Modification of ethyl 2-cyanoacrylate using silica and nitrile butadiene rubber to achieve high thixotropy and low internal stress

A mixture of fumed silica and nitrile butadiene rubber (NBR) is used to improve the viscosity and thixotropy of ethyl 2-cyanoacrylate (ECA) and to reduce the internal stress of ECA. Rheological characteristics of ECA/silica, ECA/NBR, and ECA/silica/NBR are measured using a rheometer and are presented using the viscosity and thixotropic index. The pristine and modified ECA were characterized using Fourier transform infrared spectrometer (FT-IR) and Thermal gravity analysis (TGA). The impact of additives on curing internal stress of ECA is measured and analyzed. Results shown that addition of fumed silica and NBR effectively improve the viscosity of ECA blends, which increases with an increased content of both additives. Thixotropic ECA/silica/NBR shows an apparent shear-thinning character and is well fitted by a power law equation. FT-IR spectra and TGA analysis indicated that the thixotropy of the obtained ECA/silica/NBR blends is mainly attributed to silica via the creation of hydrogen bonds between silica particles and between silica and polymers, and a synergistic effect between silica and NBR is shown to improve viscosity. The modified ECA showed considerable stability and their viscosity were slightly increased after 30 days. The presence of NBR is beneficial for silica dispersion in the ECA matrix and for a smooth surface of cured ECA. The added silica and NBR can alleviate the internal stress of the cured adhesive layer, and NBR plays a significant role in reducing internal stress. This work is devoted to developing thixotropic and low-shrinkage cyanoacrylate-based adhesives.