Distiller's dried grains with solubles (DDGS), the main coproduct in the dry mill corn ethanol industry, is finding its way toward a reinforcing filler in polymeric composite applications. In such a journey, thermal stability of DDGS is a critical factor affecting both temperature window of DDGS melt-compounding with polymers and the properties of the final biocomposite material. In this study, DDGS thermal stability was enhanced by washing with water and then used to fabricate biocomposites with Poly(1, 4-butanediol succinate) (PBS). The thermal degradation of DDGS, before and after washing, was studied with thermogravimetric (TG) and derivative thermogravimetric (DTG) analyses, showing up to 50 degrees C improvement in degradation onset temperature of DDGS after washing. Also, the degradation activation energies for water-washed DDGS were smaller than the respective values for as-received DDGS. Compositional analysis and infrared spectroscopy showed that the water-washed DDGS was higher in protein and fiber content compared to as-received DDGS. As a result of improved thermal stability of DDGS after water-washing, the DDGS burning during melt processing was highly prevented and the biocomposites processed at 160 degrees C and 190 degrees C showed constant tensile properties. On the other hand, for as-received DDGS biocomposites the tensile properties decreased as the processing temperature increased. Moreover, the increased fiber content of DDGS after water-washing resulted in biocomposites with higher tensile strength and modulus compared to as-received DDGS biocomposites. (C) 2013 Elsevier Ltd. All rights reserved.