Photoprotective effect of starch/montmorillonite composites on ultraviolet-induced degradation of herbicides

Despite the extensive research about polymer/clay composites and nanocomposites, there have been few investigations devoted to the resistance of these hybrids against ultraviolet radiation. This property is especially of interest for materials based on biodegradable polymers since they could be applied for slow release of light-degradable molecules, such as herbicides. This paper describes the photoprotective effect of starch/montmorillonite composites on the ultraviolet-induced degradation of ametryne, a commercial herbicide. The starch/montmorillonite composites highly loaded with ametryne (50% by weight), and different contents of clay were produced by the starch gelatinization method. The results showed that encapsulation of ametryne by starch/montmorillonite composites is simple and possible to be done as a one-step procedure. It was shown that the main photodegradation mechanism involves herbicide volatilization, which was significantly reduced due to formation of composites with starch and montmorillonite. The composite presented a synergistic photoprotective effect between components. 13C solid-state nuclear magnetic resonance (13C-NMR) and FTIR spectroscopy indicated that the photoprotective effect is based on absorption of ultraviolet radiation by starch/montmorillonite composites, and not due to herbicide interaction with the hybrid structure. The novel composites for controlled or slow delivery of herbicides exhibited a promising efficiency in protecting active inputs against solar light degradation in field.