Study of the isothermal curing of an epoxy prepreg by near‐infrared spectroscopy

Abstract

ABSTRACT:The commercial epoxy prepreg SPX 8800, containing diglycidyl ether of bisphenol A, dicyanodiamide, diuron, and reinforcing glass fibers, was isothermally cured at different temperatures from 75 to 110°C and monitored via in situ near-infrared Fourier transform spectroscopy. Two cure conditions were investigated: curing the epoxy prepreg directly (condition 1) and curing the epoxy prepreg between two glass plates (condition 2). Under both curing conditions, the epoxy group could not reach 100% conversion with curing at low temperatures (75-80°C) for 24 h. A comparison of the changes in the epoxy, primary amine, and hydroxyl groups during the curing showed that the samples cured under condition 2 had lower initial epoxy conversion rates than those cured under condition 1 and that more primary amine-epoxy addition occurred under condition 2. In addition, the activation energy under cure condition 2 (104 -97 kJ/mol) was higher than that under condition 1 (93-86 kJ/mol), but a lower glass-transition temperature of the cured samples was observed via differential scanning calorimetry. The moisture in the prepreg was assumed to account for the different reaction kinetics observed and to have led to different reaction mechanisms.

Mechanical properties of graphene nanoplatelet/carbon fiber/epoxy hybrid composites: Multiscale modeling and experiments

“…Finally, the data in Figure 15 also indicate that the epoxy crosslink density (shown only for the 1-layer system for clarity) has a minimal effect on the elastic modulus of the GNP/epoxy composite for M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 24 the crosslink density range considered. This is expected, considering that most structural epoxies are crosslinked in the range of 60-95% [29][30][31][32][33], which brackets the range considered in this study. Therefore, it is anticipated that in the range considered herein that the epoxies would maintain their typically-observed mechanical properties, and there would be little influence of the crosslink density in the elastic response.…”

“…It is important to note that for industrial grade epoxies, a broad range of crosslink densities of 60-95% is typically observed in experiments [29][30][31][32][33]. Therefore, the simulated crosslink densities were chosen to span part of this range.…”

Molecular modeling of epoxide-amine systems: Topological cure conversion limit and its influence on material properties

“…0 Epoxide, A and Epoxide,t A are the areas of the peak readings for the epoxide groups for un-crosslinked system and the same system after a certain curing time, respectively [1][2][3][4]. Another common technique is DSC, which monitors the heat flow within a sample when subjected to a specified thermal profile.…”

“…Experimental techniques such as Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) are commonly used to monitor the physical change in resin-hardener compound in terms of the extent of conversion X [1][2][3][4][5][6][7][8][9][10]. In FTIR, the changes in spectral features, such as the intensity of the epoxide group are utilized to calculate the extent of conversion using the following:…”

Glass fibre reinforced polymer composites toughened with acrylonitrile butadiene nanorubber

“…Dicyandiamide (DICY) cured epoxy resins are well known in industry as prepregs constituents and curable structural adhesives [1,2,3,4,5]. Solid acrylonitrile butadiene rubber (NBR) with high acrylonitrile content provides a good compatibility between the NBR and the epoxy resin [6,7].…”