Beads production

Mechanical Properties and Structural Performance. As a result of the manufacturing process, some cellular plastics have an elongated cell shape and thus exhibit anisotropy in mechanical, thermal, and expansion properties (35,36). Efforts are underway to develop manufacturing techniques that reduce such anisotropy and its effects. In general, higher strengths occur for the paraHel-to-rise direction than in the perpendicular-to-rise orientation. Properties of these materials show variabiUty due to specimen form and position in the bulk material and to uncertainty in the axes with respect to direction of foam rise. Expanded and molded bead products exhibit Httie anisotropy. 

Suspension Polymerization. At very low levels of stabilizer, eg, 0.1 wt %, the polymer does not form a creamy dispersion that stays indefinitely suspended in the aqueous phase but forms small beads that setde and may be easily separated by filtration (qv) (69). This suspension or pearl polymerization process has been used to prepare polymers for adhesive and coating appHcations and for conversion to poly(vinyl alcohol). Products in bead form are available from several commercial suppHers of PVAc resins. Suspension polymerizations are carried out with monomer-soluble initiators predominantly, with low levels of stabilizers. Suspension copolymerization processes for the production of vinyl acetate—ethylene bead products have been described and the properties of the copolymers determined (70). Continuous tubular polymerization of vinyl acetate in suspension (71,72) yields stable dispersions of beads with narrow particle size distributions at high yields. 

Two-phase suspension systems produce beaded products with broader particle-size distribution (e.g., 1-50 /rm). The microspherical particles usually need to be classified repeatedly to reduce the particle-size distribution in order to improve the resolution and efficiency in the separation for use in chromatography. The actual classification process depends on the size range involved, the nature of the beaded product, and its intended applications. Relatively large (>50 /rm) and mechanically stable particles can be sieved easily in the dry state, whereas small particles are processed more conveniently in the wet state. For very fine particles (<20 /rm), classification is accomplished by wet sedimentation, countflow setting, countflow centrifugation, or air classification. 

A. When developing a dissolution method, the design qualification is built into the apparatus selection process. The dosage form and delivery system process will dictate at least initially the equipment of choice. For example, the first choice for a beaded product may be United States Pharmacopeia (USP) Apparatus 3, which is designed to confine the beads in a screened-in cylinder. 

We have now started to discuss the equipment in the USP Drug Release General Chapter ( < 724 >). The reciprocating cylinder, as shown in Figure 11, has special utility for beaded products along with the capability of changing medium by... 

In a survey of industry practices, Heda (12) found that, as a matter of policy, 46% of the firms sampled favor direct filling of powders as a first choice over granulation prior to filling capsules. Thirty-six percent of firms allow formu-lators to make that decision at their own discretion, whereas 18% of firms favor granulation of all formulations prior to encapsulation. Yet, for half of the firms responding, only 0 10% of their hard shell capsule products are direct-fill powder formulations, and only 27% of firms reported that more than 50% of their capsules were developed as direct-fill formulations. Although some of these non-direct-fill formulations may be controlled release formulations, e.g., barrier-coated bead products, difficult powder formulation problems may, at least in part, account for this observation. 

A commercial controlled release, polymer coated spheroid/bead product (Slophyllin, Rona) was used as received. The spheroids were microtomed to expose a cross-sectional area of the inner drugladen core and the surrounding polymer film coating, and subsequently mounted on the sample holder using conductive silver paint with the microtomed surface uppermost. 

When considering the suitability of a bead production technique for imprinting, it is essential to evaluate the compatibility of the conditions used for polymerisation with those required for complex formation between functional monomers and templates. Where covalent imprinting methods are used, the covalent adducts are often highly stable and need quite harsh conditions to disrupt them. Such adducts could be used in most of the procedures described below with reasonable expectation of success. The same can be said for many metal-chelate complexes, which have stabilities approaching covalently bonded structures. The use of cyclic boronate esters is an exception. This adduct is unstable in water and hence cannot be combined efficiently with aqueous suspension polymerisation. 

Overall, the dispersion polymerisation approach might offer an effective solution to bead production in many situations if the precise balance of solvent composition, imprinting recipe and synthetic conditions can be appropriately matched to produce particles with the desired size, morphology, porosity and binding characteristics. 

Gel-form ("microporous") beads are the supports which have most commonly been used for larger-scale investigations of polymer-supported catalysts. Uniformity of bead production can be achieved by the inclusion of a water-soluble surfactant to stabilize the emulsion of organic monomers in an aqueous reaction medium. 

Figure 11.14 Glass-bead production device in the German PAMELA II process. (Courtesy of...

P. Wehrl, G. F. Palmieri, and A. Stamm, The Taguchi s performance statistic to optimize theophylline beads production in a high speed granulator, Dmg Dev. Ind. Pharm., 20, 2823-2843 (1994). 

For practical purposes, styrene—DVB copolymers have commonly been obtained by the suspension polymerization method,[53, 54] which is well known to consist of heating and agitating a solution of initiator in monomers with an excess of water containing a stabilizer of the oil-in-water emulsion. Polymerization proceeds in suspended monomer droplets and, in this way, a beaded copolymer is obtained. While looking very simple, this procedure can provide many complications that significantly change the properties of the beaded product as compared to the properties of materials prepared by bulk copolymerization. AU parameters of the suspension copolymerization have to be strictly controlled, since even small deviations from optimal conditions of the synthesis can serve as an additional source of heterogeneity in the copolymer beads. [55]... 

U. Pruesse, L. Bilancetti, M. Bucko, B. Bugarski, J. Bukowski, P. Gemeiner, D. Lewinska et al. Comparison of different technologies for alginate beads production. Chemical Papers, 62(4) 364-374, August 2008. 

Reciprocating cylinder USP 3 Reciprocating pH changes are easy Easy to automate Carryover and incomplete drainage between rows Usually only applicable to nondisintegrating dosage forms Delayed/extended release products Bead products... 

Cellulose beads are spherical particles with diameters in the micrometer to millimeter scale, which are used in chromatography, solid-supported synthesis, protein immobilization, drug release, and so forth. In principle, bead production can be simplified into two procedures dropping and dispersion. Gericke has reported a method of preparing beads by dropping... 

High viscosity of the polyolefin melt is necessary, especially in foaming equipment to produce sheets, tubes and shapes in batch and in continuous processes. On the contrary, polyolefin bead production is not so sensitive to melt viscosity. 

TVEX are macroporous styreue/diviuylbenzene copolymers containing a metal selective extractant that has been added directly to the mixture of the monomers during the bead polymerization process. The amount of extractant and degree of cross-linking in the final bead product may be varied at will. The conditions of polymerization can be varied, thus compensating for any differences in the properties of the individual extractants. Generally, by this method optimum conditions can... 

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