SynopsisStructure property relationship of four different diisocyanates is studied in detail. The isocyanates selected are TDI, MDI Crude, HDI, and IPDI. Physical properties such as mechanical, dynamic mechanical, electrical, and thermal are studied. Dynamic mechanical analyses are based on the compound resonance principle. Among all, IPDI-based polymer showed mediocre trend and TDI-based polymer showed best properties.

ABSTRACT:The thermal recovery of the stored stress in crosslinked polyethylene has been commercially exploited in the preparation of heat shrinkable materials. The study on thermally recoverable crosslinked polyethylene compositions is reported in this paper. Thermally recoverable compositions were prepared by crosslinking of four grades of polyethylenes in air using g-rays from a Co-60 source. The effect of the irradiation dose on the gel fraction and radiation dose to gelation is studied. The effect of the melt index (MI) and the density of the polyethylene on the gel fraction, radiation dose to gelation, and recovery percentage of the stored stress is also studied. It is observed that the gel fraction is higher in case of the lower MI material and that rate of recovery is higher at higher temperatures. The rate of recovery of the stored stress is higher in case of the 100 kGy irradiated sample.

SYNOPSISA study of the effect of crosslinking agents on the structure and properties of the millable polyurethane ( P U ) elastomer is reported here. Effects of the conventionally used dicumyl peroxide (DCP) and tolylene diisocyanate dimer (TDID) on the curing characteristics, mechanical properties, and relative thermal stabilities of the P U composites have been compared. Use of X-ray diffraction as a supportive evidence helps in understanding the nature of crosslinking. The mixture of DCP and TDID is also evaluated as crosslinking agents. A dramatic improvement in the mechanical properties and thermal stability is observed because of the mixed type of crosslinking obtained by the combined use of DCP and TDID. Effect of carbon black loading shows an increase in the mechanical strength with a decrease in the elongation. The results obtained from various properties measurements have been satisfactorily explained with a general model of crosslinking.

SynopsisThermal properties like glass transition temperature (T'), initial decomposition temperature (idt), integral procedural decomposition temperature (zpdt), and temperature at various % weight loss of a number of polyurethane systems are reported in this paper. Glass transition temperature was determined on TMA, and other thermal properties were determined by thermogravimetry. The experiments were designed to understand various factors such as length of chain extender moiety, flexibility of chain extender units by substitution of ether link in the diol chain, nature of bonds (unsaturation) in the extender unit, and nature of diisocyanates.

SYNOPSISThe stabilization of polypropylene-disposable medical syringes against the y-ray-induced degradation has been the subject of active research during the last decade due to the largescale use of y-irradiation for sterilization purposes. Ethylene-propylene (EP) copolymers have been suggested as suitable alternatives to polypropylene for these purposes. In this article, we investigated the effect of irradiation dose and postirradiation time on the melt index and mechanical properties of an EP copolymer. We also determined the chemical changes occurring during irradiation and storage using IR spectroscopy and have made an attempt to co-relate the changes in chemical structure to the changes in mechanical properties and melt index measurements.