Thermoplastic extrusion

Thermoplastic extrusion technology has been used to texturize many defatted vegetable protein ingredients, and produce many fibrous structures and meat-like textures. Such processes have been used extensively to prepare meat analogs (1, which have found their widest application in formulation of foods for institutional markets (3). A primary disclosure of extrusion texturization of vegetable proteins was made by Atkinson ( ). General descriptions of various extrusion processes have also been reported (1, 5-14). ... 

The development of physical methods for texturizing proteins has significantly amplified their use in several conventional and simulated foods. The principal techniques of physical modification which have been thoroughly reviewed are thermoplastic extrusion, fiber spinning and steam texturization (3,4,5). 

In his contribution entitled Thermoplastic extrusion for ceramic bodies , Frank Clemens describes the present state of this relatively young art. 

Typical thermoplastic binders which are found in literature for injection molding of ceramic bodies are, styrene-butadiene, polyethylene, polypropylene, polybutene, ethylene vinyl acetate, polymethylmethacrylate and polyoxymethylene. When selecting one of these binders for thermoplastic extrusion of ceramic bodies, it should be noted that the shrinkage of par-tially-crystalline polymers is higher than for amorphous polymers, and hence warping during cooling is more critical in the former case. This is, however, not the only criterion for selection price and processability at adequate temperatures are also important factors to consider. 

In the following, different binder systems which have been used for thermoplastic extrusion of ceramic bodies will be discussed [Lenk 97, Weg 98, Hoy 98, Cle 00, Schub 00, Bee 02, Gri 02, Tru 04, Schey 04, Pou 04, Yoo 05, Cle 05]. 

Trunec has described the thermoplastic extrusion of thin-wall tubes made of yttria-stabilized zirconia and gadolinia-doped ceria [Tru 04], These ceramics are used for solid oxide electrolyte applications, e.g. solid oxide fuel cells. The thermoplastic binder system used consists of ethylene-vinyl acetate copolymer, parafHn wax and stearic acid. With this system tubes with an outer diameter of 10.5 mm and wall thicknesses of 290 and 280 pm could be fabricated. 

Generally for the thermoplastic extrusion of ceramic bodies, a binder which melts or softens at higher temperature is used. Figure 3 shows the processing steps for the extrusion of ceramic bodies when using thermo-... 

Fig. 3 Process schematic for thermoplastic extrusion of ceramic bodies at EMPA. Depending on the process requirements in other applications of thermoplastic extrusion, the high shear mixer and single-screw extruder shown here can be replaced with pieces of equipment which have other operating principles, but perform the same function.

Perusal of the published literature on the topic of extrusion shows that a wide variety of thermoplastic binder systems have been used for the fabrication of fiber, hollow fiber, tube, sheet and honeycomb structures made of ceramic materials. Generally speaking, for thermoplastic extrusion to be successful, it is necessary that the binder system used consists of a major and a minor binder component, a plasticizer and a surfactant to ensure a good wetting of the ceramic powder. 

Tru04] Trunec M (2004) Fabrication of zirconia- and ceria-based thin wall tubes by thermoplastic extrusion. J Eur Ceram Soc vol 24 No 4 pp 645-651... 

Heiber J, Clemens F, Graule T, Hulsenberg D (2004) Fabrication of Si02 glass Fibers by Thermoplastic Extrusion. J Glass Science and Technology vol 77 No 5 pp 211-216... 

Heiber, J. Clemens, F. Graule, T. Hiilsenberg, D., Thermoplastic extrusion to highly-loaded thin green fibres containing Pb(Zr,Ti)03 , Advanced Engineering Materials 7 [5] 2005,404-408... 

Polymethyl methacrylate themioplastic, barrier vinyl topcoats Polymethyl methacrylate thermoplastic, coatings Nucrel Resins Polymethylmethacrylate thermoplastic, extrusion coatings Eastar Bio Copolyester 14766 thermoplastic, extrusion coatings food... 

Polyetheretherketone thermoplastic, engineering power tools Polyphenylene ether thermoplastic, engineering profiles Polyphenylene ether thermoplastic, engineering sheet Polyphenylene ether thermoplastic, extrusion Acetal copolymer... 

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