Showing papers by "Dipak Khastgir published in 1993"

Microscopic studies on the mechanisms of wear of NR, SBR and HNBR vulcanizates under different conditions

Abstract: Microscopic investigations, undertaken to understand the mechanism of wear of natural rubber (NR), styrene-butadiene rubber (SBR) and hydrogenated nitrile rubber (HNBR) vulcanizates abraded against hard rock, a knurled aluminium disc and a silicone carbide abrader under different conditions, are reported. The wear of NR and SBR vulcanizates against hard rock at low normal load (6 kPa) takes place by a fatigue wear mechanism and it switches over to frictional wear at high normal load (above 18 kPa). In HNBR vulcanizates the wear takes place by an abrasive wear mechanism. Ridges are observed on worn surface of swollen N R and SBR vulcanizates at low normal load, but at higher normal load the wear takes place by catastrophic fracture and extensive plough marks along the direction of abrasion are observed. The wear of NR and SBR vulcanizates proceeds by frictional wear, even at elevated temperatures. In HNBR vulcanizates, the mechanism changes from abrasive wear at 25‡C to frictional wear above 50‡C. Above 50‡C, ridges are observed and the spacing between adjacent ridges increases with rise of temperature.

Interaction between ethylene vinyl acetate copolymer and polyethylene

Abstract: Low density Polyethylene (LDPE) and Ethylene Vinyl Acetate (EVA) Copolymer have been processed at 170°C for 7 minutes. Dynamic mechanical analysis shows a single composition dependent glass transition temperature of the 50:50 EVA/LDPE blend. Infrared spectra of pure EVA processed at the same condition shows splitting of >C=0 stretching band of EVA while spectra of the 50:50 EVA/LDPE blend shows a well resolved single band. Thermogravimetric analysis of the blend shows greater stability than those of the pure components. A schematic mechanism ascribing to the synergistic effect observed is proposed.

Effect of strain rate and temperature on stress‐strain properties of EVA‐LDPE blends and the mechanism of strain hardening

Abstract: Stress-strain behaviour of different blends of poly(ethylene-co-vinyl acetate) (EVA) (28 wt-% VA content) and low density polyethylene (LDPE) is studied under various strain rates and temperatures It is found that stress-strain plots of such semicrystalline polymer blends consist of three parts, namely, elastic or Hookeian region, region of chain slippage and region of strain hardening Decrease in strain rate has an increasing effect on the strain hardening region Increase in measurement temperature adversely affects the whole stress-strain plot It is apparent from the study that at an elevated temperature the process of strain hardening is dependent on the crystalline melting point of the major component in the blend The X-ray and DSC studies reveal that the process of strain hardening is mainly due to a change in internal order of crystallites in LDPE and LDPE-rich blends, whereas in EVA and EVA-rich blends it is due to induced crystallization in the amorphous phase Das Zug-Dehnungs-Verhalten von verschiedenen Blends aus Poly(ethylen-co-vinylacetat) (EVA, 28 wt-% VA-Anteil) und Polyethylen (LDPE) wurde bei unterschiedlichen Dehnungsgeschwindigkeiten und Temperaturen untersucht Die Zug-Dehungs-Kurven solcher semikristalliner Polymerblends bestehen aus drei Teilen—elastischer oder Hookescher Bereich, Bereich des Aneinanderabgleitens der Ketten sowie Dehnungshartungsbereich Eine Verminderung der Dehnungsgeschwindigkeit bewirkt eine Vergroserung des Dehnungshartungsbereiches Die Erhohung der Mestemperatur beeinflust der Dehnungshartung bei erhohten Temperaturen vom Kristallschmelzpunkt der Hauptkomponente des Blends abhangt Rontgen- und DSC-Untersuchun-gen zeigen, das die Dehnungshartung von einer Veranderung der Kristallistruktur in LDPE und LDPE-reichen Blends ausgeht, wahrend sie in EVA und EVA-reichen Blends auf eine induzierte Kristallisation in der amorphen Phase zuruckzufuhren ist

The Effect of Moulding Time on Mechanical and Electrical Properties of Thermoplastic-Elastomer Blends of XLPE and "XL-20":

Abstract: Different thermoplastic-elastomer blends of XLPE and "XL-20" (Polysar Corporation, Canada) were prepared. It was found that both mechan ical and electrical properties of these blends were influenced with the change in moulding time. Prolonged moulding time degraded the mechanical proper ties of the blend richest in XLPE, whereas it was found to be beneficial for other blends. The moulding time has a somewhat similar effect on the varia tion of dielectric loss and mechanical properties of different blends; thus, the basic mechanism that influences these properties is expected to be the same.