Date of Award

Spring 5-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

Advisor

Douglas Bousfield

Second Committee Member

Mehdi Tajvidi

Third Committee Member

Adriaan R.P. van Heiningen

Abstract

Barrier coating layers are important in many paper grades used in food packaging and have the potential to help reduce our use of plastics in some situations. Barrier layers to produce water proof packaging such as milk or juice cartons or coffee cups are common. Water based dispersion barrier coatings have the potential to be a low-cost alternative to extrusion coated layers. Water borne coatings are reported to be easy to recycle and break down in the environment. However, barrier properties are often less than what is desired and expected for these water borne coatings. The reason for this poor performance is not well understood.

Various papers are coated with a latex intended for barrier properties as well as the latex combined with plate-like pigments with various coating methods. The laboratory coated samples are also compared to a high speed blade coater. The water vapor transmission rate (WVTR) of these samples is measured. A novel method, using cellophane, is proposed to isolate the behavior of the coating layer independent of the paper properties. Latex was also stained before coating; these samples were imaged with a confocal laser scanning microscope (CLSM). The results are compared and normalized in terms of water vapor permeability.

When coated at low speed, different application methods were found to give similar barrier performance. The effect of base substrate was found to be prominent. Coatings on cellophane yield superior barrier performance when compared to coatings on regular copy paper. The absence of pores and roughness on the surface of cellophane promote the formation of continuous uniform coating layer with little defects, important for moisture barrier performance. When typical porous paper is used, the addition of pigments was proven to not only to provide tortuous path of diffusion but also to help prevent the coating to sink into the pores. Image from the CLSM verify this mechanism.

The high speed blade coating resulted in barrier properties that were better than the low speed laboratory coating samples, especially when the pigment is used. The reason for this result may link back to the alignment that takes place in the high speed shear field under the blade.

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