Pigment-resin interactions in coating systems

Charles R. Hegedus

doi:10.17918/00000973

The thermodynamics of filler particle surface-polymer interactions have been characterized using inverse gas chromotography (IGC) and flow calorimetry. The use of IGC in this new application extends analysis to calculation of the thermodynamic properties of reversible particle-polymer interactions. This technique was used to determine solid surface energies; free energy, enthalpy, and entropy of adsorption; and work of adhesion. The values obtained agree favorably with those obtained from alternate techniques. Non-polar forces provided a large contribution to the free energy and enthalpy of adsorption. Acid-base pairs were found to undergo favorable interactions while acid-acid and base-base pairs were less likely to undergo strong interactions. Flow calorimetry was used to measure the adsorption enthalpies of methyl methacrylate and acrylic acid on TiO2 and SiO₂. The extent of reversibility/irreversibility of the resulting interactions was also assessed. Adsorption of methyl methacrylate (MMA) and acrylic acid (AA) on fillers was strong and irreversible. The adsorption enthalpy of MMA on silica was approximately 27 kJ/mole due to hydrogen bonding. Adsorption enthalpies of AA on alumina-treated TiO2 were higher than that of MMA on silica, indicating stronger acid-base interactions. The interface which resulted from filler particle-polymer interactions was investigated by determining the PMMA adlayer thickness using centrifugation and viscosity measurements. These adlayer thicknesses ranged from 9 to 110 nm. Adlayer thickness increased with particle size and PMMA-filler interaction. Values calculated from viscosity experiments were greater than those from centrifugal packing, leading to a proposed model for the polymer adlayer state. The practical aspect of this study was demonstrated by analyzing coating properties resulting from the formulation of titanium dioxide fillers in PMMA. TiO2 pigments which had more favorable adsorption with MMA resulted in coatings with better dispersion quality and stability, greater resistance to salt spray, and caused a greater increase in the Tg of the PMMA matrix. In contrast, these fillers had detrimental effects on adhesion and flexibility. These results were attributed to extensive interactions between filler and polymer which decrease permeability and increase rigidity of the polymer matrix.

Pigment-resin interactions in coating systems

Files and links (1)

Abstract

Metrics

Details

Pigment-resin interactions in coating systems

Files and links (1)

Abstract

Metrics

Details

Drexel University Social media