Specific Heat of Natural Rubber and Other Elastomers above the Glass Transition Temperature

1968 ◽  
Vol 41 (3) ◽  
pp. 564-568 ◽  
Author(s):  
Lawrence A. Wood ◽  
Norman Bekkedahl
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Natural Rubber ◽  
Specific Heat

Elastomer Structures and ‘Cold Crystallization’

1979 ◽  
Vol 52 (1) ◽  
pp. 207-212 ◽  
Author(s):  
M. Bruzzone ◽  
E. Sorta
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Melting Point ◽  
Natural Rubber ◽  
Crystallization Rate ◽  
Cold Crystallization ◽  
Structural Defects ◽  
Strain Induced Crystallization ◽  
Induced Crystallization

Abstract In a great number of applications an ideal elastomer should satisfy, to a certain extent, both of the following requirements: (1) nearly instantaneous crystallization upon application of strain (strain induced crystallization) and (2) slow or no crystallization when cooled at the temperature of maximum crystallization rate (cold induced crystallization). A noteworthy case of (2) is elastomer crystallization in a strained state. The connection between the points (1) and (2) has not been clearly understood up to now, but it is known that some crystallizable elastomers fulfil the requirements of both (1) and (2) better than others. From an experimental point of view, cold induced crystallization kinetics are substantially easier to measure than those of very fast strain induced crystallization. The phenomenon of cold induced crystallization in natural rubber, NR, has been known since the very beginning of elastomer technology and the tendency of natural rubber to crystallize by cooling has been overcome by crosslinking it with sulphur (vulcanization) without impairing its ability to crystallize by stretching (Goodyear, 1836). The synthesis of cis-polyisoprenes (IR) and cis-polybutadiene (BR) of different microstructural purity (different cis content) gave the possibility of changing the crystallization rate. It has also been reported that the very fast cold crystallization of trans-polypentenamer (TPA) could be reduced by lowering the trans content. The same fact had been observed earlier for trans-polychloroprene. There is a general agreement in postulating that the reduction of the crystallization rate, obtained either by cross-linking or by chain regularity reduction, can be linked with the lowering of the melting point. In both cases the low level of structural defects introduced in the chains does not affect the glass transition temperature in such a way as to vary the crystallization rate. The aim of this paper is to emphasize the importance of the variations of the glass transition temperature and melting point on the elastomeric cold crystallization rate and the way these may be used in planning new elastomer structures.

Formation and Evolution of Chemical-Physical Complex Network during Vulcanization in Carbon Black Filled Natural Rubber (NR)

2016 ◽  
Vol 717 ◽  
pp. 27-31
Author(s):  
Guang Shui Yu ◽  
Ji Wen Liu ◽  
Jun Mei Cheng ◽  
Chong Sun
Keyword(s):  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Carbon Black ◽  
Natural Rubber ◽  
Complex Network ◽  
Cross Linking ◽  
Weight Percentage ◽  
Critical Content ◽  
Formation And Evolution

The formation and evolution of chemical-physical complex network during vulcanization in carbon black (CB) filled NR was investigated in this work. The results showed that the cross-linking density increased with increase of CB content. The variation of torque during vulcanization was attributed to crosslinks of macromolecular chains. The critical content of CB for the forming of CB network was between 30phr and 40phr (weight percentage). The CB content did not affect the glass transition temperature (Tg) obviously.

Thermal Properties of PVP Cryoprotectants With Nanoparticles

2011 ◽  
Vol 2 (2) ◽  
Author(s):  
Baotong Hao ◽  
Baolin Liu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Aqueous Solutions ◽  
Specific Heat ◽  
Warming Rate ◽  
The Difference ◽  
Transfer Properties

Vitrification is an effective way for the cryopreservation of cells and tissues. The critical cooling rates for vitrification solution are relatively high. It is reported that nanoparticles can improve the heat transfer properties of solutions. To increase the heat transfer coefficient of aqueous cryoprotectant solutions, Hydroxyapatite (HA) nanoparticles were added into Polyvinylpyrrolidone (PVP) solutions (50%, 55%, and 60%, w/w). The glass-transition temperature, devitrification temperature, and specific heat of PVP aqueous solutions with/without HA nanoparticles (0.1%, 0.5%, and 1%, w/w) were measured by a differential scanning calorimeter at a cooling rate of 20°C/min and a warming rate of 10°C/min. The change in density of the above solutions with temperature was determined by using a straw that can reveal the volume change of solutions. The thermal conductivity was calculated based on the experimental data. A device that can be used to measure the thermal conductivity of vitrification solutions with/without nanoparticles was developed in this study. The results showed that the glass-transition temperature, devitrification temperature, and specific heat of PVP aqueous solutions with HA nanoparticles are larger than those without HA nanoparticles. The thermal conductivity of solutions with HA nanoparticles is larger than those without HA nanoparticles at a specific temperature. The lower the temperature, the smaller the difference in thermal conductivity between the solutions with and without HA nanoparticles. The calculated thermal conductivity meets the measured data well.

