We described in a previous report that a fungal consortium isolated from degraded polymeric materials was capable of growth on pre-sterilized coupons of five composites, resulting in deep penetration into the interior of all materials within 5 weeks.1 Data describing the utilization of composite constituents as nutrients for the microflora are described in this paper. Increased microbial growth was observed when composite extract was incubated with the fungal inoculum at ambient temperatures. Scanning electron microscopic (SEM) observation of carbon fibers incubated with a naturally developed population of microorganisms showed the formation of bacterial biofilms on the fiber surfaces, suggesting possible utilization of the fiber chemical sizing as carbon and energy sources. Electrochemical impedance spectroscopy (EIS) was used to monitor the phenomena occurring at the fiber-matrix interfaces. Significant differences were observed between inoculated and sterile panels of the composite materials. A progressive decline in impedance was detected in the inoculated panels. Several reaction steps may be involved in the degradation process. Initial ingress of water into the resin matrix appears to be followed by degradation of fiber surfaces, and separation of fibers from the resin matrix, Our investigation suggested that composite materials are susceptible to microbial attack by providing nutrients for growth.
Fiber-reinforced polymeric composites (FRPCS) are structural materials widely used in transportation, aviation, and aerospace. The increasing usage of these materials is primarily due to their high strength, processing flexibility and lower weight compared to metal alloys. It is expected that this class of materials will find more diversified applications in the future, These materials are frequently in contact with moisture and microbial contaminants, resulting in biofilm formation.
Fungi have been observed to penetrate into the interior of composites composed of fluorinated polyimide resins reinforced with glass fibers. Both glass and carbon fibers are also susceptible to the growth of micro-organisms. Since there are several chemically and physically distinguishable constituents in a composite, localized chemical changes resulting from growth and metabolism of microorganisms may accelerate damage of individual constituents. Damage to a composite material may significantly affect its physical integrity and fatigue performance. We recently obtained information about growth of microorganisms on composite extracts, suggesting the utilization of organic carbon from composite constituents by microorganisms as carbon and energy sources. B Fungi also colonized graphite sheets, and electronic packaging polyamides and caused degradation of polymers or constituents. Knowledge of the effect of microorganisms on the integrity of composite materials is essential for a comprehensive assessment of microbial damage and for the development of resistant materials.
The objectives of this study were to determine the constituents of the composite which are attacked by microorganisms and to monitor the electrochemical behavior of composites inoculated with fungal consortia under laboratory conditions, in order to elucidate the mechanisms of degradation.