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Assessment of New

High-Performance Fibers for Advanced Applications

Doetze J. Sikkema, Maurits G. Northolt, and Behnam Pourdeyhimi Abstract High-performance fibers, used in fabric applications ranging from bulletproof vests to trampolines, must have a sufficient number of chemical and physical bonds for transferring the stress along the fiber. To limit their deformation, the fibers should possess high stiffness and strength. Stiffness is brought about by the degree to which the chemical bonds are aligned along the fiber axis. In fiber-reinforced composites, the fibers are the load-bearing element in the structure, and they must adhere well to the matrix material. An ideal reinforcing fiber must have high tensile and compressive moduli, high tensile and compressive strength, high damage tolerance, low specific weight, good adhesion to the matrix materials, and good temperature resistance. This article reviews and compares the properties and behavior of novel high-performance fiber materials including polyethylene, aramid, polybenzobisoxazole, M5, and carbon fibers. Keywords: advanced composites, advanced fabrics, aramid fibers, carbon fibers, damage tolerance, M5 fibers (PIPD), polybenzobisoxazole (PBO), polyethylene fibers.

Introduction High-performance fibers, used in fabric applications ranging from bulletproof vests to trampolines, must have a sufficient number of chemical and physical bonds for transferring the stress along the fiber. The fibers should possess high stiffness and strength to limit their deformation. Stiffness is brought about by the degree to which the chemical bonds are aligned along the fiber axis. In fiber-reinforced composites, the fibers are the load-bearing element in the structure, and they must adhere well to the matrix material. An ideal reinforcing fiber must have high tensile and compressive moduli, high tensile and compressive strength, high damage tolerance, low specific weight (grams per square meter), good adhesion to the matrix material, and good temperature resistance. Fibers of significance with these properties include polyethylene, aramid, polybenzobisoxazole (PBO), M5, and carbon fibers. Since about 1970, spinning highperformance fibers from self-organized, MRS BULLETIN/AUGUST 2003

liquid-crystal phases has been pursued intensely. The para-aramids (Kevlar, Twaron, Technora) are the best known examples. After coagulation, the para-aramid molecules are arranged in hydrogen-bonded sheets reminiscent of cellulose I, the workhorse of engineering in living nature that provides strength to trees and that is available in a pure form in cotton and linen. Substantially higher tensile performance than in the para-aramids has been achieved by the manipulation of polymers that show no conformational mobility at all and are composed of rigid-rod structures: an example is PBO fiber, which is now commercially available from Toyobo. Although PBO shows impressive tensile properties, PBO-reinforced composites showed compressive yielding at unsatisfactorily low stress and strain. A few year