Supercritical CO2 iof LDPE films with terpene ketones as biopesticides against corn weevil (Sitophilus zeamais)

Abstract

In this work, the supercritical carbon dioxide impregnation of low density polyethylene (LDPE) films with a mixture of two terpenic ketones (thymoquinone and R-(+)-pulegone) with biopesticide activity is investigated, as a strategy for developing a packaging material or delivery device for protecting seeds, kernels and derivatives during storage and transport. Impregnation runs were performed according to a fractional factorial experimental design in order to evaluate the effect of four process variables at two levels (pressure: 10–15 MPa; depressurization rate: 0.5–2.0 MPa/min; time: 2–4 h; initial ketone mole fraction: 0.0017–0.0025) on impregnation yield and selectivity between ketones. Operational temperature was constant for all experiments and equal to 45 °C. The impregnated films were analyzed by infrared spectroscpy (FTIR) in order to confirm the presence of both ketones and determine their relative ratio in the final product. ANOVA test of the results indicate that contact time and ketone concentration are the only factors with significant effects on impregnation yield (ranging between 2.25 and 5.59%), while no factor seems to affect significantly the loading selectivity, with thymoquinone/pulegone ratios in the final product between 0.39 and 0.99. The insecticidal activity of impregnated film samples was evaluated in fumigant assays against corn weevil (Sitophilus zeamais Motschulsky), a major pest of stored kernels. The films showed a high activity level during the first 2 days (∼100% mortality), which gradually decreased until showing no toxicity after 7 days.