158 6 Tailoring Composite Materials 0 PI PEEK PPS PES ● H CH PEI CH, Figure 6.2.The mers(repeating units)of thermoplastic polymers typically used in structural composites There are many types of epoxy.The most common epoxy resin is produced by a reaction between epichlorohydrin and bisphenol A.The mers(repeating units)of thermoplastic polymers that are typically used in structural composites are shown in Fig.6.2. The properties of these thermoplastics are listed in Table 6.1.In contrast,epoxies have a tensile strength of 103 MPa,an elastic modulus of 3.4 GPa,a ductility (elon- gation at break)of 6%,and a density of 1.25g/cm3[1].Thus,epoxies are stronger, stiffer and more brittle than most thermoplastic polymers.Another major differ- ence between thermoplastics and epoxies is the higher processing temperatures of thermoplastics(300-400C). 6.1.2 Cement-Matrix Composites Component selection for cement-matrix composites involves the use ofadmixtures, which are additives included in the cement mix.These additives serve various functions,as described below:158 6 Tailoring Composite Materials Figure 6.2. The mers (repeating units) of thermoplastic polymers typically used in structural composites There are many types of epoxy. The most common epoxy resin is produced by a reaction between epichlorohydrin and bisphenol A. The mers (repeating units) of thermoplastic polymers that are typically used in structural composites are shown in Fig. 6.2. The properties of these thermoplastics are listed in Table 6.1. In contrast, epoxies have a tensile strength of 103MPa, an elastic modulus of 3.4GPa, a ductility (elon￾gation at break) of 6%, and a density of 1.25g/cm3 [1]. Thus, epoxies are stronger, stiffer and more brittle than most thermoplastic polymers. Another major differ￾ence between thermoplastics and epoxies is the higher processing temperatures of thermoplastics (300–400°C). 6.1.2 Cement-Matrix Composites Componentselectionforcement-matrixcompositesinvolvestheuseofadmixtures, which are additives included in the cement mix. These additives serve various functions, as described below: