Date of Award

5-2014

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Carl P. Tripp

Second Committee Member

Douglas W. Bousfield

Third Committee Member

Bruce L. Jensen

Abstract

Commercial grade paper is often coated with a layer consisting of mostly pigments and binders to control the physical and optical properties. These coatings are applied on paper as aqueous suspensions and dried. The final composition at the coating surface may differ from the bulk composition because of differential pigment and binder movement during the drying process. Evidence of differential movement as well as our understanding of the structure/property relationships is derived from post analysis of these coatings. To better understand the binder migration mechanism, it is important to investigate the dynamics of the binder movement during drying. The primary motivation of this dissertation is therefore to 1) develop techniques that could be used to monitor the dynamics of pigments and binders movement during drying, 2) use these techniques to gain a fundamental understanding of movement during the drying step in paper coatings and 3) finding other ways to control pigment packing and reduction of binder use. The methods described in this dissertation are based on Attenuated Total Reflection-Infrared (ATR-IR) because this method could be utilized for aqueous samples and IR bands due to each component in the suspension can be monitored dynamically.

Simple coating formulations are used that have kaolin, calcium carbonate, styrene- butadiene latex, carboxymethyl cellulose, and starch. These coatings are applied on an ATR crystal and allowed to dry. The results from two crystal compositions are compared. Each of the components has specific peaks in IR spectroscopy that can be measured dynamically by monitoring change in the height of the respective peaks. Additional experiments are performed in which caboxymethyl cellulose (CMC) is added to the formulations. Drawdown experiments of mixed binder systems on absorbent paper are compared to the surface composition of the ATR crystal. In addition, the packing behavior of kaolin particles on a ZnSe crystal under an applied external electric field was studied; polarized light is used to characterize the orientation of the particles. Coatings layers are also formed using layer-by-layer methods.

Latex binder particles have a nonlinear distribution as a function of depth of the coating. Binder is enriched at the crystal surface during drying. The relative movement of binder towards the surfaces reduces when 1 wt% of CMC was used in the formulation: the results agree with what is found for the role of CMC in coatings. The results obtained from experiments using ATR-IR on crystals also correlate to what happens on paper as has been demonstrated by the drawdown experiments on paper.

Starch migration is found to occur towards the top surface of the coating. The starch migration depends on the pigment particle size. Starch molecules do not associate with either pigment or the latex particles. The movement of starch is independent of them. Also, further evidence of capillary pore formation during the drying process is obtained from these results which are in agreement with capillary transport model for binder migration.

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