Preparation of bright yellow color sodium alginate solution.

Sodium alginate (SA) is a marine polysaccharide biomass material that is environmentally friendly and exhibits color-changing properties under certain conditions. In this study, we have discovered sodium alginate solution to be chromogenic under four conditions, namely alkali-chromogenic, thermo-chromogenic, force-chromogenic and photo-chromogenic. Under simple strong alkaline conditions, sodium alginate forms clusters of blue light-absorbing chromogenic aggregates, which exhibit a bright yellow color at a certain size. Under different temperature conditions, SA shows varying shades of yellow, and the color tends to stabilize after 48 h of resting. The aggregates can be dispersed by stirring, which changes SA from yellow to colorless. The yellow color can then be recovered after resting. Additionally, exposure to sunlight can cause the yellow SA to fade, but the color can be restored by reheating. Therefore, the force-chromogenic and photo-chromogenic properties are reversible. This makes it a promising material for use in color-developing and indicating materials. It is expected to become a sodium alginate cluster pigment with broad application prospects in the future.