This study considers the effects of pellet geometry and compatibilization on its moisture absorption and thermal degradation behavior of recycled polyethylene terephthalate (RPET) and recycled polypropylene (RPP) blend with the ultimate goal of optimizing the design of pellets to enhance their processability. The isoconversion of FlynnWallOzawa (FWO) was used for the kinetic study, which was suitable for thermal degradation of RPET/RPP blend in N-2 while the second order polynomial function was fitted for thermal oxidative degradation in air. Finer geometries, such as powders, were found to have higher moisture absorption rates due to their large surface area although they could also be easily dried. Furthermore, large surface area of fine powder as well as good interaction between RPP disperse particles and RPET matrix eased to decompose in the presence of oxygen thus accelerated chain breaking during thermal oxidative degradation especially at low heating rate. Meanwhile, larger pellets exhibited higher degradation activation energies, which suggest that they are more resistant to thermal degradation than smaller grains. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012