Photochromic paper from wood pulp modification via layer-by-layer assembly of pulp fiber/chitosan/spiropyran.

Cellulosic fiber introducing with photochromic properties can be used in many fields such as security packaging, printing paper, and rewritable paper. To introduce photochromic property to individual fiber, a polyelectrolyte composite layer composed of cationic chitosan (CS) and anionic carboxyl-containing spiropyran (SPCOOH) on pulp fibers was designed using layer-by-layer assembly technique. Scanning electron microscope observation showed that the SPCOOH was successfully absorbed onto the surface of fiber. The photochromic characteristic of LbL-treated fiber could be triggered by UV-vis absorption spectrum and the LbL-treated fibers had a good compatibility with pulp fibers. This study gives a highly effective method to impart the photochromic characteristic to paper.