Available at: http://digitalcommons.calpoly.edu/theses/1210
Date of Award
MS in Polymers and Coatings
Chemistry & Biochemistry
Dr. Raymond Fernando
Latex polymers serve as binders in a wide range of architectural paints and coatings. A latex is an aqueous colloidal dispersion of polymer particles that when dried above the polymer’s film formation temperature coalesces into a dry polymer film (Dragnevski, Routh, Murray, & Donald, 2010). The other main components of paint include associative thickeners, surfactants, pigments and fillers with the thickener being the primary area of focus for this study.
The relatively simple system of latex, associative thickener and surfactant has been studied extensively. These studies have shown the mechanism of thickening for the associative thickener, and surfactant effects on both latex and thickener; however, there are few studies conducted for a fully-formulated system. The introduction of pigments, fillers, coalescing aids, functional amines, and other additives greatly increases the difficulty of research in this area. The addition of many additives ultimately affects the stability and physical properties of the end-product. Phase separation of the paints, also called syneresis, is a major concern of paint formulators because paints need to be as stable when left sitting in a paint-can for an extended period of time. The goal of this project is to essentially probe the areas of phase separation for some hydrophobically modified ethoxylated urethane (HEUR) thickened paint systems that are very similar to commercially used paint formulations. The probing of these phase separated regions includes the careful preparation of each paint sample, physical property testing, as well as new experimental development in the area of syneresis, rheology, followed by statistical analysis of data.
Dispersion phase diagrams (DPDs) were first reported by Kostansek (2003) in a simple system of HEUR thickener, surfactant, and latex. They are a plot of the three possible dispersion states for an associative thickened system. These states include bridging flocculation which occurs at low levels of HEUR in which 50% or less of the latex particle surface is covered by the associative thickener. The second state is a good dispersion, which does not show any signs of flocculation. The third state is a mode of flocculation called depletion flocculation that occurs when the particle surfaces of the system are covered mostly with surfactant. The free associative polymer in the system is excluded from the free space in between particles, and the latex particles form aggregates (Otsubo, 1995). The three dispersion phases are then plotted with wt% HEUR on the continuous phase versus wt% surfactant on the continuous phase. The ideal end product for this project would be to use various combinations of latex, surfactant, and associative thickeners (ATs) to create multiple DPDs, which then could be used to troubleshoot formulations and samples in which flocculation is present.
Each formulation was made using a thickening package of two non-ionic HEURs: a low-shear and high-shear thickener. Surfactant additions were made after the HEUR in small incremental amounts. Each DPD would consist of one surfactant, the previously stated combination of HEURs, and an all-acrylic latex. Three different surfactants were used in the study: two non-ionic surfactants, and an anionic surfactant. The first non-ionic surfactant was not studied in full as the other two surfactants due to time constraints. Two different all-acrylic latexes were used which varied in the particle size. The first latex studied, Acrylic-A, has an average particle size of 105 nm, and the second latex was Acrylic-B with 150 nm particle size. The TiO2 used in each DPD was surface treated and used in powder form. By the end of the project, 4 full-scale DPDs were made with the following combinations: Acrylic-A and a non-ionic surfactant, Acrylic-A and an anionic surfactant, Acrylic-B and a non-ionic surfactant, and Acrylic-B and an anionic surfactant. From these DPDs the mechanistic interactions of various components of the system could be made. The DPDs could also be used to troubleshoot problematic paints and even hypothesize new formulations.