Vinyl acetate (VAc) was grafted onto poly(3-hydroxybutyrate) film by a preirradiation method. Grafting reactions were carried out in VAc /water/ surfactant emulsion, VAc/water, and VAc/methanol systems. For emulsion grafting, Nonion L-4 was ascertained to be the optimum surfactant with respect to the stability of a single emulsion layer. The emulsion with a 10: 1 (w/w) ratio of VAc to surfactant yielded the highest degree of grafting: 23%. The grafting efficiency in the emulsion and the water and methanol solvents were evaluated. The results indicated that the grafting efficiency of the emulsion was 100 times that of VAc/methanol when the same 2 wt % VAc was used in the grafting reaction. (c) 2007 Wiley Periodicals, Inc.