The evolution of electronic devices continues to move from traditional, solid, and durable single-function units towards more portable and robust multi-function devices. In tandem with this shift, heightened awareness of environmental matters has led to a surge in demand for materials that are both sustainable and recyclable. Over the past decade, significant research has been undertaken into the use of environmentally-friendly, biodegradable, or dissolvable materials for the creation of next-generation, flexible, eco-friendly devices. Cellulose, a renowned natural biopolymer, is particularly noteworthy due to numerous attributes, including cost-effectiveness, renewability, ease of processing, and biodegradability. The rapid advancements in processing technologies, fabrication tools, an...[ Read more ]

The evolution of electronic devices continues to move from traditional, solid, and durable single-function units towards more portable and robust multi-function devices. In tandem with this shift, heightened awareness of environmental matters has led to a surge in demand for materials that are both sustainable and recyclable. Over the past decade, significant research has been undertaken into the use of environmentally-friendly, biodegradable, or dissolvable materials for the creation of next-generation, flexible, eco-friendly devices. Cellulose, a renowned natural biopolymer, is particularly noteworthy due to numerous attributes, including cost-effectiveness, renewability, ease of processing, and biodegradability. The rapid advancements in processing technologies, fabrication tools, and the diverse morphology of cellulose have made this timeless natural material a promising candidate for the creation of a range of eco-friendly functional devices. These devices, owing to the inherent properties of cellulose, are anticipated to perform at levels that meet or exceed current expectations.

In this dissertation, a multitude of strategies for the optimization of cellulose materials were elaborated upon, with a particular focus on structural enhancement and the reinforcement of functional materials for application-specific customization. The complex arrangement of cellulose fibers, spanning scales from the molecular to the macroscopic, culminates in a hierarchical cellular architecture distinguished by multiscale anisotropies. These anisotropies persist across diverse scales, encompassing cells, cellulose fibrils, and molecular chains. The scope of the investigation presented herein is bifurcated based on the scale of the composite cellulose fiber under examination. Accordingly, the research is segregated into two distinct categories: paper-based functional devices and nanocellulose-based functional devices. This categorization allows for a more focused examination of the unique properties and potential applications that arise from manipulating cellulose at these different scales.

The first study focused on paper-composed functional devices with origami-enhanced performance, which undertook two distinct explorations. The first exploited the inherent global stretchability, curvature adaptability, and rigid foldability of origami to engineer a paper-based humidity sensor suitable for wearable applications. This endeavor leverages the unique properties of origami to develop sensors that are not only sensitive and reliable but also adaptable to the intricate contours and movements of the human body. The second investigation was captivated by the intriguing acoustic properties of origami metamaterials. We designed a paper-based acoustic absorber that demonstrated outstanding sound absorption performance. In addition to its acoustic capabilities, the absorber maintained the advantages of being compactable and lightweight, while also exhibiting exceptional mechanical performance. This exploration illustrates the potential of origami metamaterials in creating efficient, versatile, and mechanically robust acoustic devices.

The second investigation in this study centered on functional devices made from cellulose nanomaterials, and it encompassed two separate lines of inquiry. Cellulose materials with fibers size of nanoscale, which are derived from the breakdown of cellulose fibers using a top-down method, result in nano- or microfibrillated cellulose and cellulose whiskers. These structures serve as the foundation for creating new materials possessing exceptional properties. By integrating dissolvable cellulose nanofiber obtained through the top-down approach with functional nanomaterials, we developed a humidity sensor that can be recycled through a straightforward process allowing for the separation of the substrate and electrodes. Furthermore, using specific techniques associated with the bottom-up method, nanofibers and nanoparticles can be produced. Through a meticu-lously planned fabrication process, conductive graphite flakes were successfully aligned and connected by nanocellulose to construct a degradable thin film piezoresistive pressure sensor. These studies highlight the versatility of cellulose-based nanomaterials and their potential for sustainability and recyclability in device applications.