A thermodynamical framework is presented that describes the solidification of molten polymers to an amorphous as well as to a semicrystalline solid-like state. This framework fits into a general structure developed for materials undergoing a
large class of entropy producing processes. The molten polymers are usually isotropic
in nature and certain polymers crystallize, with the exception of largely atactic polymers,
which solidify to an amorphous solid, to an anisotropic solid. The symmetry of
the crystalline structures in the semicrystalline polymers is dependent upon the thermomechanical
process to which the polymer is subjected to. The framework presented
takes into account that the natural configurations associated with the polymer melt
(associated with the breaking and reforming of the polymer network) and the solid
evolve in addition to the evolving material symmetry associated with these natural
configurations. The functional form of the various primitives such as how the material
stores, dissipates energy and produces entropy are prescribed. Entropy may be
produced by a variety of mechanisms such as conduction, dissipation, solidification,
rearragement of crystalline structures due to annealing and so forth. The manner in
which the natural configurations evolve is dictated by the maximization of the rate
of dissipation. Similarly, the crystallization and glass transition kinetics may be obtained
by maximization of their corresponding entropy productions. The restrictions
placed by the second law of thermodynamics, frame indiference, material symmetry
and incompressibility allows for a class of constitutive equations and the maximization
of the rate of entropy production is invoked to select a constitutive equation from
an allowable class of constitutive equations. Using such an unified thermodynamic
approach, the popular crystallization equations such as Avrami equation and its various
modifications such as Nakamura and Hillier and Price equations are obtained.
The predictions of the model obtained using this framework are compared with the
spinline data for amorphous and semicrystalline polymers.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3065 |
| Date | 12 April 2006 |
| Creators | Kannan, Krishna |
| Contributors | Rajagopal, K.R. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 1252993 bytes, electronic, application/pdf, born digital |
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