Abstract: Utilization of biochar in plastic based blends offers a sustainable way to renewable materials as well as value-added use of wood waste. To investigate the interfacial compatibility and weatherability properties of biochar composites, four types of Wood-Plastic Composites (WPC) were prepared by an extrusion process. The mechanical properties, water absorptions, thermal and viscoelastic properties, and rheological behavior of the composites were also evaluated. The decolorizing carbon (NA) composite melts showed the higher modulus and viscosity, indicating better melt strength. The NA composites performed the best in tensile properties (strength of 
28.6 MPa and modulus of 3.4 GPa) and had strong interfacial interaction between particles and the matrix. The degree of HDPE crystal-linity in the biochar and carbon composites decreased relative to Douglas-fir (DF) composites, while the thermal properties of the com-posites improved compared with DF composites. For the water resistance, the DF composites displayed the highest water absorption (3.7%) and thickness swell (2.9%). During accelerated weathering tests, longer exposure time increased the color change and lightness, especially for DF composite. NA and biochar composites resulted in improved photostability. This study opens up a pathway to utilize effectively the renewable biochar as reinforcing filler in WPC in outdoor applications.

Key words: biochar, interfacial compatibility, accelerated weathering, wood-plastic composites