Expandable Polystyrene (EPS)

Production of EPS micro pellets using the Sulzer process

Compared with the conventional batch suspension polymerization process for EPS, the Sulzer EPS process represents a unique, patented process for the continuous production of expandable polystyrene micro pellets. An important feature of this process is the possibility to recycle impregnated polystyrene pellets/beads.

Process 

• A polystyrene melt is impregnated with a blowing agent, usually a mixture of pentane isomers, at high temperature and pressure. The mixture is then homogenized in an arrangement of SMX and SMX plus static mixers and cooled down in SMR static mixer-coolers to a temperature suitable for further processing. This could be, for example, upgrading with temperature-sensitive additives and underwater pelletization. 
• The temperature and pressure profile over the length of the mixing and cooling unit is optimized for ideal processing conditions with regard to customer-specific materials/specifications. Throughout the entire process, the shear rate is kept at very low levels compared to dynamic mixers. 
• The blowing agent is added by means of high-pressure pumps. Numerous kinds of additives that are required to produce high-quality EPS for the different product applications can be added through side streams, thus enabling the processing of liquid and solid additives, as well as masterbatches. 
• The necessary homogenization for uniform additive distribution within the product is achieved by additional SMX and SMX plus static mixers prior to pelletization. 
• Finally, the homogeneous, additive-loaded melt is extruded through die-holes and cut by a rotating knife in an underwater pelletizer to obtain micro pellets. Depending on customer requirements, there are several particle size classes available, ranging from 0.6 to 2.0 mm. Applying pressure to the water circuit during cutting prevents premature foaming of the particles. 
• After cutting, the EPS particles are rapidly cooled down and conveyed towards a drying unit within the pelletizing water stream. The continuous, centrifugal dryer separates the pellets from the water, which is recycled back to the pelletizer. 
• The dried EPS micro pellets are then conveyed to downstream equipment for coating and packaging, and from there are supplied to EPS converters.

Processing/molding of EPS micro pellets

EPS micro pellets from the Sulzer EPS process can be processed and converted into foamed parts, applying the same routes as for conventionally produced EPS beads. This means that the processing of the EPS micro pellets follows three stages, namely: pre-foaming, ageing, and molding.

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Sulzer EPS process unit for production of 1 400 kg/h EPS micro pellets

Customer benefits of producing EPS using the Sulzer process 

• Continuous process resulting in continuous product quality 
• The raw material is polystyrene (suitable grades of GPPS, HIPS, recycle polystyrene materials) 
• A wide range of additives (also pigments) can be dispersed in the polymer matrix, therefore making EPS with outperforming insulation values available 
• Narrow EPS micro pellet size distribution results in minimized waste production and avoids the need for fractioning of product by sieving 
• Negligible process water consumption and amounts of wastewater produced (contaminated water, slurry or similar) as compared to the classical suspension process 
• Recycling possibility for waste EPS pellets/beads/foam 
• The Sulzer EPS process is economical, compact, and easy to operate 
• Capacities range from pilot to large-scale industrial plants 
• High innovation potential (alternative polymers, blowing agents, additives) to develop your own individual recipes for future applications

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