Nanocellulose Polymer Nanocomposites

Fundamentals and Applications

Vijay Kumar Thakur

• Publisher: Wiley-Scrivener
• Year: 2014
• ISBN:
  9781118872345
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Biorenewable polymers based nanomaterials are rapidly emerging as one of the most fascinating materials for multifunctional applications. Among biorenewable polymers, cellulose based nanomaterials are of great importance due to their inherent advantages such as environmental friendliness, biodegradability, biocompatibility, easy processing and cost effectiveness, to name a few. They may be produced from biological systems such as plants or be chemically synthesised from biological materials.

This book summarizes the recent remarkable achievements witnessed in green technology of cellulose based nanomaterials in different fields ranging from biomedical to automotive. This book also discusses the extensive research developments for next generation nanocellulose-based polymer nanocomposites. The book contains seventeen chapters and each chapter addresses some specific issues related to nanocellulose and also demonstrates the real potentialities of these nanomaterials in different domains.

The key features of the book are:

• Synthesis and chemistry of nanocellulose from different biorenewable resources
• Different characterization of nanocellulosic materials and their respective polymer nanocomposites
• Physico-chemical, thermal and mechanical investigation of nanocellulose based polymer nanocomposites
• Provides elementary information and rich understanding of the present state-of- art of nanocellulose-based materials
• Explores the full range of applications of different nanocellulose-based materials.

Part 1

SYNTHESIS AND CHARACTERIZATION OF NANOCELLULOSE-BASED POLYMER NANOCOMPOSITES

Chapter 1

Nanocellulose-Based Polymer Nanocomposites: An Introduction

Manju Kumari Thakur^*,1, Vijay Kumar Thakur² and Raghavan Prasanth³

¹Division of Chemistry, Govt. Degree College Sarkaghat, Himachal Pradesh University, Summer Hill, Shimla, India

²School of Mechanical and Materials Engineering, Washington State University, Washington, U.S.A.

³Department of Mechanical Engineering and Materials Science, Rice University, Houston, Texas, USA.

^*Corresponding author: [email protected]

Abstract

Rising environmental awareness and the high demand for alternatives to non-renewable petroleum resources has led to extensive research focused on the concept of biomass-based biorenewable materials. Natural cellulosic polymers are such materials of prime choice for different applications due to their inherent advantages which include the fact that they are easily available, environmentally-friendly and have lower health risks; and also that they are economical, biodegradable, easily processed, have acceptable specific properties and have excellent insulating/noise absorption properties to name a few. These cellulosic materials in nano form, i.e., as nanocellulose, are rapidly emerging as one of the most promising future materials with outstanding physical, chemical, mechanical and thermal properties for multifunctional applications in different fields. Keeping in mind the promising characteristics of nanocellulosic materials, the present chapter gives an overview of the recent progress in the structure and applications of nanocellulose procured from different resources.

Keywords: Nanocellulose, natural fibers, structure, processing, applications

1.1 Introduction

Polymer-based materials derived from both natural and petrochemical resources are currently being extensively used in a wide range of products and in numerous applications [1-3]. These polymers have superseded the use of other materials such as metals, glasses and ceramics in a number of fields [4-6]. Compared to their natural counterparts, synthetic polymers have been widely used in a vast number of applications such as films, flexible plastic bags, composites and rigid containers to name a few [7-9]. Properties such as light weight, strength, chemical inertness and inexpensive production make them a favorable candidate for most present day applications [10-12]. However some of their other properties also cause considerable environmental problems, with their high molecular weight, chemical stability and relatively low surface area-to-volume ratio making them resistant to degradation by microbial attack, and causing them to persist in the environment long after disposal [5, 13, 14]. In addition, these polymers are produced by oil-based technology, which raises a number of pertinent issues related to increasing oil prices and dwindling resources, so the impetus to replace these polymers with renewable materials is increasing [15-17]. In order to conserve resources and avoid adding increased carbon emissions, materials must be developed that consume less energy and use raw materials that are derived from renewable resources [18].

Indeed, rising environmental awareness around the world has resulted in a renewed interest in materials procured from biorenewable resources [19, 20]. One of the common practices to prepare new environmentally-friendly materials is the incorporation of a least one component that is derived from renewable resources [21, 22]. Green materials have attracted great attention and interest in the development of biodegradable or natural polymer-derived green composites, while minimizing the generation of pollution [23]. Natural polymers, or biopolymers, are polymers that are produced from renewable resources [24, 25]. They may be produced by biological systems such as plants or animals, or be chemically synthesized from biological materials [26]. It is also desirable to make use of natural materials which do not, for example, compete with the food chain [27, 28]. A biodegradable polymer can be defined as a material in which degradation results from the action of microorganisms such as bacteria, fungi and algae [29, 30]. Therefore the use of biopolymers to replace synthetic polymers is attractive due to their obvious environmental advantages of being sustainable, renewable and biodegradable, being broken down into carbon dioxide and water when exposed to microbial flora [16, 31, 32]. In this advancement, the development of high-performance polymer biocomposite materials made from natural resources has been increasing worldwide due to environmental and sustainability issues [9, 27, 33]. The use of renewable materials such as natural cellulose (most abundant biopolymer) is becoming impellent because of the great demand for alternatives to non-renewable petroleum materials and good reinforcing material due to its availability, low cost, low density, nontoxicity, low abrasiveness, biocompatibility and biodegradability [28, 34, 35]. Biocomposites consisting of the polymer matrix and natural cellulose fibers are environmentally-friendly materials which can replace glass fiber-reinforced polymer composites, and are currently used in a wide range of fields such as the automotive and construction industries, electronic components, sports and leisure, etc. [36, 37].

