Abstract
The exterior durability of epoxies is severely affected due to its poor weathering resistance. Epoxies exhibit chalking and discoloration under UV exposure caused as a result of photodegradation. The present work aims at studying the extent to which the color change and yellowing caused due to weathering under accelerated weathering conditions, of DGEBA epoxy, could be lowered by in situ modification of the epoxy polymer backbone with a silane, namely, MTMS. The epoxy resin and silane-modified epoxy resin were formulated into a TiO2-based white coating, applied on mild steel panels, and exposed in a UV (B) weatherometer. The color change (dE) and yellowness index (YI) values of weathered panels were evaluated using a spectrophotometer. The weathered samples were also characterized using FTIR-imaging technique to study the effect of weathering on the structural backbone of the formulated coatings. The silane-modified epoxy coatings showed lowered yellowing by 45% on UV exposure and the enhanced resistance to yellowing of the modified coatings was indicated by lowered dE and YI values. The enhanced resistance to yellowing by the silane-modified epoxy was attributed to the strengthening of the epoxy backbone by introduction of Si–O–C linkage onto the epoxy polymeric chain.
Highlights
Epoxies as binders are extensively used for corrosion protection in coating industry because of their excellent corrosion resistance and adhesion to substrates
Epoxy resins were chemically modified with various silane monomers to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates and immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (Cc) decreased significantly after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation [5]
The silane-modified coating was applied on mild steel panels and subjected to accelerated UV (B) weathering and the color change and yellowness index values, evaluated during the study, showed that there was a considerable lowering of yellowing and discoloration owing to the silane modification of epoxy
Summary
Epoxies as binders are extensively used for corrosion protection in coating industry because of their excellent corrosion resistance and adhesion to substrates Their outdoor usage is restricted due to their poor weathering resistance. Epoxy resins were chemically modified with various silane monomers to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates and immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (Cc) decreased significantly after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation [5]. The silane-modified coating was applied on mild steel panels and subjected to accelerated UV (B) weathering and the color change and yellowness index values, evaluated during the study, showed that there was a considerable lowering of yellowing and discoloration owing to the silane modification of epoxy
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