CHANGES IN THE PROPERTIES OF HDPE FIBERS UPON RADIATION GRAFTING WITHACRYLIC-ACID

The morphology and the physical and mechanical properties of graft-mod ified polyethylene fibers have been studied. Two types of fibers, with the diameters of 10 mu m (1.1 dtex) and 40 mu m (7.5 dtex), were modi fied by radiation-induced grafting with acrylic acid. The extent of gr afting was determined gravimetrically. Confirmation of gravimetrically obtained values was achieved using conductometric titration. The fibe rs were hydrated at pH 2 and pH 7. The degree of swelling was 120% at pH 2 and 200% at pH 7. The transversal distribution of polyacrylic aci d in the fibers was determined. Fibers were stained and observed with an optical microscope. The diffusion of the monomer into the bulk was found to be rather fast. The changes in the total crystalline content and the lamellar thickness distributions in consequence of irradiation and grafting were determined by differential scanning calorimetry ana lysis. The measurements showed no effects of irradiation on the crysta llinity in either type of fiber, whereas a decreasing crystallinity ca used by grafting was noticed in the 40 pm fibers. The lamellar thickne ss distributions narrowed upon irradiation, indicating recrystallizati on as a result of chain scission. Wide angle x-ray scattering and Rama n analysis of dry and hydrated fibers were conducted to study the beha vior of the fibers in an aqueous environment. These results both showe d a decreasing crystalline content caused by fiber hydration. Tensile tests were carried out to evaluate how grafting, hydration and Ca2+-cr osslinking of grafts affected the fiber strength. Grafting and Ca2+-cr osslinking, as well as hydration, resulted in a decreasing E-modulus f or the 40 mu m fibers, whereas no significant change could be noticed in the 10 pm fibers. (C) 1995 John Wiley and Sons, Inc.