Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Engineering Science

First Advisor

Brenda Prager

Relational Format



Supercritical Fluids (SCFs) have received a great deal of attention for their various applications in chemical, biochemical, pharmaceutical, and materials processing. In this study, we investigate surface modification to paper substrates using supercritical impregnation (SCI) techniques, with applications in food packaging. One of the key factors required for this study is understanding the solubility of hydrophobic solutes in supercritical carbon dioxide (scCO2). Polar compounds are poorly soluble in scCO2 due to their lack of polarity and frequently co-solvents are also introduced to enhance solubility. In this study, the maximum solubility of alkyl ketene dimer (AKD)/n-heptane and vegetable wax (VW)/n-heptane solutions have been measured by “Cloud Point” methods, with heptane introduced to enhance the solubility of the AKD and VW in scCO2. Different temperatures (40, 50, 60 °C) and pressures (101.35-172.02 bar) were investigated to identify solubility conditions for subsequent paper impregnation processes, where the presence of AKD improves the hydrophobicity of the paper. Collected data demonstrates at lower temperatures, higher pressure is needed to dissolve specific amounts of wax/n-heptane solution in scCO2. Therefore, one can expect the highest solubility of the sample occurs at T = 60 °C. However, at certain temperatures and pressures, retrogradation phenomena may be observed, where the opposite becomes true, and higher solubility occurs at lower temperatures. This was experimentally observed with AKD/n-heptane solubility studies at T=40 and 50 °C conditions. Paper samples were impregnated with AKD/n-heptane at pre-determined solubility conditions and their hydrophobicity was subsequently measured by a contact angle goniometer. For example, at a temperature of T = 60 °C and 125.83 bar, the maximum solubility of AKD/n-heptane was 0.1875 mL, and the average of contact angle was 130.75 ° (this value was taken on day 14 after impregnation). However, at 40 °C, the maximum solubility of AKD/n-heptane was 0.1275 mL, and the resulting CA after 14 days was only 106.70 °.

Applying annealing treatment typically did not improve the CA significantly compared with the non-annealed values, although at T = 60 °C and 148.10 bar with 160 °C annealing temperature, the CA was much improved at earlier times compared with non-annealed samples. SEM images showed that the sample impregnated at T = 40 °C and without annealing is more uniform but at T = 50 °C, better micro-roughness was achieved after annealing (4h, 160 °C).

Design of experiment (DOE) with Design-Expert software, a powerful tool for numerical optimization, was used to analyze the collected solubility data. Results’ confirmation validates the solubility measurements for all temperatures with the cloud point method to do the experiments and furthermore proves the authenticity of the cloud point measurements with the pressure cell.



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