Kun Xiao

Effect of Nanoparticles on the Morphology, Thermal, and Electrical Properties of Low-Density Polyethylene after Thermal Aging

This paper investigates the morphology, thermal, and electrical properties of LDPE (low-density polyethylene)-based nanocomposites after thermal aging. The FTIR (Fourier transform infrared spectroscopy) spectra results show that thermo-oxidative reactions occur in neat LDPE and LDPE/SiO2 nanocomposites when the aging time is 35 days and in LDPE/MgO nanocomposites when the aging time is 77 days. Specifically, LDPE/MgO nanocomposites delay the appearance of thermo-oxidative reactions, showing anti-thermal aging ability. Furthermore, nanocomposites present lower onset degradation temperature than neat LDPE, showing better thermal stabilization. With regard to the electrical properties, nanocomposites maintain the ability to suppress space charge accumulation after thermal aging. Additionally, in comparison with SiO2 nanocomposites and neat LDPE, the permittivity of LDPE/MgO nanocomposites changes slightly after thermal aging. It is concluded that LDPE/MgO nanocomposites have better insulation properties than neat LDPE after thermal aging, which may be caused by the interface introduced by the nanoparticles.

Effect of Nanoparticle Surface Modification and Filling Concentration on Space Charge Characteristics in TiO2/XLPE Nanocomposites

This paper focuses on the space charge characteristics in TiO2/cross-linked polyethylene XLPE nanocomposites; the unmodified and modified by dimethyloctylsilane MDOS TiO2 nanoparticles were added to XLPE matrix with different mass concentrations 1 wt%, 3 wt%, and 5 wt%. The scanning electron microscope SEM showed that the MDOS coupling agent could improve the compatibility between TiO2 nanoparticles and XLPE matrix to some extent and reduce the agglomeration of TiO2 nanoparticles compared with unmodified TiO2 nanoparticles; the volume resistivity testing indicated that the volume resistivity of TiO2/XLPE nanocomposites was higher than Pure-XLPE and increased with the increase of filling concentrations. According to the pulsed electroacoustic PEA measurements, it was concluded that the space charge accumulation was suppressed by filling TiO2 nanoparticles and the distribution of electric field in samples was improved greatly. In addition, it was found that the injection of homocharge was more obvious in MDOS-TiO2/XLPE than that in UN-TiO2/XLPE and the homocharge injection decreased with the increase of filling concentration.

Research on the Thermal Aging Behaviors of LDPE/TiO2 Nanocomposites

The ability of antithermal aging of LDPE/TiO2 nanocomposites was investigated through SEM, FTIR, DSC, and dielectric properties in this paper. The results of SEM images showed that the thermal aging had a significant influence on the structure of Pure-LDPE and LDPE/TiO2 samples. The measurement of FTIR showed that the content of hydroxyl and carboxyl increased with thermal aging, but the time of emerging aging characteristic peaks for the LDPE/TiO2 samples was delayed. The DSC measurement indicated that filling TiO2 nanoparticles changed the crystallization behavior of LDPE, played a role of heterogeneous nucleation during the process of recrystallization, and improved the crystallinity of LDPE/TiO2. Similarly, the aged LDPE/TiO2 samples had lower permittivity and dissipation factor compared to the aged Pure-LDPE samples. All the results had indicated the LDPE/TiO2 samples had the significant ability of antithermal aging, especially the LDPE/TiO2-0.5 samples with good dispersion of nanoparticles. A new model was proposed to illustrate the antithermal aging behaviors of LDPE/TiO2 samples, which shows that the TiO2 nanoparticles play a role of “crosslinking points” between LDPE molecular chains, increasing the density of crystal structure and reducing oxygen diffusion into materials to break molecular structure.

Study on dielectric properties of TiO 2 /XLPE nanocomposites

This paper focuses on the dielectric properties in TiO2/XLPE nanocomposites, the TiO2 nanoparticles were added into XLPE matrix with different mass concentrations (1wt%, 3wt%, and 5wt%). It was found that the volume resistivity of TiO2/XLPE nanocomposites was higher than XLPE, which increased with filling concentrations. In addition, the TiO2/XLPE nanocomposites had lower permittivity and lower dielectric dissipation, which increased with the filling concentrations and decreased with the measured frequency. The results of pulsed electro-acoustic (PEA) measurements showed that the total space charge was suppressed and heterocharge disappeared in TiO2/XLPE nanocomposites, leaving a small amount of negative charge in middle of samples. According to the analysis in this paper, new interface regions introduced many deep traps due to filling TiO2 nanoparticles, which can shorten the effective distance of “solitary waves” migration and greatly reduce carrier mobility. On the other hand, low carrier mobility enhance the recombination process and weaken the ionization process of impurities, leading to the disappearance of heterocharge in TiO2/XLPE. Furthermore, the interface reverse electric field not only suppress the charge injecting from the electrodes, but also strengthen the electric field in the middle of matrix, so that the accumulated space charge can be transferred out of material timely.

Study on space charge behaviors and trap characteristics in LDPE/SiO 2 under thermal aging

Space charge is a threat to cable insulation materials and polythene insulation gradually degrades in long service conditions. The degradation of low density polyethylene (LDPE) affects space charge formation, accumulation and dissipation, and the presence of space charge affects the performance of dielectric. This paper focuses on the space charge characteristics of LDPE/SiO2 nanocomposites under thermal aging. The SiO2 nanoparticles were added into LDPE matrix with single mass concentration 5wt%, and the LDPE and LDPE/SiO2 samples were aged at a hot spot temperature (90 °C). During thermal aging, the space charge distribution was measured at a regular interval (0, 10, 20, and 30 days) at room temperature. And the pulse electro-acoustic (PEA) method was used for space charge measurement. It was suggested that SiO2 nano-fillers increased the density and depth of traps in LDPE/SiO2 nanocomposites, and the LDPE/SiO2 samples had a certain anti-thermal aging ability at the initial aging stage. In addition, thermal aging changed the microstructure of LDPE materials, produced many chemical defects, and also increased the density and depth of traps. Generally, long term thermal aging had significant influence on the space charge behaviors of polyethylene materials, and appropriately filling SiO2 nanoparticles could delay the degradation of LDPE insulation materials.