Strand pelletization

Pellets produced by each system have characteristics shapes. Pellets created with strand pelletization are typically short cylinders with well defined edges since they were cut when in the solid state. Underwater pelletization yields pellets that are more rounded. 

Why does the shape of compounded pellets differ between those created by underwater versus strand pelletization systems ... 

The reactively modified stream is then transformed into pellets, either by underwater or strand pelletizers. The pellets are again dried and shipped to plastic product fabricators, who need such specially modified macromolecular structures to fulfill product property... 

As shown in Fig. 14.20, the discharged product cools and hardens on a cooling belt and is cut in a strand pelletizer. Alternatively, it can be cut directly at the nozzle by a head pelletizer and cooled in a vibrating screen. 

Downstream equipment generally involves a vacuum pump, for devolatilization, and pelletizing hardware. Strand pelletizers are located at the end of a water trough, while hot-face pelletizers cut the extrudate immediately upon die exit. When direct extrusion... 

Description Liquid LC is continuously polymerized in a polymerization unit (one- or two-stage) (1) in the presence of water, stabilizer and modifying additives at elevated temperatures. The polymerization process has proven to be very reliable, easy to operate and economical. Prepolymerization is available to reduce reactor volume for large capacity units. The polycaproamide chips are formed from the melt using strand pelletizing systems and are conveyed to the extraction column (2). 

Recently we have eliminated the resuspension of the double-stranded pellet altogether. Just count the total radioactivity in 2 or 3 of the 100 il aliquots and use the average value as the total amount of radioactivity present in each tube. The % single-stranded is then calculated by dividing the radioactivity in each ss vial by the total radioactivity present in each vial. 

For polymer pellets strand pelletizer is versatile but capacity is limited by the strand handling capacity. Usually < 200 strands per machine. Water ring pelletizer not for water sensitive polymers or high melt flow polymers and tend to produce nonspherical pellets. Underwater pelletizer good for PE and PP produces spherical pellets not for nylon, PET or melts that solidify rapidly. 

As reported by Karian (1), a series of GFRP composites were compounded via a twin-screw extruder. Various levels of chopped short glass fibers were fed downstream via a side feeder. The melt extrudate was quenched in a water bath and strand pelletized. The compounded pellets were molded into ASTM tensile bars. The tensile bar specimens were used to measure tensile strength at 5 mm/ min crosshead speed. Small 5- to 20-mg samples were taken from the center cut of the molded tensile bars for DSC measurement of heat capacity versus temperature. 

Dekker [3] studied the effect of various flight geometries on solids conveying performance. He proposed that many extrusion instabilities might be due to internal deformation of the solid bed. Internal deformation is more likely to occur when the internal coefficient of friction of the polymer particles is low. Spherical particles tend to have a lower internal coefficient of friction than non-spherical (e.g. cylindrical) particles and are, therefore, more susceptible to internal solid bed deformation. This may explain the often observed difference in extrusion behavior between strand pelletized and die-face pelletized material. 

Some pelletizers cut extruded strands cooled in a water bath these are called strand pelletizers. Dicers cut extruded sheet rather than strands. The pellets from a dicer have a uniform cubic or octahedral shape. Other pelletizers cut the material right at the die exit these are called die face pelletizers. These cutting systems can be dry die face pelletizers, water ring pelletizers, and imder water pelletizers. 

In injection molding and extrusion, use of strand pellet PES resin is certainly justified from a practical and economical point of view. The strand-cut pellet PES, strand extruded on single or twin-screw extruder using processing conditions listed in Table 7, were satisfactory in appearance and internal structure. 

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