Cork as a raw material for antibacterial membranes and fibers

Abstract

Cork industry is one of the most profitable markets in Portugal with an annual pro-duction of 100000 tonnes. Yet, a large amount of cork waste is generated without com-mercial value. Currently, cork by-products are mostly used as burning fuel for energy production. Substantial valorisation can be attained if valuable components are extracted instead of burning to produce energy. Cork is a remarkable biocomposite that combines a set of uniques and astonishing properties. Suberin, the main component of cork (~30-50% of its composition) is a hy-drophobic and high thermal resistant biopolyester that plays a key role as a protective barrier between the plant and the environment. There are several depolymerisation ap-proaches to isolate suberin from cork, such as alkaline methanolysis, cholinium hexano-ate ionic liquids, or aqueous alkaline hydrolysis. Suberin films obtained from these pro-cesses show barrier properties similar to those of the suberin barrier in plants, including a potentially broad bactericidal effect. Here, we report a simple, low energy demanding and “greener” process based on aqueous alkaline hydrolysis to explore the extraction of suberin, using cork stoppers as a raw material. The concentration of cork as well as the concentration and source of al-kaline salt (LiOH vs. NaOH) is investigated throughout this work. ATR-FTIR analysis confirms the main presence of suberin peaks in the bottom pasty component, whereas only one peak appears in the top liquid phase. The suberin rich phase was selected for further study targeting antibacterial applications, while the liquid phase after drying has potential to be used as a resin-like electrolyte for electronic applications based on ionic response (iontronics). The prepared solutions exhibit antibacterial properties against both the Gram-posi-tive bacteria Staphylococcus aureus and the Gram- negative bacteria Escherichia coli. The antibacterial activity is enhanced with the increase of cork concentration, and it can be considerably improved with the addition of zinc-oxide nanoparticles in the aqueous alkaline hydrolysis process. Taking these results into account, PEO/suberin-based com-posite fibers were successfully prepared by solution blow spinning. This work brings new insights in the field of recycling of cork wastes and top-down ap-proaches to obtain suberin component from cork as a potential building-block for an in-novative generation of biopolymers with high-value in the field of biomedicine.