Date of Award

12-2000

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor

Pierre F. LePoutre

Second Committee Member

Stephen M. Shaler

Third Committee Member

Douglas W. Bousfield

Abstract

The mechanical properties of paper coatings are essential for use performance of coated paper (e.g. calendering, printing degradation during printing operations, pick). This study investigates the microscopic and macroscopic mechanisms that determine the viscoelastic behavior of pigmented latex coating films. Pigmented coating layers were prepared with different microstructures. This was achieved by using different pigment types and shapes (polystyrene plastic pigment - spheres, precipitated calcium carbonate - rhombs, clay - plates), and changing pigment volume concentration (PVC). Two styrene-butadiene latices with different degree of carboxylation (acidic level 0.3% and 4.5%) were evaluated to determine effect of adhesion. The viscoelastic material response of the coating films (film thickness between 25µm to 35µm) was determined by dynamic mechanical thermal analysis in tensile mode. Changes in viscoelastic response over entire pigment volume concentration range was found to be distinct for the three different pigment systems. Storage and loss modulus were strongly related to the thermal softening of the coating latex. Reinforcement through pigment was found to?be depending on pigment volume concentration, pigment type as well as temperature/frequency range. Above latex glass transition region the coatings showed for all pigments with increasing pigmentation an increase in storage modulus depending on the storage modulus of the pure pw-tent (Eclay>ECaC03>Eplastic pigment ) Below glass transition region calcium carbonate pigment showed an increase in storage modulus, leveling off at 7O%PVC. Clay pigment coatings performed a maximum in storage modulus at 5O%PVC. For polystyrene plastic pigment coatings the storage modulus decreased with increasing pigment volume concentration. For clay a depression behavior was observed coinciding with the latex glass transition region. For SO%PVC the depression behavior was reversible, whereas for lower pigment volume concentrations the behavior was irreversible resulting in a common transition for repeated scans. The maximum in tan Delta (damping factor) decreased for all pigments with increasing pigmentation. Glass transition temperatures determined by dynamic mechanical thermal analysis were consistently higher than measured by differential scanning calorimetry. Master curves were calculated with time-temperature-superposition and William-Landel-Ferry-theory. Tensile tests were performed in an Environmental Scanning Electron Microscope. A LWC-base-paper was coated and then analyzed to observe the influence of the coating layer.

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