Ultra-Elastic, Durable, Bio-Degradable, and Recyclable Pulp Foam as an Air Dielectric Substitute for Sustainable Capacitive Pressure Sensing

Abstract

Green carbon-based cellulosic pulp foams with excellent renewable and biodegradable properties are promising alternatives to traditional petroleum-based lightweight materials, for reducing carbon emission and plastic pollution. However, the fabrication of super-elastic and durable pulp-based foams for high-value utilization remains challenging. Herein, a novel composite bio-foam material is prepared by a simple strategy of wet foaming and ionically cross-linking. The obtained foam assembled by cellulosic pulp fibers and polylactic acid (PLA) fibers at atmospheric pressure shows an oriented lamellar structure with interconnected macropores and super-elastic property. The prepared PLA@Pulp-20 foam shows a high compressive strain of up to 90% with the maximum stress of 150 kPa, while retaining ≈91% of its original height even after 30 000 compressive cycles (far superior to the reported pulp-based foams with compressive cycles <10). Furthermore, the foam exhibits outstanding recyclability and stability in a wide range of temperature and humidity. Remarkably, the potential application of PLA@Pulp foam as a dielectric layer for capacitive sensors is first demonstrated because of its electrical non-conductivity, and low dielectric constant (comparable to air). The corresponding device achieves non-contact touch or contact touch sensing, demonstrating highly attractive performance in sustainable super-elastic pressure sensing, monitoring, and beyond.