Showing papers by "Dipak Khastgir published in 2010"

Halogen-free flame-retardant rigid polyurethane foams: Effect of alumina trihydrate and triphenylphosphate on the properties of polyurethane foams

Abstract: Rigid polyurethane foam (PUF) filled with mixture of alumina trihydrate (ATH) and triphenyl phosphate (TPP) as fire retardant additive was prepared with water as a blowing agent. In this study, the ATH content was varied from 10 to 100 parts per hundred polyol by weight (php), and TPP was used at a higher loading of ATH (75 and 100 php) in a ratio of 1 : 5 to enhance the processing during PUF preparation. The effects of ATH on properties such as density, compressive strength, morphological, thermal conductivity, thermal stability, flame-retardant (FR) behavior, and smoke characteristics were studied. The density and compressive strength of the ATH-filled PUF decreased initially and then increased with further increase in ATH content. There was no significant change in the thermal stability with increasing ATH loading. We determined the FR properties of these foam samples by measuring the limiting oxygen index (LOI), smoke density, rate of burning, and char yield. The addition of ATH with TPP to PUF significantly decreased the flame-spread rate and increased LOI. The addition of TPP resulted in easy processing and also improved FR characteristics of the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Temperature dependent electrical properties of Conductive Composites (Behavior at cryogenic temperature and high temperatures)

Abstract: Extrinsically conductive polymer composites can be developed by incorporation of conductive filler in suitable polymer matrix. The formation of conductive network in insulating matrix due to filler aggregation at and above percolation is responsible for electrical conductivity of such composites. The present investigation deals with effect of temperature on conductive composites made from different blends of Ethylene-Vinyl copolymer (EVA) and Acrylonitrile-Butadiene copolymer (NBR) filled with particulate carbon filler. The electrical properties of these composites depend on blend composition and filler loading. High temperature (303-393K) DC-resistivity against temperature for EVA and EVA blends composites show positive coefficient of temperature (PCT effect) followed by negative coefficient of temperature (NCT effect) thus passing through a maxima which corresponds to crystalline melting temperature(~348K) of EVA phase. Further the variation of conductivity during heating cooling cycle does not coincides and leads to some kind of thermal hysteresis due to change in conductive network structure. However in low temperature region (10-300K), the resistivity is found to increase with decrease in temperature (NCT effect) and hysteresis effect is also marginal compared to that observed in high temperature region. This difference resistivity/conductivity vs temperature behavior in two different temperature zones suggests that different two mechanisms are operative in the system.

Transition metal catalyzed oxidative aging of low density polyethylene: effect of manganese (III) acetate

Abstract: The paper discusses the effect of manganese (ІІІ) acetate in the degradation of low density polyethylene (LDPE). Stearic acid has been used as a dispersion promoter to circumvent non-uniform dispersion of inorganic compound like manganese (ІІІ) acetate in LDPE. A detailed study has been made to investigate the effect of dispersion promoter on degradation of LDPE. The combined effect of dispersion promoter and manganese (ІІІ) acetate has been studied in accelerated aging of LDPE. Masked degradation of LDPE has been noted in presence of natural rubber (NR). The degradation processes of LDPE eventually have been observed to follow different mechanistic pathways in presence of dispersion promoter and transitional metal catalyst. At an optimized condition of time and temperature, LDPE has been found to be degraded into a semi-solid state in combined presence of manganese (ІІІ) acetate and the dispersion promoter. The Arrhenius equation has been adopted to predict the life time of the LDPE having different amount of manganese (III) acetate.