Mechanical and thermal properties of a room temperature curing epoxy resin and related hemp fibers reinforced composites using a novel in-situ generated curing agent

Abstract

A novel self-exothermic curing agent, effectively able to cure the diglycidyl ether of bisphenol-A (E51 epoxy resin) at room temperature, has been synthesized by blending 4, 4’-diaminodiphenylmethane (DDM) and acrylic acid (AA). The chemical structure of prepared curing agent was characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR). The curing behavior of epoxy with synthesized room temperature hardener was studied by differential scanning calorimetry (DSC) and FTIR. Results confirmed that the curing reaction was completed in only 3 h, which can be attributed to the high reactivity of the acryl amide groups with epoxy and high heat release from DDM and AA reaction. The 5 wt% NaOH treated short hemp fibers (TF) were sandwiched in room temperature curing epoxy resin to obtain rapid prototyping high performance composites. The effects of fiber content on the mechanical properties of composites were studied in terms of tensile, flexural, and impact load. The tensile strength of the composites was increased with the increase of the TF content, and the elongation at break was decreased. Compared with the cured neat epoxy resin, an increase of about 233% in impact strength, 52% in flexural modulus, and 213% in Young's modulus were recorded for the cured composite having 7.5 wt% TF content. We used dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA) to study the effect of fiber content on the thermal properties of composites. The scanning electron microscope (SEM) revealed excellent adhesion between TF and epoxy resin cured at room temperature.