Nanocomposites based on magnesium-oxide/aluminum-nitride/polypropylene for HVDC cable insulation

Abstract—Polypropylene (PP) with high thermal stability and good electrical properties, has attracted much attention for its potential to take the place of cross-link polyethylene (XLPE) as HVDC insulation because PP is more easily recycled than XLPE due to its thermoplasticity. Due to the adverse effect of electric field reversal under HVDC application, there is a need to find the new polymer insulation material with higher thermal conductivity and good electrical performance. This paper investigates the effect of introducing aluminum nitride (AlN) and magnesium oxide (MgO) into PP on the electrical properties of the resulting the new nanocomposites. In the sample preparation, AlN and MgO were surface-modified by KH570 (γ- methacryloxypropyltrimethoxy silane) and then introduced into PP by the solution method to manufacture the nanocomposite materials. The measurements made were the voltage breakdown characteristics and the DC conductivity. The results obtained show that the combination of AlN and MgO can slightly decrease the DC conductivity of PP/AlN/MgO nanocomposites compared with pure PP. The breakdown strength was slightly decreased. which shows that the adverse effect of AlN on the electrical performance of PP can be compensated by introducing MgO nanoparticles. Hence, the new polymer with high thermal conductivity and good electrical properties could be manufactured by combining two kinds of nanoparticles. Keywords — nanocomposites, magnesium-oxide, aluminum-nitride, polypropylene, electrical performance

Coupled effects of climate variability and land use pattern on surface water quality: An elasticity perspective and watershed health indicators.

Understanding the coupled effects of climate variability and land use on riverine nitrogen is essential for watershed management. The climate-water relationships for ammonium (NH4-N) and nitrate (NO3-N) were determined by an elasticity approach and then the watershed health index was estimated using the reliability, resilience, and vulnerability framework. These methods were applied to an in-situ monitoring dataset of N concentrations measured during 2010-2017 from nine sub-watersheds in the Jiulong River Watershed, China. The results showed that temperature and precipitation elasticity of NH4-N and NO3-N changed substantially among various land use patterns. The N concentrations were highly sensitive to extreme climate conditions, particularly at urban and agricultural sub-watersheds. The measure of risk indicators revealed that the watershed health index varied from good health to unhealthy status. Linear regression analysis was used to analyze the interactions among watershed characteristics, climate elasticity, and watershed health. Cropland and population had strong positive correlations with climate elasticity of NO3-N. Forest and elevation had strong negative associations with climate elasticity of NO3-N. Watershed health significantly declined with increasing proportion of cropland and population density. This study demonstrated that human-impacted watersheds were less healthy to unhealthy and tend to be more sensitive to climate variability than natural watersheds, which is useful for efforts aimed at improving watershed management

Postoperative hyperphosphatemia significantly associates with adverse survival in colorectal cancer patients

BACKGROUND: Hyperphosphatemia has been implicated in the development and treatment of various cancers. However, whether it can be used as a direct prognostic marker of colorectal cancer (CRC) has remained unexplored. Given new insights into the importance of hyperphosphatemia in CRC, we sought to evaluate the association of hyperphosphatemia with the clinical outcomes of this disease. METHODS: In a retrospective analysis of a well-characterized clinic-based cohort with 1,241 CRC patients, we assessed the association of postoperative hyperphosphatemia with patient overall survival. RESULTS: Postoperative hyperphosphatemia measured within the first month after surgery was significantly associated with CRC survival. Compared to patients with a normal phosphate level, those with hyperphosphatemia exhibited a significant unfavorable overall survival with a hazard ratio (HR) of 1.84 (95% confidence interval [CI] 1.49–2.29, P=2.6×10(−8), (log-rank P=1.2×10(−7)). Stratified analyses indicated the association was more pronounced in patients with colon (HR=2.00, 95% CI 1.57–2.56, P=3.17×10(−8)) but not rectal cancer (HR=0.96, 95% CI 0.58–1.59, P=0.889) (P interaction=0.023), as well as in those not receiving chemotherapy (HR=2.15, 95% CI 1.59–2.90, P=6.2×10(−7)) but not in those receiving chemotherapy (HR=1.30, 95% CI 0.92–1.82, P=0.136) (P interaction=0.012). Flexible parametric survival model demonstrated that the increased risk for death conferred by postoperative hyperphosphatemia persisted over 150 months after surgery. CONCLUSION: Our data indicated that postoperative hyperphosphatemia might be used as a prognostic marker of CRC patients after surgery. Since phosphate level is routinely tested in clinics, it may be incorporated into clinical models to predict CRC survival

Octavinyl polyhedral oligomeric silsesquioxane on tailoring the DC electrical characteristics of polypropylene

This work reports the effect of octavinyl polyhedral oligomeric silsesquioxane (OvPOSS) on tuning the electrical performance of polypropylene (PP). OvPOSS with different content are introduced into PP using the solution method. The microstructural morphology, crystallinity behaviour, breakdown strength, DC conductivity, space charge formation, and trapping level distribution are measured. The results indicate that the OvPOSS nanofiller can be dispersed uniformly with a doping content of 2.0 phr or less. The DC conductivity is decreased, and the breakdown strength of OvPOSS/PP nanocomposites is significantly increased. The space charge accumulation of the OvPOSS/PP nanocomposites is significantly suppressed due to the introduction of deeper traps by the OvPOSS nanofiller. Finally, the experimental results demonstrate that the OvPOSS nanofiller can greatly increase the electrical performance of the base PP and the OvPOSS/PP nanocomposites have much potential for HVDC applications. They further demonstrate that the PP is environmental-friendly due to its thermo-plastic property, which can be recycled after the manufacture

Influence of octavinyl-polyhedral oligomeric silsesquioxane on the electric treeing resistance of polypropylene

Electric treeing is the electrical pre-breakdown phenomenon which can degrade the insulating ability and limit the lifespan of solid insulations. In this paper, the research work investigates the influence of introducing OvPOSS (Octavinyl-Polyhedral oligomeric Silsesquioxane) nanoparticles on tuning the electric treeing characteristics of polypropylene (PP) under the pulse voltage with the frequency of 200 Hz, including the inception voltage for treeing growth, the electric treeing propagation rate under the pulse voltage of 30 kV. Some measurements, including scanning electron microscope (SEM) and thermal stimulated depolarized current (TSDC), were utilized to analyze the mechanism of the nanoparticle effects of OvPOSS. Finally, the experimental results showed that the addition of OvPOSS nanoparticles can obviously increase the inception voltage of treeing growth and suppress the treeing propagation under 30 kV pulse voltage due to the introduction of deep traps in the OvPOSS/PP nanocomposites