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 diffusion 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 the cuticle at a relatively constant concentration gradient. The influence 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 coefficients 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 pepper fruit cuticles increased with surfactant concentration in the donor cell (from 5 to 40 g litre-1), the diffusion coefficient of OP10 in the cuticle rising from 3.79 to 21.3 x 10(-12) cm2 S-1. Surfactant penetration through pepper fruit and rubber-plant leaf cuticles was initially very rapid after droplet application, decreasing gradually after 24 h. Flux of OP16 across cuticles of both species was lower than for the other two octylphenols. Penetration of OP10 and OP16 through pepper fruit cuticles was greater at low (40%) than at high (95%) relative humidity. Transfer of OP10 increased considerably as temperature increased from 5-degrees-C to 30-degrees-C. The value obtained for the diffusion activation energy was - 70.3 kJ mol-1. The experimental results are discussed in the light of the free-volume theory with respect to diffusion of organic molecules in polymers.