Characterization of nanoclay dispersion in resin transfer molded disks and fabrication of nanoclay/waterborne epoxy composites

Although clay has been used by mankind for centuries, its application in tailoring the physical properties of polymers and their composites is relatively recent. Owing features at nanometer scale, clay (frequently referred to as nanoclay) is finding applications in reinforcing polymers. Improvements in thermal and mechanical properties are reported for various thermoplastic polymers; however utility of nanoclay with thermosetting resins is marginal. The reason for not achieving the desired improvements is most likely the ineffective dispersion of nanoclay in the polymer matrix.;In the first part of this dissertation, dispersion of nanoclay in resin transfer molding (RTM) process is qualitatively studied. Three parameters that affect the dispersion characteristics, temperature at which the nanoclay is mixed with the polymer, nanoclay type and nanoclay content, are investigated. Epon 815C epoxy resin is mixed with CloisiteRTM 15A, 25A, and 30B at 5wt.% loading using sonication at 50°C. In addition, Cloisite RTM 25A is mixed at 30°C and 75°C to investigate the effect of mixing temperature. These compounds are then mixed with Epi-cure 3282 curing agent and transferred into center-gated disk-shaped molds using a custom RTM setup. The effect of nanoclay content is studied by mixing Epon 815C resin with CloisiteRTM 25A at 50°C at loadings of 2, 5 and 10wt.%. Unlike the previous cases, these compounds are transferred into molds loaded with 6 layers of chopped strand glass fiber performs yielding a glass volume fraction of 14%. From each disk, a radial sample is extracted and its through-the-thickness surface is analyzed for dispersion of nanoclay. A combination of image analysis and wavelength dispersive spectroscopy (WDS) is used to identify nanoclay clusters. Image analysis is used to analyze nanoclay clusters larger than 1.5mum whereas the remaining smaller clusters are characterized by WDS. The dispersion of nanoclay clusters is observed to be more efficient at lower temperatures. For instance, contribution of large clusters (>50mum 2) increased from 8.9 to 10.4% as the mixing temperature increased from 30 to 75°C. It is also found that the effectiveness of dispersion increases in the order of CloisiteRTM 15A, 25A and 30B. For instance, the average content of clusters larger than 1.5mum is determined as 4.6vol.% for CloisiteRTM 15A, whereas the same values for 25A and 30B are 3.4vol.% and 3.5vol.%, respectively. Significant filtration of nanoclay clusters is observed for the systems with glass fibers. Results obtained from image analysis indicate that nanoclay clusters are filtered out by as much as 50% in the flow direction by the glass fiber preforms. In addition, increasing nanoclay content led to higher filtration, suggesting that cluster formation is more prominent at higher nanoclay loadings.;The second part of the dissertation involves development of new fabrication techniques that yield better dispersion of nanoclay. Three new methods are developed, implemented and characterized in detail. Among those methods, utilization of waterborne epoxies benefits from the hydrophilicity of natural nanoclay. Using this method, prepregs containing 0, 0.1, 0.2, 0.5. 1, 2 and 4wt.% nanoclay are fabricated and characterized. The most significant improvement is observed in moisture absorption characteristics. Over the range of nanoclay loading, the maximum moisture absorption decreased to 25% of the initial value.;Another method developed in this part, vacuum assisted deposition, involves accelerating the nanoclay particles using a pressure difference and passing them through a set of static mixers and small orifices. Using this method, woven glass/epoxy prepregs are deposited with CloisiteRTM 30B nanoclay and fabricated into laminates. Microstructural characterization of these laminates revealed that nanoclay particles broke down to sizes as small as 50nm. In addition, x-ray diffraction studies did not indicate clustering of nanoclay.;The final method is referred to as co-pulverization of solid epoxies and nanoclay. A solid epoxy resin, Bryte 250, is co-pulverized with Cloisite RTM 30B nanoclay at loadings 0, 2 and 10wt.%. The obtained powder is fabricated into disks using a rheometer and subsequently characterized. In these samples, flexural stiffness is observed to improve by as much as 28%. Microstructural characterization revealed formation of nanometer scale voids trapped within the nanoclay clusters. A heat treatment cycle is applied on the parts to force the polymer into the void areas and thus improve properties. Following the heat treatment the flexural strength improved by 30%, strain to failure improved by 50% and flexural stiffness remained constant.