Chapter 1

Lignocellulosic Polymer Composites: A Brief Overview

Manju Kumari Thakur*, 1, Aswinder Kumar Rana2 and Vijay Kumar Thakur*, 3

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

2Department of Chemistry, Sri Sai University, Palampur, H.P., India

3School of Mechanical and Materials Engineering, Washington State University, Washington, U.S.A.

*Corresponding author: shandilyamn@gmail.com; vktthakur@hotmail.com

Abstract

Due to their environmental friendliness and several inherent characteristics, lignocellulosic natural fibers offer a number of advantages over synthetic fibers such as glass, carbon, aramid and nylon fibers. Some of the advantages of lignocellulosic natural fibers over synthetic fibers include biodegradability; low cost; neutrality to CO2 emission; easy processing; less leisure; easy availability; no health risks; acceptable specific properties and excellent insulating/noise absorption properties. Due to these advantageous properties, different kinds of lignocellulosic natural fibers are being explored as indispensable components for reinforcement in the preparation of green polymer composites. With these different advantageous properties in mind, this chapter provides a brief overview of different lignocellulosic natural fibers and their structure and processing, along with their applications in different fields.

Keywords: Lignocellulosic natural fibers, structure, processing and applications

1.1 Introduction

Different kinds of materials play an imperative role in the advancement of human life. Among various materials used in present day life, polymers have been substituted for many conventional materials, especially metals, in various applications due to their advantages over conventional materials [1, 2]. Polymer-based materials are frequently used in many applications because they are easy to process, exhibit high productivity, low cost and flexibility [3]. To meet the end user requisitions, the properties of polymers are modified using fillers and fibers to suit the high strength/high modulus requirements [4]. Generally synthetic fibers such as carbon, glass, kevlar, etc., are used to prepare polymer composites for high-end, sophisticated applications due to the fact that these materials have high strength and stiffness, low density and high corrosion resistance [5]. Fiber-reinforced polymer composites have already replaced many components of automobiles, aircrafts and spacecrafts which were earlier used to be made by metals and alloys [6]. Despite having several good properties, these materials (both the reinforcement and polymer matrices) are now facing problems due to their shortcomings especially related to health and biodegradability [7]. As an example, synthetic fibers such as glass and carbon fiber can cause acute irritation of the skin, eyes, and upper respiratory tract [8]. It is suspected that long-term exposure to these fibers causes lung scarring (i.e., pulmonary fibrosis) and cancer. Moreover, these fiber are not easy to degrade and results in environmental pollution [9]. On the economic side, making a product from synthetic fiber-reinforced polymer composites is a high cost activity associated with both the manufacturing process and the material itself [10]. The products engineered with petroleum-based fibers and polymers suffer severely when their service life meets their end [11]. The non-biodegradable nature of these materials has imposed a serious threat for the environment where ecological balance is concerned [12]. Depletion of fossil resources, release of toxic gases, and the volume of waste increases with the use of petroleum-based materials [13]. These are some issues which have led to the reduced utilization of petroleum-based non-biodegradable composites and development of biobased composite materials in which at least one component is from biorenewable resources [14].

Biobased composites are generally produced by embedding lignocellulosic natural fibers into polymer matrices, and in these composites at least one component (most frequently natural fibers as the reinforcement) is from green biorenewable resources [15]. This book is primarily focused on the effective utilization of lignocellulosic natural fibers as an indispensable component in polymer composites. The book consists of twenty-three chapters and each chapter gives an overview of a particular lignocellulosic polymer composite material. Chapter 2 focuses on natural fiber-based composites, which are the oldest types of composite materials and are the most frequently used. The book has been divided into three parts, namely: (1) Lignocellulosic natural polymer-based composites, (2) Chemical modification of cellulosic materials for advanced composites, and (3) Physico-chemical and mechanical behavior of cellulose/polymer composites. In the following section a brief overview of lignocellulosic fibers/polymer composites will be presented.

1.2 Lignocellulosic Polymers: Source, Classification and Processing

Different kinds of biobased polymeric materials are available all around the globe. These biobased materials are procured from different biorenewable resources. Chapters 2-10 primarily focus on the use of different types of lignocellulosic fiber-reinforced composites, starting from wood fibers to hybrid fiber-reinforced polymer composites. Chapter 3 summarizes some of the recent research on different lignocellulosic fiber-reinforced polymer composites in the Southeast region of the world, while Chapter 6 summarizes the research on some typical Brazilian lignocellulosic fiber composites. The polymers obtained from biopolymers are frequently referred to as biobased biorenewable polymers and can be classified into different categories depending upon their prime sources of origin/production. Figure 1.1(a) shows the general classification of biobased biorenewable polymers [11, 13, 16].

Figure 1.1 (a) Classification of biobased polymers [11, 13, 16].

For the preparation of polymer composites, generally two types of fibers, namely synthetic and natural fibers, are used as reinforcement. Figure 1.1(b) shows different types of natural/synthetic fibers frequently used as reinforcement in the polymer matrix composites.

Figure 1.1 (b) Types of fiber reinforcement used in the preparation of polymer composites[11, 13, 16].

Natural fibers can further be divided into two types: plant fibers and animal fibers. Figure 1.2 shows the detailed classification of the different plant fibers. These plant fibers are frequently referred to as lignocellulosic fibers.

Figure 1.2 Classification of natural fibers [11, 13, 16].

Among biorenewable natural fibers, lignocellulosic natural fibers are of much importance due to their inherent advantages such as: biodegradability, low cost, environmental friendliness, ease of separation, recyclability, non-irritation to the skin, acceptable specific strength, low density, high toughness, good thermal properties, reduced tool wear, enhanced energy recovery, etc. [11,13,16,17]. Different lands of lignocellulosic materials are available all around the world. These lignocellulosic materials are procured from different biorenewable resources. The properties of the lignocellulosic materials depend upon different factors and growing conditions. Lignocellulosic natural fibers are generally harvested from different parts of the plant such as stem, leaves, or seeds. [18]. A number of factors influence the overall properties of the lignocellulosic fibers. Table 1.1 summarizes some of the factors affecting the overall properties of lignocellulosic fibers. The plant species, the crop production, the location, and the climate in which the plant is grown significantly affect the overall properties of the lignocellulosic fibers [18].

Table 1.1 Factors effecting fiber quality at various stages of natural fiber production. Reprinted with permission from [18]. Copyright 2012 Elsevier.

The properties and cost of lignocellulosic natural fibers vary significantly with fiber type. Figure 1.3(a-c) shows the comparison of potential specific modulus values of natural fibers/glass fibers; cost per weight comparison between natural fibers and glass and cost per unit length respectively.

Figure 1.3 (a) Comparison of potential specific modulus values and ranges between natural fibers and glass fibers.

Reprinted with permission from [18]. Copyright 2012 Elsevier.

Figure 1.3 (b) Cost per...