Preparation of micro-fibrillated cellulose fibers by a simple two-step refining process for paper- based flexible electronic devices

Abstract

Cellulose micro/nano-materials are potential substrates for energy storage/ electronics applications. However, developing efficient/cost-effective technologies that can obtain these micro/nano-materials suited for flexible electronics continue to be a challenge. In this study, we report a simple process for extracting micro-fibrillated cellulose fibers from conventional bleached kraft pulp that are particularly applicable to flexible electronics applications. The process is made of two step refining: 1) refining in a Valley beater, and 2) further fibrillation in a ball mill. The Valley beater is to induce fibrillation of pulp fibers as a result of compression and shearing forces. Subsequently, the partially fibrillated cellulose fibers are further subjected to ball milling to obtain micro-fibrillated cellulose fibers (MFCs). These MFCs have a much higher specific surface area than the conventional pulp fibers due to fibrillation and reduction in fiber size, which leads to favorable properties to the as- prepared MFCs network, including high transparence, and high tensile strength. The MFCs paper exhibits excellent transparency of 82% at 550 nm (a significant increase of about 56% for the control), with exceptionally high tensile strength (35.16 MPa). Thanks to the high surface area of these MFCs, silver nanowires (AgNWs) can be well distributed into the MFCs network so that conductive paper with high conductivity was prepared. The MFCs/AgNWs composite paper was then assembled into the paper-based triboelectric nanogenerator (P-TENG) device, which shows excellent performance. The MFCs/AgNWs composite paper- based P-TENG system can also serve as self-powered sensors for monitoring human motions. This work provides a method for the production of micro- fibrillated cellulose fibers that can be applied for the production of flexible electronic devices.