resin Tab. 3: Comparison of tensile properties in reinforced prepreg composites: AdvaliteTM hot-melt resin system vs. bisphenol A epoxy resin Mechanical property comparison (0/90 fabrics) Property 35051-00 Epoxy Tensile strength (max. load) GPa 439 416 Elongation at break % 3.7 2.4 Fibre fraction % 64.9 64.8 epoxy resin system used in high-performance composite applications - both of which show excellent tensile properties. Fig. 1: Dielectric cure response of AdvaliteTM 35051-00 prepreg resin system versus time (sec.) in automotive applications - in composites they are controlled by the part moulding mechanics and the reaction rate of the curing process. The curing mechanism for these hot-melt resins is the same as for the liquid vinyl hybrid systems, i.e. the resin is combined with a free-radical initiator and the cure is achieved by activating the initiator to start a vinyl addition polymerization. As is the case with liquid vinyl hybrid systems, AdvaliteTM hot-melt resins can modify the gel time needed for moulding purposes while maintaining fast cure. This is achieved by selecting the appropriate initiators and inhibitors without changing the polymer itself. Figure 1 shows the dielectric cure response of an AdvaliteTM 35051-00 formulated resin system used in a prepreg application. The graph shows that at the given moulding temperature (150°C), the final cure of the laminate is achieved in less than 75 seconds for a 3-mm-thick laminate, allowing for press cycles that meet a high-volume automotive production rate. The optimization of mechanical properties is a key criterion to ensure that the composite meets OEM specifications. Mass reduction can also be obtained through the use of materials with high physical properties such as those used in high-performance composites. Table 2 shows the properties of the AdvaliteTM hot-melt vinyl hybrid cast resins. In this table, the cast resins again show excellent flexural and tensile strength and modulus. The table also shows that the polymer backbone can be modified to meet the applications' needs - the ability to modify the Tg and elongation values is given as an example of this design flexibility. In addition, the hotmelt resin systems have shown comparable properties in reinforced prepreg laminates as traditional epoxy resin systems used in similar applications. The mechanical properties of composites are provided in Table 3. This table shows that the hot-melt vinyl hybrid resin is comparable in terms of properties to an The hot-melt vinyl hybrid resin system has been proven in automotive applications as it was used in the GM 2014 Chevrolet Spark electric battery tray. The performance requirements of this application called for a high-performance composite material. These specifications encompassed a long-glass-fibre prepreg composite capable of maintaining its package integrity after multiple crash tests - including 30-degree offset, side impact and rear barrier crash tests. Because of the part's placement in the vehicle, it was also critical that the part exhibit zero emissions. The prepreg manufactured with a hot-melt vinyl hybrid resin met all of these stringent requirements. The mechanical properties of a prepreg utilizing this type of hot-melt vinyl hybrid resin system are Tab. 2: Cast resin properties of AdvaliteTM hot-melt vinyl hybrids Property Unit Flexural strength X4833-37 X4710-16 MPa 155.9 130.4 Flexural modulus GPa 3.53 4.22 Tensile strength MPa 57.6 82.5 65.3 46.3 Tensile modulus GPa 3.92 3.42 3.04 3.86 Elongation % 1.6 4.0 2.5 1.3 HDT C 94 84 116 151 Dry Tg C 81 154 173 Wet Tg C 149 157 Water absorption % 1.5 0.7 Viscosity @ 100°C poise 14 18 30 jec composites magazine / No91 August - September 2014 35000-00 18 35051-00 19