Development of High Performance Polymer Fibers Using Subcritical and Supercritical CO2

Abstract : Enhancements in ballistic protective wear for soldiers rely heavily on the development of lightweight materials with increased moduli and strength. It is well established that an armors ballistic limit can be increased significantly by using materials with increased moduli and strength. The development of high performance fibers from flexible chain polymers has been a subject of intense interest over the past 30 years. However, to date the mechanical properties of commercial fibers are far below their theoretical values. This is due in large part to our inability to process the materials to achieve highly crystalline structures from highly extended chain conformations. In this STIR research program the feasibility of using subcritical and supercritical 002 in the processing of fibers with superior mechanical properties was investigated. The synergistic effects of 002 as both a pressurizing medium as well as a reversible plasticizer was shown to dramatically improve the mechanical stiffness and strength of both nylon6,6 and ultrahigh molecular weight polyethylene. In the case of Nylon6,6 fibers a greater than 30% increase in stiffness along with a 20% increase in strength was realized. Similarly, post treatment on UHMWPE fibers (Dyneema) showed an increase in modulus of greater than 50% of the commercial fibers. In both cases, the 002 treatment primarily increased the overall degree of crystallinity compared to air drawn fibers. It should be noted that, although the research has strong fundamental interests, it provides an environmentally benign approach to process fibers with superior mechanical properties. Once additional studies are conducted to isolate optimum process ranges, scale-up should be relatively quick since the polymeric materials and process equipment are all commercially available.