Controlled release of 2-heptanone using starch gel and polycaprolactone matrices and polymeric films†

Varroa jacobsoni is a parasitic mite that is threatening the honeybee industry in many parts of the world. 2-Heptanone, a natural product made by honeybees at low concentrations, is effective at elevated concentrations in controlling mite populations in honeybee colonies, especially when released over a 42 day period. An extrusion process was used to encapsulate 14, 18, and 25% 2-heptanone in a polycaprolactone (PCL) matrix. Less than 18% of the 2-heptanone was encapsulated in the PCL matrix. The high vapor permeability of PCL to 2-heptanone resulted in a high flux rate and limited the usefulness of PCL as an encapsulation matrix for controlled-release devices. A starch gel containing three times its weight in 2-heptanone was prepared from starch-based microcellular foam (MCF). The gel had compressive, tensile, and flexural strength values in the range of 0.56 to 1.9 MPa. 2-Heptanone quickly evaporated from non-laminated gels. However, when the gel was laminated with different polymeric films, a wide range of flux rates was obtained. The T50 for gels laminated or coated with poly(vinyl alcohol) (PVAL, 99% hydrolyzed) and ethylene-vinyl alcohol copolymer (EVAL) was 72 and 1030 days, respectively. The most promising film was a starch/glycerol film that released 50% of the 2-heptanone (T50) in approximately 13 days. Copyright © 2007 John Wiley & Sons, Ltd.