Abstract
Paper materials are well-known to be hydrophilic unless chemical and mechanical processing treatments are undertaken. The relative humidity impacts the fiber elasticity, the interfiber joint behavior and the failure mechanism. In this work, we present a comprehensive experimental and computational study on mechanical properties of the fiber and the fiber network under humidity influence. The manually extracted cellulose fiber is exposed to different levels of humidity, and then mechanically characterized using atomic force microscopy, which delivers the humidity dependent longitudinal Young’s modulus. We describe the relation and calibrate the data into an exponential function, and the obtained relationship allows calculation of fiber elastic modulus at any humidity level. Moreover, by using confoncal laser scanning microscopy, the coefficient of hygroscopic expansion of the fibers is determined. We further present a finite element model to simulate the deformation and the failure of the fiber network. The model includes the fiber anisotropy and the hygroscopic expansion using the experimentally determined constants, and further considers interfiber behavior and debonding by using a humidity dependent cohesive zone interface model. Simulations on exemplary fiber network samples are performed to demonstrate the influence of different aspects including relative humidity and fiber-fiber bonding parameters on the mechanical features, such as force-elongation curve, strength and extensibility. Finally, we provide computational insights for interfiber bond damage pattern with respect to different humidity level as further outlook.
Highlights
Cellulose-based fiber materials have been used for decades as packing, printing media
The values were recorded at each relative humidity (RH) level, considering the morphological change of the fiber for a precise determination of humidity-dependent elastic modulus
Hygroscopic expansion coefficient was obtained to be 0.35 using confocal laser scanning microscopy, by recording the change of fiber cross-section swelling at different relative humidity levels
Summary
Cellulose-based fiber materials have been used for decades as packing, printing media Nowadays, they even have become popular as base material for electronic and microfluidic devices on a small scale (Gong and Sinton (2017), Shen et al (2019), Schabel and Biesalski (2019), Carstens et al (2017)), and biocomposite (Pantaloni et al (2021), Regazzi et al (2019), Lee and Wang (2006)), due to their recyclability to reduce pollution and save resources. As for the RH influence on the load bearing and failure mechanism of the fiber joint, there are still unclear observations in the literature regarding the dependency of the fiber joint mechanical properties due to RH. Jajcinovic et al (2018) have shown that the strength of individual fiber bonds increases upon exposure to high RH, where as others have shown that the bond strength decreases
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