Kinetic study of the epoxy curing at the silica particles/epoxy interface using the fluorescence of pyrene label

The cure process of an epoxy-amine system was studied in composite materials based on an epoxy polymer matrix filled with silica particles. FT-NIR and Fluorimetry (based on the use of fluorescent labels) were used as analytical techniques. In order to study the effect of the structure of the interphase, the silica particles were surface coated with two different silanes: 3-aminopropyltriethoxysilane and 3-aminopropylmethyldiethoxysilane. 1-pyrene-sulfonylchloride was chemically bonded to: (i) the coated silica particles and (ii) to the epoxy polymer matrix, using its fluorescence response to independently monitor the epoxy curing at the interface region and in the bulk respectively. The cure process was followed at different temperatures to subsequently study its kinetics either by fluorescence or by FT-NIR. An extent of reaction in terms of integrated fluorescence intensity was defined and the subsequent kinetic analysis allowed us to calculate apparent activation energies of the process. Comparing the curing reaction in the polymer bulk and at the interface it could be concluded that the epoxy curing at the interface proceeded faster but only during the first stages of the reaction. This result was attributed to a higher local concentration of amino groups at the interface. Finally, a comparison between FTIR and fluorescence results showed that both techniques provide complementary information about the curing reaction.