Effects of additives on the corrosion protection performance of waterborne polymer coatings

  • Chi Him Lo

Student thesis: Phd

Abstract

Additives are essential in waterborne coating formulations for attainment of coherent and defect-free coatings. However, residual additives can influence coating microstructure development and can have an impact on the final coating properties (e.g. appearance, viscoelasticity, adhesion and/or barrier properties). This thesis investigates the formulation factors which can influence corrosion protection properties of one component direct to metal (1K DTM) waterborne acrylic coatings. Chapter 2 discusses the design and development process of the model 1K DTM waterborne acrylic coating with comparable corrosion protection performance to the reference coating. Semi-continuous emulsion copolymerisations of styrene (STY), methyl methacrylate (MMA), 2-ethylhexyl acrylate (2EHA) and methacrylic acid (MAA) are conducted to generate emulsifier containing P(STY-MMA-2EHA-MAA) latexes with varying glass transition temperatures (Tg). Coating formulations of the P(STY-MMA-2EHA-MAA) latexes are prepared for room temperature curing on cold rolled steel (CRS) and the resulting coating surfaces are characterised by SEM and AFM-IR before and after exposure to accelerated atmospheric corrosion testing. In Chapter 3, the effects of organosulphur surfactant addition on the corrosion protection performance of 1K DTM waterborne acrylic coating are elucidated with a P(STY-MMA-2EHA-MAA) coating developed in Chapter 2. A broad variety of characterisation techniques are used to examine separately the effects of surfactant addition on flash rust inhibition as well as various coating properties, including surface, mechanical, ionic barrier, adhesion and corrosion protection properties. Atomic Force Microscopy-Infrared Spectroscopy (AFM-IR) is used to elucidate surfactant-induced microstructural changes of polymer films and study the morphology of the coating-metal interface. In addition, the incorporation of commercially available polystyrene sulfonates with different molecular weights in the model coatings are investigated in Chapter 4. Morphology of the coating-metal interface was found to play a decisive role in achieving good adhesion and corrosion protection properties, while the concentration and chemical structure of surfactant additive can determine its impact on the latex film formation process and microstructure development at the coating-metal interface. A branched surfactant structure with long alkyl side chain was found to be the cause of particle coalescence inhibition during latex film formation and adhesion deterioration at the coating-metal interface, resulting in waterborne acrylic coating with deteriorated barrier properties and poor corrosion protection properties. Whereas high molecular weight linear polymer structure with repeating sulphonate groups was found to enhance adhesion and corrosion protection properties of waterborne acrylic coating.
Date of Award31 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorStuart Lyon (Supervisor) & Lee Fielding (Supervisor)

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