THE THERMAL CONDUCTIVITY OF ELASTOMERS UNDER STRETCH AND AT LOW TEMPERATURES

1950 ◽  
Vol 28a (6) ◽  
pp. 596-615 ◽  
Author(s):  
T. M. Dauphinee ◽  
D. G. Ivey ◽  
H. D. Smith
Keyword(s):  
Natural Rubber ◽  
Classical Theory ◽  
Heat Conductivity ◽  
Second Order ◽  
Rate Of Change ◽  
Order Transition ◽  
Hysteresis Phenomenon ◽  
Brittle Point ◽  
Second Order Transition ◽  
Hysteresis Phenomena

Heat conductivity of natural rubber and GR–S was studied in the range from + 50 °C. to − 170 °C. and from 0 to 100% stretch. The apparatus used was a greatly modified version of one designed by Schallamach. The conductivity of both types of rubber at 0% stretch lies in the range between 3.5 × 10−4 and 4.0 × 10−4 cal./sec. cm. deg. C. Stretching increases the rate of change of conductivity with temperature of both natural rubber and GR–S, and decreases the conductivity of the latter. On lowering the temperature and raising it again natural rubber exhibits a complicated hysteresis phenomenon, while GR–S shows a hysteresis loop caused by a second order transition near the brittle point. The hysteresis phenomena of both types of rubber near the second order transition temperature shows considerable similarity to the changes in specific heat observed by Bekkedahl and coworkers. Above and below the transition region the heat conductivity decreases approximately linearly with temperature as might be expected from classical theory. The variation through the second order transition does not agree with classical theory, but may be explained qualitatively on the basis of a diffuse lambda type transition.

Refractometric Determination of Second-Order Transition Temperatures in Polymers. V. Determination of the Refractive Indexes of Elastomers at Temperatures from 25 to −120° C

1951 ◽  
Vol 24 (3) ◽  
pp. 585-590
Author(s):  
Richard H. Wiley ◽  
G. M. Brauer ◽  
A. R. Bennett
Keyword(s):  
Natural Rubber ◽  
Second Order ◽  
Order Transition ◽  
Transition Temperatures ◽  
Refractometric Method ◽  
Second Order Transition ◽  
Refractometric Determination ◽  
Transition Points

Abstract In previous papers a refractometric method was described for determining second-order transition temperatures of polymers whose transitions occur between 75 and −60° C. In the present study, an Abbé refractometer was insulated and used to determine the refractive indexes of polymers down to − 120° C and the transition points of natural rubber and a number of synthetic rubbers.

Thermal Expansion and Second-Order Transition Effects in High Polymers. I. Experimental Results

1944 ◽  
Vol 17 (4) ◽  
pp. 802-812
Author(s):  
R. F. Boyer ◽  
R. S. Spencer
Keyword(s):  
Thermal Expansion ◽  
Second Order ◽  
Order Transition ◽  
Theoretical Treatment ◽  
Polymeric Systems ◽  
Crystalline Polymers ◽  
Brittle Point ◽  
Second Order Transition ◽  
Transition Effects ◽  
Point Determination

Abstract The results presented here on second-order transitions are in general accord with what has been known for other high polymeric systems. The value of the volume-temperature technique for investigating the nature of polymeric mixtures and the homogeneity of copolymers has been emphasized. In Part II a theoretical treatment of second-order transition effects, including the related brittle point determination, will be given. Finally, Part III will permit a more expanded treatment of the behavior of Saran and other crystalline polymers.

