Effects of surface photocrosslinking on the properties of semi-refined carrageenan film

Abstract The surface of semi-refined carrageenan (SRC) film samples were photocrosslinked with UV light using a solution of sodium benzoate as a photosensitizer. The surfaces were coated with a 6% (w/v) solution of the photosensitizer and exposed to the light source for 5, 10, 20 and 40 min. The effects of the surface crosslinking on the overall properties of the SRC films were investigated and related to the possible changes in the morphology of the substrate. The UV exposure and subsequent crosslinking were found to cause little color change in the films and increased the crystallinity as well as the thermal stability of the films. The mechanical properties were improved relative to the control sample with a ca. 36–55% range increase in the tensile strength observed, ca. 140–144% increase in the modulus but with a concomitant ca. 50–52% decrease in the elongation at break. The crosslinking decreased the inherent water content in the films by ca. 48–55% and decreased the water vapor transmission rate by ca. 10–21% relative to the control. The water sensitivity of the films, however, increased by ca. 18–44% and 9–23% for the water solubility and water uptake respectively, with decreases of ca. 18–22% in water contact angle. These changes were attributed to possible photodegradation products and the presence of residual photosensitizer that rendered the samples more hydrophilic. Under the conditions of the experiments, a UV exposure time of ca. 20 min was found to be optimal in enhancing the mechanical and water barrier properties. The results suggest photocrosslinking provides a promising step towards the production of a low-cost food packaging material from SRC raw materials.