Improved Toughness in Vinyl Ester Resins with Micro and Nano-Polymers

摘要

Low viscosity vinyl ester resins offer significant processing advantages over higher cost and higher viscosity epoxy resins in most closed mold processing. This is especially true in high fiber, infusion processes currently employed in markets such as marine, construction, infrastructure, and sporting goods, but most especially in wind energy. In addition to the obvious processing advantages of reduced viscosity, vinyl ester resins offer much improved cure under ambient cure conditions, without the sensitivity of stoiciometry balance between epoxy and suitable hardeners, as it relates to viscosity build and ultimate mechanical properties. It has also been shown that epoxy resins are much more susceptible to water absorption and reduced mechanicals, especially GII fracture toughness under wet and dry conditions1 The critique on vinyl ester resins has been that they tend to cure in a more brittle fashion over epoxy resins, which is great for chemical resistance, but poor for fatigue properties in structural and highly stressed applications. This conception is confirmed in K1c and G1c fracture toughness and in fatigue testing of prepreg based epoxy as compared to prepreg vinyl esters. This complaint though is far less true when comparing epoxy and vinyl ester resins, in infused FRP laminates, as mono and di-functional glycidal ethers must be employed to reduce the traditionally high viscosity epoxy base resins. These glycidal ethers do reduce epoxy viscosity, but in fact, do not offer anywhere near the performance of high molecular weight epoxy resins, and why they are rarely used in high performance, aerospace prepregs. Mechanical and fatigue property testing will be presented to confirm this conclusion. Further, this paper will highlight the development of significantly tougher vinyl esters that have been modified through polymer backbone enhancements as well as with the use of nano and macro-polymer additives for even further improved fatigue properties, with minimal loss of mechanical, chemical or heat resistance.