Epoxy resin thermosetting plastic

Thermosetting plastics Epoxy resin High strength when reinforced, good chemical and wear resistance. Adhesives, encapsulation of electronic components Moulding, boat and car bodies... 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121°C and 177°C). Proper selection of various hardeners, resins, modifiers, and fillers allows the development of desired properties for a particular application. Because of the wide versatility and basic adhesive qualities, epoxies make excellent structural adhesives that can be engineered to widely different specifications. Essentially no shrinkage occurs during polymerization because epoxies are completely reactive producing no volatiles during cure. Epoxy adhesives can be formulated to meet a wide variety of bonding... 

Though many researchers think that, in the future, thermoplastic matrix composites will gain popularity, there is stiU a long way to go before they achieve widespread use in the structural field. The most important thermosetting plastic matrices (resins) are polyester, epoxy, phenolic, and silicone. 

In comparison with other thermosetting polymers, epoxy resins are more expensive but show better mechanical properties, lower shrinkage, and higher resistance to moisture absorption and to corrosive environments. These good physical properties and their durability in service help to provide a favorable cost-performance ratio when compared to other thermoset plastics. 

One of the most important methods for controlling the yield behaviour of polymers is rubber modification, which is widely used to increase fracture resistance. The technique was first used in 1948 to modify the properties of polystyrene, and has since been extended to most of the major plastics, including polypropylene, polycarbonate, and rigid PVC, and to a number of the less highly crosslinked thermosets, notably epoxy resins. Between S and 20 % of a suitable rubber is added in the form of small particles, which are typically between 0.1 and S /im in diameter. Chemically reactive rubbers are preferred, because they form bonds with molecules of the surrounding matrix which can withstand tensile stress. The rubber particles have low moduli, and therefore act as stress concentrators. Accelerated deformation in the matrix adjacent to the rubber particles results in a lowering of the yield stress. 

Of all the thermosetting plastics, epoxies are more widely used than any other plastic, in a variety of applications. There are resin/hardener systems (two-part) that cure at room temperature, as well as one-part systems that require extreme heat cures to develop optimum properties (e.g., 121 °C and... 

The binder system of a plastic encapsulant consists of an epoxy resin, a hardener or curing agent, and an accelerating catalyst system. The conversion of epoxies from the Hquid (thermoplastic) state to tough, hard, thermoset soHds is accompHshed by the addition of chemically active compounds known as curing agents. Flame retardants (qv), usually in the form of halogens, are added to the epoxy resin backbone because epoxy resins are inherently flammable. 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Commonly accepted practice restricts the term to plastics that serve engineering purposes and can be processed and reprocessed by injection and extmsion methods. This excludes the so-called specialty plastics, eg, fluorocarbon polymers and infusible film products such as Kapton and Updex polyimide film, and thermosets including phenoHcs, epoxies, urea—formaldehydes, and sdicones, some of which have been termed engineering plastics by other authors (4) (see Elastol rs, synthetic-fluorocarbon elastol rs Eluorine compounds, organic-tdtrafluoroethylenecopolyt rs with ethylene Phenolic resins Epoxy resins Amino resins and plastics). 

This group includes many plastics produced by condensation polymerization. Among the important thermosets are the polyurethanes, epoxy resins, phenolic resins, and urea and melamine formaldehyde resins. 

Thermoset Plastics Alkyd, amino resin, thermosetting acrylic resin, casein, epoxy, phenolic, polyester, polyamide, silicone. 

The variety of epoxy resins offers a wide range of molecular structures that exhibit different yield behavior at the macroscopic level. The study of plastic deformation in different epoxy resins can help understand the structure/property relationship of plasticity in thermoset resins. 

The plastic deformation in several amine and anhydride cured epoxy resins has been studied. The experimental results have been reasonably interpreted by the Argon theory. The molecular parameters determined from the data based on the theory reflect the different molecular structures of the resins studied. However, these parameters are in similar enough range to also show the structural similarity in these DGEBA based systems. In general, the mechanisms of plastic deformation in epoxy resins below T are essentially identical to those in amorphouE thermoplastics. The yield stress level being related to the modulus that controls the intermolecular energy due to molecular deformation will, however, be affected by the crosslinks in the thermosets. 

Thermosets A number of thermosets have been used as adhesives. Phenolic resins were used as adhesives by Leo Baekeland in the early 1900s. Phenolic resins are still used to bind together thin sheets of wood to make plywood. Urea resins have been used since 1930 as binders for wood chips in the manufacture of particle board. Unsaturated polyester resins are used for body repair and PUs are used to bond polyester cord to rubber in tires, and vinyl film to particle board, and to function as industrial sealants. Epoxy resins are used in the construction of automobiles and aircraft and as a component of plastic cement. 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

C. Epoxy ROSins. The epoxy resins are thermosetting plastics which have great strength and the ability to form tenacious bonds with most surfaces. Furthermore, the cured resin is resistant to many solvents and chemicals. (Some epoxy resins are decomposed by acetic acid, and all are attacked by very strong oxidizing agents.) Because of this combination of properties, epoxy cements are frequently used to bond metal, glass, wood, and plastics. 

Thermoset A resin or plastic compound that in its final state is substantially infusible and insoluble. It cannot be repeatedly softened by heating and hardened by cooling. Examples of thermosets are epoxy, phenol-formaldehyde, some types of polyester, some types of... 

For commodity applications, there are four major classes of resins that are used in FRP applications. They are phenolic resin, epoxy resin, unsaturated polyester resin, and epoxy vinyl ester resins. A more complete description of these types of resins and their many variations can be found in Handbook of Thermoset Plastics. This is not a comprehensive list of resins used in composite manufacture, as commodity materials like polyurethanes and isocyanurate resins are sometimes used as well to make FRP parts. However, these materials are not covered in this chapter owing to their limited use, but, the principals of fire safety that apply for the resins described subsequently apply to these materials as well. 

The broadest classification for plastics is the old thermoplastic and thermosetting . Examples of the former group are polyethylene, polystyrene, and poly-(methyl methacrylate) examples of the latter are urea-formaldehyde condensation polymers, powder coatings based on polyesters, epoxy resins, and vulcanized synthetic elastomers. 

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