Improving the mechanical properties of waterborne nitrocellulose coating using nano-silica particles

Abstract

Abstract In this study several nitrocellulose emulsions containing different percentage of nano-silica particles were prepared, and the effect of different content of nano-silica particles on the drop size, morphology and stability of nitrocellulose emulsions as well as optical and mechanical properties of the resultant films was investigated. Incorporation of nano-silica particles up to 2% not only did not adversely affect the properties of nitrocellulose emulsions and appearance of the formed films but also the glass transition temperature (Tg), storage modulus, tensile strength, elongation at break, Young’s modulus and pendulum hardness all increased with increasing nano-silica particles content. High content of nano-silica particles (3% and 4%) surprisingly resulted in emulsion phase inversion from oil in water emulsion (O/W) to water in oil emulsion (W/O). Theses phase inversions were attributed to the presence of the nano-silica particles at the oil-water interface which conducted the large variation in the affinity of stabilizers. Formation of multiple drops prior to phase inversion indicated that catastrophic phase inversion was responsible for these inversions. In comparison with bare nitrocellulose film, at 2% nano-silica particles, the Young’s modulus increased by 91.1%, the tensile strength increased by 46.6%, elongation at break increased by 12.7%, the Tg increased from −7.3 °C to 6.8 °C, and pendulum hardness increased from 31 to 40. The results demonstrated a homogenous dispersion of nano-silica particles in the nitrocellulose resin matrix and strong interfacial interaction of the nano-silica particles with the nitrocellulose resin matrix which caused improvement in mechanical performance of waterborne nitrocellulose coating.