Analysis of Melting Point Depression of Benzene in Crosslinked Natural Rubber by a Frozen Tube Network Model

2005 ◽  
Vol 78 (5) ◽  
pp. 827-843 ◽  
Author(s):  
Y. Hoei
Keyword(s):  
Free Energy ◽  
Melting Point ◽  
Natural Rubber ◽  
Network Model ◽  
Melting Point Depression ◽  
Tube Model ◽  
Melting Thermodynamics

Abstract Literature reports from studies by Jackson and McKenna show a large difference in melting point depression between highly and lightly crosslinked (concentrated) natural rubber/benzene samples. Here, an equation for a tube model is developed to describe particularly the highly crosslinked mixtures at both swelling-and-melting equilibrium. On the basis of Flory-Huggins and Gibbs-Thomson equations, the model involves a swelling-and-melting thermodynamics that includes an elastic contribution to a free energy for a “real chain” network swollen in a good solvent. The freezing of the good solvent, then, occurs within the network chains which act as a confining (frozen) hard tube (having an unfrozen good solvent within). Consequently, the model can explain reasonably well the melting point depression of the highly crosslinked samples in the comparison of their estimates for crystallite (frozen tube) dimensions with certain corresponding literature values.

Effect of Strain on Thermodynamic Melting Temperature of Polymers

1967 ◽  
Vol 40 (3) ◽  
pp. 788-800
Author(s):  
W. R. Krigbaum ◽  
J. V. Dawkins ◽  
G. H. Via ◽  
Y. I. Balta
Keyword(s):  
Free Energy ◽  
Melting Point ◽  
Natural Rubber ◽  
Sonic Velocity ◽  
X Ray Diffraction ◽  
Elongation Ratio ◽  
Flory Theory ◽  
X Ray ◽  
Theoretical Predictions ◽  
Crystallization Conditions

Abstract X-ray diffraction, sonic velocity, and birefringence measurements were used to study the variation of the apparent melting point of strained natural rubber and polychloroprene vulcanizates with elongation ratio and crystallization temperature. The procedure of Hoffman and Weeks was employed to obtain the thermodynamic melting point, tm, for each elongation ratio α. The parameter β relating to the distribution of fold lengths is unusually large for low elongation ratios and decreases into the usual range only at higher elongations. Observed variations of tm with α for these two polymers are compared with the theoretical predictions of Flory and Roe and Krigbaum. Although the predictions of the Flory theory depend somewhat upon the value assigned for the number of repeating units per statistical link, and this parameter is not well known for polychloroprene, we nevertheless conclude that his treatment offers a better representation of the melting point elevation for high elongations. Due to the approximations introduced, the treatment of Flory is not valid for lower elongations. Any attempt to improve this treatment must begin by specifying the free energy of the semicrystalline system, which implies a knowledge of the distribution of crystallite orientations and how this distribution varies with strain and with the crystallization conditions.

Melting point depression study of polyacrylonitrile

1960 ◽  
Vol 43 (142) ◽  
pp. 467-488 ◽  
Author(s):  
W. R. Krigbaum ◽  
Noboru Tokita
Keyword(s):  
Melting Point ◽  
Melting Point Depression

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.

Standard enthalpy of fusion of N,N′-ethylenebis (2,4-pentanedion-iminoato)nickel(II) complex by DTA-based melting point depression studies

2005 ◽  
Vol 59 (11) ◽  
pp. 1334-1337 ◽  
Author(s):  
S. Arockiasamy ◽  
P. Antony Premkumar ◽  
O.M. Sreedharan ◽  
C. Mallika ◽  
V.S. Raghunathan ◽  
...  
Keyword(s):  
Melting Point ◽  
Standard Enthalpy ◽  
Enthalpy Of Fusion ◽  
Melting Point Depression
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