Non-destructive Methods for Evaluating the Physical and Mechanical Aging of Composites

Abstract

Abstract Wood-plastic composites (WPC) have been developed into new and important wood-based materials because of their benefits for the environment, their economy and their recyclability. When WPCs are used outdoors, they are subjected to a climate with moisture and temperature fluctuations. It is therefore necessary to obtain information on the effects of climate aging on WPCs. This study explores the relationship between laboratory aging, physical and mechanical changes, and the results of non-destructive testing of wood-polymer composites. This was done by testing 45 pieces of composite with 60% wood fibre, 35% low-density polyethylene (LDPE) and 5% additives. A laboratory aging process consisting of a water immersion at 20 and 50°C for a total of 56 days was carried out on composite specimens. During the aging test, several specimen batches were extracted and tested to record their physical (density) and mechanical properties (bending strength and modulus of elasticity). Non-destructive testing was also carried out with ultrasound and stress wave, screw withdrawal resistance meter and penetration tester devices. Temperature was found to have more influence than humidity on the deterioration of the material. A barely significant decrease in density (2-4%) and a clear drop in mechanical properties (20-60%) was also observed. The non-destructive methods used were reliable estimators of composite properties, especially ultrasound wave propagation, coinciding with previous works on other materials.