Polyester-epoxy matrix, mechanical properties

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. 

Table I. Mechanical Properties of a Matrix with a Polyester-to-Epoxy...

The mechanical properties of fiber-reinforced polymer composites are cmitroUed by factors such as nature of matrix, fiber—matrix interface, fiber volume or weight fraction, fiber aspect ratio, etc. Due to the hydrophilic nature, the fibers pulled out from polyester and polyethylene matrices, they were compared with the fibers pulled out from the epoxy matrix, which carry polymer particles on their surfaces. On the other hand, fracmre of the fibers occurs at the crack plane in phenolic composites. From SEM microstructures of different composites, it was observed that the bonding of sisal fiber with the four matrices are found to be in the order of phenolic > epoxy > polyester > polyethylene [58, 59]. 

Many matrix choices are available, and each type has an impact on the processing techniques, physical and mechanical properties, and enviromnental resistance of the finished part. Thermoplastic and thermoset materials can be resin matrices. Thermoplastic matrices have been developed to increase hot/wet use temperature and the fracture toughness of composites. Thermosetting resins, however, are more common. The common thermoset matrices for composites include polyester and vinyl esters, epoxy, bismaleimide, polyimide, and cyanate ester and phenolic triazine resins. 

Epoxy resins are mainly used for carbon strengthening. Alternatively, the use of a polyester matrix with this kind of strengthening would lead to a composite with dramatically lower mechanical properties. Specifically, it would result in a reduction... 

The APC materials typically nsed for on-site rehabilitation of timber and concrete are composed of glass, carbon or aramid fibres and a polyester, epoxy or polynrethane polymeric matrix. Glass fibres are the most frequently used due to their moderate cost and good mechanical properties when compared to carbon fibres. They are used normally in the form of pultruded profiles or strips, fabrics (tissues) or mats. Carbon fibres are mainly used in the form of pultruded profiles of solid, open or hollow cross-sectional shapes. While in timber applications both thermoplastic and thermosetting matrix types are used, in concrete applications only the latter type is used. 

The most widely used and least expensive polymer resins are the polyesters and vinyl esters. These matrix materials are used primarily for glass fiber-reinforced composites. A large number of resin formulations provide a wide range of properties for these polymers. The epoxies are more expensive and, in addition to commercial applications, are also used extensively in PMCs for aerospace applications they have better mechanical properties and resistance to moisture than the polyesters and vinyl resins. For high-temperature applications, polyimide resins are employed their continuous-use, upper-temperature limit is approximately 230°C (450 F). Finally, high-temperature thermoplastic resins offer the potential to be used in future aerospace applications such materials include polyetheretherketone (PEEK), poly(phenylene sulfide) (PPS), and polyetherimide (PEI). 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

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