Additives to Improve Performance of Alginate Fibers

Abstract

In view of the relatively low mechanical properties of alginate fibers, efforts have been made to improve the tensile properties and stability by adding various additives and also by cross-linking. In one such attempt, cellulose nanocrystals (CNC) were isolated and used as fillers to improve the properties of alginate fibers with the expectation that cellulose and alginate would have good compatibility and that the negatively charged sulfate groups on cellulose crystals would have electrostatic interaction with the Ca2+ ions in the coagulation bath [10Ure]. Various levels of the nanocrystals (0–10 %) were added into the fibers, and the fibers were extruded at different jet-stretch ratios. It was found that increasing the level of CNC in the fibers decreased, whereas increasing the jet stretch increased the strength and elongation. The tenacity (0.1–0.22 g/den) of the fibers was very low even with the addition of CNC and extrusion at the highest jet speed possible [10Ure]. However, the fibers had about 38 % increase in tenacity and 123 % increase in modulus due to the addition of the filler and optimization of jet speed [10Ure]. Further investigation on the arrangements of the CNC in the alginate fibers showed that the degree or orientation decreased with increasing load of CNC. The interaction of the nanoparticles with the polymer introduced twists opposite to the direction of drawing, and at high concentrations, the crystallites oriented themselves in a spiral manner in the alginate matrix, similar to the arrangement of fibrils in native cellulose [11Ure]. Such spiral arrangement decreased the strength and modulus of the fibers. However, it was reported that fibers with improved toughness could be obtained by controlling the processing conditions without sacrificing the strength of the fibers [11Ure]. Table 31.1 presents some of the properties of the fibers at two different jet-stretch ratios and different levels of nanoparticle loading.