Thermoplastic foam extrusion extrudate

C.D Han, Analysis of the Performance of a Cooling Extruder in Thermoplastic Foam Extrusion, Conference Proceedings, 45 SPE ANTEC (1987)... 

Extrusion is the principal process for producing film and sheet. It is also used to create open (weather stripping) and closed (soda straws) profiles. Dual extruders can be used to produce laminates, a process called coextrusion. This is often done to provide barriers to ultraviolet light or moisture vapor. Two colors can also be extruded side-by-side for interesting effects. All thermoplastics can, theoretically, be extruded including foamed and reinforced materials. However, in practice, the highest melt temperature thermoplastic extruded in any volume is polycarbonate. Thermosets can also be extruded on a limited basis as they require special equipment and are slow to process. 

The main use of thermoplastic starch alone is in foam applications. Starch-based foams have been found to be an effective alternative to PS foam in loose-fill protective packaging. Starch-based foams offer the advantage that they are readily biodegradable if they escape into the environment. They also offer superior antistatic properties. Starch-based foam, however, has some disadvantages it is brittle and the density is higher than PS. Foamed, starch-based articles are prepared by heating starch in an extruder in the presence of water with subsequent extrusion. 

The combination of starch with a water soluble polymer such as PVOH and/or polyalkylene glycols has been widely considered since 1970 [157]. Recently, the system, thermoplastic starch/PVOH has been studied mainly for producing starch-based loose fillers as a substitute for expanded PS [158-164], As an example, Lacourse and Altieri developed a technology based on hydroxy propylated high amylose starch containing small amounts of PVOH for improving foam resiliency and density [158-162]. In this case loose fill was produced directly by a twin-screw extruder. Recently more advanced processes and alloys have been developed which have resulted in foams with lower foam densities (8-6 kg/m ) and better performance [165-167]. Other applications of modified starch/PVOH can be in the sector of sheet extrusion/thermoforming. 

A review is presented of developments by Berstorff in machinery for the processing of thermoplastic elastomers, including co-rotating twin-screw extruders for continuous compounding and extrusion and coextrasion lines for the production of solid and foamed profiles. Reference is also made to the development by Berstorff and Advanced Elastomer Systems of a process for the extrusion of foamed profiles using water as blowing agent. 

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