Comparing cracking time and structure changes of different high-density polyethylenes during stress and photo-oxidative aging

Study on the Aging Behavior of an Ultra-High Molecular Weight Polyethylene Fiber Barrier Net in a Marine Environment

In the present work, the performance of ultra-high molecular weight polyethylene (UHMWPE) barrier nets in marine environments is investigated by Fourier transform infrared spectroscopy, thermogravimetry, scanning electron microscopy, and tensile experiments. The chemical, morphological, thermal stability, and strength changes after aging in salt spray, hygrothermal, and ultraviolet (UV) environments are characterized. An environmental spectrum is designed to simulate a real service environment and predict the service life of UHMWPE. The results show that UV energy can activate UHMWPE molecules and lead to chain breaking, which lowers the breaking strength more efficiently than salt spray. In a hygrothermal environment, the UHMPE fibers bond into clumps, which causes a slight increase in breaking strength after the initial rapid decrease with aging time. The acceleration ratio of the environmental spectrum increases with increasing aging time, which may be caused by the cross-linking and degradation of macromolecular chains in the material. The environmental spectrum given by this work can be used to evaluate performance and predict the service life of UHMWPE barrier nets in marine environments.

Consequences of Radiothermal Ageing on the Crystalline Morphology of Additive-Free Silane-Crosslinked Polyethylene

The radiothermal ageing of silane-crosslinked low-density PE (Si-XLPE) films was studied in the air under three different γ dose rates (8.5, 77.8, and 400 Gy·h−1) at a low temperature close to ambient (47, 47, and 21 °C, respectively). Changes in crystalline morphology were investigated using a multi-technique approach based on differential scanning calorimetry (DSC), wide- (WAXS) and small-angle X-ray scattering (SAXS), and density measurements. In particular, the changes in four structural variables were accurately monitored during radiothermal ageing: crystallinity ratio (XC), crystalline lamellae thickness (LC), long period (Lp), and interlamellar spacing (La). Concerning the changes in XC, a perfect agreement was found between DSC and WAXS experiments. Successive sequences of self-nucleation and annealing (SSA) were also performed on aged Si-XLPE samples in the DSC chamber in order to assess the thickness distribution of crystalline lamellae. This method allowed the thermally splitting of the melting domain of Si-XLPE into a series of elementary melting peaks, with each one characterised by a distinct thickness of crystalline lamellae. DSC (used with the SSA method) showed a slight increase in LC during the oxidation of Si-XLPE, while SAXS confirmed a catastrophic decrease in La. The critical value of the interlamellar spacing characterising the ductile/brittle transition of Si-XLPE was found to be of the same order of magnitude as that for linear polyethylene (LaF≈6 nm). This structural end-of-life criterion can now be used for predicting the lifetime of Si-XLPE in a nuclear environment.

Effects of Tensile Stress and Soil Burial on Mechanical and Chemical Degradation Potential of Agricultural Plastic Films

Plastic film mulching is widely practiced in arid and semiarid farming systems, but the accumulation of plastic residues in soils can negatively affect soil properties. Therefore, efficient means of plastic film degradation are urgently needed to mitigate its unfriendly environmental impacts for sustainable land use. Here, we characterized the effects of tensile stress (TS) and soil burial (SB) on potential degradation properties of three film types: Polyethylene film (PEF), oxo-biodegradable film (OBDF), and biodegradable film (BDF). Weight loss, mechanical properties, hydrophilicity, functional groups, and crystallinity were recorded after TS and SB treatments. The results indicated that: (1) Weight loss of plastic films was associated with SB, although the extent of weight loss depended on film type and was highest in BDF, (2) application of TS before SB weakened the mechanical properties of the films and increased their hydrophilicity, creating favorable conditions for the settlement of microorganisms on the film surface, (3) PEF treated with TS and SB had higher functional group indices and lower crystallinity. Our results highlighted that the combination of TS and SB has the potential to accelerate plastic film degradation.