scholarly journals Equilibrium Melting Temperature of Polymorphic Poly(l-lactide) and Its Supercooling Dependence on Growth Kinetics

Polymers ◽  
2017 ◽  
Vol 9 (11) ◽  
pp. 625 ◽  
Author(s):  
Ri-Chao Zhang ◽  
Dan Sun ◽  
Ai Lu ◽  
Meiling Zhong ◽  
Guangyao Xiong ◽  
...  
Keyword(s):  
Melting Temperature ◽  
Growth Kinetics ◽  
Equilibrium Melting Temperature

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.

Pressure dependence of equilibrium melting temperature of poly (lactic acid)

Polymer ◽  
2017 ◽  
Vol 118 ◽  
pp. 297-304 ◽  
Author(s):  
David Rohindra ◽  
Keiichi Kuboyama ◽  
Toshiaki Ougizawa
Keyword(s):  
Lactic Acid ◽  
Melting Temperature ◽  
Pressure Dependence ◽  
Poly Lactic Acid ◽  
Equilibrium Melting Temperature

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.

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