Dong / Umer / Tak Lau Fillers and Reinforcements for Advanced Nanocomposites

1. Auflage 2015
ISBN: 978-0-08-100082-3
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 586 Seiten

Reihe: Woodhead Publishing Series in Composites Science and Engineering

Fillers and Reinforcements for Advanced Nanocomposites reviews cutting-edge, state-of-the-art research on the effective use of nanoscaled fillers and reinforcements to enhance the performance of advanced nanocomposites, both in industrial and manufacturing applications. It covers a broad range of topics such as nanocelluloses, nanotubes, nanoplatelets, and nanoparticles, as well as their extensive applications. The chapters provide detailed information on how fillers and reinforcements are used in the fabrication, synthesis and characterization of advanced nanocomposites to achieve extraordinary performance of new materials and significant enhancements in their mechanical, thermal, structural and multi-functional properties. It also highlights new technologies for the fabrication of advanced nanocomposites using innovative electrospinning techniques. - Covers topics such as nanocelluloses, nanotubes, nanoplatelets, and nanoparticles, as well as their extensive applications - Discusses the latest research on the effective use of nanoscaled fillers and reinforcements to enhance the performance of advanced nanocomposites - Explains how fillers and reinforcements are used in the fabrication, synthesis and characterization of advanced nanocomposites

Autoren/Hrsg.

