Extruder concentric-screw mixer

Polyolefins LDPE, LLDPE, HDPE, PP Solid concentrates Internal mixers, continuous mixers, multiple-screw extruders... 

Elucidation of degradation kinetics for the reactive extrusion of polypropylene is constrained by the lack of kinetic data at times less than the minimum residence time in the extruder. The objectives of this work were to develop an experimental technique which could provide samples for short reaction times and to further develop a previously published kinetic model. Two experimental methods were examined the classical "ampoule technique" used for polymerization kinetics and a new method based upon reaction in a static mixer attached to a single screw extruder. The "ampoule technique was found to have too many practical limitations. The "static mixer method" also has some difficult aspects but did provide samples at a reaction time of 18.6 s and is potentially capable of supplying samples at lower times with high reproducibility. Kinetic model improvements were implemented to remove an artificial high molecular weight tail which appeared at high initiator concentrations and to reduce step size sensitivity. 

Figure 8.30 Cross-sectional views [53] of the extrudate samples using a conventional screw with segmented tip for the testing of different types of dynamic mixers a) conventional screw with no mixer, b) Twente Mixing Ring, and c) Barr Fluxion ring mixer. The extruder was operated at a screw speed of 80 rpm and a letdown ratio of 220 1 of a white pigmented ABS resin to a black color concentrate...

Carbon-black-filled rubber compounds are usually produced on Banbury-type mixers, while conductive thermoplastics are preferably produced on twin-screw extruders. Unlike other filled compounds or polymer blends it is essential to adhere very precisely to the carbon-black concentration and the production parameters, since a very delicate balancing act is usually required to stay on the tight-rope of optimum composition and avoid falling into the pits of insufficient conductivity, inadequate mechanical properties or sharply increased viscosity. 

The second application of the CRD mixer was in the production of color concentrates (CC) on a single screw compounding extruder. The machine was a two-stage extruder and two CRD mixers were used at the end of the first and second stages. The CC quality was improved to the point that dispersing agents could be eliminated from the compounds run on this extruder. CRD mixers are used in single screw extrud-... 

Generally, the anti-blocks are dry blended with other additives and stabilizers in a carrier resin. The concentration of anti-block may range from 5 to 10% for synthetic silica to 30-50% for DE or talc. The other additives will be in concentrations that yield the proper final additive levels when let down. To achieve the most thorough mixing, the blended materials are then fed into a mixer/compounder which may be batch equipment, such as a Banbury or Henschel or into a twin-screw compounding extruder and melt compounded. The pelletized concentrate will be blended with barefoot pellets and let down to the desired final concentration. 

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