Light Weight Hybrid Composites Made from Carbon and Glass Fabrics with High Modulus Polypropylene Fiber
Brian Morin
Innegrity LLC
President
Greenville, SC
Lecture was presented at Techtextil North America Symposium 2008
Rising fuel prices have driven the use of carbon fiber in composite materials to expand dramatically over the last several years, and this is expected only to accelerate with the advent of the Boeing 787. Even with glass reinforced composites, there is a drive to lower weight through the use of innovative constructions and core materials. What is clear is that lowering weight is important to everything that is moved by fossil fuels.
High modulus polypropylene (HMPP) fibers made through a melt extrusion process are light weight and tough. These fibers have a highly elongated polymer conformation as exhibited in wide- and small- angle x-ray scattering experiments. The fibers have a tenacity which ranges from 8 to 12 g/d, and a modulus in excess of 200 g/d. The fibers have a surface structure reminiscent of bamboo, with rings running perpendicular to the fibers, and also voids that run parallel to the fiber direction. Such surface structure enhances mechanical adhesion.
Because of the extraordinarily low density and high modulus, HMPP fibers can be used with carbon, aramid and glass fibers in a sandwich core structure to reduce the weight and increase the toughness of the composites. As an example, when an 8 layer carbon composite has the four middle layers replaced with HMPP, the specific modulus is increased by 20%, while the use of carbon is reduced and the cost of the structure is reduced dramatically. Since there is no core material, the shear strength and compressive strength and modulus remain high.
Hybrid composites allow an achievement of composite properties that is better than either component material, while also giving the opportunity to reduce costs. Applications include marine, electrical, and aerospace structures.
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