Morphology Development and Fracture Properties of Toughened Epoxy Thermosets

Kwon, Ojin

Morphology Development and Fracture Properties of Toughened Epoxy Thermosets

dc.contributor.author	Kwon, Ojin	en
dc.contributor.committeechair	Ward, Thomas C.	en
dc.contributor.committeemember	Marand, Hervé L.	en
dc.contributor.committeemember	Schug, John C.	en
dc.contributor.committeemember	Wightman, James P.	en
dc.contributor.committeemember	Wilkes, Garth L.	en
dc.contributor.department	Chemistry	en
dc.date.accessioned	2014-03-14T20:22:23Z	en
dc.date.adate	1998-09-04	en
dc.date.available	2014-03-14T20:22:23Z	en
dc.date.issued	1998-06-08	en
dc.date.rdate	1999-09-04	en
dc.date.sdate	1998-06-08	en
dc.description.abstract	The phase separation process of a rubber modified epoxy system during cure was analyzed by a model developed on the basis of a thermodynamic description of binary mixture and constitutive equations for nucleation and growth rates. As epoxy resins are cured, rubber molecules are precipitated from the epoxy matrix to a non-equilibrium composition due to the decrease in the configurational entropy and the increase in the viscosity with conversion. If phase separation takes place in a metastable region, this model can monitor the changes of rubber compositions in both phases as well as the changes in the number and size of rubber particles upon conversion of polymerization. The particle size distribution at the completion of phase separation was also calculated. The effect of cure temperature on the final morphologies of a rubber modified epoxy system was discussed. The computed particle size distributions for piperidine and diaminodiphenyl sulfone cured systems showed good agreements with experimentally measured values. Depending on the activation energy for viscous flow of the epoxy matrix relative to that for the polymerization, the particle size distribution may show bimodal or unimodal distribution. The size of rubber rich phase increases to a maximum and then decreases with an increase in cure temperature. However, due to limitations of temperature range to probe in an actual experiment, one may observe only either decreasing or increasing particle size as cure temperature increases. The number of rubber particles per unit volume increases for the DGEBA/DDS/ETBN system as cure temperature increases in the temperature range of 30 °C to 220 °C. Fracture toughness of cured DGEBA/DDS/ETBN system was analyzed in terms of morphologies generated by the temperature variation. Since the volume fraction of rubber particles did not change with cure temperature, the critical stress intensity factor did not vary significantly with cure temperature as expected. However, increases in cure temperature produced smaller but more numerous particles. The critical stress intensity factor normalized by the number density of particles exhibited dependence on the radius of particles to the third power. On the other hand, the critical stress intensity factor normalized by the radius of particles showed a linear dependence with respect to the number density of particles.	en
dc.description.degree	Ph. D.	en
dc.identifier.other	etd-6998-234430	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-6998-234430/	en
dc.identifier.uri	http://hdl.handle.net/10919/30660	en
dc.publisher	Virginia Tech	en
dc.relation.haspart	titlepage.PDF	en
dc.relation.haspart	Abstract.PDF	en
dc.relation.haspart	THESIS3.PDF	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	Rubber Toughened Epoxy Thermosets	en
dc.subject	Image Analysis	en
dc.subject	Morphology	en
dc.subject	Phase Separation	en
dc.subject	Fracture Toughness	en
dc.title	Morphology Development and Fracture Properties of Toughened Epoxy Thermosets	en
dc.type	Dissertation	en
thesis.degree.discipline	Chemistry	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en