Processing and Characterization of Fiber Reinforced Polymer Nanocomposites and their Degradation under Hygrothermal Loading

Abstract

Studies on the effect of different processing parameters (premixing parameters, curing time and curing temperature, post-curing temperature, resin to hardener mix ratio) on mechanical properties of fiber reinforced epoxy-clay nanocomposites containing 2 phr of Cloisite® 15A have been carried out. Further, Cloisite® 15A has been modified via a new silanization route with different quantities (0.1, 0.5, 2, 4 and 6 times the weight of clay (X)) of two different silane coupling agents viz. 3-aminopropyltriethoxysilane (APTES) and 3-glycidyloxypropyltrimethoxysilane (GPTMS). The silylated clay minerals have been characterized using Fourier transform infrared (FTIR) spectroscopy, Small angle X-ray scattering (SAXS) and Thermogravimetric analysis (TGA) to confirm the successful grafting of silanes on clay minerals. A detailed study has been done with regard to the effect of silanization of clay minerals on properties of glass fiber epoxy-clay nanocomposites as a function of two important parameters: chemical structure of silane and concentration of silane coupling agent used in grafting reaction. The silane modified clays have been dispersed in epoxy resin by using high shear homogenization and sonication. The fiber reinforced epoxy-clay nanocomposites were manufactured using vacuum assisted wet layup or vacuum assisted resin infusion molding. An optimum quantity of silane for successful modification of large surface area of clay mineral layers and curing schedule of fiber reinforced epoxy-clay nanocomposites were also arrived at. The fiber reinforced epoxy-clay nanocomposites containing silane modified clay minerals have been characterized using Small angle X-ray Scattering (SAXS), Transmission electron spectroscopy (TEM) and Differential scanning calorimetry (DSC). The results indicate that the silane treatment of Cloisite® 15A aided exfoliation of clay mineral layers as evidenced by SAXS and TEM, promoted interfacial adhesion as suggested by the significant increase in mechanical properties. The incorporation of silane treated clay minerals led to an increase in tensile modulus, tensile strength, flexural modulus and flexural strength by 30%, 37%, 139% and 146%, respectively in nanocomposites containing clay minerals modified using 4X aminopropyltriethoxysilane. The fracture surfaces were also examined by Scanning electron microscopy (SEM), which revealed a considerable difference in failure modes of fiber reinforced epoxy nanocomposites containing Cloisite® 15A and those containing silane modified clay minerals.

The behavior of these novel fiber reinforced nanocomposites under different hygrothermal aging conditions had also been studied in detail. The amount of silane used for functionalization of clay minerals and polarity of silane groups influenced the long-term durability of fiber reinforced epoxy-clay nanocomposites in seawater. The incorporation of clay minerals in epoxy hindered the degradation of fiber reinforced nanocomposites, and those containing silylated clay minerals modified using a small amount of silane coupling agents (0.1X, 0.5X) exhibited better retention of tensile and flexural strength after exposure to seawater. The polarity of the organic moieties and morphology of clay minerals in epoxy significantly influenced the durability of nanocomposites in seawater.