Effects of cyanuric acid (CA) on nonisothermal and isothermal crystallization, melting behavior, and spherulitic morphology of bacterial copolyesters of poly(3-hydroxybutyrate), i.e., poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), have been investigated. CA has excellent acceleration effectiveness on the melt crystallization of bacterial PHB, PHBV, and PHBH, better than the nucleating agents reported in the literatures, such as boron nitride, uracil, and orotic acid. PHBV and PHBH do not crystallize upon cooling from the melt at 10 degrees C/min, while they are able to complete crystallization under the same conditions with an addition of 1% CA, with a presence of sharp crystallization exotherm at 7595 degrees C. Isothermal crystallization kinetics of neat and CA-containing PHBV and PHBH were analyzed by Avrami model. Crystallization half-times (t1/2) of PHBV and PHBH decrease dramatically with an addition of CA. The melting behavior of isothermally melt-crystallized PHBV and PHBH is almost not influenced by CA. Spherulitic numbers of PHBV and PHBH increase and the spherulite sizes reduce with an incorporation of CA. Nucleation densities of PHBV and PHBH increase by 34 orders of magnitude with a presence of 1% CA. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013