The aim of this study was to investigate the effect of zinc borate (ZnB) on the fire and thermal degradation behaviors of a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3,4)HB]-containing intumescent flame retardant (IFR). The IFR system was composed of ammonium polyphosphate, pentaerythritol, and melamine. The fire properties of P(3,4)HB/IFR/ZnB blends were evaluated by limited oxygen index, Underwriters Laboratories 94, microscale combustion calorimetry (MCC), and cone calorimetry (CONE) testing. The results of MCC and CONE show that the peak heat release rate, which is an important indicator of material fire hazard, of P(3,4)HB/IFR decreased when a small amount of the IFR was substituted by ZnB. The thermal degradation behavior of the P(3,4)HB/IFR/ZnB blends were measured by thermogravimetric analysis and thermogravimetric analysisinfrared (TGIR) spectrometry. The data of TGIR showed that the flammable gas products of P(3,4)HB released during the thermal degradation process were greatly decreased. Scanning electron microscopy analysis revealed that more compact char residues were observed with the incorporation of ZnB. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012