Composite materials--Biodegradation

This research tests the use of sensitized lanthanide ions to determine if they can
detect water-borne explosive traces and produces two designs for a field-deployable
underwater explosive trace detector. 1,1 0-phenanthroline and thenoyltritluoroacetone are
evaluated as sensitizing ligands to absorb energy and initiate the fluorescence process in
europium ions. Different compounds obtained via ligand choice and mixing order are
evaluated for their ability to produce a large fluorescence differential between explosive-laden
and explosive-absent solutions. Optimal excitation and emission wavelengths for
several different compounds are determined, as well as practical wavelengths to be
applied in the field. The effect of methanol as a solvent to deliver the reagents is
evaluated and rough solubility limits are determined. The effects of seawater constituents
on detection are investigated and explosive detection limits are determined. It was found
that this method and device are viable for underwater explosive trace detection. A field-deployable
device is designed, characterized, and proven.

The degradation of polymer composites in moist environments is a limiting
factor in the advancement of composite technology. The key to mitigate this
degradation is to maintain the integrity of the fiber/matrix (F/M) interface. In this
study, the F/M interface of carbon/vinyl ester composites has been modified by
treating the carbon fiber with polyhedral oligomeric silsesquioxane (POSS). Two
POSS systems, namely octaisobutyl and trisilanolphenyl, have been
investigated. A set of chemical and mechanical procedures has been developed
to coat carbon fibers with POSS, and fabricate layered composites using vinyl
ester resin. lnterlaminar shear, transverse tension, and low velocity impact tests
on composites have indicated around 10-38% improvement in mechanical
properties with respect to control samples. Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) tests have also shown
significant improvement in glass transition temperature (T9). Hygrothermal tests,
under various environments, have demonstrated that POSS reduces water
absorption by 20-30%.

This research proposed to characterize any microbial induced degradation of carbon fiber/polyetheretherketone (PEEK) composites from acid-producing bacteria (APB) and sulfate-reducing bacteria (SRB). Electrochemical impedance spectroscopy (EIS) was used to provide a measure of degradation of the composite system as a function of exposure time. In addition, mechanical testing and microscopic evaluation of the specimens were utilized to determine if changes in the EIS spectra as a function of exposure time correlated to changes in the mechanical properties. Results from most EIS scans were consistent with a well-consolidated and undamaged composite system. Changes in the EIS response of specimens exposed to the SRB environment were not matched by a reduction in the flexural strength. Mechanical testing also indicated no reduction in the flexural strength in any of the other exposure environments. Environmental scanning electron microscopy (ESEM)/energy dispersive x-ray spectroscopy (EDS) were inconclusive, though changes in the EDS spectra were seen. No definitive degradation was seen to occur in this composite system.