The effect of natural weathering exposure time on the poly (3-hydroxybutyrate-co-3 hydroxyvalerate) (PHBV)/paddy straw powder (PSP) biocomposites was studied. These biocomposites were naturally exposed to tropical climate weathering conditions in Perlis, Malaysia for 6 months. Tensile test, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM) were applied to investigate the degradation that happened during natural weathering of the biocomposites. Tensile tests indicated that the weathered PHBV/PSP biocomposites caused lower ultimate strength and elongation to break, but increased the modulus of elasticity. As the exposure time prolonged to 6 months, the concentration of O-H groups became pronounced, indicating severe deterioration of the biocomposites. With a carbonyl chromophoric group in its structure, PHBV can absorb UV radiation directly, which could lead to reactions of Norrish forms I and II. Generally, the addition of PSP has increased the degradability of PHBV. Besides, the exposed PHBV/PSP biocomposite surfaces have undergone surface crazing upon weathering. The surface of the PHBV without the addition of the PSP did not show any crack and fungus colonisation. The higher PSP content loaded in the biocomposites (i.e. 20 wt. %) caused more fungi colonisation, resulting in larger cracks and pores formed on the surface of the samples.
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