Shaped polymer fabrication compression molding

After synthesis, the modified carborane-siloxane gums were fabricated into shaped components using standard siloxane vulcanization and fabrication technology. Di-chlorobenzyl peroxide (1% by wt) was used as the cross-linking agent and mixed into the polymer formed in scheme 7. Shaped rubber components were readily prepared by compression molding operations at 70°C. Postcure operations were typically at 120°C for 24 hours. 

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

Solvent casting Exposed to low thermal and mechanical stress Targeted molecular weight Control porosity amount, size, and shape via particulate leaching Alter polymer properties through additives Typically can he dissolved and reused as raw material Simple process Preformed implant, fabricated before implantation Limited by mold shape Must use solvent Polymer must be soluble in volatile solvent Residual solvent can be toxic Often requires additional fabrication techniques, such as compression molding Siemann (2005), Boccaccini and Blaker (2005), and Liu et al. (2007)... 

Another area in which preceramic polymers can be utilized effectively is as binders for ceramic powders in near net shaping fabrication processes, such as compression or injection molding with subsequent sintering. Alternatively, an active filler and a polymer [67,68], as reported by Greil and Seibold, can be used in such fabrication. Other potential applications of preceramic polymers is in the general area of coatings, especially for carbon-carbon composites [69], and in the synthesis of nanostructured ceramic particles and composites [70-73]. 

Development work has been going on for several years at The Carborundum Company on p-oxybenzoyl polymer systems. 3 The early work mainly focused on the homopolymer (EKONOLjI This polymer has excellent thermal stability and also very good friction and wear properties and has found use recently as an additive to PTPB for molded shapes and coatings. The homopolymer however is very difficult to fabricate by itself and this has led to the development of copolymer systems which retain the excellent thermal stability of the homopolymer but have sufficient flow for compression and injection molding. 

Consideration of orientation and fiber length for a particular composite depends on the level and nature of the applied stress as well as on the fabrication cost. Production rates for short-fiber composites (both aligned and randomly oriented) are rapid, and intricate shapes can be formed that are not possible with continuous fiber reinforcement. Furthermore, fabrication costs are considerably lower than for continuous and aligned fibers fabrication techniques applied to short-fiber composite materials include compression, injection, and extrusion molding, which are described for unreinforced polymers in Section 15.22. 

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