A Study on the Reliability of Polyester Insulators Blended with Borax
Tracking is the main factor which limits the safe working electric stress of insulation in power system applications. Polymer samples have been tested in laboratory conditions according to ASTM D2303 on accelerated inclined plane tracking test. In this paper, a model based on improved Weibull statistics is proposed for estimating the breakdown time of polymeric insulating materials with borax. The confidence intervals of the Weibull shape parameter and the Weibull scale parameter are determined for the borax concentration values using the Weibull 7++ program.
Improvement of flame retardant properties in polyester insulators
In this study the effect of boron concentrations on tracking and erosion resistance of polyesters has been investigated. Samples with different boron concentrations were tested in an inclined plane tracking test apparatus. The results indicate that lower concentrations (0.1%-0.2%) of boron prevents the formation of free carbon over the surface of the composite samples and hence the specimens are mostly damaged by the erosion of the surface. However by increasing the boron quantity (0.4%-0.6%) in polyester samples, the tendency of the resulting composites changes again and samples are mostly damaged by surface tracking rather than erosion.
Performance of an intumescent‐flame‐retardant master batch synthesized by twin‐screw reactive extrusion: effect of the polypropylene carrier resin
A novel way of preparing an intumescent flame retardant (IFR) and its master batch by the reactive extrusion of melamine phosphate and pentaerythritol, together with a polypropylene (PP) carrier, in a twin-screw extruder has been established. The effect of the PP carrier resin on the flame retardancy and water resistance of the intumescent-flame-retarding PP materials was investigated by using the limited oxygen index (LOI), UL94 test, elemental analysis (EA), thermogravimetric analysis (TGA) and water solubility testing, respectively. In addition, the mechanism of the carrier effect was analysed by melt flow index (MFI), scanning electron microscopy (SEM), and TGA. The experimental results show that with increasing content of carrier resin (PP) in the IFR master batch from 0 to 15 wt%, the flame retardancy LOI of the PP/IFR (25 wt% loading) blend increased from 29.5 to 32, and the UL94 level at 1.6 mm thickness was improved from failure to a V-0 rating. In addition, the water resistance of a flame-retarded composite at 25 wt% IFR loading was greatly improved, i.e. after treatment with hot water at 70 °C for 168 h, the reducing rate of element N in the IFR/PP blend decreased from 18.3% with 5 wt% carrier resin to 12.9% with 15 wt% carrier resin, and the LOI reduction rate decreased from 15.3% without any carrier resin to 10.9% with 15 wt% carrier resin, while the flame-retarded PP with an IFR master batch containing 10–15 wt% carrier resin maintained its UL94 V-0 rating at 3.2 mm thickness. The improvement in flame retardancy was attributed to the improved flame-retardant (FR) dispersion due to the carrier resin, while the improved water resistance was explained by the lowered water solubility of the IFR, the improved FR dispersion and the improved compatibility of the FR with the matrix resin due to the carrier resin. Reactive extrusion is a novel way to obtain pelletissed IFRs without powder pollution and their corresponding flame-retarding materials with a number of desired properties. Copyright © 2004 Society of Chemical Industry