Cellulose and nanocellulose-based flexible-hybrid printed electronics and conductive composites – A review

Highlights

• Significant market opportunities for biopolymers in flexible-hybrid printed electronics.

• High smoothness and transparency can be achieved with TEMPO oxidation/nanocellulose.

• Doping or ionizable grafting is required for conductivity in cellulose.

• Grafted negative charged side chains on cellulose can help in positive ion conduction.

• Nanocellulose shows piezoelectric properties due to crystalline asymmetry.

Abstract

Flexible-hybrid printed electronics (FHPE) is a rapidly growing discipline that may be described as the precise imprinting of electrically functional traces and components onto a substrate such as paper to create functional electronic devices. The mass production of low-cost devices and components such as environmental sensors, bio-sensors, actuators, lab on chip (LOCs), radio frequency identification (RFID) smart tags, light emitting diodes (LEDs), smart fabrics and labels, wallpaper, solar cells, fuel cells, and batteries are major driving factors for the industry. Using renewable and bio-friendly materials would be advantageous for both manufacturers and consumers with the increased use of (FHPE) electronics in our daily lives. This review article describes recent developments in cellulose and nanocellulose-based materials for FHPE, and the necessary developments required to propagate their use in commercial applications. The aim of these developments is to enable the creation of FHPE devices and components made almost entirely of cellulose materials.

Introduction

Flexible-hybrid printed electronics is a rapidly growing field because it provides high throughput manufacturing of electronics that enables economies of scale resulting in more affordable products. Printing for electronics has been available since the 1950s (Suganuma, 2014). Today, different printing processes like gravure, flexography, screen, offset, inkjet, and laser induced forward transfer are used (Hrehorova et al., 2011; Hrehorova et al., 2005; Inui et al., 2015; Kattumenu et al., 2018; Mandal et al., 2012; Sico et al., 2016; Suganuma, 2014). Because products printed using these processes are electrically functional, various types of substrates and inks are utilized to get a desired circuit with a priori necessary mechanical properties. Paper can be one of those substrates (Kattumenu et al. 2018; Keskinen et al., 2012). Environmental concerns and end-of-life disposal challenges are grand challenges for 21^st century society that demand an examination of renewable resources such as cellulose and its offspring, nanocellulose, for mitigation of these issues. Theoretically, any substrate can be used for the creation of electronics. Some examples of substrates that have been used are: glass (Hrehorova et al., 2011), polydimethylsiloxane (PDMS) (Larmagnac et al., 2014), paper (Merilampi et al., 2009), polyimide, polyethylene terephthalate, polyvinylchloride with fabric, polytetrafluoroethylene (Lim et al., 2013), polyethylene (Mandal et al., 2012), and polyethylene naphthalate (Suganuma, 2014).

In the printing industry, cellulose is most commonly used in the form of paper. Apart from being used as a flexible (non-conductive) substrate for printed circuits, cellulose can also be used in the design of conductive substrates in conjunction with various functional inks including dielectric, conductive, semi-conductive, and photo-voltaic. Therefore, it can be used in the development of sensors, lights/displays, solar cells, and membranes in batteries. To improve upon the electrically functional properties of cellulose, researchers have blended it with other materials or grafted functional groups onto its surface. However, such research is still in the early stages and is not yet ready for commercial applications. Currently, simple systems utilizing inorganic materials are favored for use in commercial applications.

Electrically functional components are often made using a single material to provide their performance. This is often the case with conductive inks (Larmagnac et al., 2014; Merilampi et al., 2009; Suganuma, 2014), which use a single metal element. More complex systems using a combination of materials may also be used to increase performance and functionality. As an example, metallic inks made of silver (Bollström, 2013; Hrehorova et al., 2011; Inui et al., 2015; Larmagnac et al., 2014; Mandal et al., 2012; Merilampi et al., 2009), gold (Bollström, 2013; Mandal et al., 2012), and copper (Abhinav et al., 2015; Bollström, 2013; Mandal et al., 2012) may be used. By combining copper and silver, printers are provided the additive benefits of low oxidation and high conductivity from each of the component parts. Organic based conductive inks made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (Mandal et al., 2012; Sico et al., 2016), polyaniline (PANI) (Mandal et al., 2012), graphene (Huang et al., 2011), and carbon nanotubes (Beecher et al., 2007) have also been explored. Implementation of cellulose-based materials can provide the platform for conductive inks. Cellulose has been used as a matrix for conductive materials, or as a backbone for grafted electrically functional material (Dogome et al., 2013). In this review, the current state of research pertaining to these cellulose-based materials and their modifications are described as they pertain to the development of substrates and functional inks in the field of flexible and hybrid printed electronics.