Thermal Properties of PVP Cryoprotectants With Nanoparticles

2009 ◽  
Author(s):  
Baotong Hao ◽  
Baolin Liu ◽  
Senjie Rong ◽  
Yan Zhou ◽  
Zhixin Gao
Keyword(s):  
Thermal Conductivity ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Aqueous Solutions ◽  
Specific Heat ◽  
Warming Rate ◽  
Specific Temperature ◽  
The Difference ◽  
The Heat Transfer Coefficient

Vitrification is an effective way for the cryopreservation of cells and tissues. The critical cooling rates for vitrification solution are relatively high. It is reported that nanoparticles can improve the heat tranfer properties of solutions. To increase the heat transfer coefficient of aqueous cryoprotectant solutions, HA nanoparticles were added into PVP solutions (50%, 55%, 60%, w/w). The glass transition temperature, devitrification temperature and specific heat of PVP aqueous solutions with/without HA nanoparticles (0.1%, 0.5% and 1%, w/w) were measured by differential scanning calorimeter (DSC) at the cooling rate of 20°C/min and warming rate of 10°C/min. The change of density of above solutions with temperature was determined by using a straw that can reveal the volume change of solutions. The thermal conductivity was calculated based on the experimental data. A device that can be used to measure the thermal conductivity of vitrification solutions with/without nanoparticles was developed in this study. The results showed that the glass transition temperature, devitrification temperature and specific heat of PVP aqueous solutions with HA nanoparticles are larger than that without HA nanoparticles. The thermal conductivity of solutions with HA nanoparticles is larger than that without HA nanoparticles at a specific temperature. The lower the temperature, the smaller the difference of thermal conductivity between solutions with and without HA nanoparticles. The calculated thermal conductivity meets the measured data well.

Some Properties of the Glass Transition in the Amorphous Sb-As-S-Se-I System

2007 ◽  
Vol 555 ◽  
pp. 165-170
Author(s):  
F. Skuban ◽  
S.R. Lukić ◽  
D.M. Petrović ◽  
Mirjana Šiljegović
Keyword(s):  
Activation Energy ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Specific Heat ◽  
Heating Rate ◽  
Glass Composition ◽  
Transition Process ◽  
Abrupt Increase ◽  
Pseudobinary System

Transformations of glasses from the multicomponent pseudobinary system (As2Se3)100−x(SbSI)x were analyzed from the aspect of determining the glass transition temperature Tg, activation energy of the process Et, and characteristic changes of the specific heat. The established dependence of Tg on glass composition and heating rate served as the basis for determining the activation energy of glass transition process Et. An abrupt increase in the specific heat cp at the glass transition temperature was analyzed with the aim of classifying the materials according to the criterion of the so-called 'fragility'. It was found that the investigated glasses, i.e. their melts, belong to the group of thermodynamically 'strong' melts.

Canonical-glass-like behavior of the polycrystalline relaxor ferroelectric (1–x)PbMg1/3Nb2/3O3–xPbZrO3: Heat-capacity study

2003 ◽  
Vol 18 (2) ◽  
pp. 531-536 ◽  
Author(s):  
Gurvinderjit Singh ◽  
V.S. Tiwari ◽  
Arun Kumar ◽  
V.K. Wadhawan
Keyword(s):  
Heat Capacity ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Specific Heat ◽  
Lead Zirconate ◽  
Relaxor Ferroelectric ◽  
Capacity Curves ◽  
Ferroelectric Behavior ◽  
Lead Magnesium

A solid solution of lead magnesium niobate (PMN), a relaxor ferroelectric, with lead zirconate (PZ), an antiferroelectric, gives rise to a system that behaves like a relaxor ferroelectric for lower concentrations of PZ, and like a normal ferroelectric above 50% substitution by PZ. This paper reports the heat-capacity behavior of (1 –x)PMN–xPZ for the composition rangex= 0.30 to 0.95 and temperature range 300–600 K. It was observed that, although the atomic structure of the material is basically crystalline throughout, with sharp x-ray diffraction peaks, the crossover from normal–ferroelectric behavior to relaxor–ferroelectric behavior (on decreasingx) is accompanied by a matching crossover from crystalline behavior to glassy behavior, as exhibited in the heat-capacity plots. In other words, the heat-capacity curves for the relaxor compositions bear resemblance to those observed for canonical or conventional glasses, with the glass-transition temperature and the continuous step in specific heat changing gradually as a function of the composition parameterx. However, not all properties match those for canonical glasses. For example, soaking for 24 h at a temperature or 10 to 20 K below the mean glass-transition temperature does not raise the specific heat to a value nearly equal to the value in the unfrozen state. Similarly, the glass-transition temperature (for 0.7PMN–0.3PZ) increases, though only marginally (from 337 K to 343 K), when the rate of heating across the transition is increased by a factor of 50 (from 0.1 K per minute to 5 K per min.). Further, the temperature interval ΔT over which most of the glass transition occurs in the relaxor ferroelectric is typically as large as 30–40 K, compared to only about 10 K for canonical glasses.

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