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The physical and mechanical properties (density, modulus of elasticity, and modulus of rupture) of standard and humidity-resistant types of particleboard and fiberboard were determined by standardized test and wave propagation velocity, obtained from the natural frequency in a nondestructive longitudinal vibration test. Four batches of 66 specimens for each type of panel (particleboard and fiberboard) and for each kind of panel (standard and humidity resistant) were tested under initial conditions and after each one of the three aging cycles defined in European Standard EN 321:2001. Each aging cycle consisted of immersion in water, freezing, and high-temperature drying. The decreasing ratio of wave velocity was used to predict the decreasing ratio of properties. There was a strong relationship between both variables, and an exponential regression model is proposed to predict physical and mechanical properties, with a determination coefficient (R2) from 0.93 to 0.98.

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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.