Thermodynamics of Crystallization in High Polymers. Natural Rubber

1955 ◽  
Vol 28 (3) ◽  
pp. 718-727 ◽  
Author(s):  
Donald E. Roberts ◽  
Leo Mandelkern
Keyword(s):  
Natural Rubber ◽  
Melting Temperature ◽  
Low Temperatures ◽  
Rapid Heating ◽  
Heat Of Fusion ◽  
Low Molecular Weight ◽  
Heating Rates ◽  
Equilibrium Melting Temperature ◽  
Clapeyron Equation ◽  
Melting Temperatures

Abstract The existence of an equilibrium melting temperature, T0m, at 28 ± 1°, for unstretched natural rubber has been established, using dilatometric methods. The lower melting temperatures previously observed are a consequence of the low temperatures of crystallization and the rapid heating rates employed. From melting point studies of mixtures of the polymer with low molecular-weight diluents, the heat of fusion per repeating unit, ΔHu has been evaluated as 15.3 ± 0.5 cal./g. The values of ΔHu and T0m have then been combined with data of other workers to obtain the following information concerning natural rubber: (1) The variation of melting temperature with applied hydrostatic pressure has been calculated from the Clapeyron equation to be 0.0465° C/atm. (2) The degree of erystallinity resulting from maintaining a sample at 0° until the rate of crystallization is negligible has been calculated, by three independent methods, to be in the range 26 to 31 per cent. (3) Analysis of the stress-strain-temperature relationship has indicated that crystallization is the cause of the large internal energy changes that are observed at relatively high elongations.

Nature of Stark Rubber

1955 ◽  
Vol 28 (4) ◽  
pp. 1007-1020 ◽  
Author(s):  
Donald E. Roberts ◽  
Leo Mandelkern
Keyword(s):  
Natural Rubber ◽  
Melting Temperature ◽  
Melting Behavior ◽  
X Ray Diffraction ◽  
Equilibrium Melting Temperature ◽  
X Ray ◽  
Melting Temperatures ◽  
Controlled Conditions ◽  
Previous Assignment ◽  
Diffraction Patterns

Abstract The melting behavior and x-ray diffraction patterns of four different samples of stark rubber have been investigated. The melting temperatures, 39° to 45.5° C, are substantially higher than that observed for natural rubber crystallized by cooling. The x-ray diffraction patterns indicate that the crystallites in stark rubber are oriented. This observation can explain the higher melting temperatures. Thus, the previous assignment of an equilibrium melting temperature, 28° (±1°) C, to unoriented crystalline natural rubber is shown to be appropriate. Several different methods that have been used successfully in preparing stark rubber under controlled conditions in the laboratory are outlined.

Effect of Deformation on the Crystallization of Supercooled Cured and Uncured Rubbers

1964 ◽  
Vol 37 (2) ◽  
pp. 404-407 ◽  
Author(s):  
M. F. Bukhina
Keyword(s):  
General Theory ◽  
Natural Rubber ◽  
Mechanical Stress ◽  
Melting Temperature ◽  
Crystallization Kinetics ◽  
Crystallization Rate ◽  
Approximate Expression ◽  
Supercooled Liquids ◽  
Half Time ◽  
Equilibrium Melting Temperature

Abstract 1. The dependence of the polymer crystallization rates on temperature is considered on the basis of the general theory of crystallization kinetics for supercooled liquids. The coefficients in the equations relating the crystallization half time, τ½, to the degree of supercooling are calculated for natural rubber. 2. An approximate expression is obtained which relates the equilibrium melting temperature of deformed rubber with the mechanical stress applied when crystallization starts. 3. The acceleration of crystallization which is induced by deformation is shown to be basically associated with an increase of the equilibrium melting temperature. 4. The possibility of calculating the crystallization rate at all temperatures and stresses from the results of a small number of experiments is established.

The Crystallization of Vulcanized Natural Rubber at Low Temperatures

1952 ◽  
Vol 25 (3) ◽  
pp. 397-411 ◽  
Author(s):  
E. W. Russell
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Low Temperatures ◽  
Maximum Rate ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Cross Links ◽  
Temperature Rate ◽  
Two Stages ◽  
Natural Rubber Vulcanizates

Abstract A series of natural rubber vulcanizates have been crystallized at −36° − 26° −17.5° and −2° C and the changes followed dilatometrically. As for raw rubber there is a maximum rate of crystallization at about −26° C; vulcanization decreases the rate and alters the shape of the temperature-rate curve. The amount of combined sulfur is the chief factor in determining the rate and extent of crystallization of pure-gum vulcanizates. Cross-linking, where it is efficient so that the chains between the cross-links are chemically unaffected, also depresses the rate and extent of crystallization. The use of vulcanizates which crystallize slowly permits melting to be accomplished at much lower rates of heating than was previously possible with raw rubber. Two stages of melting are distinguished the first occurring under the influence of forces between the crystalline and amorphous regions and the second analogous to the melting of low molecular weight crystalline substances.

Melting Temperatures of Several Oxides under Pressure

2007 ◽  
Vol 546-549 ◽  
pp. 1817-1820
Author(s):  
S. Zhang ◽  
Shu Sheng Jia
Keyword(s):  
Phase Diagram ◽  
Melting Temperature ◽  
Magnesium Oxide ◽  
Model Prediction ◽  
Surface Stress ◽  
Clapeyron Equation ◽  
Melting Temperatures ◽  
Pressure Phase ◽  
Effect Of Surface ◽  
Volume Difference

The melting temperature-pressure phase diagram [Tm(P)-P] for corundum (Al2O3), wustite (FeO) and magnesium oxide (MgO) are predicted through the Clapeyron equation where the pressure-dependent volume difference is modeled by introducing the effect of surface stress induced pressure. The model prediction is found to be consistent with the present experimental results.

Probing boron thermite energy release at rapid heating rates

2021 ◽  
Vol 231 ◽  
pp. 111491
Author(s):  
Jennifer L. Gottfried ◽  
Elliot R. Wainwright ◽  
Sidi Huang ◽  
Yue Jiang ◽  
Xiaolin Zheng
Keyword(s):  
Energy Release ◽  
Rapid Heating ◽  
Heating Rates

DC-AC hybrid rapid heating method for lithium-ion batteries at high state of charge operated from low temperatures

Energy ◽  
2022 ◽  
Vol 238 ◽  
pp. 121809
Author(s):  
Shanshan Guo ◽  
Ruixin Yang ◽  
Weixiang Shen ◽  
Yongsheng Liu ◽  
Shenggang Guo
Keyword(s):  
Lithium Ion Batteries ◽  
Low Temperatures ◽  
Rapid Heating ◽  
Lithium Ion ◽  
State Of Charge ◽  
High State ◽  
Heating Method

Melting Temperature of FeO under Pressure

2013 ◽  
Vol 717 ◽  
pp. 184-187
Author(s):  
Shuai Zhang ◽  
Lei Chen
Keyword(s):  
Phase Diagram ◽  
Melting Temperature ◽  
Surface Stress ◽  
Clapeyron Equation ◽  
Metallurgical Processes ◽  
Pressure Phase ◽  
Effect Of Surface ◽  
Volume Difference

The melting temperature-pressure phase diagram [Tm(P)-P] for wustite (FeO) is predicted through the Clapeyron equation where the pressure-dependent volume difference is modeled by introducing the effect of surface stress induced pressure. FeO plays an important role in many metallurgical processes and in the Earths mantle mineralogy. FeO is also of great interest in the field of state solid physics and chemistry because of its electrical, magnetic, structural and non-stoichiometric properties.

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