High Performance Thermoset Resins

Polyurethanes (PU or PUR) and polyureas are classified as TS resins, but their chemistry is so flexible that they can be formulated different ways. There are moldable solid and expanded TSs, with (RPUR) or without reinforcement, flexible and rigid foams, elastomers and thermoplastic molding compounds. As RPs they are important in reinforced reaction injection molding (RRIM) (Chapter 5) and are also available as reinforced thermoplastic molding compounds. A variant on the process employs a structural preform of the reinforcement that is placed in the mold cavity and is called structural reaction injection molding (SRIM). 

PURs are noted for their high impact strength, toughness and excellent resistance to abrasion. They bond well with reinforcements (one of the main applications of PURs is as adhesives) and offer very good resistance to chemicals. 

A reasonably high quality of surface finish can be achieved (depending on mold cavity quality) and a form of in-mold coating system can also be employed to achieve Class A finishes. 

RPURs can also be formulated for use as SMC type materials, foamed panels, and filament winding. The RIM process operates at low pressure, allowing inexpensive materials to be used for molds, and the mixing/ injection head is usually flushed out between injection cycles. Because of the need for accurate dosing, and the speed and sensitivity of the reaction, the process is often controlled by computer. 

RRIM is used increasingly for medium/large automobile parts, such as external body panels (where the general toughness of the material makes it an interesting candidate for damage-prone panels such as front fenders). 

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Epoxy resins are high-performance thermosetting resins, which display a unique combination of properties. Epoxy resins have been commercially available for almost a half-century. Epoxy resins are arguably one of the most versatile polymers with uses across an enormously wide variety of industries. The outstanding physical properties exhibited by epoxy resins include... 

A.J.DeMaio (1991). Engineering High Performance Thermoset Resins from Polyethylene Terephthalate) Thermoplastics. Proceedings of the 46th Annual Conference of the Composites Institute of the Society of Plastics Institute, pp. 18C/1-18C/5. 

Ghosh N N, Kiskan B and Yagci Y (2007), Polybenzoxazines. New high performance thermosetting resins Synthesis and properties . Prog Polym Sci, 32, 1344—1391. 

Epoxy resins are considered to be one of the most important classes of thermosetting polymers. They are now widely utilized as high-performance thermosetting resins in several industrial applications. Thanks to their range of useful properties, they are used as protective coatings, structural adhesives and matrix resins for fiber-reinforced polymer (FRP) composites. 

Yang, L., Klang, J. and Cai, G., Process for making high-performance polyetherester resins and thermosets, US Patent 5 696 225, 1997. 

FRP materials are made up of the polymer and reinforcing fibers. The polymer is typically a thermoset polymer thermoplastics can be used as well. Some typical thermoset polymers used are epoxy resins, unsaturated polyester resins, epoxy vinyl ester resins, phenolic resins, and high performance aerospace resins such as cyanate esters, polyimides, and bismaleimides. These resins... 

Adapted from Table 8.4 in Lin, S.-C. Pearce, E.M. High-performance epoxy resins. Chapter 8. In High-Performance Thermosets, Chemistry, Properties, Applications Hanser New York, 1998, p. 259.)... 

The classic thermosets, such as ebonite, phenolics, ureas, melamines and polyesters as well as the epoxies, when reinforced with fiberglass or graphite fibers could also be classified as high performance thermosets. While these plastics cannot be readily extruded or injection molded, they are resistant to the effects of moderately high hostile environments. Phenolic resin mortars have been used for over a half century for the construction of chemical resistant vessels and for joining brick and tile used as linings in hot acid environments. (1.)... 

Epoxy resins are among the most important of the high performance thermosetting polymers and have been widely used as structural adhesives and matrix for fiber composites. Epoxy resins are characterized by the presence of epoxide groups before cure, and they may also contain aliphatic, aromatic, or heterocyclic structures in the backbone. The epoxy group can react with amines, phenols, mercaptans. 

Table 3.2 also includes data for the advanced thermoplastic resins (PEEK) and for a thermosetting resin, an end-capped bismaleimide (BMI) called PMR-15. Moisture contents tend to be lower for these advanced materials [12,13]. One way to overcome the environmental sensitivity of epoxide resins is to employ these advanced resins, as demonstrated in Table 3.2. However, changing to other resin systems brings with it other concerns. For example, PEEK relies on crystallinity for its higher temperature performance. Its glass transition temperature is only 143°C and a change in modulus can be observed at that temperature. In addition, higher process temperatures are required both for high performance thermosets and thermoplastics. The consequent higher residual thermal stresses can off-set some of the advantages of a higher service temperature, in comparison with advanced epoxy resins.

The global thermoset resins market is expected to reach as high as 95 million metric tons by 2016 (Axis Research Mind report 2012). Excluding the alkyd resins, which are used primarily in the coatings, commercially important major types of thermoset resins, altuig with their relative % market share, estimated from literature (Fosdyke and Starr 2002), can be categorized as follows Polyurethanes (31 %), PhenoUcs (18 %), Amino resins (18 %), Unsaturated polyesters (12 %), Epoxies and other specialty/high performance thermosets (12 %), such as silicones, polyimides, bismaleimides (BMl), cyanate ester thermosets, etc. 

Yang P and Gu Y (2012), Synthesis of a novel benzoxazine-containing benzoxazole structure and its high performance thermoset , J Appl Polym Sci, 124, 2415-2422. Yoonessi M, Toghiani H, Wheeler R, Porcar L, Kline S and Pittman Jr C U (2008), Neutron scattering, electron microscopy and dynamic mechanical studies of carbon nanofiber/phenolic resin composites . Carbon, 46, 577-588, and references therein. Yosomiya R (1990), Adhesion and Bonding in Composites, New York, Marcel Dekker, l-A. 

The use of high-performance epoxy resin systems in the civil engineering field has greatly increased since 1960. Nowadays these thermosetting polymers are widely used in this field as matrices for fiber-reinforced materials. In particular, their principal applications are in the following fields ... 

Das, S. et al. Phenolic-Triazine Resins Yield High-Performance Thermoset Composites. Modern Plastics, pp. 72-79, Feb. 1990. 

Polyesters are one of the most versatile classes of polymers ever produced, covering a wide range of properties and applications. Polyesters are present in fibers, engineering thermoplastics, and high-performance polymers as well as in thermosetting resins and elastomers. Table 2.1 lists the chemical structure, abbreviations, and uses of some commercially important thermoplastic polyesters. 

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