabeum for 12 weeks. Moisture content and weight loss of the specimens were determined after 12 weeks. Matched field stakes were placed above and in-ground in Madison, WI, and Saucier, MS, for ultimate comparison.