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The effect of annealing poly(lactic acid) (PLA) and PLA grafted with itaconic anhydride (IA) at different temperatures was studied using differential scanning calorimetry (DSC) and wide angle X‐ray scattering (WAXS). For PLA, two crystal forms were obtained when annealed between 110 and 120 °C, transforming into only the α‐form at 130 °C while a mixture of α′ and α‐form were obtained in grafted PLA. Grafting increased the percentage crystallinity of PLA, but it was mostly unaffected by the degree of grafting. The rate of crystallization was strongly dependent on the degree of grafting; when annealed at 100 °C, the crystallinity increased from 27.7 to 43.1% while the crystallization halftime reduced from 10.7 to 4.4 min at the lowest degree of grafting. It was thought that the increase in crystallization rate was likely due heterogeneous nucleation in the presence of grafted chains. © 2016 Wiley Periodicals, Inc. J …