Abstract
Vinyl ester resins are widely used in sandwich composite structures. Because of their good resistance to chemicals, flexibility and easy processing, these sandwich are extensively applied in the marine sector. These composites are typically manufactured by liquid molding processes, especially infusion. In this study, RTM light was used to inject the polymeric resin into the mold cavity, flowing in the space between the impermeable core and the mold walls, where the fibrous medium was. In this process, viscosity, gel time and curing time of the resin are very important parameters. This work addressed the curing and post-curing characteristics of a vinyl ester resin, and also the characteristics of neat and reinforced vinyl ester using dynamic mechanical analysis (DMA). The increase in shear rate did not significantly influence resin viscosity within the studied range. Differential scanning calorimetry showed the efficiency of the post-curing stage, with the decrease in residual enthalpy. With DMA, it was possible to determine gel time and gel temperature, which yielded similar values to those found by the SPI (Society of the Plastics Industry) method, indicating that the simpler SPI method can be reliably used for that.
Highlights
Vinyl ester resins (VER) result from the reaction between bisphenol-A based epoxy oligomers and unsaturated carboxylic acids, such as acrylic or methacrylic acid which provides unsaturated terminal sites [1]
resin transfer molding (RTM) light was used to inject the polymeric resin into the mold cavity, flowing in the space between the impermeable core and the mold walls, where the fibrous medium was
Sandwich composite structures are chosen and the easy processing of VER allows the use of liquid molding techniques, such as infusion and RTM light
Summary
Vinyl ester resins (VER) result from the reaction between bisphenol-A based epoxy oligomers and unsaturated carboxylic acids, such as acrylic or methacrylic acid which provides unsaturated terminal sites [1] This resin is one of the most important thermoset polymers that combine the chemical, mechanical and thermal properties of epoxy resins with the fast cure of unsaturated polyester resins (UPRs) [2-3]. Sandwich composite structures are chosen and the easy processing of VER allows the use of liquid molding techniques, such as infusion and RTM light. Calorimetry has been used to determine the effect of the initiator concentration and oxygen on the rate of cure [5] These resins generally contains 30-60% styrene by weight, which serves as diluents to enhance linear chain extension and to reduce viscosity of the resin, allowing for easy processing and room temperature curing [6]. These processes are rapidly becoming very popular because they are ecofriendly, being carried out in closed molds [8]
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