Some molecular contributions and curing considerations: Physical properties of thermoset network materials
Twardowski, Thomas E., Jr
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https://hdl.handle.net/2142/21344
Description
Title
Some molecular contributions and curing considerations: Physical properties of thermoset network materials
Author(s)
Twardowski, Thomas E., Jr
Issue Date
1992
Doctoral Committee Chair(s)
Geil, Phillip H.
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Plastics Technology
Language
eng
Abstract
Three topics on the molecular basis of, and processing effects on, thermoset network behavior are investigated: (1) processing thick section prepreg epoxy materials, (2) characterization of the contributions to rubbery elastic behavior and (3) improved epoxy resins through lightly cross-linked stiff molecular backbones.
An experiment has been designed to test simulation results and process changes. Experiments demonstrate the importance of the insulative effects of the vacuum bag, consolidation effects, composition and the effects of asymmetric temperature application. An improved viscosity model is proposed. A simulation has also been developed that recovers the thermal behavior of a 5 cm thick, unidirectional AS4/3501-6 prepreg charge, cured in a one dimensional manner. Some common assumptions are checked. The simulation recovers temperature profiles, the effect of asymmetric temperature application, the importance of consolidation and the effect of different prepreg compositions. The implications for thicker parts are investigated.
The random tube model of rubber elasticity is used to evaluate the deformation behavior of a network formed by cross-linking a strained melt in simple elongation, equibiaxial extension and pure shear. The random tube model recovers the qualitative behavior, and indicates that entanglement contributions are stronger than those of cross-links. Fitting melt stress-strain behavior indicates time dependent entanglement behavior. Model independent Hookean analysis of networks cross-linked in simple extension shows that 75% of the small strain equilibrium modulus is due to entangements; the entanglement contribution modulus is approximately equal to the rubber plateau modulus of uncross-linked polymer.
Three monomer pairs are used to examine the effect of increasing backbone stiffness on the material properties. Bisphenol F, resorcinol and 2,7-dihydroxynaphthalene and their diglycidyl ether analogs are chosen for ease of processing and to avoid the complicating influences of steric hindrance, polar interactions between chains and liquid crystallinity. Oligomeric precursors were solution grown to insure stoichiometric imbalance determined cross-link density. The T$\sb{\rm g}$s of the bisphenol F, resorcinol and 2,7-dihydroxynaphthalene LXTs are 55.8$\sp\circ$C, 67$\sp\circ$C and 105$\sp\circ$C, respectively, by DSC. The modulus of the bisphenol F and resorcinol LXTs are 3.04 and 3.47 GPa, respectively.
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