Composite Materials Research Progress

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W.H. Zhong, R.G. Maguire, S.S. Sangari et al.
Integran has its Nanovar technology in which finely grained metal is applied to a composite
surface to increase wear in leading edges and for Invar tool repair. The reduced grain size
leads to increased hardness and strength by the inverse relationship to the square root of the
grain size. Other methods are in development to apply monodisperse metallic coating to
composites for weight reduction, improved surface finish, alternatives to environmentally
unacceptable coatings, and greater design freedom.
In the nano-scale composites, hybridization of nanoparticles offers the potential of a rich
soup in which some additives e.g. CNTs, are added for mechanical and electrical properties,
some, e.g. POSS (Polyhedral Oligomeric Silsesquioxane) or nanoclay can be added for flame
resistance, and others, e.g. nano gold particles, can be added for color.
As we become more fluent in the use of new materials and less prejudiced in the use of
older materials hybridization will become a natural trend for those who want it all.
3. Alternatives to Carbon Fibers and Next Generation Carbon
Fibers
Alternatives to Carbon Fibers With the growth of applications of composites using the high
specific strength and stiffness of carbon fibers, comes also the growing demand for those
fibers in many sectors of industry: aerospace, energy, transportation, infrastructure, medical,
sports equipment, etc. There is also the issue of galvanic corrosion in some applications
where carbon forms one of the three elements of a circuit with metals like aluminum, and
water. As a result there is a growing interest in non-carbon fibers, many of which have been
looked at in the past, but now being considered with a hungrier eye, if some of their
shortcomings can be overcome without sacrificing their benefits, especially in tensile
strength.
One example is liquid crystal polymers (LCP). Celanese developed a thermotropic
polyester-polyarylate LCP in the mid 1970’s and commercialized the Vectra family of resins
in 1985. Vectran® is an example of an LCP fiber. The molecules of the liquid crystal
polymer are rigid and position themselves into randomly oriented domains. The polymer
exhibits anisotropic behavior in the melt state, leading to the term thus the term “liquid crystal
polymer.” The molten polymer is extruded through spinneret holes and the molecules align
parallel to each other along the fiber axis. The highly oriented fiber structure results in high
tensile properties.
Vectran differs from other high-performance non-carbon fibers, aramid and ultra-high
molecular weight polyethylene (UHMWPE), in that is thermotropic, melt-spun, and melts at a
high temperature. Aramid fiber is lyotropic, solvent-spun and does not melt at high
temperature. UHMWPE fiber is gelspun and melts at a relatively low temperature. In all
these fibers the high modulus/high tensile strength is achieved through the oriented linear
molecules called microfibrils. And all these fibers have an order of magnitude lower
compression strength than tensile strength.
In general, organic fibers, such as aramid fiber (e.g. Kevlar®), ultra high molecular
weight polyethylene (UHMWPE) fiber (e.g. Spectra®), and Poly(p-phenylene-2,6benzobisoxazole)
(PBO) fiber (e.g. Zylon®), have excellent mechanical and physical
properties. Kevlar® provides excellent impact resistance and is one of the lightest structural