Showing papers by "Dipak Khastgir published in 1996"

Effect of electron beam radiation on mechanical and electrical properties of poly(ethylene-co-vinyl acetate)

Abstract: Ethylene-vinyl acetate (EVA) copolymer (12% vinyl acetate content) is subjected to electron beam irradiation using trimethylolpropane trimethacrylate (TMPTMA) as a radiation sensitizer. Mechanical and electrical studies of these irradiated samples show that the strength properties (tensile strength, elongation at break) are increased with radiation dosage up to an optimum radiation dose and sensitizer level above which the properties begin to deteriorate. Crosslinking of the polymer takes place on irradiation which is attributed to an increased gel content with increasing radiation dose. Compared to the original samples both dielectric constant and dielectric loss factor decrease for samples subjected to irradiation. Ein Ethylen-Vinylacetat-Copolymeres (EVA) mit 12% Vinylacetat-Gehalt wurde mit Trimethylolpropantrimethacrylat (TMPTMA) als Sensibilisator mit Elektronen bestrahlt. Die mechanischen und elektrischen Eigenschaften der bestrahlten Copolymerproben wurden untersucht. Die Resultate zeigen, das sich Zugfestigkeit und Bruchdehnung zunachst mit zunehmender Strahlungsdosis verbessern und bei Uberschreiten einer optimalen Strahlungsdosis und Sensibilisatorkonzentration wieder verschlechtern. Durch die Bestrahlung wird eine Vernetzung des Polymeren ausgelost, die auf den sich mit der Strahlungsdosis erhohenden Gelanteil zuruckgefuhrt wird. Im Vergleich mit den Originalproben nehmen sowohl die Dielektrizitatskonstante als auch der dielektrische Verlustfaktor durch die Elektronenbestrahlung ab.

Electron beam initiated grafting and crosslinking of ethylene vinyl acetate copolymer. Part II : Mechanical and electrical properties

Abstract: Mechanical, dynamic mechanical and electrical properties of electron beam modified ethylene vinyl acetate (EVA) copolymer in presence of trimethylolpropane trimethylacrylate (TMPTMA) and triallyl cyanurate (TAC) as sensitizer have been described. The tensile strength of the TMPTMA modified EVA increases with increase in radiation dose up to a certain level due to the development of network structure, while it does not change significantly for the TAC based system due to poor stress transfer. The tensile strength deteriorates sharply at higher radiation doses because of the predominating effect of breakdown of the network structure. However, the tensile strength changes marginally with TMPTMA level and decreases with an increase in TAC level. DMTA studies indicate mainly two transitions (namely γ and α) in the order of increasing temperature for both TMPTMA and TAC based samples. The γ-transition temperature shifts to higher values and the α-transition shifts to lower values with an increase in radiation dose due to modification of the main chain and to a decrease in crystallinity. Dielectric analysis shows a sharp transition at around -20°C for all uncured and cured samples due to movement ofthe highly polar acetate groups present in EVA. The loss factor decreases sharply at high temperature with increase in radiation dose due to crosslinking.