Hygrothermal characterization of nano-reinforced vinyl ester syntactic foam

Syntactic foams are light-weight particulate composites consisting of hollow microballoons embedded in a resin matrix. They are commonly used in weight sensitive applications of marine and aerospace structures. Syntactic foams are preferred over other materials because of their superior properties such as low density with high modulus, strength, damage tolerance, and low moisture absorption. In this study, plain syntactic foams were fabricated by mixing Vinyl Ester resin and S22 micro balloon at 60% volume fraction. Nano-reinforced syntactic foams were also fabricated with 1, 2 and 5% weight fractions of Nanomer I.30E nanoclay. Ultrasonic mixing technique was used for uniform dispersion of the nanoclay platelets in the resin matrix. The effects of three roll mill mixing method on the properties of syntactic foams were also investigated. Hygrothermal studies were carried out by immersing the test samples in de-ionized water and sea water at room temperature. Quasi-static tests were performed on dry and wet samples for comparison of their compressive strength and modulus. In addition, low velocity impact tests at 1, 1.5 and 2 m/s were carried out by using a DYNATUP 8250 machine on plain and nano-reinforced samples under dry and wet conditions. Furthermore, Dynamic Mechanical Analysis (DMA) test was done on the samples to understand the viscoelastic behavior of these nano-reinforced syntactic foams and determine the glass transition temperatures. Test results indicate that exposure to hygrothermal conditions brings about significant reduction of strength and modulus of syntactic foams. Initiation energy was also found to decrease under hygrothermal conditions. It is observed that syntactic foams fabricated with 1% nanoclay and without involving three roll mill mixing method gives higher values of initiation energy and glass transition temperature.