Due to the inherent hydrophilic nature and porosity of the paper fibers, hydrophobic polymeric materials, waxes, and inorganic fillers have been widely utilized as coatings and fillers, respectively, on a fiber-based substrate. Coatings also impart oxygen, aroma, and oil barrier properties desirable for food packaging applications. In addition, coatings improve the functional properties and characteristics of paper, including reduced water absorbance, enhanced surface finish, gloss finish, printability, readability, dimensional stability of the substrate, and antimicrobial performance. Such functional properties are highly desirable for consumer packaging applications. However, such coatings may limit the repulpability, recyclability, biodegradability, and compostability of paper and paperboard. In addition, the contamination of the substrate by-product also limits the recyclability of the fiber-based substrates, and the paper, paperboard, or corrugated material ends up in landfill sites. This review focuses on bioderived, biodegradable, compostable, and functional organic, inorganic, and hybrid hydrophobic coatings, which promote the circular economy by improving the repulpability or reduces carbon footprints.

Hydrogen-bonding-induced ordered assembly of poly(3-alkylthiophene)s derivatives bearing carboxylic acid groups has been investigated from diluted and concentrated solutions to solid films using ultraviolet–visible absorption spectroscopy, polarized optical microscopy, and four-point probe conductivity measurements. In dilute solutions, the polymer undergoes a spontaneous structural transition from disordered coil-like to ordered rodlike conformations, which is evidenced by time-dependent chromism. Many factors such as alkyl-chain length, types of solvents, and temperature are studied to understand the assembly behavior. Transition kinetics of the assembly process reveals a universal second-order rate law, indicating an intermolecular origin due to hydrogen bonding. When more concentrated, hydrogen bonding drives nematic liquid-crystalline gelation above a critical concentration and the gels are thermally reversible. Under an appropriate balance of mechanical and thermal stresses, uniform liquid-crystalline monodomains are obtained through the application of a mechanical shear force. The dried films made from the sheared solutions display both optical and electrical anisotropies, with a more than 200% increase in charge transport parallel to the direction of shear as opposed to that in the perpendicular one.