Abstract: Wheat straw powders (WSP) were surface-modified by grafting with styrene. Contact angles were measured by a capillary rise method for the WSP before and after surface modification, and then the surface free energy was evaluated by the Washburn equation according to Owens’ method. The results indicated that the modified WSP achieved 24.77 mN·m-1 in surface free energy as well as 19.79 mN·m-1 in its nonpolar part, whereas the pristine WSP only obtained 18.90 mN·m-1 and 3.75 mN·m-1 for these two parameters. This implicates that graft modification is a useful means for nonpolarization of WSP. Moreover, SEM observation confirmed that the modified WSP had better interfacial compatibility with thermoplastics.

Key words: surface contact angles, surface free energy, interfacial compatibility, dispersion