Available at: http://digitalcommons.calpoly.edu/theses/1030
Date of Award
MS in Polymers and Coatings
Chemistry & Biochemistry
PART I ABSTRACT
STABILIZATION OF NEPHELINE SYENITE FILLER IN A UV-CURE
POLYURETHANE DISPERSION WOOD COATING
Nepheline syenite is a naturally occurring, silica deficient, sodium potassium aluminum silicate functional filler used in polymeric coatings, adhesives, and inks. Due to its unique optical characteristics, it can be utilized in formulating a low-viscosity polyurethane dispersion UV-cure clear wood coating system to enhance its functional properties. However, when the coating is formulated with the ultrafine filler, especially at a high loading level (e.g. >10% solids), the filler rapidly settles after formulated, forming a densely packed sediment layer shortening its shelf-life. Suspension of the filler was attempted using rheology additives while minimizing their negative effects on the coating’s optical properties. Compatibility of the additives in the polyurethane dispersion system was qualitatively screened using a starting-point UV-cure polyurethane dispersion formulation. A design of experiments was set up to investigate optimum loading levels of the additives given by the screening step. The starting-point formulation was modified using the potential additives at the optimum loading levels and nepheline syenite with a median particle size of 1.7 μm (Minex 12®) at 15% solids. The starting-point formulation was also modified with both rheology additives. The modified samples were heat-aged for up to 28 days at 50ºC to evaluate their anti-settling performance. Optical properties, pH, package stability and viscosity of the samples were also assessed.
A polymeric dispersant was used to prepared a nepheline syenite slurry, which was then incorporated into the polyurethane dispersion formulation. As previously discovered, the polymeric hyper-dispersant, Solsperse 46000 at 8%, was the best dispersant. Therefore, this dispersant was used in all the modified samples.
Soft-pack settling was observed in most samples modified with the rheology additives. The sediments could be re-dispersed into the coating system. A near-perfect suspension of the filler was observed in a 1.0% Rheotech 4800 modified sample. A pH drop in the sample lowered the viscosity and increased the haze significantly to 6%. The best optical properties were obtained with a combination of 0.8% Byk425 and 3.0% Aquatix8421. However, the low-shear viscosity of this sample (3500 cP/ 3.5 Pa.s) is about 3 times higher than that of the Rheotech 4800 modified sample. Although most optimized samples had soft-pack settling with some degree of suspension of the filler, their high viscosities may not be desirable in most coating formulations requiring a low-viscosity system.
PART II ABSTRACT
VISCOSITY STABILIZATION OF TINTED LATEX ARCHITECTURAL COATINGS
Associative thickeners are sensitive to surfactant concentration in waterborne pastel base coatings. When a highly surfactant concentrated colorant is added, the surfactant disrupts the thickening mechanism of the associative thickeners, which lowers the viscosity of the coating significantly. The pastel base coatings are generally formulated to have viscosities around 100 KU. After addition of the colorants, the coating’s viscosity is reduced by 30-38 KU. The loss in viscosity negatively impacts the rheology properties of waterborne architectural coatings that require a high viscosity (e.g., 101 – 103 Pa. s) under low shear rates (e.g., 10-3 - 10-1 s-1) is required to control the settling, sagging, leveling and the film thickness. In this research project, five latex emulsion pastel base coatings were prepared with five different lower-shear viscosity (KU) builders (one cellulosic thickener, and four associative thickeners), but one high-shear viscosity (ICI) builder, cellulosic thickener, is used in all the coatings. Seven low-VOC Universal colorants were used. The rheology characteristic of these coatings before and after addition of the coating is investigated.
Cellulosic thickener showed no sensitivity to surfactants contained in colorants. Newly developed associative thickener showed viscosity stabilization in high shear rate regions although it is sensitive to colorants at low shear rates. No major variation in tint strength was observed in tinted pastel bases. Tint strength does not appear to depend upon the types of thickeners.