Graphene composite paper synergized with micro/nanocellulose-fiber and silk fibroin for flexible strain sensor.

The fabrication of uniform and strong graphene-based conductive paper is challenging due to easy aggregation and poor film formability of graphene. Herein, on the basis of good dispersing effect of nanocellulose, high content graphene (50 wt%) composite paper with micro/nanocellulose fibers and silk fibroin (SF) was manufactured via simple casting method. The synergistic effects of cellulose microfibers (CMFs), cellulose nanofibers (CNFs) and SF result in the paper with ideal combination of flexibility, electrical conductivity and mechanical strength, where CNFs, CMFs and SF act as dispersing and film forming for GNPs, dimensional stability, and interfacial binding agents, respectively. Extraordinarily, by adding SF, graphene nanosheets are tightly coated on the surface of CMFs. The composite paper shows a tensile strength of 49.29 MPa, surface resistance of 39.0-42.1 Ω and good joints bend sensing performance. Additionally, it is found that CMFs can hinder the micro-cracks from propagating during the cyclic elbow bending test. The graphene-based conductive paper is helpful for the development of smart clothing wearable biosensing devices.