Processing, thermoplastics twin - screw extrusion

Continuous processing of filled elastomers by twin-screw extrusion and achievement of viable mixing distribution characteristics present formidable challenges. A thermoplastic elastomer, HyTemp, is plasticised with DOA and filled with ammonium perchlorate powder and additives. It is found that the extruder geometry, the order of ingredient addition and die pressmisation have profoimd effects on the mixing distribution characteristics of the elastomer-based extraded profiles. The mixing distribution characteristics are quantitatively determined by X-ray diffraction techniques. 16 refs. 

Extrusion is a cost effective manufacturing process. Extrusion is popularly used in large scale production of food, plastics and composite materials. Most widely used thermoplastics are processed by extrusion method. Many biopolymers and their composite materials with petroleum-based polymers can also be extruded. These include pectin/starch/poly(vinyl alcohol) (Fishman et al. 2004), poly(lactic acid)/sugar beet pulp (Liu et al. 2005c), and starch/poly(hydroxyl ester ether) (Otey et al. 1980), etc. In this study, composite films of pectin, soybean flour protein and an edible synthetic hydrocolloid, poly(ethylene oxide), were extruded using a twin-screw extruder, palletized and then processed into films by compression molding process or blown film extrusion. The films were analyzed for mechanical and structural properties, as well as antimicrobial activity. 

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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