Facile preparation of fluorescence-labelled nanofibrillated cellulose (NFC) toward revealing spatial distribution and the interface

Abstract Nanofibrillated cellulose (NFC) has been widely used in bio-composites and plays a critical role of interface phase in determining the final physical properties. However, it remains difficult to directly observe NFC and its network-like phase within its related composite. Herein, we report a facile and low-cost approach to visualize three-dimensional (3D) distribution of NFC and its interfacial morphology with confocal laser scanning microscopy. In this work, coumarin-3-carboxylic acid (C3) was chemically linked with TEMPO-oxidized nanofibrillated cellulose (TNFC) via amidation process with the aid of ethylenediamine, leading to the formation of fluorescent labelled nanocellulose (TNFC-C3). TNFC-C3 was then compounded with poly(vinyl alcohol) (PVA) as a reinforcing nanofiller because of abundant molecular hydrogen-bonding interactions. The spatial distribution and interfacial bonding characteristics of TNFC in composites were investigated. Fluorescence scanning shows a clear 3D network structure of TNFC-C3 in TNFC-C3/PVA composite. More importantly, TNFC-C3/PVA composites show increased mechanical strength from 7.5 to 23.2 MPa with the increase of TNFC-C3 content, indicating that a small number of C3-grafting result in high-quality of fluorescence resolution without sacrificing molecular interactions and reinforcing effect. Graphical abstract