Electromechanical properties of cellulose, including piezoelectricity, have been investigated for decades due to their potential applications in biocompatible sensors and actuators. Individual cellulose nanocrystals (CNCs) have been predicted to be piezoelectric due to their non-centrosymmetric crystal structures. However, there has not been convincing evidence of macroscale piezoelectricity for bulk materials consisting of CNCs. When polar CNCs are arranged in bulk materials, their random distribution favors an anti-parallel structure, hence the net polarity, and consequently their piezoelectricity, is cancelled. Through an exhaustive review of the literature, we find that the reported piezoelectric coefficients for cellulose vary over several orders of magnitudes, from 0.001 to 1000s pC/N. It raises the critical questions: what is the inherent piezoelectricity of cellulose and can it be translated from nanocrystals to macroscale materials? Piezoelectricity in cellulose can be convoluted with other electromechanical mechanisms present in the structure such as electrostatic deformations, electrochemical effects, electrostriction and flexoelectricity. It is important to identify the contribution of each electromechanical property from measured values to properly design and develop sensor and actuator devices. In this presentation, we aim to provide proper approaches and guidelines to investigate the intrinsic electromechanical properties of cellulose. The true electromechanical coupling mechanisms and their relationship to each other will be covered. The molecular origin of piezoelectricity of CNCs and key requirements to translate this piezoelectricity to CNC-based composites will be discussed. The preparation and characterization methods for polar ordering in cellulose will be presented.

Critical discussion of electromechanical coupling properties of cellulose

256th National Meeting (2018)

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