Integrating Antioxidant Functionality into Polymer Materials: Fundamentals, Strategies, and Applications

While antioxidants are widely known as natural components of healthy food and drinks or as additives to commercial polymer materials to prevent their degradation, recent years have seen increasing interest in enhancing the antioxidant functionality of newly developed polymer materials and coatings. This paper provides a critical overview and comparative analysis of multiple ways of integrating antioxidants within diverse polymer materials, including bulk films, electrospun fibers, and self-assembled coatings. Polyphenolic antioxidant moieties with varied molecular architecture are in the focus of this Review, because of their abundance, nontoxic nature, and potent antioxidant activity. Polymer materials with integrated polyphenolic functionality offer opportunities and challenges that span from the fundamentals to their applications. In addition to the traditional blending of antioxidants with polymer materials, developments in surface grafting and assembly via noncovalent interaction for controlling localization versus migration of antioxidant molecules are discussed. The versatile chemistry of polyphenolic antioxidants offers numerous possibilities for programmed inclusion of these molecules in polymer materials using not only van der Waals interactions or covalent tethering to polymers, but also via their hydrogen-bonding assembly with neutral molecules. An understanding and rational use of interactions of polyphenol moieties with surrounding molecules can enable precise control of concentration and retention versus delivery rate of antioxidants in polymer materials that are critical in food packaging, biomedical, and environmental applications.

In Situ ATR FTIR Spectroscopic Study of the Formation and Hydration of a Fucoidan/Chitosan Polyelectrolyte Multilayer

The formation of fucoidan/chitosan-based polyelectrolyte multilayers (PEMs) has been studied with in situ Fourier transform infrared (FTIR) spectroscopy. Attenuated total reflectance (ATR) FTIR spectroscopy has been used to follow the sequential build-up of the multilayer, with peaks characteristic of each polymer being seen to increase in intensity with each respective adsorption stage. In addition, spectral processing has allowed for the extraction of spectra from individual adsorbed layers, which have been used to provide unambiguous determination of the adsorbed mass of the PEM at each stage of formation. The PEM was seen to undergo a transition in growth regimes during build-up: from supra-linear to linear. In addition, the wettability of the PEM has been probed at each stage of the build-up, using the captive bubble contact angle technique. The contact angles were uniformly low, but showed variation in value depending on the nature of the outer polymer layer, and this variation correlated with the overall percentage hydration of the PEM (determined from FTIR and quartz crystal microbalance data). The nature of the hydration water within the polyelectrolyte multilayer has also been studied with FTIR spectroscopy, specifically in situ synchrotron ATR FTIR microscopy of the multilayer confined between two solid surfaces. The acquired spectra have enabled the hydrogen bonding environment of the PEM hydration water to be determined. The PEM hydration water is seen to have an environment in which it is subject to fewer hydrogen bonding interactions than in bulk electrolyte solution.