Abstract
Here, we propose a novel attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy method for simultaneously monitoring the curing reaction and the diffusion behavior of curing agents at the surface of rubber in real-time. The proposed scheme was demonstrated by fluorine rubber (FKM) and FKM/carbon nanotube (CNT) nanocomposites with a target curing agent of triallyl-isocyanurate (TAIC). The broadening and the evolution of the C=O stretching of TAIC were quantitatively analyzed to characterize the reaction and the diffusion. Changes in the width of the C=O stretching indicated the reaction rate at the surface was even faster than that of the bulk as measured by a curemeter. The diffusion coefficient of the curing agent in the course of heating was newly calculated by the initial increase in the absorbance and our model based on Fickian diffusion. The diffusion coefficients of TAIC during curing were evaluated, and its temperature and filler dependency were identified. Cross-sectional ATR-FTIR imaging and in situ ATR-FTIR imaging measurements supported the hypothesis of the unidirectional diffusion of the curing agent towards the heated surface. It was shown that our method of in situ ATR-FTIR can monitor the degrees of cure and the diffusion coefficients of curing agents simultaneously, which cannot be achieved by conventional methods, e.g., rheological measurements.
Highlights
The change in the full width at half maximum (FWHM) is attributed to the progress of the curing reaction of TAIC in FKM, which is highly correlated with the change of the crosslinking density and Young’s modulus [34]
We proposed methods for characterizing the curing reaction and the diffusion behaviors of the curing agent at the surface of rubber in real time using in situ
From the investigated increases and broadenings of the C=O stretching band of the TAIC curing agent, both reaction and diffusion kinetics were quantitatively evaluated, which was difficult with the conventional method of bulk characterization through rheological measurements
Summary
Rubbers have become indispensable materials in various applications in our daily lives, such as sealing materials, tires, and stretchable devices. The advantages of rubbers in these industrial applications are their lightweight, soft/flexible, shock-resistant, and moldable characteristics. The elasticity is important for any type of rubber application. The elasticity of rubber products is controlled by both the reinforcing fillers and the curing reaction of the polymer chain. A three-dimensional network is formed with polymer chains and curing agents. Such a network largely affects the hardness, compressive force for sealing, and long-term stability of rubber products. Precise control of the curing behavior of rubber in the presence of fillers is important to obtain the desired properties with stable production
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