Abstract
The performance of waterborne (meth)acrylic coatings is critically affected by the film formation process, in which the individual polymer particles must join to form a continuous film. Consequently, the waterborne polymers present lower performance than their solvent-borne counter-polymers. To decrease this effect, in this work, ionic complexation between oppositely charged polymer particles was introduced and its effect on the performance of waterborne polymer films was studied. The (meth)acrylic particles were charged by the addition of a small amount of ionic monomers, such as sodium styrene sulfonate and 2-(dimethylamino)ethyl methacrylate. Density functional theory calculations showed that the interaction between the selected main charges of the respective functional monomers (sulfonate–amine) is favored against the interactions with their counter ions (sulfonate–Na and amine–H). To induce ionic complexation, the oppositely charged latexes were blended, either based on the same number of charges or the same number of particles. The performance of the ionic complexed coatings was determined by means of tensile tests and water uptake measurements. The ionic complexed films were compared with reference films obtained at pH at which the cationic charges were in neutral form. The mechanical resistance was raised slightly by ionic bonding between particles, producing much more flexible films, whereas the water penetration within the polymeric films was considerably hindered. By exploring the process of polymer chains interdiffusion using Fluorescence Resonance Energy Transfer (FRET) analysis, it was found that the ionic complexation was established between the particles, which reduced significantly the interdiffusion process of polymer chains. The presented ionic complexes of sulfonate–amine functionalized particles open a promising approach for reinforcing waterborne coatings.
Highlights
The global market of polymer-based paints and coatings is projected to grow substantially over the period of 2019–2025, owing to the worldwide increasing demand by many different sectors, such as the construction and automotive sectors, aerospace, mining and packaging production industries [1,2]
Before studying the formation of the ionic network in the polymer film, one important point was to ensure that the interactions between the opposite charges of NaSS and DMAEMA were energetically favored over their corresponding counterions
Density Functional Theory (DFT) calculations were performed to study the interactions between the NaSS and DMAEMA ionic monomers in terms of binding energy
Summary
The global market of polymer-based paints and coatings is projected to grow substantially over the period of 2019–2025, owing to the worldwide increasing demand by many different sectors, such as the construction and automotive sectors, aerospace, mining and packaging production industries [1,2]. Many industrial polymer production processes relay still on the use of organic solvents, which contributes to increase emissions of volatile organic compounds (VOC). The stringent environmental standards for VOC’s emission have been a driving force for replacing processes that use solvents by cleaner water-based ones [3,4,5]. The water-based polymers still present lower mechanical performance than their solvent-based counter products [6,7]. The worst mechanical performance and considerable water sensitivity of waterborne films is directly related to the film formation process [8,9] and is usually responsible for the lower performance of the films, which slow down the replacement of the solvent-borne coatings by the waterborne ones on the market
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