ABSTRACT:The effects of different color pigments on the durability of wood-flour/high-density polyethylene composites (WF/HDPE) were evaluated by UV-accelerated weathering tests. WF/HDPE composites were dyed using three different color inorganic pigments, which were added at 2% based on the weight of the composite. Samples were weathered in Q-panel UV aging equipment for 1500 h. All samples showed significant fading and color changes in exposed areas. Changes in surface chemistry were studied using spectroscopic techniques. X-ray photoelectron spectroscopy (XPS) was used to verify the occurrence of surface oxidation. Changes in carbonyl groups (C¼ ¼O), PE crystallinity, cellulose CAO, and lignin aromatic C¼ ¼C were detected by Fourier transform infrared (FTIR) spectroscopy. The results indicate that surface oxidation occurred immediately within exposure 250 h for all samples; the surface of the control WF/HDPE composites was oxidized to a greater extent than that of the dyed WF/HDPE. This suggests that the addition of pigments to the WF/HDPE composites results in less weather-related damage. The surface configuration observed by scanning electron microscopy revealed that WF/HDPE composites degraded significantly on accelerated UV aging, with dense cracking apparent on the exposed surface. Carbon black had a more positive effect on color stability than the other pigments.

Four kinds of iron oxide pigments were added into wood-fiber/high-density-polyethylene composites (WF/HDPE) at three different concentrations, to determine the effects of pigments on the changes in the color and mechanical properties of the composites before and after UV accelerated weathering. HDPE, wood fibers, pigments and other processing additives were dry-mixed in a high-speed mixer. The mixtures were extruded by two-step extrusion process with a self-designed twin-screw/single-screw extruder system. Color of the samples was determined according to CIE 1976 L * a * b * system by a spectrophotometer and the bending properties were tested to evaluate the mechanical properties before and after accelerated UV weathering. The result shows that the modulus of elasticity of WF/HDPE did not obviously changed after incorporating with the pigments, but the bending strength increased. After accelerated aging for 2000 h, both color and mechanical properties significantly changed. Iron oxide red and black performed better than the other two pigments, and the pigments dosage of 2.28% in the composites is favourable.

Paper mill sludge (PMS) is a waste material from pulping. In this article it was used to replace part of a wood fiber (WF) filler to reinforce high‐density polyethylene (HDPE). The properties of the PMS/WF/HDPE composites were investigated. When half of WF was replaced with PMS, the bending strength and modulus of WF/HDPE composites decreased by 16.08% and 29.91%, respectively, but their impact strength increased by 11.31%. Dynamic mechanical analysis demonstrated that with PMS addition, the storage modulus decreased and the loss tangent increased. Although the flexural properties of the PMS/WF/HDPE composites decreased compared to WF/HDPE composite, they still had satisfactorily high strengths. The 30:30:36 PMS/WF/HDPE composite presented bending and impact strengths of 61.00 MPa and 12.11 kJ m−2, respectively. The 50:20:26 PMS/WF/HDPE composite presented bending and impact strengths of 55.02 MPa and 10.37 kJ m−2, respectively. Rheological test proved that substituting part of WF with PMS would not affectmanufacture processing. This study indicated that paper mill sludge could be used in wood plastic composites, which would reduce pollution from paper manufacturing. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

In China, rice-hull powder is widely used as a fiber component to reinforce polymers because of its ready availability and lower cost compared to wood fibers. However, an issue concerning these composites is their weathering durability. In this study, the effects of two ultraviolet absorbers (UVAs), UV-326 and UV-531, on the durability of rice-hull/high-density polyethylene (HDPE) composites were evaluated after the samples were exposed to UV-accelerated weathering tests for up to 2000 h. All of the samples showed significant fading and color changes in exposed areas. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to detect surface chemical changes. The results indicate that surface oxidation commenced immediately within the first 500 h of exposure for all of the samples. However, the control rice-hull/HDPE composites underwent a greater degree of oxidation than those with the UVAs. Scanning electron microscopy revealed that the rice-hull/HDPE composites degraded significantly upon accelerated UV aging, with dense cracking on the exposed surface. The UVAs provided effective protection for the rice-hull/HDPE composites, and UV-326 had a more positive effect on the color stability than UV-531. The results reported herein serve to enhance our understanding of the efficiency of UV stabilizers in the protection of rice-hull/HDPE composites against UV radiation, with a view toward improving their formulation.