Drawing in high pressure CO2 -: A new route to high performance fibers -: In memory of the late Roger S.!Porter

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra-high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO2 using a custom high-pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post-treatment process. With PET, the technique is not effective at temperatures at or below 130 degreesC. In contrast, the process is highly effective for nylon 6,6 where CO2 drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO2 drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in a second stage, resulting in large increases in tensile modulus and small improvements in tensile strength.