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The objective of this investigation was to characterize two cyanate ester resins and a eight harness satin (8HS) graphite fabric for use in resin film infusion (RFI) processing. Two cyanate ester resin systems were characterized to determine their cure-kinetics, and viscosities during cure. A 8HS graphite fabric was tested in compaction and through the thickness permeability. A one-dimensional, through the thickness, flow and cure computer simulation was run. The resin cure-kinetics models predicted the curing behavior of the resins as functions of time, temperature, and degree of cure. The proposed viscosity models determined the resin viscosity as a function of temperature and degree of cure. The 8HS graphite fabric was tested in compaction and through the thickness permeability to determine the effect of compaction pressure on fiber volume fraction and in turn on through the thickness permeability. The one-dimensional RFI flow and cure simulation combined the cure-kinetics and viscosity models of the resins with the characteristics of the graphite fabric and determined resin infiltration and cure times. The proposed cure-kinetics and viscosity models were more than adequate in modeling the cure and flow behavior of the cyanate ester resin systems. Power law curve fits accurately represented the compaction and through the thickness permeability of the 8HS graphite fabric. Finally, the one-dimensional RFI flow and cure simulation showed that resin viscosity was the major influence on the infiltration times. / Master of Science

In our study, the Finite Volume Method (FVM) is successfully implemented to simulate thermal process of polymerization. This application is verified based on the obtained plots compared with those from other two methods as well as experimental data. After the verification, a method is developed to optimize heat history in order to reduce processing time and in the meantime to maintain the uniformity of cure state. Also sensitivities of cure state to different parameters are examined. Besides, a correlation between temperature and the degree of polymerization profile on sample surface is found using on-line monitoring method.

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The goal of this work was to achieve a homogeneous morphology of carbon nanotubes in a polyimide matrix, characterize the resulting nanocomposite properties, and understand structure-property relationships. Melt-mixing was used as an effective method for dispersing multiwall nanotubes and carbon nanofibers in a phenylethynyl terminated imide resin where aggregation occurred only in particle-saturated systems. Particle network formation within the nanocomposites was studied using rheology and impedance spectroscopy; results showed that the electrical percolation threshold occurred at a lower particle loading than the rheological percolation threshold, consistent with the oligomer size in comparison to the distance for electrical conductivity (~5 nm). Thermomechanical analysis showed that the addition of nanoparticles enhanced the polyimide storage modulus and thermal behavior indicated that the nanoparticles restricted polymer motion to higher temperatures. A study of the cure mechanism of the oligomer with and without nanoparticles showed that the nanoparticles reduced the activation energy required for cure initiation while increasing the obtainable extent of cure at various isothermal temperatures. The work presented in this dissertation shows that an easy, time effective processing method can be used to homogeneously disperse nanoparticles in an imide oligomer, and the resulting nanocomposites exhibit enhanced properties. A business plan is also presented that reflects the market potential of this technology.

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The initial objective of this research project was to determine the feasibility of manufacturing carbon fiber-reinforced (CFR) composites with a matrix consisting of a phenylethynyl-terminated version of a thermoplastic poly(etherimide) termed PETU. Successful composite manufacture with 3,000 g/mol (3k) PETU led to a survey of CFR 3kPETU mechanical properties for comparison with other high-performance composites. Encouraging results led to a study of moisture sorption effects on CFR 3kPETU properties. The success of these initial studies spawned the large scale production of 2,500 g/mol (2.5k) PETU. Thermal characterization of neat and CFR 2.5kPETU via differential scanning calorimetry, dynamic mechanical thermal analysis, and parallel plate rheometry resulted in an understanding of the influence of cure time and temperature on reaction progress via both reaction kinetics and monitoring of the glass transition temperature. From the rheological characterization, a two-stage, dual-Arrhenius model was developed to successfully model isothermal complex viscosity over the range of processing temperatures. Neat 2.5kPETU and CFR 2.5kPETU specimens were exposed separately to elevated temperature environments of different moisture and different oxygen concentrations to evaluate the effects of moisture absorption, moisture desorption, and thermal oxidation on material properties. Moisture absorption took place in a 90 °C / 85% relative humidity environment followed by moisture desorption in a 90 °C / 10% relative humidity environment. Thermal-oxidative aging for up to 5000 hours took place at 204 204 °C in environments of four different oxygen partial pressures: 0.0 kPa, 2.84 kPa, 20.2 kPa, and 40.4 kPa. Following exposure to the different aging environments, the specimens were tested for retention of mechanical properties. In addition, moisture sorption properties were measured. Results from the moisture sorption studies on CFR 3kPETU and CFR 2.5kPETU suggest that fully cured composites will withstand moisture absorption and desorption with negligible effects on mechanical properties, whereas, lack of full cure allows moisture sorption to permanently damage the composites. Despite a lack of mass loss or visual evidence of degradation following thermal-oxidative aging, a decline in mechanical properties was observed with the reduction becoming greater with longer aging times and higher oxygen partial pressures. / Ph. D.

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No description available.