Scalable Fabrication of Piezoelectric Paper Composite: The Interplay of Pulp Fibrillation, BaTiO3 Particle Loading, and Aging Effects of Refined Pulp

Abstract

This paper reports the fabrication process of a piezoelectric material with a peak piezoelectric coefficient, d33 = 48 ± 6 pC/N, achieved using highly refined wood pulp at 528 kWh/t specific refinement energy (the highest level tested). The process involves functionalization of pulp fibers with a single layer of the cationic polymer, poly(diallyldimethylammonium chloride) (PDDA). The external fibrillation achieved through refinement increases the loading of BaTiO3 (BT) particles from 20% (unrefined pulp) to 78% (refined pulp) and the d33 from 3 ± 2.3 to 48 ± 6 pC/N, comparable to PVDF-based composites (35.4 pC/N). Refinement increases the fiber’s surface area and accessibility to chemical modification, resulting in a robust piezoelectric composite with improved stress transfer, while the reduction in d33 uncertainty with increased refinement suggests higher uniformity across the composite. A pulp aging study (days 0 to 225) demonstrates the importance of fibril formation in fiber-to-fiber binding for piezoelectric paper performance: over time, the fibers show lower fibrillation and particle loading capacity, which translates to reduced piezoelectric performance. Environmental conditions such as changes in the moisture content can lead to hygroexpansion of the pulp, potentially affecting alignment between the BT particles and the performance of the composite. An attempt to regenerate lost fibrillation increased fibrillation and particle loading; however, the performance remained below that of freshly refined pulp, suggesting that piezoelectric performance depends on the quantity of BT particles as well as the strength of the interlocking fiber network. This simplified fabrication process achieves among the highest reported piezoelectric performances for lead-free paper-based piezoelectric composites, and its practical application is demonstrated through a tactile sensor, and it is suitable for a range of sensing applications.