Controlled release materials, agricultural

One particular example of controlled release is sustained release. In this form the desired material is continuously released over a period of time at a constant rate. Two timely publications (3)(4) cover the general area of controlled release, which can also include the controlled release of agricultural materials and biological materials, far example, pheromones. In using the term microencapsulation in this article, the author intends to refer to capsules in the size range of 1 micron to 1000 microns. Capsules below 1 micron in size are frequently referred to as nanocapsules and they are made by one or more very specialized methods (5). The term capsule refers to macro objects in the order of 1 millimeter or larger. This term of capsule is frequently used in the delivery of pharmaceuticals. 

The indiscriminate use of such agricultural chemicals as pesticides, herbicides, and fertilizers is an important source of environmental pollution. A novel application of polymer-bound materials has been made in the controlled release of agricultural chemicals (Allan et al., 1973 Beasley and Collins, 1970 Shambu et al., 1976 Schacht et al., 1977, 1978 reviews of Neogi and Allan, 1974 Scher, 1977). When these chemicals are covalently bound to a polymer from which they can be slowly released into the environment, they not only check pollution but their duration of action is prolonged. The same effect can be obtained by encapsulation of the chemicals in polymeric beads from which they can be released slowly, e.g., 2,4-dichlorophenoxyacetic acid and 4-amino-3,5,6-trichloropicolinic acid have been used in polymer-bound form. 

Degradable materials also offer new perspectives in agriculture (e.g., the controlled release of fertilisers, insecticides and herbicides)... 

Polyesters are also used in controlled-release forms of drugs and agricultural products such as fertilizers and herbicides. By coating the active material with a polyester selected so as to degrade over time, the material is released gradually rather than all at once. 

The Proceedings of the International Symposium on the Controlled Release of Bioactive Materials published annually since 1973 (Controlled Release Society, Deerplain, 111.), and the Volumes on Pesticide Formulations and Application Systems (eg, Vol. 13, ASTM STP 1183,1993 American Society for Testing and Materials, Philadelphia, Pa.) are useful sources, as are some issues of the following journals Journal of Controlled Release Journal of Microencapsulation Journal of Agricultural and Food Chemistry Chemosphere and Pest Management Science. 

Materials such as metal, plastic, wood, paper, and leather are coated with pofymers primarily for protection and for the improvement of their properties. For this purpose, cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) are the most important classical and solvent-based cellulose esters of the coating industry [44]. Cellulose esters are widely used in composites and laminates as binder, filler, and laminate %ers. In combination with natural fibres, they can be used to some extent as composites from sustainable raw materials with good biodegradability. An additional domain of cellulose esters is their use in controlled-release systems, as well as membranes and other separation media [44, 47]. In the field of controlled-release systems, eellulose esters are used as enteric coatings, hydro-phobic matrices, and semipermeable membranes for appheations in pharmacy, agriculture, and cosmetics. 

The field of organic chemistry has seen the most extensive use of polymeric materials as aids in effecting chemical transformation and product isolations. Polymers have been used in other, related areas of chemistry. Applications have been made in analytical chemistry (pH indicators and electrode modifiers), pharmaceutical and agricultural chemistry (controlled-release drugs, pesticides, herbicides, and fertilizers), and biochemistry (enzyme immobilization and affinity chromatography). Applications of polymers to solid-phase enzymo- and radioim-mune assays (Landon, 1977 Chard, 1978) will not be discussed since they are mainly analytical in scope. 

More recently Veith [25] has completed a thesis on silicas as potential flavor delivery materials. She chose to prepare emulsions of model aroma compounds in water and then allow silica to form a matrix around the flavoring droplets. The ability to control silica structure allowed her to study the relationship between silica structure and performance. The concept of forming silica particles around flavorings is novel. She is in the process of publishing her results in the Journal of Agricultural and Food Chemistry and the Journal of Controlled Release. 

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