J. Indian Chern. Soc., Vol. 77, July 2000, pp. 332-335 Curing exotherm and processing temperature of a family of epoxy resins in the light of fabrication of composites G. S. Mukherjee •, R. K. Singh and G. N. Mathur Defence Materials and Stores Research & Development Establishment, (P.O.) DMSRDE, G. T. Road, Kanpur-208 013, India Manuscrtpl reutved 5 July 1999, revtsed 17 January 2000, accepted 3 March 2000 A group of cyanocthylated amine has been synthesised and utilised as hardener for the curing of epoxy resin. The effect of cyanoethyla· lion of amine on their curing reaction with epoxy resin having equivalent of 189 has been studied with the help of differential scanning calorimeter. The processing temperature during the fabrication of composites is prescribed. The exotherm of such curing reaction (M/0) and the degree of cyanoethylation (CEt) of the amine follow the relation, Mlr = (324-68.40 CEt) kJ kg" 1 • Epoxy resins. one of the most coveted resins used in the manufacture of composite materials, undergo curing reac- tion exothermically 1 -4. The very exothermic nature of epoxy curing system makes it difficult to handle bulk quan- tities of resin mix for fabrication of thick and large com- posite laminates because such composite systems consisting of resins are basically poor conductors of heat 3 , causing accumulation of large amount of liberated heat which leads to the development of hot spots, nonuniformity in distribution of internal stresses and degradation of properties 1 3 -{i. For example, composites based on ultrahigh molecular weight polyethylene (UHMWPE) fabric 3 • 7 may loose their dimensional stability under the processing con- dition of temperature and pressure if the evolution of such heat exotherm is excessively high. Therefore, from the practical standpoint, the quantity of epoxy resin in bulk to be handled during curing is determined by the degree of exotherm So prior knowledge of the magnitude of exotherm is essential while considering the processing of polymer composites. And this can be understood well in advance conveniently from the thermogram provided by differential scanning calorimeter (DSC). The matrix resin may be characterised according to the curing temperature in a DSC thermogram. Such tempera- tures depend upon the desired speed of operation and resin content to be maintained in the composite laminateS- 10 . But during the fabrication of composite by compression mould- ing there is some confusion about the selection of process- ing temperature (i.e. the temperature at which pressure to be applied) because of the fact that there are three prominent temperatures 10 in the DSC curing thermogram such as onset curing temperature ('7;). peak temperature (Tp) and final curing temperature (T 1 ) 10 • So at what temperature the pressure needs to be applied during 332 processing requires some justification. Therefore, such temperature is a process control parameter and it provides the proper temperature data for application of full pressure on the resin impregnated substrate or laminate in a com- pression or matched die mould 1 • In this communication, the selection of processing temperature and evaluation of curing exotherm of a family of epoxy system based on the diglycidyl ether of his- phenol-A (DGEBA) resin and different cyanoethylated aliphatic amines synthesised are reported. Results and Discussion A family of hardeners was synthesised by cyanoethyla- tion of triethylenetetramine (TETA). Curing of DGEBA epoxy resin was carried out at a particular heating rate in the presence of stoichiometric proportion of hardeners en- dowed with progressively increasing proportions of cyanoethyl group in the constituent amme hardener. The characteristic curing temperatures 8 - 10 , such as T, Tr as well as T 1 and the exotherm developed (!!He) during the curing of the selected resin compositions in the DSC experiment are summerised in Table I. A typical DSC thermogram is shown in Fig. I. Table 1. DSC results of cunng of d1flcumt epoxy sy,tem' System Resm compositiOn 7, Tp 1"1 X 10 3 "C "C "C J kg-• I DGEBA+TETA 316 66 99.2 I'U II DGEBA + (monocyanoethylated-TET A) 268 705 104.5 144 Ill DGEBA + (d1cyangethylated-TET A) 190 71.7 118 () 189 5 IV DGEBA + (tncyanoethylated-TET A) 114 87 3 143 3 195 The dynamic scans of the resin systems showed that the sharpness of the exotherm is brodened with the incorpora- tion of cyanoethyl moiety into the constituent hardener