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dc.contributor.authorTyberg, Christy Sensenichen_US
dc.date.accessioned2014-03-14T20:08:38Z
dc.date.available2014-03-14T20:08:38Z
dc.date.issued2000-03-22en_US
dc.identifier.otheretd-03302000-20270052en_US
dc.identifier.urihttp://hdl.handle.net/10919/26554
dc.description.abstractPhenolic resins are important components of the composite industry because of their excellent flame retardance and cost effectiveness. However, the common procedure for curing phenolic novolac resins uses hexamethylenetetramine (HMTA) and releases volatiles during the cure, which produce networks with numerous voids. This results in materials that lack the toughness necessary for structural applications. An alternative to curing with HMTA is to crosslink the pendant phenolic groups in the novolac resin with epoxy reagents. This reaction proceeds by nucleophilic addition without the release of any volatiles, thereby creating a void-free network. Flame retardance can be achieved by using an excess of the phenolic component. Network densities can also be controlled to maximize both toughness and stiffness by tailoring the stoichiometry of the reagents. Structure-property relationships of phenolic/epoxy networks have been investigated. Glass transitions decreased, and toughness increased, as the phenolic content in the network was increased. Both results could be correlated to the decrease in network densities along this series, which was investigated by measuring the rubbery moduli well above Tg. Fracture toughness of phenolic/epoxy networks measured by K1c reached 1.03 MPa-m1/2, compared with an epoxy control with K1c = 0.62 MPa-m1/2 and phenolic control with K1c = 0.16 MPa-m1/2. In addition, an increase in novolac content improves flame retardance rather dramatically. The peak heat release rate (PHRR) dropped from 1230 kW/m²⁺ for the epoxy control to 260 kW/m²⁺ for the phenolic/epoxy networks, which approached that of a phenolic resol (PHRR = 116 kW/m²⁺). Phenolic/epoxy composite flame retardance also showed significant improvement when compared to epoxy composites. Melt processability of phenolic/epoxy composites has been achieved through the use of latent nucleophilic initiators. Kinetics of the phenolic/epoxy cure reactions with latent initiators demonstrated that monomeric phosphine initiators yielded faster cure reactions as compared to polymeric initiators. These latent initiators allow composite melt processing, such as prepregging or pultrusion, without premature curing. In addition, cure cycles can be reduced from 4 hours to less than 30 minutes. Composites prepared using these latent initiators had toughness exceeding that of epoxy composites and fatigue limits significantly higher than those of vinyl ester composites. Vita removed, June 10, 2013, per author's request. GMcen_US
dc.publisherVirginia Techen_US
dc.relation.haspart01Dissertation.pdfen_US
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectcompositeen_US
dc.subjectflame-retardanten_US
dc.subjectlatent initiatoren_US
dc.subjectphenolicen_US
dc.subjectepoxyen_US
dc.titleVoid-Free Flame Retardant Phenolic Networks: Properties and Processabilityen_US
dc.typeDissertationen_US
dc.contributor.departmentChemistryen_US
dc.description.degreePh. D.en_US
thesis.degree.namePh. D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen_US
thesis.degree.disciplineChemistryen_US
dc.contributor.committeechairRiffle, Judy S.en_US
dc.contributor.committeememberWard, Thomas C.en_US
dc.contributor.committeememberHedrick, Jeffrey C.en_US
dc.contributor.committeememberLesko, John J.en_US
dc.contributor.committeememberMcGrath, James E.en_US
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-03302000-20270052/en_US
dc.date.sdate2000-03-30en_US
dc.date.rdate2001-04-04
dc.date.adate2000-04-04en_US


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