Mary Ellen Rogers-Moore, Ph.D. (2010) 

Dissertation Topic:  Synthesis and Characterization of Brominated Resole Phenolic Resins and Silicon-Based Resole Phenolic nanocomposites

Major Professor:  Dr. Mahesh Hosur, Research Professor of Materials Science & Engineering

M.S.:  Polymer Science, University of Southern Mississippi, Hattiesburg, MS

B.S.: Polymer Science, University of Southern Mississippi, Hattiesburg, MS

Employment:  Missile Defense Agency, Huntsville, AL

Dissertation Abstract:

Phenolic resins have been used extensively for high temperature applications in aerospace and non-aerospace industries because of their inherent properties of low smoke generation, low flame spread, and decreased toxicity. Strict fire mandates and regulations have caused the modification of phenolic resins to further enhance fire and thermal properties of the resins.  One modification that is commonly used to enhance these properties is to incorporate halogens (e.g., bromine and chlorine) into the resin formulation. To add to the body of research concerning halogenated phenolic resins, the current research focused on the synthesis and characterization of brominated resole phenolic copolymer resins and nanocomposites.

The current research had two major objectives.  The first objective was to synthesize a series of brominated resole phenolic copolymer resins which varied only by the position of the bromine substituent relative to the phenolic hydroxyl group (e.g., meta, ortho, or para.) These materials were produced to examine how the presence and position of bromine influenced the structural, thermal, thermo-mechanical, and fire properties of the resins. The effect of bromine on the isothermal cure kinetics and non-isothermal decomposition kinetics was also examined.  The results showed that the presence of bromine reduced the crosslink density which resulted in a less brittle material.  The presence and position of bromine was also observed to affect the dimensional stability with increased stability seen for the meta-brominated resin.  A decrease in the thermal and thermo-oxidative stabilities was also seen that was most due to the decreased crosslink density and the inherent decomposition mechanism presented by the bromine additive.  The fire performance was observed to be best when bromine was located in the ortho position.  The second objective of this study was to fabricate silicon-based nanocomposites using para-brominated resole phenolic copolymer resin as a host matrix. Three silicon-based nano-additives, organically modified montmorillonite nanoclay, halloysite clay nanotubes, and amorphous silicon oxide nanoparticles, were used to compare how the each affected properties of the resin.  Nanocomposite were also fabricated using a non-brominated resole phenol-formaldehyde resin as a matrix to assess the combined property effects of incorporating two fire retardants, bromine and silicon-based nano-additives.  The resulting nanocomposite materials were analyzed to examine the flexural properties, morphology, thermal and thermo-oxidative stabilities, thermo-mechanical properties, and fire properties. Results of this study showed that the presence of both bromine and/or nano-additives caused a decrease the brittleness of the material which was evident by the flexural properties and storage modulus results obtained from dynamic mechanical analysis.  The presence of nano-additive only was seen to increase the thermo-oxidative stability of the materials below 500°C.  An overall increase in the thermal stability was observed at all temperatures with the incorporation of only nano-additive.