Interaction of acrylic latex with calcium carbonate fillers
Alvarez Espejo, Verónica
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Most of the surface paints and coatings that surround us every day are mainly pigment/polymer latex (binder) blends. Pigments are solid particles insoluble in the application medium and although most pigments are natural minerals, others are manufactured chemically. Pigments can be divided into two different categories: functional or specialty fillers and extenders or mineral fillers. Functional fillers, such as titanium dioxide and precipitated calcium carbonate, improve or provide film properties whereas extenders, such as clay, chalk and ground calcium carbonate (GCC) are cheaper and they are primarily used to lower the formulation costs of the final product. Among them, calcium carbonate (CaCO3) is the most used filler in Europe. Further, the binders are polymer particles dispersed in water, for the case of waterborne coatings. The task of the binders is to bind pigment particles to each other and to bond them to the substrate onto which the coating is applied after the latex forms a continuous film upon drying.The pigment volume concentration (PVC) is one key-parameter for the majority of paints. The PVC value quantifies the filler loading of the system. The higher the PVC, the lower is the content of polymeric binder within the paint and the higher is the portion of filler particles. The PVC value thus strongly determines, among others, application properties such as gloss, scrub resistance and tensile strength.The objective of this PhD thesis is to investigate the main factors affecting the interaction of acrylic polymer dispersions with fillers. A very good dispersion and adhesion of the filler to the binder are needed to obtain high quality paints. Such aspects are mainly determined by the latex formulation and morphology (i.e., stabilizers, functional monomers, surface particle composition). To accomplish the objective of this project, different filler/polymer latex blends will be prepared and the effects of several variables (filler and latex types, their surface coverage, particle sizes and filler/latex ratio) on the film properties (scrub resistance, tensile properties, water uptake, gloss and weathering) will be investigated.More precisely, first, CaCO3/acrylic latex blends were prepared with NaPA dispersing agent and with two different types of thickeners; a non-associative thickener and an associative one. Final paint-like films properties were analysed and the effect of each kind of thickener on the CPVC value was investigated. Afterwards, latexes with different particle sizes, with and without the functional monomer and at different pH were synthesized. The effect of these variables were studied on the final properties of CaCO3/acrylic latex films prepared with the help of NaPA. Moreover, in this Chapter a brief study is done to analyse different CaCO3 samples.Then, the interaction between different acrylic latex with calcium carbonate filler was studied in fully formulated waterborne paints, with the combination of a design of experiment (DOE) and High-Throughput Experimentation (HTE). In this Chapter, the effect of the filler particle shape on packing efficiency was also studied. Due to the need to avoid the use of additives, in order to isolate the study of the interaction between polymer-filler particles, at last a new strategy was developed in which blends were prepared without the use of any additive. Latexes were synthesized with different amounts of different functional monomers and with different surfactants and these effects were analysed on final paint-like films.