Polyester Microspheres

Expandable VDC copolymer microspheres are prepared by a microsuspension process (191). The expanded microspheres are used in reinforced polyesters, blocking multipair cable, and in composites for furniture, marble, and marine appHcations (192—195). Vinylidene chloride copolymer microspheres are also used in printing inks and paper manufacture (196). 

Since unsaturated polyester resins alone would have insufficient strength for structural application, reinforcements are used to enhance the physical strength of such resins. Typically, tensile strength, impact strength and stiffness are the physical properties of most interest. Reinforcements can be regular particulates, as in glass microspheres, irregular particulates, as in flakes, or fibers. 

Syntactic foamed plastics (from the Greek ovvxa C, to put together) or spheroplastics are a special kind of gas filled polymeric material. They consist of a polymer matrix, called the binder, and a filler of hollow spherical particles, called microspheres, microcapsules, or microballoons, distributed within the binder. Expoxy and phenolic resins, polyesters, silicones, polyurethanes, and several other polymers and oligomers are used as binders, while the fillers have been made of glass, carbon, metal, ceramics, polymers, and resins. The foamed plastic is formed by the microcapsular method, i.e. the gas-filled particles are inserted into the polymer binder1,2). 

Spray methods for obtaining microspheres have a number of disadvantages. High temperatures and bulky and complicated equipment are needed moreover they pose fire and explosion hazards. Low temperature methods, such as using emulsified thermoplast solutions, saturated polyester resins in liquid heat carriers, or suspension polymerization, are preferable1,3S). 

Telegina et al. 72> showed that the activation energy for the viscous flow of a polyester oligomer filled with glass microspheres is 46.9 kJ/mol, while that of an epoxy oligomer is 78.3 kJ/mol. They also established the important fact that the addition of microspheres to an oligomer composition does not change the temperature viscosity coefficient. This means that the viscosity of a mixture with microspheres can be controlled, if the temperature dependence of the viscosity of the binder is known. 

Unsaturated polyester syntactic foams are cheaper than epoxy foams, although the latter are stronger, more water resistant, and shrink less if cured at room or high temperatures 83,136). One merit of polyester syntactic foams is the low apparent density that can be obtained. But the mechanical characteristics depend upon the apparent density e.g. for the Soviet polyester syntactic foams (SPB), using phenolic microspheres (BV-01)1 ... 

Many papers have shown that the water absorption of a syntactic foam is proportional to that of its binder. Polyester syntactic foams, for example, absorb more water, even with dressing additives (silanes, vide infra) than do epoxy syntactic foams (Fig. 11)1. The hydrolytic stability of epoxy foams is increased when the glass microspheres are replaced by carbon ones (Table 19)40). 

The methods used to increase the water resistance of a glass microsphere foam are basically those applied to glass-reinforced plastics, filled thermoplasts, and elastomers, viz. hydrophobic adhesion compounds are added to binder and microsphere dressing 147). The compounds added are alkyl alkoxysilane derivatives, amino or epoxy alkoxysilanes for epoxy and phenolic resins, vinyl or methacryloxy alkoxysilanes for polyester resins. The dressing agents used are aminoethoxysilanes (y-aminopropyl-... 

Fig. 18. Variation of the dielectric constant e with binder concentration C for polyester syntactic foams with PVC microspheres Original polyester dielectric constants (1) 2.0, (2) 2.2, (3) 2.4, and (4) 2.6 521...

For many years syntactic foams have been used in construction, in sandwich structures, or as imitation wood or marble 22,57 180). Many types of these materials are applied in the boat-building industry 17 66). For example, recently PVDC microspheres with polyester binder were used to produce the decks of a 10 m sail-boat, with a weight reduction of 100 kg (from 250 to 150 kg)46). 

SMC based on hollow microspheres and polyester resin are being used in the manufacture of food containers for replacing aluminum containers46. ... 

Arshady, R. Preparation of biodegradable microspheres and microcapsules 2. Polylactides and related polyesters. J. Contr. Rel. 17 1—22, 1991. 

A nine-component composition has been tested in developing a new composite material. Three components were the binder of the composite material polyester EPX-279-1, polyester EPX-187-3 and styrene. These materials have been used as fillers ash, marble powder, glass microspheres, saran microspheres, wollastonite and powder made by grinding shells. Component properties with variation range of their proportions are given in Table 3.58. 

The present paper reports on a study which was conducted to investigate the effect of NaOH on the in vitro release profiles of microspheres prepared with polylactides (2) Since these polyesters degrade by hydrolysis (4), it is possible that the molecular weight of the polymers can be decreased by the alkaline pH of the sodium oleate emulsifier solution (pH 10) during fabrication. This in turn could affect the release kinetics of the microspheres. 

Another contribution to drug release was indicated in a previous paper (5) which reported on the hydrolysis of polyesters catalyzed by encapsulated amine drug such as thioridazine. The microsphere batches prepared for this investigation have identical drug loadings. Therefore, any contribution due to the amine drug should be equal for all the samples being compared. 

Al-Azzam W, Pastrana EA, King B et al (2005) Effect of the covalent modification of horseradish peroxidase with poly(ethylene glycol) on the activity and stability upon encapsulation in polyester microspheres. J Pharm Sci 94 1808-1819... 

A mixture of microspheres and the plastic can be formulated into a moldable mass that can then be shaped or pressed into cavities and molds much as molding sand and clay. The properties of the finished hardened or cured mass can then be tailored by a suitable plastic formulation. A mixture of TS polyester plastic and small hollow glass spheres, for example, can create synthetic wood. 

Shao, P. G., and Bailey, L. C. (2000), Porcine insulin biodegradable polyester microspheres Stability and in vitro release characteristics, Pharm. Dev. Technol., 5,1-9. 

Polyurethane [117] and polyester [118] particles have also been prepared by the dispersion polyaddition of ethylene glycol (EG) and toluene diisocyanate (TDI) in paraffin, and the polycondensation of acid and ester at a high polymerization temperature, respectively. Table 3 provides an overview of microspheres of monomers other than vinyl monomers obtained by dispersion polymerization. 

Tetanus toxoid (the vaccine for tetanus) encapsulated in polyester microspheres was produced for single-injection immunization. The entrapment efficiency of the protein vaccine was significantly improved by coencapsulation with excipients such as trehalose and y-hydroxypropyl cyclodextrin. However, these excipients did not impart stabilizing effect on tetanus toxoid. In contrast, bovine serum albumin was foimd to be the most prominent stabilizer for protein in the body after administration by injection. 

In topical formulations, particularly cosmetics, it is used for its softening and conditioning effect on the skin. Lactic acid may also be used in the production of biodegradable polymers and microspheres, such as poly(D-lactic acid), used in drug delivery systems.See also Aliphatic Polyesters. 

The materials employed for making hollow microspheres include inorganic materials such as glass and silica, and polymeric materials such as epoxy resin, unsaturated polyester resin, silicone resin, phenolics, polyvinyl alcohol, polyvinyl chloride, polyjM-opylene and polystyrene, among others, commercial jx oducts available are glass, silica, phenolics, epoxy resin, silicones, etc. Table 36 shows low-density hollow spheres. Table 37 shows physical properties of glass microspheres, and Table 38 shows comparison of some fillers on the physical properties of resulting foams (10). 

The matrix is considered to be the binder for the microspheres. Typical matrix materials include (a) thermosetting resins such as epoxy resins, unsaturated polyesters, vinyl esters, phenolics, polyurethanes, and silicones (b) thermoplastic resins such as polyethylene, polystyrene, polyvinyl chloride (c) asphalt and (d) gypsiun and cement. 

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