A comparison of selected physico-chemical properties of calcium alginate fibers produced using two different types of sodium alginate.

Sodium alginate is a non-toxic natural polysaccharide found in marine brown algae. It is able to form solid gels by the action of poly-valent cations (commonly calcium but not magnesium) which cross-link the polysaccharide chains at the guluronic acid groups. Alginate-based products are popular in many industries, including food production and in pharmaceutical and biomedical applications. It is utilized in manufacture of wound-care products due to its biocompatibility and gel forming capabilities upon the absorption of wound exudate. Considering the potential influence of the alginate composition on the properties of the resultant fibers, two sodium alginate powders were selected based on their contrasting compositions. The GHB alginate was high in guluronic acid whereas the LKX alginate was high in mannuronic acid. The sodium alginate solutions (4% w/w) were extruded into a calcium chloride (3% w/v) bath to produce calcium alginate fibers. The fibers were dried at 22 °C and 32% relative humidity for 72 h. Selected properties of the blank (unloaded) fibers were analysed: diameter measurements by optical microscopy, mechanical strength using a universal testing machine, morphology by scanning electron microscopy, and calcium content by inductively coupled plasma atomic emission spectroscopy. One of the key aims of this work was to evaluate the variability of these properties along moderately large lengths of fiber and to determine the difference (if any) between replicate lengths of fibers. This study showed that the alginate type influenced selected properties of the resultant fibers. The mean diameter and calcium content of the GHB fibers were 232 µm and 2.79µmoles/mg respectively, whereas the LKX fibers were about 10% thicker and had 2.58µmoles/mg calcium ion content. The fibers of each alginate could be distinguished visually based on gross differences as well as differences in their microstructure. Mechanical testing of the fibers produced stress-strain plots displaying largely non-elastic behaviour. There was no statistically significant (p < 0.05) difference between the Young's modulus or the strain at break for the two types of fibers, namely about 5-5.6 GPa and 0.123-0.131 respectively. All the measured properties were found to be consistent along the nine sampling positions along the lengths of fibers and were reproducible between the different batches of fibers.