Covalent and non‐covalent action‐enhanced cellulose‐based thermally conductive composite (<scp>TCC</scp>) films fabricated via vacuum‐assisted self assembly with high thermally conductivity and superior mechanical performance

Abstract As is known, to establish covalent or non‐covalent interaction between filler and matrix, which helps to reduce the interface thermal resistance (ITR) as well as construct good thermal conduction channels, is a good strategy for dealing with the risk of thermal runaway in the extreme service environment of electronic equipment. In this paper, carboxylated nanocellulose fiber (c‐CNF) was used as matrix, and a hybrid filler (M‐CoNPs@GNP) was fabricated by coating cobalt‐nanoparticles (CoNPs) and grafting maleimide on graphene nanosheets (GNPs). M‐CoNPs@GNP/c‐CNF thermally conductive composite (TCC) films were successfully fabricated by combining with c‐CNF. As zero‐dimensional particles, CoNPs can effectively prevent GNPs agglomeration due to surface effects, and “‐NH” in maleimide dehydrates with “‐COOH” in c‐CNF to form “C‐N‐C” covalent bonds, with strong hydrogen bond formed between filler and matrix, which remarkably enhances the interface compatibility between matrix and filler. The ITR has been reduced to form a well‐defined three‐dimensional thermal conduction path, achieving an ultra‐high in‐plane TC (35.9 W·m −1 ·K −1 ) for MCGC40, which is 7.9 times that of pure c‐CNF film, in addition to a sufficiently high tensile strength of 123.3 MPa. The combination of high in‐plane TC, excellent mechanical flexibility and good electrical insulation jointly justifies the potential application of M‐CoNPs@GNP/c‐CNF TCC films in effective thermal management of flexible electronic products. Highlights CoNPs effectively inhibit GNPs agglomeration. GNPs exhibit hydrophilicity after modification. Modified fillers interact fairly well with the matrix. High tensile strength and exceptional flexibility are achieved. TCC films exhibit both electrical insulation and hydrophobicity.