Polycarbonate pellets

For more thorough flash removal, moderately abrasive material is added to the tmnhhng method described previously. This media deflashing allows both internal and extemsd flash to be removed. The parts to be deflashed are loaded into a sealed container (Fig. 9.16). Once the tumbling starts, an abrasive media material (ground walnuts, hard nylon, polycarbonate pellets, etc.) is directed at the parts vmder air pressing and at hi velocity. Modem deflashers recycle the blast media and use dust collectors to minimize air pollution. 

Methods for isolation of the product polycarbonate remain trade secrets. Feasible methods for polymer isolation include antisolvent precipitation, removal of solvent in boiling water, spray drying, and melt devolatization using a wiped film evaporator. Regardless of the technique, the polymer must be isolated dry, to avoid hydrolysis, and essentially be devoid of methylene chloride. Most polycarbonate is extmded, at which point stabiUzers and colors may be added, and sold as pellets. 

Poly(ethylene carbonate). Like polyesters, polycarbonates (qv) are bioabsorbable only if the hydrolyzable linkages are accessible to enzymes and/or water molecules. Thus pellets of poly(ethylene carbonate), ( OCOOCH2CH2 )n weighing 200 mg implanted ia the peritoneal cavity of rats,... 

Liquid colors are compatible with a wide variety of polymers, including PVC, polyethylene vinyl acetate (EVA), nylons, PET, polycarbonate, alloys, high-temperature polymers, and the full range of polyolefins and styrenics. Many liquid colors are suitable to color food-contact polymers and comply with all government regulations worldwide for shipping, use, and disposal. Lead times for liquid color are typically less than those for pellet or other melted color concentrates, since the processing is quick and efficient. 

Optimal Amounts of Reagents. The functional purity of [ I]PA and the optimal amounts of beads and tracer to use for routine assay of fluid-phase (PA reactive) IgG are determined from the binding curves shown in Fig. 1. Increasing amounts of beads (0.1 ml 5-200 /ag of beads corresponding to 15-600 ng of rabbit IgG) are incubated for 60 min at 30° with [125IJPA (0.1 ml). The beads are washed with two 3-ml portions of buffer by centrifugation at 1500 g (4°) for 5 min or by filtration on polycarbonate filters, and the radioactivity in the bead pellets is determined. In this ex-... 

The production of the most common polycarbonate resin pellets ( 1.93) involves the reaction of bisphenoi A (BPA) (polycarbonate grade 0.86, epoxy grade 0.82, and phosgene 0.55) [106]. The reaction is carried out in a convenient solvent such as methylene chloride, and this process offers an excellent illustration of phase-transfer catalysis [85,94],... 

Cell lysate is transferred to polycarbonate ultracentrifuge tubes and tared using membrane buffer. Ultracentrifugation is performed at 40,000 Xg and 4 °C for 30 min to pellet the membranes. 

Polycarbonate (PC) is a clear, colorless polymer used extensively for engineering and optical applications. It is available commercially in both pellet and sheet form. Outstanding properties include impact strength and scratch resistance. The most serious deficiencies are poor weatherability and chemical resistance. Some typical properties are Glass Transition Temperature, Tg = 145° C Melting... 

For more thorough flash removal, the tumbling action may be augmented by a blast of moderately abrasive material, or media, either an organic type (such as ground walnut shells or apricot pits) or a polymeric type (such as small pellets of nylon or polycarbonate) directed against the tumbling parts. 

In most materials, small amoimts of moisture will cause a change in the polymer s melt viscosity which, in turn, will affect the way it processes. When polymers, such as polycarbonate and polyester, are heated above the melt temperature, small amounts of moisture in the pellets or on the surface will cause a chemical reaction. This reaction can degrade the polymer, changing its molecular weight, melt viscosity, and mechanical strength. Larger amounts of moisture may result in a rough and scaly surface finish and even bubbles and voids in the product. 

Moisture can accumulate on the surface of any plastic material, and some polymers actually absorb moisture into the pellet itself. Materials that absorb moisture—usually engineering-grade materials like nylon or polycarbonate—are called hygroscopic. Those that do not have the same attraction or affinity for moisture, and do not absorb it, are called nonhygroscopic polymers. They include commodity polymers such as polyolefins. 

Processing aides are available in many forms including low-viscosity liquid, powders, and pellets. They are used at a level of 0.1-2 percent by weight of the resin. Processing aids are often used with polyvinyl chloride, nylon, polycarbonate, and polyethylene terephthalate resins. 

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