Constructing sustained-release herbicide formulations based on poly-3-hydroxybutyrate and natural materials as a degradable matrix

Abstract

Slow-release formulations of three herbicides (metribuzin, tribenuron-methyl, and fenoxaprop-P-ethyl) were constructed as granules and pellets, with the active ingredients loaded into the matrix of biodegradable polymer poly(3-hydroxybutyrate) blended with the natural fillers (clay, wood flour, or peat). Differences in the structure and physicochemical properties of the formulations were studied as dependent on the type of the matrix; herbicide release and accumulation in soil were associated with the solubility of the herbicide. IR spectroscopy showed that no chemical bonds were formed between the components in the experimental formulations. The study conducted in laboratory soil microecosystems demonstrated that degradation of the formulations in soil was chiefly influenced by the shape of the specimens (granules or pellets) while the effect of the type of the filler was insignificant. The use of the granules enabled more rapid accumulation of the herbicides in soil: their peak concentrations were reached after three weeks of incubation while the concentrations of the herbicides released from the pellets were the highest after 5 to 7 weeks. Loading of the herbicides into the polymer matrix composed of the slowly degraded P(3HB) and natural materials enabled both sustained function of the formulations in soil (lasting between one and a half and three or more months) and stable activity of the otherwise rapidly inactivated herbicides such as tribenuron-methyl and fenoxaprop-P-ethyl.