Encapsulation and pH-responsive release of an optical brightener (CBUS) from chitosan microcontainers for optical bleaching of cellulosic fabrics

Encapsulation of an industrially used optical brightener, namely disodium 4,4'-bis[(4-anilino-6-morpholino-1,3,5-triazin-2-yl)amino]-stilbene-2,2'-disulfonate (CBUS), with a biodegradable natural chitosan biopolymer is studied. CBUS-loaded chitosan microcontainers were produced by the simple coacervation/precipitation method. Their morphologies in dry state were investigated by scanning electron microscopy. Controlled release of CBUS from the microcontainers in response to pH was monitored by using ultraviolet-visible (UV-Vis) and fluorescence spectrophotometry in water, with almost 100 % of the encapsulated CBUS being released within the first 90 min at pH 2. Fluorescent microscopy measurements indicated that such encapsulation of CBUS with natural chitosan biopolymer is an effective way to protect and improve light stability. The increase in both whiteness and total color change at pH 2 for the cellulosic fabric demonstrates the great potential of CBUS-loaded chitosan microcontainers as smart pH-responsive whitening agents for optical bleaching of cellulosic fabrics.