Two formation mechanisms and renewable antioxidant properties of suspensible chitosan–PPy and chitosan–PPy–BTDA composites

Treatment of chitosan together with pyrrole (Py) by oxidant sodium nitrite (NaNO2) forms unique chitosan–polypyrrole composites suspensible in diluted acetic acid. It was discovered that the reactive species polymerizing Py into polypyrrole (PPy) are the aldehydes, formed in situ during the depolymerization reaction of chitosan with NaNO2. In situ UV–vis and FTIR measurements identify typical porphyrin signals, shedding light to the formation mechanism. To improve the film formation of the composites, the application of additional cross-linking agents such as 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) was investigated. The obtained suspensible chitosan–PPy–BTDA composites showed renewable (by electrochemical means) antioxidant properties comparable in strength to those of natural vitamins.