In this article, the compatibility of blends produced from recycled materials-cellulose acetate (from sugarcane bagasse) and polystyrene (from plastic cups)was studied using diffusion of water, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and scanning electron microscopy. With these techniques, it was possible to confirm the existence of miscibility microregions in blends produced according to what has already been pointed out in a previous paper (Filho et al., J Appl Polym Sci 2005, 96, 516). In addition, all the results present a transition occurring in blends containing 30% polystyrene. This composition indicates the starting limit for a possible inversion between the matrix and the disperse phase in the system. (c) 2007 Wiley Periodicals, Inc.