Polyamide microcapsules

Polyamide, collodion (cellulose nitrate), ethylcellulose, cellulose acetate butyrate or silicone polymers have been used for preparation of permanent microcapsules. This method offers a double specificity due to the presence of both the enzyme and a semipermeable membrane. Moreover, it allows simultaneous immobilization of many enzymes in a single step and the surface area for contacting the substrate and the catalyst is large. The need of high protein concentration and the restriction to low molecular weight substrates are the main limitations of enzyme microencapsulation. 

The behavior of two other formulations, microcapsules and small plastic laminate flakes, containing tetradecenol formate, were compared in applictions to plots of mature corn at Beltsville, in August 1980. (8) The Z-9-tetradecen-1-ol formate (TDF) is a mating disruptant, rather than a true pheromone, of the Heliothis species of moths. It was selected in these experiments because reliable analytical methods were available (9) and its behavior was expected to be similar to that of the actual pheromones, whose chemical structures and properties are also similar. The two formulations were polyurea-polyamide microcapsules 5-microns in diameter supplied by ICI at Bracknell, Berkshire, England, and a small (3 mm side) plastic laminate formulation supplied by the Herculite Corporation of York, PA. The microcapsules were applied at 300 g of TDF per hectare and the flakes at 285 g/h. Both formulations were applied by air to mature corn 240-270 cm in height in clear, hot weather with a daily maximum temperature of 39°C. 

Figure 11.4a,b show the microcapsules as initially formed with Listeria monocytogenes and Staphylococcus aureus attached to the forming polyamide capsule wall. The bacteria, respectively rod and coccoid shaped, were clearly visible on the outside surface of the capsules when labelled with ethidium bromide, as evidenced by confocal optical sections. Variation of the initial bacterial concentration and... 

Mathiowitz [35 0] realizes reservoir-type delivery systems recurring to a photochemical control. Microcapsules, built up by interfacial polymerization of polyamide, also contain azobisisobutyronitrile, a substance that emanates nitrogen due to a photochemical action. Accordingly, after exposition to light, microcapsules internal pressure increases (as a result of nitrogen release) until membrane rupture and consequent contents release. 

Mathiowitz E and Cohen MD. Polyamide microcapsules for controlled release. I. Characterization of the membranes. J. Membr. Sci. 1989 40 1-26. 

Figure 8.32 Process for the preparation of nylon 6.10 microcapsules by interfacial polymerisation the hexamethylenediamine in the aqueous phase reacts with the sebacoyl chloride in the nonpolar phase to form on interfociol polyamide film.

Liver. The liver performs a wide variety of chemical reactions in the body and is the main locus of detoxification. Successful liver transplantation is somewhat rare, and no true artificial liver seems likely in the near future. The process of hemoperfusion, which is sometimes termed an artificial liver, can be used to supplement or relieve the normal liver functions for short time periods. In this technique, the patient s blood is passed through a column or bed of some sorbent material that removes toxic chemicals from the blood. This technique is often used in cases of drug overdose, poisoning, and acute hepatitis. The sorbent material can be charcoal, ion-exchange resins, immobilized hepatic material, or liver material enclosed in artificial cells (microcapsules, usually made from a polyamide). The column is usually a plastic material, and plastic tubing is used to direct the blood flow to and from the device ( 1, 57, M). 

Microcapsules having polyamide or polyester shells are produced by polycondensation of functional chloranhydrides with diamines or glycols, correspondingly. 

The formation of a microcapsule wall through interfacial polycondensation/addition takes place in two steps. First step is the deposit of the oligomer (initial wall) at the oil droplet, and the second step is the wall thickness builds up. As described earlier, the polymerization occurs in oil phase, and the formed initial wall can limit the diffusion of the reactants. This reduces the polymerization rate that has great impact on the surface morphology and thickness of the microcapsule wall. - - Polycondensation by which polyamide, polyester, and polycarbonate microcapsules are prepared can generate acid byproduct during the process therefore, a base is needed to neutralize the acid and drive the reaction to complete. ... 

In order to prepare the microcapsule with expected structure, the chosen polymer wall material should match with the core material. The affinity interaction between the polymer wall and the core material can determine the structure of the microcapsule. Highly cross-linked polyurea and polyurethane can form so-called compact capsules with 2-methylbenzothiazole homogeneously distributed in the polymer matrix, while in the case of polyamide core-shell structure capsules were... 

Aliphatic or aromatic structure, as weU as liner or branched structure of the reactants, can give the microcapsule shell different porosity and permeability, which can greatly inflnence the release performances. Multifunctional reactants can help to achieve more thermal mechanical stable microcapsules since the wall is a three-dimensional cross-linked polymer network. Experiments have shown that dichlorides with less than eight carbon atoms do not prodnce qnahty polyamide microcapsules. The reason behind this is the competition between interfacial condensation and the hydrolysis reaction of dichlorides. More hydrophobic dichlorides can favor the polymerization and slow the hydrolysis. Similarly, for polyurethane and polyurea type microcapsules, polymeric isocy-nates are preferred because they might favor the formation of less permeable miCTocapsnles for the hydrolysis of isocynate groups are limited, which consequently reduced the COj release that contribute to the porosity increase of the polymer wall." ... 

Many efforts have been devoted to the microcapsules with tailored structure and the fabrication methods thereof. Examples like double-shell microcapsule of polyurea/polyurethane show improved thermal mechanical property and ethanol resistance, poly(acrylonitrile-divinylbenzene-styrene)/polyamide two-layer microcapsule was prepared to encapsulate water, and self-bursting microcapsules " may have potential application in agricultural field because of its unique release profile. Additionally, monodispersed microcapsules based on miCTofludic processes like SPG (Shirasu... 

Heinrich, R. Erensch, H. Albrecht, K. Pressure-resistant microcapsules with a polyamide outer shell and an inner composition structured by polyurethane-polyurea and their use. DE 3020781, 1981. 

Persico, P. Carfagna, C. Danicher, L. Frere, Y. Polyamide microcapsules containing jojoba oil prepared by inter-facial polymerization. Journal of Microencapsulation (2005), 22(5), 471-486. 

Zydowicz, N. Chaumont, P. Soto-Portas, M. L. Formation of aqueous core polyamide microcapsules obtained via interfacial polycondensation—Optimization of the membrane formation through pH control. Journal of Membrane Science (2001), 189(1), 41-58. 

Mathiowitz, E. Cohen, M. D. Polyamide microcapsules for controlled release. II. Release characteristics of the microcapsules. Journal of Membrane Science (1989), 40(1), 27—41. 

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