SWELLING BEHAVIOR OF STIMULI-RESPONSIVE CELLULOSE FIBERS

Environmental scanning electron microscopy (ESEM) and dynamic contact angle (DCA) measurements showed to be a powerful combination for inves tigating the swelling behavior of stimuli-responsive cellulose fibers in various environments. The stimuli-responsive fibers were prepared b y ozone-induced graft polymerization of acrylic acid onto regenerated cellulose fibers. Atomic force microscopy (AFM) in the tapping mode sh owed that a smooth polyacrylic acid layer covered the fiber surfaces. X-ray mapping of sodium atoms by EPMA/EDS (electron probe micro analyz er/energy dispersive spectrometer) analysis showed that NaOH-treated g rafted polyacrylic acid was evenly distributed, not only at the surfac e but also in the cross-section of the fiber. By using ESEM, it was po ssible to vary the humidity around the fibers in a controlled manner a nd to study a controlled fiber swelling at high magnification. It was observed that the fiber swelling was dependent on the degree of crossl inking of the cellulose-supported hydrogel. Dynamic contact angle meas urements using the Wilhelmy plate technique proved to be another techn ique for studying the swelling behavior of the grafted single fibers. A pH-sensitive swelling, with a perimeter increase from 122 mu m at pH 2 to 228 mu m at pH 5, was established for the acrylic acid-grafted r ayon fibers. (C) 1998 published by Elsevier Science Ltd. All rights re served.