Extruding compounds, commercially available

Ground/cracked cast acrylic and PE-based materials are the main purging agents, but others also are commercially available for certain machines and materials. Cast acrylic, which does not melt completely, is suitable for virtually any resin. About one pound for each ounce of injection capacity will be needed (5-10 Ib/in. of screw diameter in an extruder). With extruders, special conditions and preparations are required, which suppliers of the purging compound can recommend (remove dies, screen packs, etc.). 

Heat-cured silicone rubber is commercially available in several forms as gum stock, reinforced gum, or partially filled gum. These compoimds can be im-catalyzed, catalyzed, or can contain catalyst dispersions. Catalyzed compounds are ready for use without additional processing. Silicone rubber is often freshened, ie, the compound is freshly worked on a rubber mill until it is a smooth continuous sheet. The freshening process eliminates the structuring problems associated with pol5uner-filler interactions. Rubber can be extruded on wire and cured in place (479). 

In almost all cases, additives are compounded with PBT in a single or twin-screw extruder after polymerization. The extrusion process is carried out independently of the polymerization process. Moreover, many additives can be combined with each other and with PBT pol)oners of different molecular weights. As a result of the various additives available for the formulation of the final PBT product, and the various levels of additives that can be combined with PBT, many different commercial PBT grades exist. Each of... 

The methods used to synthesize poly(imide-siloxanes) have been reviewed by Lee who points out that electronic and microelectronic applications are key factors for the development of low-modulus, low-stress new materials [171]. The patent literature indicates that copoly(imide-siloxanes) have been synthesized with all available dianhydrides such as PMDA, BTDA, BPDA, OPDA, and the diether dianhydride used to produce the thermo-plastic polyimide Ultem 1000. These compounds were opposed to aromatic diamines in combination with siloxanediamine 113 with a degree of polycondensation m varying from 0 to 8 or more. Commercial polymers generally include only 5-10 mol% of siloxane units in order to maintain a glass transition temperature higher than 200°C. For example, preimidized thermoplastic copolymers have TgS in the range of 200-220°C and can be extruded at temperatures below 300°C... 

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