Papers by Keyword: Photo-Oxidation

Abstract: This study investigates the mechanical degradation of nylon 6,6 under tensile stress, induced by accelerated aging via ultraviolet (UV) radiation [1-3]. Specimens were fabricated and exposed to controlled UV doses, simulating outdoor weathering conditions. Tensile properties were evaluated, revealing a significant reduction in tensile strength and elongation at break with increasing UV dose. The predominant degradation mechanism was photo-oxidation, evidenced by polymer chain scission and the formation of functional groups altering the material's molecular structure[4,5]. Specimen surfaces exhibited cracks and fissures, contributing to mechanical strength loss. These findings are critical for nylon 6,6 applications in telecommunications and energy industries, where UV exposure is unavoidable. Understanding this degradation is essential for optimizing the durability and reliability of critical infrastructure. This study lays the foundation for developing advanced protective materials and coatings, enhancing the safety and efficiency of outdoor systems.

Abstract: To study photo-oxidation behavior of PVC-coated membrane material under different UV radiation intensities, three intensities of Ultraviolet (UV) irradiation were carried out. The yellowness indexes under different weathering conditions were measured, as well as UV-Vis spectrometry. Result shows that the photo-oxidation mechanism doesn’t change under different UV intensities, but the photo-oxidation reaction rates are not equal when the cumulative UV radiation energy is same. A conclusion is obtained that photo-oxidation reaction rate under different intensities is out of proportion to UV intensity. And according to Schwarzschild’s law, an equation form is established to predict material’s life.

Abstract: The flow state of both the solid and gas phase in the fluidized-bed photo-oxidation reactor for Shenfu coal was studied by cold-model tests. The results showed that the appropriate pipe diameter, particle size of coal, and the coal addition for the gas-solid fluidized-bed reactor were 22 mm, 60-80 mesh, and 10g, respectively.

Abstract: Polypropylene (PP) nanocomposites with 0.1, 0.2, 0.5, 0.8, 1.0 and 2.0 wt% multi-walled carbon nanotubes (MW-CNTs) were prepared via meltcompounding in a twin-screw extruder followed by injection molding. The effects of MW-CNTs additions on the structure, mechanical and photo-oxidation behavior of PP were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), tensile tests and FT-IR apparatus. XRD results showed that only α-PP crystals form in the PP/MW-CNTs composites. DSC results confirmed that the corporation of MW-CNTs enhanced the nucleation process on PP crystallization. Results of the tensile tests showed that before photo-oxidation, the tensile strengths of the samples increased with the increase of MW-CNTs contents when the MW-CNTs contents were less than 1% wt, whilst the tensile strength decreased at higher MW-CNTs contents (>1% wt). When subjected to photo-oxidation, the tensile strengths of the samples decreased with the increasing photo-oxidation time. The resistance to accelerated photo-oxidation of PP/MW-CNTs composites was also compared with the photo-oxidation behaviour of the original polypropylene sample. At short photo-oxidation time, such as under 250 h, the rates of carbonyl formation for the PP/MW-CNTs composites are similar to that observed for the original polypropylene but at longer photo-oxidation times the carbonyl formation increases for lower MW-CNTs contents (0.1, 0.2, 0.5 and 0.8% wt), and decreases for higher MW-CNTs contents (1 and 2% wt). It was found that the MW-CNTs showed both anti-degradation and pro-degradation effects at different concentrations.

Abstract: The natural photo-oxidation of PP bars containing nucleating agent (TMB-5) were studied by using infrared microscope (IM), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and polarizing optical microscope (POM). The results indicated that nucleating agent accelerated the oxidation of PP significantly. The oxidation began from the surface and developed into the interior with time. There is a transition region near the surface, caused by the fast cooling during the injection moulding. This region is prior to be oxidized because of the low density. Therefore, it corresponded to the surface oxidation layer in PP and PP/TMB-5 bars. The nucleating agent helped to reduce the spherulite size of PP and broaden the transition region greatly – from about 25 μm to more than 200μm, covering the morphology of amorphous, fine crystals to relatively perfect crystals. More crystal boundaries, i.e. low density, and broad transition region led to higher oxidation degree and further oxidation along the depth. However, the thickness of the surface oxidation layer maintained nearly constant till the fragments dropped from the seriously damaged surface.

Abstract: Photo-oxidation of polyethylene (PE) has been studied thoroughly these years owing to its high output and various applications, which makes knowledge about its degradation of vital practical importance. Polyethylene products often suffer from service environment factors including ultraviolet, heat or chemicals, which may deteriorate their mechanical properties. The degradation behavior varies with the chain structure and morphology of polyethylene, e.g., branches, linear segments length and crystallization. Natural degradation of three kinds of polyethylene (HDPE, LDPE and LLDPE) has been examined in samples using different annealing conditions in this work. The extent of degradation, described as carbonyl index, was evaluated by Fourier transform infrared spectroscopy (FTIR). Crystallinity measurements were made using differential scanning calorimetry(DSC). The investigation indicates that the branch structure plays a dominant role in the photo-oxidation of polyethylene. Annealing will change the crystallinity of polyethylene before aging, but do not show obvious dependence on the oxidation.

Abstract: The photo-oxidation stability is crucial for the materials that are exposed to outdoor application. For polyethylene, it has been investigated thoroughly and the auto-oxidation mechanism has been widely accepted. Nevertheless, the photo-oxidation of polyethylene composites, the most widely used materials, has not attracted enough attention yet. It is well known that the mechanical properties of composites are of great difference to that of matrix polymers, due to the introduction of the fillers and the different interfacial interactions between the matrices and the fillers. Also the oxidation behavior of composites have interesting characteristics owing to the various fillers and interfacial interactions, which always depend on the coupling agents. In the present work, the natural photo-oxidation of high-density polyethylene composites was studied. The results showed that the coupling agent had the most important but different influence on the oxidation stability of the composites, according to the different fillers.