Urea-formaldehyde Matrix Research Articles

Starch urea‐formaldehyde matrix encapsulation. IV. Influence of solubility and physical state of encapsulant on rate and mechanism of release

AbstractThe influence of the physical state and solubility of the encapsulant on the rate and mechanism of release and swelling of the cross‐linked starch‐urea formaldehyde (St‐UF) matrix has been studied by encapsulating model organic compounds. The release and swelling data have been analyzed in terms of the generalized equation Mt/M∞ = ktn applicable for swellable controlled‐release systems. This matrix system shows and an inverse relationship of release rate with the cross‐link ratio for all the encapsulants studied. The solid encapsulants have n values in the range of 0.22–0.41, indicating a Fickian or anomalous mechanism. Further, the release rate increases with solubility of the encapsulant. The liquid encapsulants have n values in the range of 0.5–1.5, indicating Case II transport mechanism. The release rates for liquid encapsulants are lower by one to three orders of magnitude than those for solid encapsulants and are not influenced by encapsulant solubility. This indicates a polymer chain relaxation‐controlled mechanism of release for liquid encapsulants. © 1993 John Wiley & Sons, Inc.

Starch urea formaldehyde matrix encapsulation of solid agrochemicals. I. Matrix synthesis and characterizations

AbstractA starch urea formaldehyde (starch‐UF) matrix has been studied for application to the encapsulation of a solid insecticide. The pertinent parameters relating to the matrix synthesis have been identified and the influences of these parameters on release of the insecticide from the starch UF matrix have been investigated. The key parameter controlling the rate of release is the urea to starch ratio. It is shown that the release process can be described in terms of the generalized equation Mt/M∞ = ktn where k and n vary with system variables.

Starch urea formaldehyde matrix encapsulation of solid agrochemicals. II. Release mechanism and release modeling

AbstractBased on experimental observation, a mechanism is proposed to describe the release of carbofuran from a starch‐UF matrix. A simple mathematical model is developed to describe the diffusion‐controlled release of a solid insecticide from a porous starch‐UF matrix undergoing both volume and surface erosions. The model is tested with the release data collected for different matrices and with different pH values of the environmental liquid. The comparison between the model predictions and data is found to be reasonably good. The model describes the release process at different pH values by accounting for the influence of pH on the erosion rates.