Microspheres expandable

Expandable SAN microspheres are prepared by polymerizing a mixture of styrene and AN with a volatile liquid blowing agent in an encapsulating system. Expandable microspheres of larger size, narrower size distribution and improved expansion characteristics are obtained using an alcohol in the polymerization system, i.e., methanol (7). 

Modified varieties of SAN can be manufactured by grafting, as well as by using varied monomers instead of the basic monomers, i.e., styrene and acrylonitrile. 

SAN can be modified, for example by grafting. For example, maleic anhydride (MA) can be grafted onto SAN. This process occurs preferably in a twin-screw extruder by reactive extrusion. An advantage of reactive extrusion is the absence of solvent as the reaction 

SAN-g-MA is used as compatibilizer in various compositions (11). The reactive functionalized MA groups bound to the polymer can be further allowed to react with reactive stabilizers that are in turn fixed to the polymeric backbone (12). In other words, when the stabilizer is bound to a polymer a better blend obtained when the stabilizer is prevented from migrating out from the polymer. 

A variety of SAN consists in the use of n-methylstyrene instead of ordinary styrene (13). The modified copolymer are produced just in the same way as ordinary SAN copolymers. 

Another approach is to use thermoplastic microspheres encapsulating a gas, in unexpanded or pre-expanded form. When heated (usually at about 100°C), the 

Expanding polyacrylonitrile microspheres, filled with pressurized iso-pentane which expand when the shell softens at moulding temperatures, are offered by Akzo Nobel Casco Products Division, under the Expancel name. New applications include shoe soles and slush-moulded PVCs. 

Fly ash floaters - tiny hollow spheres of ash from the scrubbers of power plants - are used by the US processor Power Composites for mechanical and acoustic properties in a polyurethane mix, for moulding automobile loudspeaker enclosures. They flow easily and uniformly in the mould as part of the polyurethane mixture, giving good additional strength to the enclosure. 

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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). 

J.L. Gamer, Polymerization of styrene acrylonitrile expandable microspheres, US Patent 3 945 956, assigned to The Dow Chemical Company (Midland, MI), March 23,1976. 

Names plastic microspheres, expandable microspheres, PTFE, PE, PI... 

Expanded microspheres 551,461, and 091 expanded hollow particles available in wet (WE) and dry (DE) forms. There also grades of the same type of shell but in different dimensions. The lines differ in particle diameter, density, and solvent resistance... 

Grade composed of poly(vinyhdene chloride) copolymer is less resistant to heat and solvent. Micropearl F-30, F-50, F-80, FlOO - expandable microspheres available in wet and dry forms. These microspheres are marketed for Matsumoto Yushi-Seiyaku, Co., Ltd. Japan... 

Fire resistance is an important property of phenolic resins. The combination of phenolic resin with Expancel expandable microspheres leads to many useful products. Composites for high speed train interiors take advantage of the light weight, excellent fire rating, and very low thermal conductivity. Polyester filled with aluminum hydroxide is an alternative solution for train interior materials. The resin and filler can be easily processed when viscosity regulating additives are added. 

Material containing expandable microspheres. [Data from Peretti, G Pasetto,... 

Expandable microsphere Thermoplastic microspheres are droplets of hquid hydrocarbon encapsulated in a shell of a thermoplastic polymer. When exposed to heat, the shell softens and the hydrocarbon gasifies, and the microsphere expands firom, typically, 12 to 40 pm and the density drops from 1000 to 30-40 kg/m. The microspheres can be used either as a form of blowing agent, or may be supphed in expanded form for use as a lightweight filler. The activating temperature of mold and material is lOOC (212F). 

Uses Blowing agent in printing inks, PU, PVC plastisols, fabrics, paper expanded microspheres as ultra-low density tillers tor use in engineered prods, in which other fillers would not be suitable, e.g., syn. marble and wood, coatings, sealants, explosives, auto, marine fillers, molding compds., composites, paint and crack fillers, cable fillings, elastomers Features Unexpanded microspheres Expancel 551 DE 20 [Expancel]... 

Uses Filler in coatings, sealants, paints, cable fillings Features Wet, expanded microspheres ultra-low dens. 

Table 21.1 The effect of foaming PP with heat expandable microspheres on its thermal...

Table 21.2 Density of five common thermoplastics upon injection molding into 5 mm thick plaques with simultaneous foaming using different heat expandable microspheres.

Thermosets also benefit from the foam structure, as evidenced by improved thermal insulation, sound dampening and mechanical stress absorption responses to temperature changes or impact. Hollow spheres with an already set volume are normally used, that is, pre-expanded microspheres. The reason is that the curing reactions often interfere with any expansion before a sufficient volume increase has been obtained. Hollow organic spheres are found in products such as sealants, adhesives, putties, pipes, cultured marble, body fillers, model-making materials, and pastes [2, 3, 19]. Common suitable matrix materials are epoxies, PUR, and polyesters. 

Jonsson, L. (2005) Expandable microspheres as foaming agents in thermoplastics, diermosets and elastomers. Proceedings of the Advances in Plastics Technology Conference, Inst, for Plastics Processing, November 2005, Katowice, Poland. 

Elfving, K. (2003) New developments with expandable microspheres. Proceedings of the RAPRA Conference, Blowing Agent and Foaming Processes, Munich, Germany. 

Kawaguchi, Y. and Oishi, T. (2004) Synthesis and properties of thermoplastic expandable microspheres the relation between crosslinking density and expandable property. J. Appl. Polym. Sci., 93, 505-512. 

There are also synthetic fillers such as hollow, solid and expandable microspheres made of glass or polymer (several are available in coated or metalled form). 

Bara I, MeUul M. New cosmetic or dermopharmaceutical compositions in the form of aqueous gels modified by the addition of expanded microspheres 1997. Patent US 5593680 A. 

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