TEMPO-Oxidized Cellulose Handsheet with Low and Adjustable Relative Permittivity for Superior Printed Electronic Substrate

The development of the Internet of Things (IoT) is accompanied by the innovation of wireless communication technology. Currently, high-frequency communications urgently require cost-effective and environmentally friendly low dielectric radio frequency substrates. Paper is one of the most mature industrial products, derived from cellulose. Due to its rich pore structure, paper exhibits a low relative permittivity. In this work, TEMPO-mediated oxidation was employed to enhance the water dispersibility of cellulose pulp and the handsheets were prepared by vacuum filtration and hot-press drying. The strong interaction between oxidized pulp fibers resulted in handsheets with a substantially reduced forming pressure of ∼1.2 kPa and tensile properties comparable to those of commercial copy paper. The oxidation degree of the oxidized pulp directly influenced the porosity and relative permittivity of the handsheets. The relative permittivity of handsheets can be readily adjusted between low- k (ε r ∼ 3) and ultra-low- k (ε r ∼ 2) by blending oxidized pulps or stacking filter cakes. The bottom surface of the handsheets manifested considerable compactness, thereby ensuring printability. Finally, the handsheets with printed silver patterns can be safely disposed of by incineration or redispersion, demonstrating notable competitiveness in the application of low-cost and disposable Sub-6 GHz printed substrates.