Hydrophobic coatings are of utmost importance for many applications of paper-based materials. However, to date, most coating methods demand vast amounts of chemicals and solvents. Frequently, fossil-based coating materials are being used and multiple derivatization reactions are often required to obtain desired performances. In this work, we present a solvent-free paper-coating process, where olive oil as the main biogenic component is being used to obtain a hydrophobic barrier on paper. UV-induced thiol-ene photocrosslinking of olive oil was pursued in a solvent-free state at a wavelength of 254 nm without addition of photoinitiator. Optimum reaction conditions were determined in advance using oleic acid as a model compound. Paper coatings based on olive oil crosslinked by thiol-ene reaction reach water contact angles of up to 120°. By means of Fourier transform infrared spectroscopy and differential scanning calorimetry, a successful reaction and the formation of a polymer network within the coating can be proven. These results show that click-chemistry strategies can be used to achieve hydrophobic polymeric paper coatings while keeping the amount of non-biobased chemicals and reaction steps at a minimum.
Plasma‐enhanced chemical vapor deposition is a highly promising tool for coating deposition due to its versatility, tunability, low chemical consumption, and cost‐effectiveness, with an increasing scope of deposition methods at both low and atmospheric pressure. Adhering to green chemistry principles, biobased precursors have recently shifted into the focus of research interests. This review gives an overview of the main biogenic substance classes that have been used for the deposition of plasma polymer coatings, including natural oils, terpenes, enzymes, and lactic acid‐based precursors. The common feature of these precursors is not only their biogenic origin, but additionally the manifold properties of the resulting plasma‐deposited thin films, ranging from antimicrobial properties to tunable surface‐wetting characteristics, electrical conductivity, or biodegradability. This combination of unique features makes plasma‐derived polymers based on natural precursors immensely attractive for manifold applications.
A new class of hydrophobic/lipophilic cellulose microspheres are made from carboxylated cellulose nanocrystals (cCNC) by adding silk fibroin (SF) protein in the course of spray-drying from aqueous suspension. We found mere 2% SF addition could leverage the surface energy with an increase of contact angle from 27.5° to 60.4°. Besides the complete altered surface energy from cellulose beads, the hybrid SF-cCNC microspheres also show improved mechanical properties and prolonged diffusion kinetics for transporting water-soluble ions / molecules (e.g., methylene blue). Depth profiling of the SF-cCNC microspheres reveals that SF is more concentrated at the surface in comparison with the core, and this surface localization is the reason for the tuned properties. Moreover, post methanol treatment of the SF-cCNC hybrid microspheres induces a β-sheet phase transition to the Silk II structure, which can further enhance the mechanical properties and slow down the small molecule transport of the microspheres. Therefore, a new method has been established that could tune the physical properties of functional cellulose microspheres through the control of SF structural transformation, which could significantly benefit for controlled drug release and microplastic beads replacement applications.
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