Dong, Yu

Umer, Rehan

Tak Lau, Alan Kin

Leseproben

1 Properties and characterization of electrically conductive nanocellulose-based composite films
D.Y. Liu1, G.X. Sui1,  and D. Bhattacharyya2     1Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China     2The University of Auckland, Auckland, New Zealand Abstract
Nanocellulose is attracting more and more attention from the scientists due to its high mechanical strength and environmental sustainability. Nanocellulosebased conducting composite film shows promise in the application of nanopaper-based sensors, flexible electrodes, and conducting adhesives. This chapter first briefly introduces the fundamentals of nanocellulose and conducting polymer polyaniline (PANI). Then, it describes the synthesis and properties of electrically conductive nanocellulose-based composite films. PANI was used as electrical function component. The effects of the concentration of aqueous nanocellulose suspension on the structures and properties of the composites are discussed. Keywords
Conducting polymer; Nanocellulose; Nanocomposites; Polyaniline (PANI) 1.1. Introduction
1.1.1. The fundamentals and applications of nanocellulose
Interest is increasing in developing biobased products derived from renewable sources and innovative processing technologies that can reduce the dependence on fossil fuels and encourage the movement toward a sustainable material basis (Espert et al., 2004; Pandey et al., 2005). Cellulose is one of the most abundant natural polymers on Earth, and the annual biomass production is about one trillion tons (Moon et al., 2011). Cellulose fibers have been widely used due to their sustainability and good mechanical properties. The term “nanocellulose” usually refers to the cellulose materials having at least one dimension in the nanometer range. Isolated cellulose fibers or whiskers possess lateral dimensions around 5–20 nm and longitudinal dimension in a wide range from tens of nanometers to several micrometers. The round-shaped cellulose nanoball with diameters of 20–40 nm is extracted from sweet potato residue (Lu et al., 2013). The rodlike polymeric nanomaterials have a low coefficient of thermal expansion, high thermal stability, high aspect ratio, and low density (~1.5 g/cm3). Cellulose nanowhiskers, also called cellulose nanocrystals (CNC) or nanocrystalline cellulose, are usually produced by the acid hydrolysis of natural cellulosic material after removing noncellulosic substance including dewaxing, hemicelluloses, and lignin. Most show a high crystallinity index and a lower aspect ratio; therefore, we expect that the CNWs extracted from tunicates exhibit a high aspect ratio of 38 (Eichhorn, 2011). The degree of crystallinity, size, and morphology depend on the source of raw materials and preparation methods. Cellulose nanofibers, also called micro/nanofibrillated cellulose (MFC/NFC), are obtained by mechanical disintegration after the raw cellulosic materials were chemically or enzymatically pretreated to get pure cellulose. Thus, the MFC has a high aspect ratio with a length over 1000 nm including crystalline and amorphous cellulose (Siro and Plackett, 2010). Microfibrillar cellulose (MFC) shows more commercial production availability than hydrolyzed CNC (Brinchi et al., 2013). Nanocellulose, as a natural nanomaterial, has recently gained attention from researchers and industry because it has a high tensile modulus (138 GPa), which is higher than that of the S-glass (86–90 GPa) and comparable to Kevlar (131 GPa), rendering them good reinforcement for natural and synthetic polymer matrices (Nishino et al., 1995; Liu et al., 2010; Lin et al., 2011). It has some unique properties, including good renewability, excellent mechanical properties, high specific surface area, biodegradability, and biocompatibility (Geyer et al., 1994). Moreover, cellulose, rich in hydroxyl groups, has good affinity with a variety of polymers, including conducting polymers (Richardson et al., 2006; Johnston et al., 2009; Mo et al., 2009; Nystrom et al., 2009). Nanocellulose can be prepared from a variety of sources, such as wood pulp, plant fibers (e.g., hemp, sisal, flax, ramie, jute, algae) (Strømme et al., 2002); microbial (Acetobacter xylinum) (Gelin et al., 2007); sea creatures (tunicates) (Sturcová et al., 2005); fruit skin (banana and grape) (Cherian et al., 2007); fruit husk (coconut) (Rosa et al., 2010), and even agricultural products (e.g., cornhusk, wheat straw) (Alemdar and Sain, 2008), which makes them more attractive and applicable. Three methods are available for producing nanocellulose, namely, chemical acid hydrolysis, chemical treatment in combination with mechanical refining, and the enzymatic method. Nanocellulose can be extracted from numerous raw natural materials on the Earth. It shows potentials in nanocomposites, paper making, coating additives, food packing, cosmetics, and gas barrier fields. However, producing nanocellulose in an economic and environmental way and exploring its functional products are the tasks for the researchers. It will promote the development of nanocellulose-based hybrid nanostructures. 1.1.2. The fundamentals and applications of polyaniline
Polyaniline (PANI), as an intrinsically conducting polymer, is a very promising material because of its ease of synthesis, low-cost monomer, tunable properties, and high environmental stability. It is thermally stable up to 250 °C and can be easily synthesized chemically and electrochemically via oxidative polymerization in various organic solvents and/or in aqueous media (Syed and Dinesan, 1991). PANI can be transformed to conducting materials from their insulating state through the doping techniques, and the highest conductivity of ~1000 S/cm is achieved for the freestanding film (Lee et al., 2006). PANI can be produced through chemical or electrochemical polymerization methods. The aniline reacts with an excess amount of an oxidant in a suitable solvent, such as acid. The polymerization takes place spontaneously and requires constant stirring. Electrochemical polymerization involves placing both counter and reference electrodes (such as platinum) into the solution containing diluted monomer and electrolyte (the dopant) in a solvent. After applying a suitable voltage, the polymer film immediately starts to form on the working electrolyte. Chemical polymerization has large possibility of mass production at a reasonable cost (Toshima and Hara, 1995). The electropolymerization technique is the direct formation of conducting polymer films that are highly conductive, simple, and suitable for use especially in electronic devices (Okamoto et al., 1998). Due to its outstanding properties, PANI has potential applications in antistatic and electromagnetic interference shielding, sensors, electrodes, and battery fields (Sengupta et al., 2006; Soto-Oviedo et al., 2006; Hoang et al., 2007; Wang et al., 2012). However, the commercial applications of PANI have been limited due to harsh chemical conditions in the synthesis and purification procedure that often lead to an inflexible polymer. The practical application of PANI is limited due to its lack of solubility resulting from the stiffness of its main chain and the existence of a strongly conjugated p-electron system. Thus, it is very difficult to produce the neat PANI films with satisfied properties, and poor solubility in all available solvents except doping with a suitable dopant or modifying the monomer (Bhadra et al., 2008). 1.1.3. The potential applications of nanocellulose/PANI composite
Cellulose has been recognized as good matrix/substrate for biodegradable batteries, sensors, and actuators (Kim et al., 2008, 2010). The polymer composites containing PANI are mostly investigated for blending with commercial polymers to obtain improved processability and fairly good mechanical properties together with good conductivity for practical applications (Annala and Lofgren, 2006; Barra et al., 2001; Khalid and Mohammad, 2007). However, the electrical conductivity of the composite was not improved effectively; in particular, the composites become more brittle due to the addition of PANI. Recently, cellulose fibers have been used to reinforce brittle conducting polymers, such as polypyrrole (PPy), PANI, and polythiophene (PTP) for energy-storage applications (Nyholm et al., 2011), such as cellulose and PPy all-polymer composite batteries with high reported charge capacities and charging rates (Nystrom et al., 2009). Recently, PANI-based aqueous suspensions containing PANI contents ranging between 5 and 80 wt% have been successfully developed; the composite films showed a high mechanical strength of 178 MPa, and a percolation threshold of electrical conductivity of 4.57 vol% of PANi content (Luong et al., 2013). Compared with PPy and PTP, PANI has relatively high theoretical specific capacity. Combining cellulose nanowhiskers and PANI is promising for...