The Temperature Shift of the Second Order Transition of Natural Rubber by Crosslinking

1962 ◽  
Vol 35 (3) ◽  
pp. 776-793 ◽  
Author(s):  
H. D. Heinze ◽  
K. Schmieder ◽  
Gg Schnell ◽  
K. A. Wolf
Keyword(s):  
Natural Rubber ◽  
High Energy ◽  
Second Order ◽  
Order Transition ◽  
Transition Range ◽  
High Energy Radiation ◽  
Energy Radiation ◽  
Dynamic Mechanical ◽  
Sulfur Vulcanization ◽  
Second Order Transition

Abstract The present article reports on dynamic mechanical and infrared spectroscopic tests of natural rubber crosslinked by sulfur, peroxide or high energy radiation. The effect of these vulcanization methods upon the rate of crosslinking, the position of the second order transition temperature and the double bond structure is discussed. Whereas the temperature displacement of the transition range from the second order transition phase to the rubber elastic state during crosslinking by high energy radiation or by peroxide arises from the increasing hindrance of chain movement by the crosslinks, the intramolecular addition of sulfur predominantly is responsible for the much greater temperature displacement—related to the same crosslink density—during sulfur vulcanization. The change of the double bonds which proceeds in the sulfur vulcanization at a much faster rate than in the crosslinking by irradiation also can be considered as indication of intramolecular rings being formed along the chain during sulfur vulcanization. Vulcanization by sulfur and crosslinking by irradiation appear, principally, to be based on the same mechanism. The influence of oxidation on the mechanical properties of the vulcanizates is studied in natural rubber irradiated in an oxygen atmosphere. The two damping maxima observed at the dynamic mechanical test can be ascribed, with the aid of infrared spectroscopy, to the influence of crosslinks and oxidation products on the chain mobility.

Beta Ray Absorption in Polymers and Determination of First and Second-Order Transition Temperatures

1963 ◽  
Vol 36 (2) ◽  
pp. 459-472 ◽  
Author(s):  
R. Zannetti ◽  
P. Manaresi ◽  
L. Baldi
Keyword(s):  
Phase Transitions ◽  
Natural Rubber ◽  
Good Accuracy ◽  
Second Order ◽  
Order Transition ◽  
Beta Radiation ◽  
Transition Temperatures ◽  
Inorganic Substances ◽  
Second Order Transition

Abstract It is possible to determine the first- and second-order transition temperatures of polymers, copolymers, and other organic and inorganic substances with good accuracy and reproducibility by measuring their absorption of beta radiation. Variations in the measured absorptions are in essence related to variations in the product of the density and thickness of the sample, so that the method can be employed, in practice, when seeking information concerning variations in density, with the temperature or the time. The technique was used to investigate a number of polymers, e.g., polyethylene terephthalate, polystyrene, polyethylene, 1,4-cis polybutadiene, natural rubber, polyisobutylene, polybutene-1, polypropylene, and certain copolymers of ethylene/propylene and ethylene/butene-1. Finally, data pertaining to phase transitions in organic and inorganic substances are presented. The results are discussed., and compared with those obtained by other methods.

Thermal Expansion Measurements and Transition Temperatures, First and Second Order

1959 ◽  
Vol 32 (4) ◽  
pp. 1005-1015
Author(s):  
Mark L. Dannis
Keyword(s):  
Thermal Expansion ◽  
Transition Temperature ◽  
Physical Properties ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Second Order ◽  
Rate Of Change ◽  
Order Transition ◽  
Abrupt Changes ◽  
Second Order Transition

Abstract When any pure material goes through a change in state, its physical properties change greatly. In each phase the physical properties are relatively constant or change slowly enough with temperature that the rate of change of a property such as volume is a constant. This rate of change of volume is the thermal expansion coefficient, (∂V/V)/∂T. The thermal expansion coefficient is almost constant, experimentally, as long as the temperature range over which measurements are made does not include a phase transition. At the transition temperature, abrupt changes in volume are found as illustrated in Figure 1. Polymeric materials often show changes in physical properties not necessarily accompanied by abrupt changes in volume, even though the expansion coefficient does change. Since the expansion coefficient changes, some change in internal structure is suspected, and the name second-order transition (Tg) has been adopted. This kind of change is roughly diagrammed in Figure 2. This latter change at the second-order transition temperature can be found in every known polymer, even though many polymers possess clear, first-order, crystalline transitions as well. Hevea rubber, for example, has a crystalline melting point of 28° C, compared to its Tg about −70°. These data are shown, copied from Boyer and Spencer, as Figure 3.

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