Properties of poly lactic acid/cellulose nanofibre/graphene oxide/thymol nanocomposite insecticide repellent film

Abstract

Inefficient delivery of pesticides by conventional methods such as fumigation and direct application can cause adverse effects to the environment and organism. These issues can be avoided by polymer modification as a pesticide carrier with the ability to regulate the release of pesticides. Nanomaterials such as graphene oxide (GO) and cellulose nanofibre (CNF) have unique properties that can be incorporated into polylactic acid (PLA) based packaging to reinforce its mechanical and physical properties. A novel combination of both nanomaterials’ functional properties can also be manipulated to regulate the release of pesticides so that the release of pesticides can be controlled as desired. GO and CNF from oil palm empty fruit bunch fibre was obtained via modified Hummer’s method and hydrolysis method, respectively. The solution casting method was used in film preparation. The CNF, GO, and thymol loading in making hybrid nanocomposite was selected using response surface method. and conventional method. As a result, the loading of CNF and thymol was fixed to 0.5 phr and 5 phr respectively, whereas the GO loading was varied from 0-1.5 phr. The formed films were analysed based on their physical properties (tensile test and water vapour transmission rate), morphology (field emission scanning electron microscopy), and chemical properties (Fourier transform infrared (FTIR)). The release of active compound, thymol from the film was analysed for 9 days. In vivo study of insect repellency was done using rice as food simulant, and rice weevils (Sitophilus oryzea) as a test subject to determine the effectiveness of the nanocomposite film in protecting food and repelling insects. Results obtained show that the addition of both CNF and GO in a polymeric system synergistically improved the mechanical, physical, and release properties of the film. PLA incorporated with 5 phr of thymol, and 0.5 phr of CNF designated as PLA/5Thy/0.5CNF film showed the highest tensile strength up to 39.71 MPa after 1.00 phr of GO was added. The incorporation of 0.5 phr of GO in PLA/5Thy/0.5CNF film gave the highest elongation percentage of 40.8 %. Chemical characterisation by FTIR demonstrated that thymol interaction in the matrix was influenced by CNF and GO loading, which affects the thymol release behaviour. Cross-section morphology of nanocomposite film demonstrated a unique matrix arrangement with the addition of GO, affecting the mechanical properties and thymol release of the film. In vivo test on packaging towards rice weevils showed an increment in the repellency effect as well as the mortality rate of the rice weevils. Moreover, unsuccessful or no penetration of insects with minimal scratch was observed on the packaging incorporated with GO. In conclusion, the combination of CNF and GO enhanced the mechanical and physical properties of PLA based film. Interestingly, thymol release can also be modulated by varying the loading of CNF and GO. The formed synergy allows the insect repellent packaging to be specifically designed in order to suit the intended purposes.