Compounding and Extrusion

The extrusion step is not particularly costly in comparison with the price of the raw materials, but the cost is still significant and impacts on the overall economics of the final material. It is therefore worthwhile to devote effort to optimisation of the extrusion process in terms of increased thronghpnt (productivity) and decreasing energy consumption and machine wear. In the author s opinion, the subject of throughput does not receive the attention it deserves. There are conntless reports of the mechanical properties of thermoplastic composites hut no mention of the extension characteristics of the materials. For a meaningful comparison of different composites, one mnst consider not only their mechanical and aesthetic properties, bnt also the relative economics of extrusion. 

There are two classes of extruder, single-screw and twin-screw. The primary drawback of single-screw extruders is that they give poor dispersion of fillers compared to the 

Machine wear is a concern, partly because it costs money to replace a worn barrel or screw. The main problem though, is the loss of productivity when the machines must be shut down for maintenance. Potentially, wear may lead to significant metal contamination levels with accompanying polymer stability problems. Although machine wear is an issue, it is not a subject that has received much attention. 

There are a few studies that have investigated the effect of filler properties on wear [17, 30]. One simple method is to extrude through a plate of soft metal and measure weight loss from the perforated plate at regular intervals. It was concluded that hard, large irregular particles cause most wear. Surface treatment with a lubricating additive such as stearic acid helps alleviate wear because the additive forms a protective layer around the particles. 

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Blends of poly (ethylene terephthalate) (PETP) and polypropylene (PP) with different rheological properties were dry blended or compounded, and extrusion foamed using both physical blowing and chemical agents, and the foam properties compared with those of foam produced from the individual components in the absence of compatibilisers and rheology modifiers. The foams were characterised by measurement of density, cell size and thermal properties. Low density foam with a fine cell size was obtained by addition of a compatibiliser and a co-agent, and foamed using carbon dioxide. The presence of PP or a polyolefin-based compatibiliser did not effect... 

Such machines are particularly suitable when there is a requirement for compounding as well as extrusion—as with unplasticized PVC. If compounding and extrusion of the formulation can be carried out in series, so that it is not necessary to heat it twice, the quantity of heat stabilizer added can be reduced. For reasons such as this the manufacture of unplasticized PVC pipe has become a typical use for twin-screw units. 

The twin-screw injection molding extruder is an injection molding machine that is capable of both blending/compounding and extrusion in one step. Because it is a one step process, the fibers never go through the entire extrusion process as well as the pelletization that limits the fiber size, but are blended into the molten plastic before injection. The screw part of this machine is based on a non-intermeshing, counterrotating twin-screw extruder (Chapter 5). One of the screws in this machine is capable of axial movement and has a non-return valve on the end. This action enables the screw to inject and mold parts. 

Density (specific gravity) of WPCs does not depend on the particle size of the wood flour. It appears that during compounding and extrusion, cellulose fiber is compressed to the maximum density of 1.3-1.5 g/cm. ... 

Biocides for WPCs should be fairly thermostable, in order to withstand compounding and extrusion temperatures. Table 13.8 shows a thermostability and efficiency of a number of biocides after they were exposed in a mix with molten... 

Emac. [Qievron] Ethylene methyl acrylate copolymm resins for inj. mold-iiig, blown film, compounding, and extrusion ai cs. 

ASTM Dl896-93. Practice for transfer moulding test specimens of thermosetting compounds and extrusion materials, American Society for Testing Materials Publication. Philadelphia. 1993. 

Post-Doc on extrusion of fine ceramic stractnres and project manager for compounding and extrusion of ceramic structnres at EMPA... 

Team leader compounding and extrusion at EMPA Since 2003 Associate lecturer at ETH Zurich Composite Materials (Diploma and Batchelor course). Department of Materials Since 2005 Associate lecturer at ETH Zurich Advanced Composite and... 

The materials that degrade into small stable particles are blends often starches are blended with non-degradable thermoplastics such as PE. The same considerations noted in this section on multiphase polymers hold true for these blends. For instance, the interfacial energy and rheology play a role in the size of the dispersed phases. These blends can often be processed by standard melt forming polymer techniques, by compounding and extrusion into films and fibers and injection or blow molded to form polymer... 

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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