Structural properties of vegetable oil thermosets: Effect of crosslinkers, modifiers and oxidative aging

Abstract

The present work is focused on the study of the formulation effect of cationically polymerized vegetable oil thermoset on their aging behavior. Toward this aim, tung oil-based biopolymers were prepared using different comonomers or adding a modifier. Specifically, synthetic and natural comonomers (styrene, divinylbenzene and a methyl ester of tung oil) and a modifier (acrylated epoxidized soybean oil) were used to prepare different crosslinked samples with a fixed weight ratio of tung oil/comonomer (or modifier) = 70/30. The chemical aging suffered by the fatty acid segments of the matrix, which is known as autoxidation of unsaturated fatty acids in oils and alkyd resins, was followed by Fourier transformed infrared spectroscopy, dynamic-mechanical analysis, positron annihilation lifetime spectroscopy and thermogravimetric analysis. As a result, values of the glass transition temperature, the storage moduli, tanδ and the free nanohole volumes were obtained. To study the influence of the aging process on the network structures at molecular level, the evolutions of the experimental parameters mentioned were followed for one year at two different aging conditions: room temperature and 50 °C. The chemical changes leading to nanostructural variations in all the studied samples are discussed in terms of the formed networks and the degradative processes during aging.