Degradation Mechanism Research Of Degradable Mulching Film On The Cotton Plantation Area Of The Northern Slope Of The Tianshan Mountains In Xinjiang

The background of this subject was existed severe “white Pollution” problem leaded by the widespreadapplication of agricultural mulch film. The ordinary polyethylene film was hardly degraded, the amount ofresidue led to the “white pollution”. A series of degradable films was prepared, and the two formulas ofpolyethylene (PE) films with the highest degradable performance were experimentally determined. The twotypes of films were denoted as PE-3and PE-4(containing3.43%and0.44%degradablemasterbatch, respectively). Their degradability was studied in a laboratory-controlled composting testand UV aging experiment. These films were used to assist in cultivating crops under different ecologicalregions in Shihezi, Kuitun and Bole of Xinjiang. Polyethylene film without any additive (CK) was used asa control. The course of degradation was studied from mechanical properties (tensile strength andelongation at break), viscosity-average molecular weight and carbonyl index. The degree of degradation ofthe PE films was studied through determination of carbonyl index, crystallinity, molecular weight, andmechanical properties (tensile strength and breaking elongation rate). The thermal properties of the PEfilms were determined through differential scanning calorimetry (DSC).The experimental results showed that degradation rates of PE-3and PE-4films were faster by UVA-Birradiation. Lost of the mechanical properties PE-3and PE-4films needed250h and300h, respectively.While, lost of the mechanical properties PE-3and PE-4films need800h and1000h by UVA irradiationand need600h and800h by UVB irradiation, respectively. So the high frequency wave of UVA-B plays avery important role in the fracture of polymer chain.Through composting and burying test, the results indicated high level degradation of PE-3and PE-4films were exhibited through the increase of carbonyl index (CI), crystallinity (Xc) and decrease ofviscosity-average molecular weight (M). Composting test after aging films, M of PE-3, PE-4and CKfilms dropped36.8%,26.5%and10%, respectively. Soil burial test after natural aging films, M of PE-3,PE-4and CK films dropped31.6%,22.1%and6.7%, respectively. It showed that the degradation wasoccur on PE film but the degree of degradation was not large. Under composting conditions, it was moreconducive to the degradation of the polyethylene film than buried conditions. After composting and burying,exposed film could be further degraded. It provided a theoretical basis for the film, which was used asmulching cultivation, buried in the soil could be biodegradable.The impact of climate conditions (solar UV radiation, relative humidity and temperature) on filmdegradation was investigated. The results showed that the differences of three regions climate had a certaininfluence on degradation of the films, the films were used to assist in cultivating crops about73days underdifferent environmental conditions in Shihezi, Kuitun, and Bole of Xinjiang.M of PE-3film was dropped from9.6×10~4to0.4×10~4,0.8×10~4and1.2×10~4, respectively. M of PE-4film dropped from9.3×10~4to0.8×10~4,1.2×10~4and1.8×10~4, respectively. With the same photosensitizercontent, film degradation was found to be more easily under stronger solar UV radiation, higher relativehumidity and temperature (Shihezi, Kuitun, Bole fell in turn). With higher photosensitizer content, the photosensitizer was found to exhibit enhanced degradable effects. Therefore, PE film degradation could becontrolled and the requirements of mulching films under different climatic conditions can be achieved byadjusting photosensitizer content.