Preferred partitioning: the influence of coalescents on the build-up of mechanical properties in acrylic core–shell particles (I)

Abstract

The partitioning of three coalescents of different polarity in different phases of multiphase acrylic particles was studied to provide a rationale for obtaining the desired performance of binders for wood coatings in terms of the ideal balance between hardness development, blocking resistance, and blushing resistance. Minimum film formation temperature-and aqueous differential scanning calorimetry-measurements on the hard phase polymer by itself showed the different extents to which both hydroplasticization and plasticization by the coalescent occur. Dynamic mechanical thermal analysis was subsequently used to visualize wet-T g effects of three different coalescents in the hard and soft polymer phase of these multiphase acrylic particles. The results have important consequences for the formulation of such binders in applications for exterior wood coatings and coatings in general.

Influence of coalescing aids on the latex properties and film formation of waterborne coatings

“…In the first few days, the more hydrophilic BG apparently increased the water sensitivity of the film and facilitated ion diffusion from the test electrolyte; this resulted in higher values of σ c d c . According to past studies, better mechanical properties were obtained with more hydrophilic coalescing aids, whereas better early water resistance was obtained with more hydrophobic coalescing aids . The differences in the mechanical properties and Warburg diffusion could be explained by the partitioning of the coalescing aids during film formation.…”

“…Formulations with BG gave harder films and also a faster hardness buildup than PnB, even though the latter had a 20% higher evaporation rate. This might have been due to differences in the hydrophilicity and partitioning during drying, and indeed, other researchers have also found that the addition of hydrophilic coalescing aids to waterborne coatings leads to harder films than the addition of hydrophobic coalescing aids …”

“…This prevents tackiness and softness in the dried film but complicates film formation. Several ways of tackling with this problem are available, for instance, the addition of coalescing aids, the use of blends of different particles, the use of multiphase particles, or a combination of these measures …”

“…The addition of coalescing aids is a convenient and flexible way of solving the so‐called film‐formation paradox and has been a subject of many research articles. The effects of coalescing aids have been studied by researchers in terms of partitioning in the wet stage and T g reduction, dispersion stability and viscosity, polymer interdiffusion, and film formation in general …”