UNDERGRADUATE RESEARCH

Comprehensive Microstructural Evaluation of E-Glass Reinforced Polymer Matrix Composites and Their Components

by Gabrielle Gaustad
Advisor: Dr. Rebecca DeRosa

Summary: Billions of pounds of thermoset composite materials are shipped each year in the United States alone. Most of these materials end up in dumps or non-biodegradable landfills because little research has been done on the recycling of these composites. Unlike thermoplastics, thermoset composites cannot be melted down and re-formed. The only current method of recycling glass reinforced thermoset composites being used in industry is to grind them up and combine the recyclate with virgin material. However, composites made with recycled material are much weaker. There are many hypotheses as to why this may be true. One hypothesis is that aging effects may be at work, for example, polymer and glass fiber degradation due to moisture in the air. Other hypotheses blame weakened chemical or mechanical bonding. The hypothesis that seems most likely is that there is poor bonding in the composite itself, whether it be between new and old matrix or at the interface between fiber and matrix. To test this hypothesis and further understand the make-up of recycled thermoset composites, one must look to the microstructural level.

Half and quarter inch virgin E-glass chopped strand fibers were obtained and analyzed using optical and electron microscopy. They were found to have an average individual fiber diameter of 13.5 micron and a smooth surface. The quarter inch chopped strand had a much rougher end, which would suggest different chopping procedures. Recycled sheet molding compound was obtained from Mecelec, a French recycling company. This was found to have varying fiber diameters and lengths, good percent coating of resin, and surface roughness. The recyclate was also analyzed for change in surface roughness, dispersion, and integrity as well as interfacial surface tensions. The recyclate was combined with virgin materials in different ratios and composite bars molded using a Carver flat plate press. The bars were broken using a three-point bending strength test.

The broken bars were sectioned, sputtered, and then fractographically analyzed using optical and electron microscopy. The dominant failure mechanism of bars made with solely virgin chopped strand was found to be failure of the fiber-matrix interface indicated by fiber-matrix debonding, fibrillar crazing, and fiber pull-out. The bars exhibit good fiber to resin bonding and the large amounts of fiber allow for significant bridging which accounts for their high strength. This can be seen in the very jagged fracture surface, which is due to the plastic deformation failure; these bars fail at several unique crack origins that eventual branch together resulting in slow crack propagation. Bars containing solely recyclate were found to have a more brittle failure mechanism. Once a crack appears, catastrophic failure ensues rapidly. There was much less fiber, less fiber bridging, and a high amount of resin pull-out. Radial cracking shows good fiber to matrix bonding. Bars containing both recyclate and virgin fiber exhibited a combination fracture as expected. Failure originates around pieces of thermoplastic additive contained in the recyclate that act as inclusions.

Electron and optical microscopy was also performed on SMC recyclate that had undergone a variety of surface treatments to improve bonding characteristics. These treatments included a variable KOH soak, a plasma treatment, and a KOH soak followed by treatment with propylene glycol and maleic anhydride. The recyclate was analyzed for changes in surface roughness, surface dispersion, percent fiber exposed or coated, fiber packing, and onset of cracking.

Unpublished Paper

Gaustad, Gabrielle, Advisor: Dr. Rebecca Derosa, November 22, 2002, Comprehensive Microstructural Evaluation of E-Glass Reinforced Polymer Matrix Composites and Their Components, Final Report to the Center for Environmental and Energy Research at Alfred University, Summer Undergraduate Research Fellowships 2002

CEER is funded in large part by the United States Environmental Protection Agency.

Home | Research | Education | Site Map | Email: vascott@alfred.edu
AU Homepage | AU @ a Glance | Academics | Admissions
Alumni | Parents | Faculty & Staff | News | Athletics
Research & Outreach | Student Life | Info Technology