MATERIALE PLASTICE ♦ 46♦ Nr. 2 ♦ 2009 129 Curing Kinetic of an Epoxy-amine System by Calorimetric Method and FT-IR Spectroscopy VALENTIN RADITOIU*, LIVIU DUMITRACHE, ALINA RADITOIU, MAGDALENA LADANIUC, SEVER SERBAN, LUMINITA WAGNER Research and Development National Institute for Chemistry and Petrochemistry - ICECHIM, 202 Splaiul Independenþei, 060021, Bucharest, Romania The study presents experimental data regarding the curing reactions of some epoxy systems consisting of diglycidyl ethers of bisphenol A and different amine hardeners at room temperature and at microwaves. The curing reaction of the system composed of an epoxy resin (ROPOXID P 401) and 4,4’-diamino- diphenylmethane (HT 972) was studied by differential scanning calorimetry (DSC) and FT-IR spectroscopy. The degree of conversion obtained using FT-IR method is very close to that obtained using calorimetric method. Keywords: epoxy, amine, microwaves, kinetic Epoxy resins are very important due to their multiple applications as adhesives, coatings, encapsulates, casting materials, and binders and as matrix material for high performance composites [1-9]. Epoxies offer high strength, low shrinkage, excellent adhesion to various substrates, effective electrical insulation, chemical and solvent resistance. An important aspect of thermosetting resin such as an epoxy is the cure kinetics associated with the material in order to optimize the processing conditions to generate specific physical and mechanical properties [10-16]. Epoxy resins react with a large number of hardeners such as aliphatic and aromatic amines, anhydrides, substituted ureas, thiols, dicyandiamide, but the most commonly used chemical classes of curatives are amines [17,18]. The aim of this work was to study the results obtained for the curing process of an epoxy resin based on diglycidyl ether of bisphenol-A (ROPOXID P 401) with 4,4’- diaminodiphenylmethane (HT 972) under microwaves. The curing kinetic of the so-called “hot system” was investigated using differential scanning calorimetry and FT-IR spectroscopy. Experimental part Epoxy resins used for the experiments: ROPOXID 500 (dynamic viscosity 14580 mPa.s (25 0 C); 0.523 - equiv. Epoxy/100g; M=382) and ROPOXID P 401 (dynamic viscosity 1725 mPa.s (25 0 C); 0.41 - equiv. Epoxy/100g; M=488) were supplied by Policolor and used as received. Hardeners used for the curing reactions : triethylenetetramine (TETA) (M=146; m.p.=12°C; b.p.=266-267°C; amine index=1410-1460 mg KOH/g), aliphatic amine adduct with propenoxide (T) (amine equivalent – 1.85 %; dynamic viscosity 392.8 mPa.s (25 0 C) and 4,4’-diaminodiphenylmethane (HT 972) (M=198; m.p.= 89-91°C ; b.p.=221°C) were provided by Fluka and used as received. Curing reactions were conducted into a microwave oven EG 1031NP-DK-1 Hyundai ( Power – 1000 W; Frequency – 2.45 GHz; Volume - 31 L, multimode cavity), the power of the microwaves being adjusted only by modifications on irradiation time. The epoxy resin – amine mixtures were prepared at room temperature by adding the curing agent while continuously stirring and heating at a temperature value less than the curing temperature until a homogeneous solution was obtained. The curing grade obtained by irradiation of the reaction mixtures at microwaves was determined by calorimetric measurements using a Du Pont 2000 thermal analysis system. The calorimeter was calibrated using indium standard for temperature calibration. The heating rate was 10 0 C/min., all the samples were about 5-10 mg in weight of binary mixtures epoxy resin/ hardener prepared before performing each experiment. The flowing gas was 99.99999% pure nitrogen from Linde. Samples were introduced in aluminum pans hermetically closed and then introduced in the calorimeter at room temperature. FT-IR spectra were recorded with a JASCO FT-IR 6300 spectrometer on an ATR Specac Golden Gate (sapphire/ diamond) accessory. Results and discussions The cure reaction of epoxy resins is a complex process that involves the formation of a rigid three-dimensional network. For studying the curing conditions at microwaves four different epoxy systems were selected as “cold systems” for comparison with the investigated “hot system” as it can be seen in table 1. As it is well known curing at microwaves accelerates up the crosslinking process. After 30-40 min from the introducing in the oven, probes were completely crosslinked. Differences between classic processes and curing at microwaves are observed analyzing DSC results. Reaction heat determined after curing at microwaves showed a total reticulation comparatively with the same probe at room temperature in the same period of time when a very small grade of reticulation is recorded. In order to evaluate the optimum resin / hardener ratio necessary for isothermal study, a dynamic study was carried out. The end of the curing reaction was indicated by the absence of any thermal effects. Comparative determinations were done for the same epoxy systems at room temperature and after crosslinking at microwaves. Comparing these two sets of evaluations it clearly results the advantage of curing at microwave which is the total http..//www.revmaterialeplastice.ro/ * Tel.: 0744178414