Thermosetting system unsaturated polyesters

Certain state highway authorities are studyiag the use of ftber-reiaforced polymers, typically thermosets such as epoxy or unsaturated polyester, for bridge constmction. On an even more futuristic scale, fiber optics that employ polymeric jacketing and, ia some cases, optically active polymeric cores, may someday be employed ia place of wines for home security systems, climate control, etc (10,91). 

Cole reviews the nse of Raman spectroscopy to monitor the curing of different thermoset composite polymer systems, thongh he cautions that it is not suitable for certain materials [215]. Cruz et al. studied the effect of elevated pressure on the cure rate and the degree of cnre of unsaturated polyester and other thermoset materials [216,217]. The approach worked well, though the experimental set up required addi-... 

Both thermoset and thermoplastic resin systems are employed in the construction of composites (Table 8.3). The most common thermoset resins are polyimides, unsaturated polyesters, epoxys, PFs, and amino-formaldehydes. A wide variety of thermoplastic resins have been developed. 

The solution of the precursors of the thermosetting polymer (mixture of monomers or oligomers with or without initiators, catalysts and different additives) is usually a liquid at room temperature e.g., unsaturated polyester styrene, some epoxy anhydride and epoxy amine formulations, cya-nate esters, one-stage phenolics, etc. Cooling any of these solutions below room temperature leads to a glass. The temperature at which the glass-liquid transition of the initial formulation takes place is denoted as Tg0. Some other particular formulations, such as two-stage phenolics (novo-lac-hexa mixtures), some epoxy-amine systems, etc., exhibit a Tg0 above room temperature. 

Additives and comonomers in thermoset, moisture, UV, and catalytically curing resins or coatings (e.g., acrylic, epoxy, melamine, and unsaturated polyester systems)... 

The polymer eomponent, whieh is a thermosetting resin, forms eross-linked bonds between chains of molecules, whieh enhanees the eharacteristic of the produet. Unsaturated polyesters and vinyl esters are primarily used as resin systems. Epoxies are also used in some eases, but the eure eyele is longer. Phenolic resins have gained importanee these days because of their inherent properties, especially in applications that require lower flammability, reduced smoke generation, and higher thermal stability. New resin systems such as... 

Typical systems are unsaturated polyesters, usually filled with mineral fillers and/or fibres. Newer systems such as thermoset-thermoplastics using reactive solvents for processing high-performance engineering polymers are being researched. 

Many thermoset polymers of major commercial importance are synthesized by step-growth polymerization, as the case of unsaturated polyester, polyurethanes, melamines, phenolic and urea formaldehyde resins, epoxy resins, silicons, etc. In these systems, the crosslinking process, which leads to a polymer network formation, is usually referred to as curing. 

Unsaturated polyesters are mainly used as the matrix for glass fibre reinforcement, (in glass fibre reinforced thermoset systems). These are most commonly used in the manufacture of small boats, chemical containers, tanks and repair kits for cars. 

A low molecular weight (liquid) polyester with unsaturated double bonds, that can enter reaction with a monomer (i.e., styrene) to yield to a crosslinked thermoset system. 

Although the data concerning these polymers are quite limited, both TCBP euid TCBS (as well as some of their appropriate derivatives) have been incorporated into thermoplastic and thermoset resin systems including polycarbonates (9,10,11), polysulfones (12), thermostable (aromatic) polyesters (13), alk polyesters ( ), unsaturated polyesters Tl5,16) and epoxy resins (16). 

Unsaturated polyester thermoset systems use styrene as a reactive dilnent (sometimes along with substituted styrenes such as vinyl styrene or methyl methacrylate). Some of the styrene evaporates in the process (the emission factor is estimated at about 1-3% of the styrene for composites and a little higher for continuous lamination) and poses a threat as a hazardous air pollutant. The time-weighted average (TWA) for styrene is 50 ppm (or 213 mg/m ). In 1996 the Occupational Safety and Health Administration (OSHA) endorsed a proposal by the styrene industry to voluntarily adopt the 50-ppm exposure limit. 

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