Review article

Advanced processes of expandable polystyrene production

Zvonimir JANOVIĆ ; University of Zagreb, Faculty of Chemical Engineering and Technology, Zagreb
Karla SARIĆ ; University of Zagreb, Faculty of Chemical Engineering and Technology, Zagreb
Ante JUKIĆ ; University of Zagreb, Faculty of Chemical Engineering and Technology, Zagreb
Stanislav JURJAŠEVIĆ ; Society for Plastics and Rubber Engineers

Abstract

A number of processes have been developed to prepare polystyrene foams and the two most important are extrusion and the preparation of expandable beads. In the former process, the blowing agent is mixed into the molten polymer in an extruder under pressure, vaporising as the pressure decreases, causing the
polymer to expand. However, the most applied process is by far the modified route of styrene suspension polymerization, incorporating the blowing agent, some low volatile hydrocarbons, mostly pentane isomers, in polystyrene beads. Recently, some advanced suspension processes have been developed. Their achievement is a narrow polymer particle size distribution and using bifunctional peroxy initiators to obtain a higher rate of polymerization and molecular mass and also its narrow distribution, in comparison with classical monofunctional initiators. The undesirable emissions of hydrocarbons as blowing agent and its high flammability stimulated the development of new processes, particularly using water as the blowing agent. Water is trapped inside the polystyrene matrix through introduction of hydrophilic polystyrene part via the use of effective emulsifiers, modified starch and cellulosic esters, or mostly by copolymerization reaction of styrene with sodium styrenesulphonate, vinyl pyrolidone, (met)acrylic acid, maleic anhydride, and other hydrophilic monomers during the suspension polymerization. However, the most promising area is the preparation of polymer-clay nano-composite foams. The presence of nanoclay
like montmorilonite in the mixture with an emulsifier, apart from leading to higher water content in the beads will also enhance cell nucleation, reduce flammability and increase the mechanical properties of the foam. Brominated cyclic compounds are still the major flame retardants for polystyrene foam such as hexabromocyclododecane, tetrabromoethylcyclohexane and brominated cyclic
allyl ethers. Addition of small amounts of organic peroxides results in obtaining the synergistic effect.

Keywords

expanded polystyrene; expanded polystyrene of low flammability; expandable polystyrene; blowing agents; water expanding; suspension polymerization

Hrčak ID:

25526

URI

https://hrcak.srce.hr/25526

Publication date:

18.7.2008.

Article data in other languages: croatian

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