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In this work, the effect of blend composition and previous photodegradation on the biodegradation of polypropylene/poly(3-hydroxybutyrate) (PP/PHB) blends was studied. The individual polymers and blends with or without the addition of poly(ethylene-co-methyl acrylate-co-glycidyl methacrylate) [P(E-MA-GMA)] as a compatibilizer (in the case of 80/20 blend) were exposed to UV light for 4 weeks and their biodegradation was evaluated. The biodegradation of PHB phase within the blends was hindered as PHB was the dispersed phase and PP fibrous particles were observed at the surface of the blend samples after biodegradation. Previous photodegradation lessened PHB biodegradation but enhanced the biodegradation of PP and the blends within the biodegradation time studied. Photodegradation resulted in cracks at the surface of PP and the blends, which probably facilitated the biotic reactions due to an easier access of the enzymes to deeper polymer layers. It also resulted in a decrease of molecular weight of PP phase and formation of carbonyl and hydroxyl groups which were consumed during biodegradation. Size exclusion chromatography analysis revealed that only the short chains of PP were consumed during biodegradation. POLYM. ENG. SCI., 53:2109–2122, 2013. © 2013 Society of Plastics Engineers