Capsule wall materials

Fig. 35. C-NMR-spectra of aqueous dispersions of poly- -butylcyanoacrylate nanocapsules after 3 h of annealing at different temperatures (a) 50°C, (b) 100°C, (c) 130°C. The ( H)- C crosspolarization spectra (tcp = 1 ms, left column) indicate the loss of the solid capsule wall at higher temperatures (see also Fig. 36). The narrow signals superimposed on the solid-state spectrum of the polymer derive partially from the adsorption of the triglyceride oil and the surfactant to the capsule surface (compare Section 4.4), partially from the residual cp in the liquid phase. The direct excitation spectra (right column) show the liquid and dissolved components with an increasing indication for traces of the n-butylcyanoacrylate monomer which results from depolymerization of the capsule wall material (arrows, see also Fig. 37). ...

Fig. 37. Comparison between enlarged sections of direct excitation spectra of dispersed poly-n-butylcyanoacrylate nanocapsules after 3 h annealing at 130°C (top line) and a solution of n-butylcyanoacrylate in CHCI3 (bottom line). The new signals appearing after the thermal treatment a, b, c, and d may be assigned to traces of the monomer resulting from the depolymerization of the capsule wall material. The shift variation observed for the carbonyl carbon signal (a) may result from an interaction with the solvent. The assignments to the monomer carbons are given in the insert. ...

Phase separation process takes advantage of the phenomenon called polymer- lymer incompatibility. The process utilizes two polymers that are soluble in a common solvent yet do not mix with one another in the solution. The polymers form two separate phases one polymer intended to form the capsnle walls, the other incompatible polymer meant to induce the separation of the two phases, but not meant to be part of the capsule wall material. This process is somewhat related to the complex coacervation process. The phase separation process is considered as the oldest true encapsulation technology first developed by the National Cash Register Company for carbonless copy-paper. Microencapsnlation by coacervation involves the phase separation of one or more hydrocolloids from the initial solntion, and the subseqnent deposition of the newly formed coacervate phase around the active ingredient suspended or mnulsified in the same reaction media. The size of the miCTocapsules formed may be in the range of 10-250 pm. 

A variety of materials can be used as capsule wall materials with miniemulsion polymerization technique. In the conventional anulsion polymerization, diffusion of monomm in the aqueous phase is required, and monomers should have certain solubility in water to be useful in the process. 

Macro-coating is used mainly to stabilise fragrances or transform them from liquid to free-flowing solid powder. Microencapsulation or nanoencapsulation is the process of enclosing a substance inside a miniature capsule. These capsules are referred to as microcapsules or nanocapsules. The substance inside the capsule can be a gas, liquid or solid. The capsule wall can consist of various materials, such a wax, plastic or biopolymers like proteins or polysaccharides. 

Spinning disk. A new method was developed by Professor Robert E. Sparks at Washington University in St. Louis. This method relies upon a spinning disk and the simultaneous motion of core material and wall material exiting from that disk in droplet form (11). The capsules and particles of wall material are collected below the disk. The capsules are separated from the wall particles (chaff) by a sizing operation ... 

The term aqueous phase separation is often more simply described as oil-in-water microencapsulation. The two encapsulation processes described above are examples of this oil-in-water encapsulation. In this process the core material is the oil and it should be immisible in the continuous phase, namely water. A commercial example of aqueous phase separation would be the microencapsulation of an oily flavor such as sour cream with a gelatin wall. These microcapsules would then be dispersed in a dry cake mix. The mechanism of release would be during the moist baking cycle of the cake, moist-heat causing the capsule walls to first swell and then rupture. 

The suspension polymerization process allowed the formation of capsules of l-30 rm consisting of migrin oil as core and polyurea as wall material. The latter was formed by interfacial polycondensation reactions between different diisocyanates and emulsified ethylenediamine [106],... 

The solvents used to dissolve the polymeric materials are chosen according to the polymer and drug solubilities and stabilities, process safety, and economic considerations. Substances can be incorporated within microspheres in the liquid or solid state during manufacture or subsequently by absorption. Fig. 1 shows two types of microspheres Microcapsules, where the entrapped substance is completely surrounded by a distinct capsule wall, and micromatrices, where the entrapped substance is dispersed throughout the microsphere matrix. 

Other microcapsules are produced by surface and in situ polymerization methods or, generally, interfacial reactionsThe capsule walls may be soluble or insoluble and impermeable or permeable, whereby the rate of release of the encapsulated material or the exchange of material through the membrane walls can be adjusted and controlled. Originally, drugs, chemicals, toner materials, pigments, and the like were encapsulated to improve handling and... 

Possibilities of sample losses on the surface of matrices used in solid sampling are of some concern. While such phenomena were not observed in work with urinary volatiles [49] and steroids [50], Lines et al. [51] found some response non-linearity with pesticide samples that appeared to originate from the excessive sample retention on the capsule wall. Silylation of the capsule material visibly improved quantita-... 

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