Coating of polyamide fibers with polyelectrolyte multilayer thin films to improve wash fastness

Abstract

Polyelectrolyte multilayer thin films (PEM) were coated on polyamide fibers, namely nylon and silk fibers, using the Layer-by-Layer technique and characterized using the spectrophotometry technique. PEM built from poly (diallyldimethylammonium chloride) (PDADMAC) and Scarlet acid dye were coated on nylon fibers and the parameters controlling the growth of the PEM were found to be: deposition time, salt concentration, polyelectrolyte concentration, and dye concentration. The deposition of the PEM was complete and constant even with deposition time as short as 15 seconds. The growth of the PEM increased with increasing salt concentration and polyelectrolyte concentration up to 0.5 M and 1 mM, respectively. Beyond either of these concentrations, the deposition of the PEM films decreased. Although PDADMAC concentration above 1mM lead to a decrease in film thickness, increasing dye concentration had a different effect and lead to a constant increase even with concentration as high as 50 mM. Regarding the acid dye loading and release behavior on silk, it was found that the main parameters influencing its loading were exhaustion time, salt concentration, and pH condition of dye bath. On the other hand, the spinning rate of the fibers in the solution shown to have no effect on the dye loading. The results also indicated that the rate of dye release depended mainly on the immersion time at constant temperature and on the pH of the soaping solution. When the pH of the soaping solution was increased, the amount of dye release was also increased. In the last part of the work, PEM were coated on dyed silk to improve the wash fastness of the fibers. The efficiency of the dye release protection was investigated by coating PEM built from PDADMAC with poly (4-styrenesulfonic acid-co-maleic acid) (PSS-co-MA) and PDADMAC with poly (sodium 4-styrene sulfonate) (PSS) at pH 4.5 and pH 3, respectively. It was found that increasing thickness of the PDADMAC/PSS-co-MA PEM did not improve the efficiency of dye release protection. Contrarily, increasing thickness of the PEM assembled from PDADMAC and PSS resulted in a better dye release protection especially when the top layer was PSS. In that case the dye release was found to be about 47 percents less than conventional uncoated dyed silk (no PEM).