Abstract
Sol-gel coatings offer excellent properties such as scratch resistance, barrier properties, outdoor stability and high thermal stability. However, the precursors (silanes) used for these coatings are very expensive and require special care for handling and application on substrate. One approach to solve this problem is the incorporation of conventional organic polymer as the organic modifying component in silane coating formulation. Incorporation of organic polymer will reduce the cost and will make sol-gel coatings readily acceptable in industry.
The aim of the present work is to prepare and evaluate the performance of a waterborne polyester resin incorporated sol-gel coating based on 3-glycidoxypropyltrimethoxysilane (GPTMS) and methyltrimethoxysilane (MTMS). Hexamethoxymethylmelamine (HMMM) and paratoluenesulphonic acid (p-TSA) were used as crosslinking agent and an acid catalyst respectively. The coating solution was prepared by addition of 30 wt% of HMMM and 1 wt% of p-TSA to the mixture of polyester resin and primary sol (MTMS:GPTMS =1:2 mol. ratios). Coating was applied on aluminum and magnesium substrates by dip coating method and cured at 130°C for 45 min.
SEM and AFM analysis confirm the continuous and crack free coating on aluminum and magnesium substrates. The anti-corrosion behavior was evaluated using potentiodynamic polarization studies and it was observed that the coating with 10 wt% polyester has excellent corrosion resistance. However, for all coating formulations, the corrosion current of coated substrate was decreased more than one order of magnitude than the corresponding bare metals, confirming enhanced corrosion resistance. Water contact angle of coatings was found in the range of 63-71° and it was observed that it increases with increasing polyester resin content in the coating.
