Curing kinetics and thermal stability of epoxy blends containing phosphorous-oxirane with aromatic amide-amine as curing agents

Abstract

This article describes the synthesis of a series of aromatic amide-amines and their potential use as epoxy hardeners. These amines were synthesized by the reaction of L-phenylalanine (PA) with diamines of different structures i.e. 1,4-phenylene diamine (PD), 1,5-diamino naphthalene (N), 4,4′-(9-fluorenyllidene)-dianiline (F), 4,4′-diaminodiphenyl sulphide (DS) and 3,4′-oxydianiline (O) in a stoichiometric ratio (1:1). Structural characterization of synthesized amide-amines was done with the help of elemental analysis and spectroscopic techniques viz. FT-IR, ¹H-NMR and ¹³C-NMR. An epoxy blend was prepared by mixing tris(glycidyloxy) phosphine oxide (TGPO) with conventional epoxy i.e. diglycidyl ether of bisphenol-A (DGEBA) in an equivalent ratio of 2:3 to incorporate phosphorous into the main chain. The curing kinetics of the epoxy blend with synthesized aromatic amide-amines was investigated by non-isothermal DSC technique using multiple heating rate method (5, 10, 15 and 20 K/min.). The activation energies were determined by fitting the experimental data into Kissinger and Ozawa kinetic models. The activation energies obtained through Ozawa method were slightly higher than those of Kissinger method but were comparable. However, both the energies were found to be dependent on the structure of amines. The thermal stability and weight loss behavior of isothermally cured thermosets were also investigated using thermogravimetric analysis (TGA) in nitrogen atmosphere. All the samples showed improved thermal stability in terms of char yield than using only amines as hardeners.