To investigate the evolution of biodegradable mulch films in different environments, biodegradable mulch films with the raw materials of PBAT/PPC/additives (BDM1) and PBAT/PPC/wheat straws/additives (BDM2) were set as the research objects in this study. The evolution of their mechanical and water vapor barrier properties were studied carefully with ultra-violet (UV) irradiation and deionized water (DW) immersion, and the degradation process of biodegradable mulch films was analyzed with microscopic morphologies, Fourier transform infrared spectroscopy and X-ray diffraction. The results showed that the deterioration of both mechanical and water vapor barrier properties was taken place in both UV and DW environment while the rate of deterioration is greatly influenced by the cumulative irradiation intensity and the immersion duration. Compared with the films under 0.77 W/m² UV irradiation, the films immersed in DW exhibited a relatively lower deterioration rate of the mechanical and water vapor barrier performance. The tensile strength loss of BDM in both machine direction (MD) and transverse direction (TD) exceeds 85% with 320-h (equal to 5.40 kJ) UV irradiation and 77% after immersing in DW for 165 d. Meantime, the WVP after 320-h UV irradiation is 2.64 and 3.85 times that of original BDM1 and BDM2, while the WVP value after165-d immersion is 2.22 and 3.48 times that of original BDM1 and BDM2, respectively. The FT-IR results confirmed that the degradation rate of methylene in biodegradable mulch films is slightly lower than that of ester groups during UV irradiation. During DW immersion process, the hydrolysis rate of ester groups in the films is first lower than that of methylene groups, then the hydrolysis of the ester groups will be promoted and faster than the degradation rate of methylene groups. At the same time, the addition of a small amount of wheat straws endows the films with a slightly delayed regression of mechanical properties resulted from the enhanced UV- and hydrolysis-resistance properties.

The maximum intensities for the film usability under the supervision of national standards for biodegradable mulching films was increased from about 2.2 kJ to about 2.3 kJ with UV irradiation while the maximum time was increased from about 82.8 d to about 89.4 d with water immersion. However, no obvious effect was observed on the degradation of water vapor barrier properties with the addition of wheat straws. The XRD results indicate that the degradation rate of crystals in PBAT nearly have no change with the addition of straws under UV irradiation. However, the hydrolysis of the crystals in the films is accelerated during water immersion with the addition of wheat straws. Although cracks generated during aging may have adverse impact on the mechanical and water vapor barrier properties of BDM, the variation of PBAT molecular structure is believed as the leading cause for the deterioration of mechanical and water vapor barrier properties of biodegradable mulch films during aging in different environments. Therefore, it is highly recommended to seek effective pathways for slowing down the deterioration rate of the performance of biodegradable mulch films through delaying the change of PBAT molecular structures.