ISSN:
0022-3832
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
The variations of elastic modulus and mechanical tan δ with temperature and frequency have been studied for polyvinyl chloride, natural rubber, Hycar OR-15, GR-S 65, and GR-I using pulsed ultrasonic waves of 2.67 and 8.01 Mc. Tricresyl phosphate and dioctyl phthalate were used as plasticiziers for polyvinyl chloride. PVC-plasticizer system, when the amount of plasticizer is large, shows the steep decrease in effective modulus and the peak of the value of tan δ within the range of measuring temperature from 10 to 90°C. The peak of tan δ shifts to lower temperature with an increase of the amount of plasticizer, and its value becomes smaller. Heat and enttropy of activation derived from the difference between the temperatures of peaks in two frequencies decrease with the amount of plasticizer. Within the range of measuring temperature from -60 to + 80°C., all rubbers used in this measurement show a sudden decrease of the modulus of elasticity and the peak of tan δ. The peaks become higher in the order of GR-S, Hycar OR, natural rubber, and GR-I, and heat and entropy of activation become smaller in this order. As a mechanism of viscoelasticity to explain the results of this measurement, we think of the break and remake of secondary bonds by thermal motion of segments and assume that shear modulus is proportional to the number of segments per cc. The changing of modulus of elasticity with temperature, the effect of plasticizer, and the relation between tan δ and heat, and entropy of activation can be understood on this assumption. The dielectric constants of the samples of PVC-plasticizer systems used in this experiment are measured at the same frequency. As a result of comparison with those dielectric constants, it can be said that electrical tan δ shows the peak at 40-50°C. higher temperature than mechanical tan δ, and that heat and entropy of activation show considerable differences.
Zusätzliches Material:
15 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1955.120188707
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