Slow release behavior of starch-g-poly(vinyl alcohol) matrix for 2,4,5-trichlorophenoxyacetic acid herbicide

Starch-g-poly(vinyl alcohol) as a new material for encapsulating agrochemical for slow release has been studied. By encapsulating 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) as model herbicide within polyvinyl alcohol-grafted starch matrix, the effects of the graft modification on the matrix behaviors and release rate of the herbicide were evaluated. The polyvinyl alcohol branches attached onto starch enhance the association of the grafted starch macromolecules, which make the matrix show a tightening effect. Therefore, the swellability of the matrix is decreased and the rate of the herbicide released from the matrix in wet environments can be reduced. Increasing the grafting ratio is favorable to the slow release. Moreover, the influences of the mole ratio of sodium hydroxide to acetate, herbicide content, and particle size upon the matrix behaviors and release rate were also investigated. The grafted starch is especially suitable for encapsulating the alkali-sensitive chemicals such as carboxylic-containing herbicides because the cross-linking procedure under alkali condition in encapsulation is avoided.