Najuma Abdul Razack, Lity Alen Varghese Department of Chemical Engineering, National Institute of Technology, Calicut, Kerala,India. Abstract Epoxy resins have been known to possess good mechanical properties and excellent adhesive properties and thus have been widely used in industry, such as adhesive, coating, laminating and composite applications. In this study , a low molecular weight epoxy resin, diglycidyl ether of bisphenol A (DGEBA) is cured with both aliphatic and aromatic hardeners and a comparison was done based onmechanical characterization, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) studies. Four different hardeners (2 aliphatic and 2 aromatic) were used in the stoichiometric amounts for the study. They include Triethylene tetramine (TETA), Dicyandiamide (DICY), Diaminodiphenyl sulphone (DDS), and m-phenylenediamine (mPDA). The mechanical characterization comprised the shear and peel strength experimentations which concluded that the aromatic ones are better compared to the aliphatic ones. From the DSC studies the effectiveness was found to be in the order TETA<DICY<DDS<mPDA which was consistent with the thermo gravimetric analysis (TGA) studies. Keywords — curing, epoxy resin, hardener, mechanical properties, thermogravimetric analysis. 1. Introduction Epoxy resins forms a big class of compounds containing two or more epoxy groups, which reacts with a variety of curing agents containing active hydrogens such as amines and anhydrides[1]. These resins linked with amine hardeners are widely used as structural adhesives because they have good thermal and mechanical properties [2]. Amine compounds are classified into primary, secondary, and tertiary amines, in which one, two, and three hydrogen molecule(s) of ammonia (NH 3 ) have been substituted for hydrocarbon, respectively. Amines are called monoamine, diamine, tri-amine, or polyamine according to the number of amines in one molecule. According to the types of hydrocarbons involved, amines are classified into aliphatic, alicyclic and aromatic amines and they all are important curing agents for epoxy resin. Resins that have been cured using aliphatic amines are strong, and are excellent in bonding properties. They have resistance to alkalis and some inorganic acids, and have good resistance to water and solvents, but they are not so good to many organic solvents. Aromatic amine has been developed to achieve greater heat resistance and chemical resistance than those of aliphatic amine. Depending on the crosslinking agent, the final properties of the epoxy network are also different. It was observed that the properties and performance of cured compounds of epoxy resins are dependent on the type of curing agent and curing conditions [3]. When the curing agent is an aliphatic amine, the curing process occurs at room temperature, but the reaction is slow [4]. On the other hand epoxy resins cured with aromatic amines generally present good thermal and chemical resistance.Sometimes the aromatic ring was introduced into epoxy backbone during synthesis, for example, naphthalene ring and biphenyl group were often used to improve the heat resistance of epoxy resin [5-9]. During cure of aliphatic amines, each primary aliphatic amine reacts with an epoxy group of DGEBA, via ring opening, to form a CH 2 -NH bond and a pendant hydroxyl group, the presence of which is known to accelerate subsequent ring opening reactions. The resulting secondary amines react in a similar manner with remaining epoxy rings to crosslink the polymer chains, though at a slower rate. In the aromatic amines, the amine group is separated by rigid benzene rings rather than flexible chains of molecules as in the aliphatic amines [10]. The stoichiometric relationship between curing agents and resins has a great effect on the physical and the mechanical properties of the epoxy resin. Four different amines were chosen for the present study, viz. Triethylene tetramine, Dicyandiamide, Diaminodiphenyl sulphone and m-phenylenediamine. The amine/epoxy reaction occurs at room temperature and it can be accelerated with an elevated temperature cure [11]. TETA is a common primary polyamine which is in the liquid form, having a pot life of 30 min at 75 0 F. DICY is the most commonly employed latent curing agent that forms crystals having a high melting point of 207°C to 210°C. It is the dimer of cyanamide and is amphoteric. However cyclisations take place easily The Effect of Various Hardeners on the Mechanical and Thermal Properties of Epoxy Resin 2662 International Journal of Engineering Research & Technology (IJERT) Vol. 3 Issue 1, January - 2014 ISSN: 2278-0181 www.ijert.org IJERTV3IS10876