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Thermoset Polymer Matrix–Based Natural Fiber Composites
Published in Shishir Sinha, G. L. Devnani, Natural Fiber Composites, 2022
Curing of vinyl ester resin can be done at elevated or room temperature. The curing condition affects mechanical properties. Vinyl ester resins are assortments of methacrylate epoxy compound with styrene. By altering the content of styrene and molecular weight of ether of the resin, viscosity can be controlled. The curing of this is done by free radical copolymerization where styrene acts as diluent and vinyl ester acts as cross-linking agent. The primary curing initiates with induction. The availability of inhibitors result in micro-gel formation. These micro-gels delimited the area of cross-linking density disseminates with unreactive monomers. These micro-gels when coagulated into clusters result in the cured resin (Ziaee & Palmese, 1999). Vinyl ester resin is characterized by a specific type of denatured epoxy resin that is obtained by reacting bisphenol with methacrylic acid. Vinyl ester resin possesses great properties like great curability, good corrosion resistance, fracture toughness, good strength, and thermal resistance. Vinyl ester resin has mainly been used for fiberglass-reinforced composites, commercial, and military applications.
Experimental study of two-way FRP composite slab
Published in Peter J. Moss, Rajesh P. Dhakal, Progress in Mechanics of Structures and Materials, 2020
D. Huang, G.M. Van Erp, T.J. Heldt, C.L. Cattell
A prototype of the composite slab (2020 mm × 1620 mm) was constructed for the experimental study. A total of eight layers of unidirectional laminates with stacking sequence [0°/90°]4 were laminated on both sides of the 120 mm core resulting in an overall thickness of 129 mm. In this study, E-glass and vinyl ester resin were used to construct the prototype testing slab. Vinyl ester resin has advantages such as excellent chemical resistance, low viscosity, fast curing, and a good balance between mechanical properties and cost. However, the volumetric shrinkage of vinyl ester resin is in the range of 5–10%, which can cause cracking during the manufacturing process if the volume of PFR core is large. A modular manufacturing approach was adopted to overcome this exotherm problem (Huang et al. 2002). In this manufacturing approach, the shrinkage is controlled by first fabricating small element (modules) which are later combined into large assemblies. Due to the smaller volume of material involved in the modules, shrinkage is restricted to an acceptable level and does not result in cracking. In addition to the efficient control of the exotherm and shrinkage, the advantages of this modular approach also include cost effectiveness, flexibility of section shapes and suitability for both small and large structures (Huang 2004).
Matrix Materials
Published in P. K. Mallick, Processing of Polymer Matrix Composites, 2017
Vinyl ester molecules are produced by the chemical reaction of an unsaturated carboxylic acid, such as acrylic acid and methacrylic acid, and an epoxy resin (Figure 3.13). The C=C double bonds (unsaturation points) occur only at the ends of a vinyl ester molecule, and therefore, cross-linking can take place only at the ends, as shown schematically in Figure 3.13. Because of fewer cross-links, a cured vinyl ester polymer is more flexible and has a higher fracture toughness than a cured polyester resin which has a larger number of cross-links in its molecule. The presence of ester groups in vinyl ester and polyester molecules makes them susceptible to hydrolysis in the presence of water. However, since vinyl ester molecules contain fewer ester groups than polyester molecules, they have a higher resistance to degradation from water exposure. Another unique characteristic of a vinyl ester molecule is that it contains a number of OH (hydroxyl) groups along its length (Figure 3.14). These OH groups can form hydrogen bonds with similar groups on the glass fiber surface resulting in excellent wet-out and good adhesion with glass fibers.
Improvement of the chemical adhesion of EPDM rubber to Sheet Moulding Compound (SMC) by the addition of phenolic resin as adhesion promoter
Published in The Journal of Adhesion, 2021
Alexandra Allue, Koldo Gondra, Isabel De Marco, Gorka Díez
The chemical degradation of polyester and vinyl ester resins in aggressive environments is basically concentrated on the carbon-carbon double bonds. Additionally, the polyester resins can be chemically attacked by hydrolysis of the ester group at the ends of the chains. The good chemical resistance of vinyl ester resins is because the double bonds at the ends of the chains are extremely reactive, and disappear almost completely during polymerization; consequently, only a minimum number of double bonds are vulnerable to chemical attack.