Aging Studies and Stabilization of PBO Fiber - Polymer Science and ...

Katherine BestJoined group in December 2006B.S. Materials Science and Engineering, Rensselaer Polytechnic Institute, 2006M.S. Polymer Science and Engineering, University of Massachusetts, 2007Contact: kbest@mail.pse.umass.eduAging Studies and Stabilization of PBO FiberI am currently studying the kinetics of the hydrolytic degradation of poly-p-phenylenebenzobisoxazole (PBO) fibers. PBO is part of a class of high performance fibers known for theirhigh strength to weight ratios. PBO has been commercialized by Toyobo under the trade nameZylon and has found applications in ballistic protection, sporting equipment and space. One ofthe main challenges in using this fiber is that it undergoes photoactive and hydrolytic degradationthereby losing a significant amount of its tensile strength. In order to quantify the kinetics of thehydrolytic degradation, fibers are being weathered at a variety of temperature and relativehumidity conditions. Fibers are periodically removed and their degradation is monitoredmechanically using single fiber tensile tests. Other characterization techniques including X-Rayscattering and FT-IR are employed to help monitor degradation and identify whether a chemicaland/or physical process occurring.6.56.0RT 60-65% RH50C 60-65% RH71C 60-65% RH71C 100% RH110C 60-65% RHTensile Strength (GPa)5.55.04.54.03.53.00 5 10 15 20 25 30 35 40 45 50 55 60Time (days)This type of study should help when making lifetime predictions for fiber performance as well asbetter understanding the nature of hydrolytic degradation of PBO.Another part of this project involves washing experiments aimed at stabilization orextending the useful lifetime of PBO fiber. The fiber is processed using a poly phosphoric acid,so there is inherently some residual acid trapped within microvoids in the fiber. This acid isknown to be a catalyst for hydrolytic degradation of the fiber so anything that can be done toreduce the amount of residual acid should in theory extend fiber lifetime. With this in mind weare running a series of washing experiments in super critical CO 2 with selected polar co-solvents.Supercritical CO 2 is chosen because it is a useful processing aid since it has both the diffusivityof a gas and solubility similar to a liquid. Polar co-solvents are added to increase interactions

etween the acid trapped in the fiber and the solvent. The hydrolytic degradation of treated fiberswill then be monitored for changes in rate or behavior.Improving the Fracture Toughness of Optical Grade PC LensesMy second project is aimed at enhancing the fracture toughness of an optical gradepolycarbonate system in order to prevent slow crack growth. Epoxy has been chosen as theprimary toughening agent and three strategies are being employed to reach this goal:1. Epoxy/PC interpenetrating network2. Cross-linking and chain extending PC3. PC nanocomposite with reactive POSS particlesThe first strategy involves using a difunctional epoxide which can be cross-linked with severaldifferent amine curing agents to form a highly branched network within the PC. The secondstrategy involves using a multifunctional epoxide both to cross-link and chain extend the PCchains. A catalyst has been chosen which promotes the reaction of the epoxide with the chainend groups of PC. Currently work is being done to find the composition of this system whichoptimizes the toughness of the material. The third strategy relies on a similar concept of crosslinkingand chain extending the PC via POSS particles which have been functionalized withepoxide groups. The POSS particles have been found to aggregate within the PC creating ananocomposite-like structure. This however, significantly decreases the transparency of the PC.