Investigation into the effect of nano-silica particles on the protective properties of polyurethane coatings

摘要

The effect of nano-silica particles on the protective properties of polyurethane (PU) coatings has been investigated. Up to now organic clear coats revealed insufficient scratch, abrasion resistance and corrosion resistance. The investigation has been focused on incorporating non-polar nano-silica particles to 2K polyurethane matrix as a protective properties modifier. Three levels of addition (0%, 5% and 10%) have been incorporated into acrylic polyol/ HDI polyisocanate based polyurethane and cured at three different temperatures (20°C, 70°C and 110°C). PU coatings have been applied on Q-steel panels and exposed to 3% NaCI solution for 1000h. To evaluate protective properties DC resistance and Electrochemical Impedance Spectroscopy (EIS) have been employed. Free films were used to evaluate trends in water- uptake calculated using coating capacitance in the early stages of exposure. Also the effect of nanoparticles on cross-linking density and glass transition temperature (Tg) was investigated by Dynamical Mechanical Thermal Analysis (DMTA). Abrasion resistance test was carried out on Taber machine by estimating the weight loss from a coated panel. Dispersion/ agglomeration of nano-silica particles in polymeric matrix was studied using AFM with Energy Dispersive X-ray (EDX) analysis being used to identify the elemental composition of samples. Electrochemical results showed a positive effect on the permeability properties for PU coatings with 5% of embedded nano- silica particles. Also coatings cured at higher temperatures showed improved protective properties. The T_g also increased with increase of curing temperature; this was attributed to an increase in cross-linking density. The Taber abrasion test indicates that both, nano- silica particles and higher curing temperatures enhance abrasion resistance. AFM analysis showed that nanoparticles are well dispersed in the polyurethane matrix without signs of agglomeration. EDX analysis proved that nanosilica particles were incorporated into the polyurethane matrix.