Plastics are one of the most widely used classes of synthetic products due to their lightweight nature, affordability, and versatility. However, commonly used plastics are non-biodegradable and have low recycling rates that have created environmental issues. Paper is considered to be an excellent alternative to plastics in certain packaging applications due to its biodegradability, low-cost, and good mechanical properties. However, the porous texture and polar chemistry of paper make them unfit for containing liquid products and thus limit its applicability. This problem is circumvented by applying plastic and per- and polyfluoroalkyl substances (PFAS) coatings onto paper. However, plastic is non-biodegradable, and PFAS is harmful, and their accumulation in ecosystems poses threats to human health and the environment.This thesis work is aimed to address the current non-sustainable challenges associated with coated paper. Three approaches were used to develop environmentally friendly and sustainable coatings. The aim of Approach 1 is to develop chitosan- and zein-based dual-layer coatings as novel paper coating materials because both chitosan and zein are biobased, biodegradable, and food safe materials. Kraft paper was coated with an oil-resistant chitosan solution as the first layer and subsequently by a hydrophobic zein solution as the top layer. The resultant chitosan-zein-coated paper showed significant water resistance (Cobb 60 value of 4.88 g/m2) and oil repellency (kit rating of 12/12). Scanning electron microscopy (SEM) analysis showed that the pores were masked upon coating with chitosan and zein dual-layer coating that led to the improvement in water- and oil- resistance. The desirable mechanical properties of the coated paper were retained after the coating treatment. In addition, the pulp was recovered from the chitosan-zein-coated paper to validate the recyclability of this novel approach percentage of recovery and properties of recoverable materials. Approach 2 is aimed to replace chitosan with a less expensive material such as starch in the dual layer paper coating. Again, starch is widely available, and due to the similar chemical structure with that of chitosan, it shows the same oil resistance as chitosan. Accordingly, starch and zein dual-layer coatings were applied onto a Kraft paper and yielded a low Cobb 60 value of 4.81 g/m2. In addition, the coated paper exhibited excellent grease resistance with a kit rating of 12/12. SEM characterization confirmed that the dual-layer coating filled the pores of the paper substrate. The mechanical properties, as well as the thermal stability of the paper, remained essentially unchanged after the coating treatments. Approach 3 is focused on the use of single-layer coating to obtain water and oil resistant coatings. Here, sunflower oils were first modified and then grafted onto chitosan using industry-relevant epoxidation chemistry. The obtained chitosan-graft-oil was coated onto paper for the water and oil resistance properties. Cobb 60 and kit rating values were determined to be 8.00 g/m2 and 7.66, respectively, for the optimal formulations. Considering the excellent sustainability i.e., ability to be reused without depletion of natural resources, of our developed paper (e.g., thermoplastic-free, PFAS-free, repulpable, and biodegradable), this work offers a multitude of packaging applications with invaluable benefits for human, animal health, the environment, as well as industry.
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