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

Mass transfer kinetics and diffusion coefficient estimation of bioinsecticide terpene ketones in LDPE films obtained by supercritical CO2‐assisted impregnation

“…The impregnation of the LDPE films has been described and analyzed in a previous paper, as mentioned. Briefly, film samples were impregnated with an equimolar mixture of thymoquinone and R ‐(+)‐pulegone using scCO 2 as solvent under different combinations of four process parameters at two levels, according to a 3/4 fractional factorial experimental design of 12 runs: (A) pressure (10 and 15 MPa); (B) depressurization rate (0.5 and 2 MPa min −1 ); (C) contact time (2 and 4 h); (D) initial ketone concentration in the fluid phase (0.0017 and 0.0025, mole fraction).…”

“…Absorbance spectra were obtained in an infrared imaging microscope (Nicolet iN10 Mx, Thermo Fisher Scientific, Waltham, MA) in transmission mode, with a resolution of 4 cm −1 , in a wavenumber range of 400–4000 cm −1 with 16 scans, at room temperature (24 °C). Based on the analysis of spectra of the pure ketones, original LDPE film, and impregnated film samples, reported in a previous work, characteristic absorbance peaks were identified and their relative absorbance values were quantified after multipoint linear baseline correction. Measurements were performed at five different positions of each film, including points near the edges (upper and lower), and far from the edges (“center”), in order to check the homogeneity of ketones distribution.…”

“…The ratio between the concentration of both ketones in the films was assessed by comparing the relative absorbance values of the characteristic peaks for each compound. For that purpose, a calibration curve was prepared using different ketone mixtures dissolved in paraffin oil (in order to obtain a molecular environment similar to LDPE) with thymoquinone:pulegone mass ratios ranging from 25:75 to 75:25, as reported in a previous work . The total ketone concentration in all the mixtures assayed was constant and equal to 5% (wt/wt), close to the initial concentration of ketones in the impregnated films.…”

“…In a previous work, the authors have studied the scCO 2 ‐assisted impregnation of a commercial semi‐crystalline low density polyethylene (LDPE) film with an equimolar mixture of two natural terpene ketones [ R ‐(+)‐pulegone and thymoquinone]. These ketones have been previously investigated as potential bioinsecticides against the maize weevil, Sitophilus zeamais Motschulsky, a common primary pest of stored grains.…”

“…These parameters were as follows: impregnation pressure (10 and 15 MPa), depressurization rate (0.5 and 2 MPa min −1 ), contact time (2 and 4 h), and initial ketone concentration in the fluid phase (0.0017 and 0.0025, mole fraction). The impregnated material, with total ketone content ranging from 2% to 6% (wt/wt), proved to be effective in creating a lethal fumigant atmosphere against S. zeamais adults in confined environments, suggesting its possible application as delivery device for the protection of grains during storage and/or transport . For example, it could be envisaged as a part of multilayer silo bags in order to avoid the proliferation of weevils into the bag if it is damaged.…”