DIFFUSION OF 3 ETHOXYLATED OCTYLPHENOLS ACROSS ISOLATED PLANT CUTICLES

The diffusion of three polydisperse [H-3]ethoxylated octylphenols (5, 10 and 16 EO) through isolated plant cuticles was studied using diffus ion half-cells and droplet application. The diffusion half-cells were used to determine the influence of ethylene oxide (EO) content and of surfactant concentration on the diffusion of the surfactants across th e cuticle at a relatively constant concentration gradient. The influen ce of EO content, of temperature and of surrounding relative humidity on diffusion of the surfactants across the cuticle was determined with droplet application. Measurements in diffusion half-cells showed that flux was lowest for OP16 in comparison to OP5 and OP10. Diffusion coe fficients were 0.92, 3.17 and 2.18 x 10(-12) cm2 s-1 for OP5, OP10 and OP16 respectively in pepper fruit cuticles. Flux of OP10 across peppe r fruit cuticles increased with surfactant concentration in the donor cell (from 5 to 40 g litre-1), the diffusion coefficient of OP10 in th e cuticle rising from 3.79 to 21.3 x 10(-12) cm2 S-1. Surfactant penet ration through pepper fruit and rubber-plant leaf cuticles was initial ly very rapid after droplet application, decreasing gradually after 24 h. Flux of OP16 across cuticles of both species was lower than for th e other two octylphenols. Penetration of OP10 and OP16 through pepper fruit cuticles was greater at low (40%) than at high (95%) relative hu midity. Transfer of OP10 increased considerably as temperature increas ed from 5-degrees-C to 30-degrees-C. The value obtained for the diffus ion activation energy was - 70.3 kJ mol-1. The experimental results ar e discussed in the light of the free-volume theory with respect to dif fusion of organic molecules in polymers.