Void-Free Flame Retardant Phenolic Networks: Properties and Processability
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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. GMc
- Doctoral Dissertations