ABSTRACT
The use of polymer matrix composites (PMCs) in aerospace and civil engineering as well as in sports and leisure applications is rapidly increasing. PMCs have found a wide range of applications in structural components in which the substitution of PMCs for metals has substantially improved performance and reliability. The high tensile strength of PMCs is mainly derived from the high strength of the carbon or glass fibers embedded in the matrix. Fibers typically have high strength in tension. However, their compressive strength is generally much lower due to the fact that under compression the fibers tend to fail through buckling well before compressive fracture occurs. Also, fiber misalignment and presence of voids during manufacturing processes contribute to a further reduction in compressive strength. In fact, the overall compressive strength of a PMC is only about 50% of the tensile strength. The strength of the surrounding polymer matrix plays a key role in characterizing the critical buckling loads of the fibers by constraining the fibers from buckling. Consequently high-strength polymer resins such as PEEK and PPSalthough very expensive-are typically used for applications requiring high compressive strength. Low-cost commodity resins such as polypropylene (PP) suffer primarily due to low compressive strength. Because the critical buckling stress in the fiber is directly related to the stiffness and yield strength of the surrounding matrix material, any increase in these matrix properties would directly result in an improvement in the compressive strength of the composite. In this context, it has been observed that the addition of small amounts of nanostructured montmorillonite (MMT) clay (~5 wt%) significantly improves the stiffness, strength, gas barrier, and fire resistance properties of most thermoplastic resins, with only small effect on flexibility. These nanoclay fillers are only slightly more expensive than glass (a few dollars per pound), yet generally far less expensive than carbon fibers (~$100/lb) or carbon nanotubes (~$50,000/lb). Additionally the small amounts of nanofillers required to enhance properties enables these materials to compete more effectively with traditional glass-fiber reinforcements.