Recently, the research on biobased nanocomposites which are reinforced with both natural fibers and nanofillers is actively proceeding in order to offer higher thermal and mechanical properties, transport barrier, thermal resistivity and flame retardance in comparison with the conventional biocomposites [20, 38]. Nanocomposite describes a two-phase material where one of the phases has at least one dimension in nanometer range (1–100 nm) [39]. They differ from conventional composites by the exceptionally high surface-to-volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio. The reinforcing material can be made up of particles (e.g., minerals), sheets (e.g., exfoliated clay stacks) or fibers (e.g., carbon nanotubes, electrospun fibers or cellulose nanofibers) [40]. Large reinforcement surface area means that a relatively small amount of nanoscale reinforcement can have an observable effect on the macroscale properties of the composites. The ability to control the material features at the nanoscale and evaluation of their influence on the micro- and macroscopic properties provides a new aspect to the development of nanocomposite systems. There has been enormous interest in the commercialization of nanocomposites for a variety of applications, and a number of these applications are already found in the market [41]. Nanocomposites are currently used in a number of fields and new applications are continuously sought after.

In line with the development of nanotechnology and recent concern about environmental issues, more attention has been paid to the utilization of biobased nano-materials. In this regard, nanocellulose has gained much more interest because of its promising characteristics such as biodegradable nature, renewability and lower price [19]. Nanocellulose-based materials are gaining significant interest as potential nano-fillers for nanocomposites due to their nanoscale dimension (very high surface area-to-volume ratio), high aspect ratio and impressive mechanical properties (or nanostrength), which are imparted to the desired nanocomposites [42]. The advantages for the use of nanosize cellulosic materials are not only related to these properties; in fact, its dimensions, in the nanometer scale, open a wide range of possible properties yet to be discovered. Nanosize cellulosic materials can be isolated from a variety of cellulosic resources, including plants, animals (tunicates), bacteria and algae, and in principle could be extracted from almost any cellulosic material by using different procedures. Remarkable achievements have been witnessed in the green technology of cellulose nanomaterials in the field of materials science, including the development of bio-nanocomposites. The growing interest in green product and unsurpassed physical and chemical properties of nanocellulose have resulted in increased academic and industrial interest towards the development of cellulose nanocomposites. However, there are still some issues to be overcome and the main challenges in the field are related to an efficient separation of nanosize cellulosic materials from the natural resources [43]. The incompatible nature of nanocellulose with most polymers is also a crucial issue for its application in nanocomposites. In addition, the drying process of nanocellulose for application in polymer composite is another challenge. The last but not least point is related to finding a process for obtaining a higher yield in nanocellulose isolation. All these challenges and drawbacks have become the strong driving force for discovering more efficient processes and technologies to produce nanocelluloses for application in nanocomposites, and for inventing new applications as well [15]. Chapters 2–9 of this book discuss in detail the synthesis and characterization of different types of nanocellulose-based polymer composites, while Chapters 10–17 discuss in detail the processing and multifunctional applications of cellulose-based polymer nanocomposites.

1.2 Nanocellulose: Source, Structure, Synthesis and Applications

Human society has used natural cellulose-based materials for thousands of years, both knowingly and unknowingly [44]. All the industries around the world are looking for materials that can be easily procured from renewable and sustainable resources. However, although cellulose-based materials offer a number of advantages, for advanced applications some of the imperative properties such as functionality, uniformity and durability are not achieved using traditional cellulosic materials. Fortunately, the use of cellulose in nanoform can solve these issues. By suitable extraction of cellulose from different biorenewable resources at the nanoscale, next generation of multifunctional polymer nanocomposites can be obtained by employing a new cellulose-based “building block” known as nanocellulose. Nanocellulose offers a number of advantages such as high aspect ratio, low density (1.6 g cm⁻³), and a reactive surface of –OH side groups compared to the parental cellulose, and these functional groups also facilitate the attachment of desired functional groups onto these nanocellulose surface to achieve different surface properties. Nanocellulose can be obtained in different forms depending upon the source material and the intended applications. Chapters 2–9 of this book discuss in detail the different types of nanocellulosic materials. Natural cellulosic fibers are one of the most promising resources for the synthesis of nanocellulose. Natural cellulosic fibers can be divided into different types (Figure 1.1) [45].

Figure 1.1 Classification of cellulosic fibers.

Reprinted with permission from [45]. Copyright 2010 Wiley.

It has been reported that cellulose fibrils (micro/nano size) or cellulose whiskers can be easily procured from cotton fibers as well as cellulose filter papers [46]. Nanocellulose can be obtained from different resources such as wood, plants, tunicates, algae and bacteria. Figure 1.2 shows the structure of cellulose. Cellulose is a non-branched linear polysaccharide molecule that is comprised of two anhydroglucose rings (C₆H₁₀O₅) n; n = 10000 to 15000, where n depends upon the source of cellulose. These rings are linked together through the β 1–4 glucosidic bond [44].

Figure 1.2 Schematic structure for carbon atoms in an anhydroglucose unit of cellulose.

Cellulose is one of the most abundant natural polymers on earth and provides strength/stability to the plant cell walls [45]. The properties and economics of fiber production for various applications are influenced by the amount of cellulose in a fiber. In natural cellulosic fibers, stiff semicrystalline cellulose microfibrils have been found to be embedded in a pliable amorphous matrix (Figure 1.3) [45].

Figure 1.3 Plant plasma membrane...