Date of Award

5-2012

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

William N. Unertl

Second Committee Member

Douglas W. Bousfield

Third Committee Member

Michael D. Mason

Abstract

Styrene-butadiene latexes are used in a variety of applications such as binders, paper coatings and paints. Coating strength is influenced by latex material parameters such as elastic modulus, the work of adhesion and the thermal flow. Latexes are usually characterized by average properties such as mean particle size or by bulk properties of films formed from the particles such as glass transition temperature and gel content. The relationship between these characteristics and the material properties of the individual latex particle has not yet been established. The main goal of this research is to determine how size variation, flow properties, surface chemistry and mechanical properties of individual latex particles determine their performance in paper coatings.

Individual particles from three commercial styrene-butadiene copolymer latex emulsions were isolated on glass slides. The latexes had different styrene to butadiene monomer ratios, gel content and glass transition temperatures of 9°C, 19°C and 48°C. Atomic Force Microscopy (AFM) was used to characterize the degree of spreading, contact angles, mechanical and adhesion properties of individual particles. Properties of coatings on paper made with the three latexes were measured using a printing pick test.

The primary result of this thesis is that there is significant heterogeneity in the properties of the individual particles for each of the latex studied. The mean contact angles have standard deviations of only a few degrees. In contrast, the moduli and adhesion energies have large variations, even for particles of same size. We also found a weak correlation exists between the modulus and adhesion energy. Of all the latexes evaluated, the best pick performance was obtained for the 9°C Tg latex which had broad particle size distribution, lowest Tg, and lowest mean contact angle. The poor binding behavior of Latex 48 cannot be predicted by these tests. A strong correlation between a particular latex property obtained by AFM and pick strength was not found for these three latex types.

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