Swelling behavior of stimuli-responsive cellulose fibers

Abstract

Environmental scanning electron microscopy (ESEM) and dynamic contact angle (DCA) measurements showed to be a powerful combination for investigating the swelling behavior of stimuli-responsive cellulose fibers in various environments. The stimuli-responsive fibers were prepared by ozone-induced graft polymerization of acrylic acid onto regenerated cellulose fibers. Atomic force microscopy (AFM) in the tapping mode showed that a smooth polyacrylic acid layer covered the fiber surfaces. X-ray mapping of sodium atoms by EPMA/EDS (electron probe micro analyzer/energy dispersive spectrometer) analysis showed that NaOH-treated grafted polyacrylic acid was evenly distributed, not only at the surface but also in the cross-section of the fiber. By using ESEM, it was possible to vary the humidity around the fibers in a controlled manner and to study a controlled fiber swelling at high magnification. It was observed that the fiber swelling was dependent on the degree of crosslinking of the cellulose-supported hydrogel. Dynamic contact angle measurements using the Wilhelmy plate technique proved to be another technique for studying the swelling behavior of the grafted single fibers. A pH-sensitive swelling, with a perimeter increase from 122 μm at pH 2 to 228 μm at pH 5, was established for the acrylic acid-grafted rayon fibers.