Reinforced thermoset molding

In joining reinforced thermosetting pipe it is particularly important that the pipe be cut without chipping or cracking it. It is also important to sand, file, or grind any mold-release agent from the surfaces to be cemented. Joints are built up layer by layer of adhesive-saturated reinforcement by following the manufacturer s recommended procedure. Application of adhesive to the surfaces to be joined and assembly of these surfaces shall produce a continuous bond and provide an adhesive seal to protect the reinforcement from attack by the contents of the pipe. Unfilled or unbonded areas of the joint are considered defects and must be repaired. 

ALLYL ESTER RESINS. The allyl radical (CH2CH=CH2) is the basis of the allyl family of resins. Allyl esters arc based on monobasic and dibasic acids and are available as low-viscosity monomers and thermoplastic prepolymers. They are used as crosslinking agents for unsaluraied polyester resins and in the preparation of reinforced thermoset molding compounds and high-performance transparent articles. All modem thermoset techniques may be used for processing allyl resins. 

By analogy with compression molding, thermosetting resins plus fibrous reinforcement can be pressed between matching mold halves, with heat and moderate pressure, and cured directly into finished products. Typical cure cycle is about a minute. Half of all reinforced thermoset products are made in this way. Major applications are in the automotive, electrical/electronics, appliance, and business machine industries. 

Instead of applying pressure in a closed mold, the mix of liquid resin and reinforcing fiber may be laid into an open mold, and optionally pressed gently at room temperature until cured. To accelerate low-temperature cure, more active catalyst systems are added. Alternatively, the assembly may be UV or oven cured. This requires less capital investment but more skilled labor, so it is useful for prototype and small production runs. It permits unlimited size, so the largest reinforced thermoset products are made in this way, for example, large tanks and whole boat hulls. 

Reinforced thermoset (RTS) plastic B-stage sheet material can be processed with its required heating cycle. However the most popular is to use reinforced thermoplastic (RTP) sheets usually using polypropylene plastics. Compared to injection molding RTPs, these stamped products can provide improved mechanical and physical properties with its longer fibers such as impact strength, heat distortion temperature, and much less anisotropy. 

The thermoset (TS) plastics and reinforced thermosets (RTSs) are more suitable to meet tight tolerances. With amorphous and crystalline thermoplastics (Chapter 1) reinforced thermoplastics (RTPs), and particularly unreinforced thermoplastics (UTPs) can be more complicated tolerance-wise if the fabricator does not understand their behavior. Crystalline plastics generally have different rates of shrinkage in the longitudinal (melt flow direction) and transverse directions when injection molded. 

Contact Molded Glass Fiber Reinforced Thermoset Resin Chemical Resistant Tanks (ASTM D-4097-82)... 

While polymers with moderately high performance qualities, such as cellulose in wood and cotton have been known for years, these linear polymers could not be extruded or injection molded. However, they were able to withstand the effects of moderately hostile environments. The classic reinforced thermosets could be compression molded and could also be classified as high performance plastics. In contrast, the general purpose thermoplastics, introduced in the 1930 s, were readily extruded and Injection molded but were not useful at boiling water temperatures. 

Melby, E.G. Castro, J. M. (1989) Glass-reinforced thermosetting polyester molding materials and processing, in Allen, G. (Ed.) Comprehensive Polymer Science, Oxford Pergamon. Mijovic, J., Bellucci, F. Nicolais, L. (1995) J. Electrochem. Soc., 142, 1176-1182. 

Small amounts of TAIC together with DAP have been used to cure unsaturated polyesters in glass-reinforced thermosets (131). It has been used with polyfunctional methacrylate esters in anaerobic adhesives (132). TAIC and vinyl acetate are copolymetized in aqueous suspension, and vinyl alcohol copolymer gels are made from the products (133). Electron cure of poly(ethylene terephthalate) moldings containing TAIC improves heat resistance and transparency (134). 

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