Fabrication and characterization of novel liquid rubber modified epoxy
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Date
2017-11
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
A series of liquid rubber modified epoxies (LREs) were fabricated by dispersing pyrolysis derived liquid rubber (PLR) with concentrations ranging 0-25 wt. % into a commercially available epoxy resin (CY-230) followed by curing with triethylene tetramine (TETA, HY-951). The qualitative dispersion of PLR into cured epoxy was ascertained through atomic force microscopy (AFM) and DC conductivity. The nature of bonding of PLR with epoxy was studied using FTIR spectra. The LREs were cast into different dimensions according to ASTM D specifications. The effect of PLR on their mechanical and thermal properties has been evaluated. With PLR concentration, a regular decrease in hardness, tensile, flexural and compressive properties has been observed. This is attributed to the increase in size of phase separated rubber particles (RPs) as well as plasticization of epoxy matrix due to PLR addition. The impact strength and fracture toughness (KIC) of LREs improved gradually up to 15 wt. % of PLR concentration. This is attributed to the increase in size of plastic zone due to the presence of in the LREs. In order to correlate the improvement in impact strength and KIC values, specimens recovered from these tests were subjected to fractography using FESEM. Cavitation of RPs followed by shear yielding of epoxy matrix was observed to be the most prominent toughening mechanism in LREs. The effect of PLR on thermo-oxidative stability of cured epoxy as well as LREs was investigated through simultaneous thermogravimetric-differential thermal analysis-differential thermogravimetry (TG-DTA-DTG).
Micromechanical modeling of LREs was conducted using a finite element (FE) model assuming bcc arrangement of RPs in epoxy matrix. The model was used to explain the lowering of stiffness using a novel scheme based on isotropic stiffness matrix and numerical homogenization technique (NHT). The model was employed to substantiate the experimental findings through stress analysis. Finally, the model was used to predict the effect of RP properties on the elastic properties and stress distributions in LREs.
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