Anti-ultraviolet, antioxidant and pH-responsive cellulose-based composite film incorporated with alizarin for intelligent packaging applications

The pH-responsive color-changing indicator films are necessary for the intelligent packaging systems. However, casting and evaporation techniques are usually employed to prepare these indicator films, which are time-consuming and energy-wasting, limiting their large-scale production. Hence, a sol-gel transformation approach was proposed to fabricate cellulose/alizarin composite films by using low-cost waste paper cups as cellulose resource in this work. It was found that cellulose/alizarin composite films displayed homogeneous structures due to the extensive hydrogen bonding between cellulose and alizarin, and their properties varied obviously with the content of alizarin, Specially, the cellulose/alizarin composite films showed noticeable color transition with an increasing pH from 1.0 to 13.0, and cellulose/alizarin composite films with low content (＜7.5 %) of alizarin were much more sensitive to pH change. It was also proved that the as-prepared cellulose/alizarin films possessed good mechanical properties, high UV barrier capacity and impressive antioxidant activity. Particularly, the tensile strength of the cellulose/alizarin composite films can reach as high as 31 MPa, while UV-shielding performance and radical scavenging capacity were enhanced significantly with increasing the content of alizarin. Finally, the cellulose/alizarin films were successfully employed to monitor fish freshness as intelligent indicator films. Therefore, UV shielding, antioxidant and pH-responsive cellulose-based composite films incorporated with alizarin were manufactured successfully, which demonstrated great potentials to be used in intelligent packaging fields.