The influence of accelerated weathering on the mechanical and physical properties of wood-plastic composites

Abstract

This research concentrates on the effect of moisture absorption and UV radiation on the mechanical and physical properties of wood-plastic composites (WPC). The goal is also to evaluate the importance of wood flour fraction size on the mechanical properties of WPC and their influence on the accelerated weathering results. Wood flour reinforced composites with three different fractions of wood flour made from birch (Betula) chips were prepared. Additionally, Bleached-Chemi-Thermo-Mechanical aspen (Populus tremula) pulp (Aspen BCTMP) was used. Thermoplastics (LLDPE-g-MAH, PP) were used to prepare composites. Wood flour and BCTMP surface were treated with two different coupling agents: 3-aminopropyltriethoxysilane (APTES) and polyvinyalcohol (PVA). The WPC specimens were prepared by injection molding. Accelerated weathering tests were carried out to evaluate the influence of weathering on the mechanical and physical properties of composites. Three-point bending test and Charpy impact test were used to test mechanical properties. The test results showed that using wood flour as a filler material in composites made the WPC material more rigid and brittle. Due to the water absorption and swelling of WPC, the flexural modulus (MOE) and strength decreased and impact strength increased by making the material weaker with increasing the deflection of the WPC. The UV radiation decreased the composites flexural strength and MOE, while impact strength was increased. After the accelerated weathering cycles, cracks and voids were found on the surface of the WPC materials. After the UV radiation treatment, also the WPC colour was lightened.

Combined effect of water uptake and temperature on wood polymer composites

“…Figure shows that the energies for unsaturated samples are substantially the same and temperature independent, while, as reported in Figure , initiation energy is greater than propagation energy for saturated samples. This can be explained by the wood particles softening effect due to water uptake . Although with high standard deviations, the lowest propagation values for the saturated sample tested at 40 °C may be a further indication that the interface has failed and the sample does not require high propagation energy to reach complete failure.…”

“…However, unlike HDPE, wood particles are anisotropic and their swelling is not the same in all directions. For this reason, the anisotropy mismatch between matrix and particles gives rise to shear stresses at the interface, whose properties are already reduced due to the presence of absorbed water . These stresses can cause the fracture of the interface.…”

“…For this reason, the anisotropy mismatch between matrix and particles gives rise to shear stresses at the interface, whose properties are already reduced due to the presence of absorbed water. 28,34 These stresses can cause the fracture of the interface. Since SEM observations have not been taken during saturation but only after drying and re-equilibrating the sample, particles tend to recover their initial volume due to water loss, while the matrix remains deformed plastically.…”

“…The dependency of mechanical properties of WPC on moisture absorption has been widely investigated [11][12][13][14][15][16][17][18][19][20][21][27][28][29] while, to the authors' knowledge, not enough attention has been paid to the influence of water soaking in conjunction with thermal conditioning. 10 Since WPCs are mainly used in outdoor applications, where temperature can vary in a quite large range, understanding the complex interplay between these two factors is very important to predict the performance reduction.…”

Wood‐based composites with thermoplastic polyurethane as matrix polymer

“…Wood fillers in composites are known to be lightweight, eco‐friendly, nonabrasive, abundant, and inexpensive. Owing to the advancements in processing technology, growing environmental awareness, and economic factors, wood‐based thermoplastics (WPC) have gained worldwide attention . Compared to thermoset resins, thermoplastics offer advantages such as recyclability and are free of formaldehyde .…”