Renewable chitin based nanomaterials from fungi

Abstract

Fungal cell walls are rich in structural fibers made of chitin and glucan. These fibers were covalently linked, forming a ready-made nanocomposite fabric which is potentially useful in the development of a single-sourced bioreinforcement material that combines the strength of chitin and the toughness of glucan. In this study, chitin-glucan material was extracted from common mushroom (Agaricus bisporus) and tree bracket fungi (Daedaleopsis confragosa). Animal chitin extracted from crab shells (Cancer pagurus) was used as a comparison. We adopted mild extraction process to preserve the native quality of chitin-glucan within the fungal source. Six themes will be discussed: (1) comparison between fungal-based and animal-based chitin, (2) the effect of grammage on fungal chitin film, (3) the effect of blending time on fungal chitin film, (4) composite preparation using combination of different fungal extracts, (5) preparation of high volume fraction fungal-based chitin laminates, and (6) utilization of fungal chitin nanofiber as a natural binder for loose flax fiber. Extracts from common mushroom were found to be (1) readily disintegrated into nanofiber dimension (10–20 nm wide, several micrometers long) without any post-mechanical treatment, (2) more hydrophobic than animal based chitin, and (3) possess a film forming capability. Extracts from tree bracket fungi assumes microfiber dimension (1–2 µm wide, several micrometers long) and require specialized equipment for further nanofibrillation. Chitin to glucan ratio in common mushroom was found to be nearly equal at 40:50, while glucan predominates in bracket fungi (chitin to glucan, 1:99). This translates to distinct mechanical properties, in which strong films having tensile strength of ~200 MPa were produced from common mushroom extract, while tough films with elongation at break exceeding 10% were produced from bracket fungi. The strength of common mushroom nanofibers is further extended as a reinforcement in epoxy laminated composite and as a binder for nonwoven flax preform.