Degaradation characteristics of PBAT mulch in maize field

Abstract: In China, the mulch film is one of the important materials during agricultural production progress. The application of mulch film cover technology promotes the development of agricultural production. And the production mode is also changed. However, a series of environment problems are caused by this technology. In order to reduce environmental pollution, a series of biodegradable materials are developed, such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), polybutylene succinate (PBS), poly (butylene succinate adipate) (PBSA), poly (butyleneadipate-co- terephthalate) (PBAT), and so on. Among them, PBAT is the most promising material that can substitute polyethylene (PE) because of its excellent biodegradability and mechanical properties. PBAT belongs to thermoplastic polymer, which is obtained with aliphatic and aromatic copolyesters. PBAT possesses good processability, such as extensibility, stretchability, impact resistance, and heat resistance. The experiment was carried out in the Institute of Agricultural Facilities and Equipment, Jiangsu Academy of Agricultural Science, China. The degradation process of PBAT mulch film applied in maize farmland was investigated in this research. The chemical composition, chemical structure, physical morphology and properties were determined during the application progress. The tensile strength and elongation at break during the degradation were tested. In addition, the Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope in the degradation process were applied to characterize the PBAT mulch film with various degradation time. The results showed that the tensile strength and elongation at break decreased at the same time. The change of mechanical property was greater in the first 4 weeks, which decreased from 0.27 to 0.11 MPa, and then a slow decline began, which decreased from 0.27 to 0.04 MPa from the 4th week to the 16th week. The elongation at break decreased from 48% to 15% in the 4th week, and then decreased from 15% to 1% from the 4th week to the 16th week. The ester bonds in PBAT molecule were broken due to Norrish I and II reaction under the action of photooxidation, hydrolysis, enzymolysis, and so on. The bonding energy of C1s moved from 287.33 to 283.61 eV. And, the bonding energy of O1s moved from 534.86 to 530.58 eV. The bonding energy of C1s and O1s decreased. The result showed that the PBAT was easier to degrade. The ratio of C to O decreased from 4.07 to 1.06 with X-ray photoelectron spectroscopy. The content of carbon element decreased from 79.3% to 45.0%. The content of oxygen element increased from 19.5% to 42.3%. The oxygen element increased, which illustrated that the degradation process of the PBAT is also an oxidation process. At the same time, the bonding energy of carbon and oxygen elements decreases. The crystalline region of PBAT is destroyed gradually. At the same time the amorphous region increases relatively in the degradation process. The crystallinity of PBAT after 0, 4, 8, 12 and 16 weeks degradation is 46.5%, 44%, 41%, 38% and 29%, respectively. There are cracks and irregular bulges in degraded PBAT mulch film. The degradation of PBAT film is inhomogenous, due to that the degradation of amorphous region is easier than crystalline region. And, the BA molecules in PBAT degrade faster than BT molecules. PBAT mulch can be applied in the southern rainy area of China to conserve moisture, and increase temperature due to that the hydrolyticaction does not play a dominant role in the initial duration. The theoretical basis is provided in this research for the application of PBAT in the middle and lower reaches of Yangtze River.