Application of Infrared Spectroscopy in Research on Aging of Silicone Rubber in Harsh Environment.

Polymer insulators using silicone rubber materials as sheds and sheaths are widely used in power systems to replace traditional porcelain and glass insulators which are heavy, inconvenient to install, and prone to pollution flashover. However, in recent years, polymer insulators that have been operating in harsh outdoor environments for many years have experienced different degrees of aging. The aging degree and aging products of silicone rubber are the focus of research. Fourier transform infrared spectroscopy (FTIR) is a technical method to analyze the internal molecular bonds and functional groups of materials, and it is often used to study the aging degree and aging products of silicone rubber. In this paper, the aging characteristics of silicone rubber samples in a high altitude area, salt fog environment, and acid environment were studied by FTIR. The results showed that the silicone rubber in a harsh environment, such as strong radiation, salt fog, and acid fog was degraded to some extent, and its main chain was cut off, the degree of polymerization was reduced, and the content of hydrophobic functional groups was reduced. Infrared spectroscopy can be used to analyze the aging phenomenon of polymers.

Research on Silicone Rubber Sheds of Decay-Like Fractured Composite Insulators Based on Hardness, Hydrophobicity, NMR, and FTIR.

The safety and stability of power systems are seriously threatened by the decay-like fracture of composite insulators. This paper analyzes the aging characteristics (physical properties, NMR, and FTIR) of the silicone rubber sheds of the decay-like fractured insulator. The same V-string insulator and a new insulator are used for comparison. The study shows that the sheds' degradation is concentrated on the side with heavy pollution. The physical properties (appearance, pollution, hardness, and hydrophobicity) of the high voltage end decrease significantly compared to other positions, but there is no direct connection between the physical properties of sheds and the decay-like fracture of the core rod. The severity of aging increases with a decrease in the equivalent transverse relaxation time T2. The main chain of the PDMS material was severely damaged at the location of the insulator fracture. NMR and FTIR can well judge the aging degree of silicone rubber housings. However, no definite characteristic quantity can characterize the decay-like fracture. It is challenging to evaluate the decay-like fracture of the silicone rubber shed only by its aging degree.

Sap flow of Salix psammophila and its principal influencing factors at different slope positions in the Mu Us desert.

The changes in sap flow of Salix psammophila growing on a gentle slope (lower slope, P1), a middle slope (P2), and an upper slope (P3), and the response of sap flow to meteorological factors at the different slope positions were studied using the continuous and synchronized observations, the instrument were wrapped stem flowmeter EMS 62 sap-flow heat-balance-based system and the LSI-LASTEM automatic weather station. The results revealed that the soil moisture content was the highest and the growth conditions of Salix psammophila were the best at P1, followed by P2. At P3, however, although good apical dominance was observed, the proportion of dead branches was the highest. Furthermore, the daily variation patterns of sap flow on the three slopes presented as multi-peak bell-shaped curves. The daily accumulation changes in sap flow showed a trend of P1 > P3 > P2, and within the same diameter range, the sap flow at P1 was significantly different from that at P2 and P3, whereas the sap flow at P2 and P3 did not vary significantly. All the three slopes showed a significant and positive correlation with photosynthetically active radiation, atmospheric temperature, and vapor pressure difference, and a significant and negative correlation with relative humidity; however, the degrees of correlation varied slightly. The stepwise regression analysis showed that, at different slopes, different variables were selected for different branch diameters, but photosynthetically active radiation and atmospheric temperature played dominant roles on all slopes. This study reveals the sap flow pattern of Salix psammophila on different slopes and its response mechanism to meteorological factors, which was essential for understanding the restoration ability, physiological adaptability, and ecosystem stability of Salix psammophila communities.

Using matrix solid-phase microextraction (matrix-SPME) to estimate bioavailability of DDTs in soil to both earthworm and vegetables.

This study was conducted to find an appropriate approach for the assessment of bioavailability of DDTs in soil to both earthworm and vegetables. Four chemical approaches--Soxhlet extraction with n-hexane, n-butanol agitation extraction, water agitation extraction, and matrix solid-phase microextraction (matrix-SPME)--were used to assess the relationships between the extractability of 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (p,p'-DDE), 1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl) ethane (o,p'-DDT), 1,1-dichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDD), and 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDT) in soil and their amounts uptaken by the earthworm (Eisenia foetida), Chinese cabbage (Brassica campestris L. spp.), and cole (Brassica napus L.). These results indicated that the extractability and bioavailability of DDTs in soil decreased with time of aging. Correlation analysis showed that n-butanol extraction or 12-h matrix-SPME could be used to assess the bioavailability of DDTs to the earthworm, and Soxhlet extraction, n-butanol extraction, or 12-h matrix-SPME could be used to predict the bioavailability of DDTs to both Chinese cabbage and cole. As a solventless, time-efficient, and negligible-depletion technique, it could be concluded that matrix-SPME is a better approach to predict the bioavailability of DDTs to both the earthworm and vegetables, compared with Soxhlet extraction, n-butanol extraction, and water extraction.

Effects of repeated applications of fungicide carbendazim on its persistence and microbial community in soil.

Carbendazim, a systemic benzimidazole fungicide, is applied repeatedly to control plant diseases including soilborne diseases, over a growing season. Studies were carried out under laboratory conditions to assess the effects of repeated carbendazim applications on its persistence and microbial community in soil. The results indicate that dissipation of carbendazim in soil was accelerated with its application frequency. The degradation rate constant of carbendazim was increased significantly from 0.074 d(-1) to 0.79 d(-1). The corresponding half-life was shorten markedly from 9.3 d to 0.9 d after four repeated applications. No significant inhibitory effect of carbendazim on soil microbial utilization of the carbon sources was observed after first treatment, but a slight increase in average well color development (AWCD) was shown after second, third, and fourth applications. It suggested that soil microorganisms become adapted to carbendazim after repeated application. Simpson and Shannon indexes of soil microbial community from carbendazim treated soil were also similar to those from the control soil, indicating that the richness and dominant character of soil microorganisms remain unchangeable after repeated application. However, after first, second, and third addition of carbendazim, McIntosh indexes on day 21 were significantly higher compared with the control, suggesting that balance of soil microorganisms was altered due to the enrichment of the specific carbendazim-adapting strains in soil.