Cellulose Fibers: Bio- and Nano-Polymer Composites

This chapter deals with the structure, properties and applications of natural fibres. Extraction methods of Natural Fibres from different sources have been discussed in detail. Natural fibres have the special advantage of high specific strength and sustainability, which make them ideal candidates for reinforcement in various polymeric matrices. Natural fibres find application in various fields like construction, automobile industry and also in soil conservation. It is the main source of cellulose, an eminent representative of nanomaterial. Extractions of cellulose from plant-based fibres are discussed in detail. Various methods used for characterization of cellulose nanofibres and advantages of these nanofibres have also been dealt with.

Chemical functionalization of cellulose aims to adjust the properties of macromolecule for different purposes, particularly, as a chemical feedstock for production of cellulose derivatives for a variety of applications. The conventional sources of cellulose include cotton linters and wood pulp which now-a-days are discouraged on account of the cost of the former and environment conservative regulations associated with the latter. Further, renewable raw materials are gaining considerable importance because of the limited existing quantities of fossil supplies. In this regard, cellulose-rich biomass derived from the nonconventional sources such as weeds, fibers, bamboos, and wastes from agriculture and forests, etc. acquires enormous significance, as alternative chemical feedstock, since it consists of cellulose, hemicellulose, and lignin, which contain many functional groups suitable to chemical functionalization. Etherification of cellulose through methylation, carboxymethylation, cynaoethylation, hydroxypropylation, single or mixed, is one of the most important routes of cellulose functionalization. Chemical composition and rheological characteristics make possible the selection of the modified cellulose to serve special applications. Prompted by above facts, possibility for chemical functionalization of cellulose rich biomass derived from bamboo, Dendrocalamus strictus (DCS), and noxious weeds – Lantana camara (LC) and Parthenium hysterophorus (PH) for their utilization was examined and results are reported. Proximate analysis of these materials was conducted and processes were standardized for production of α-cellulose on 1 kg batch scale. The percent yield, Av. DP, and the percentage of α-cellulose content of the obtained celluloses were found in the range of 35–40, 400–825, >90 (Brightness 80% ISO), respectively. Processes were optimized for production of water-soluble carboxymethyl cellulose (DCS, LC, and PH), cyanoethyl cellulose (DCS) and water-soluble hydroxypropyl cellulose (DCS and PH). The optimized products were characterized by IR spectra. Rheological studies of 1% and 2% aqueous solutions of the optimized carboxymethyl celluloses and hydroxypropyl celluloses showed their non-Newtonian pseudoplastic behavior. Thus, abundantly available biomass from Dendrocalamus strictus bamboo and the weeds – Lantana camara and Parthenium hysterophorus seem to be a potential feedstock for production of α-cellulose and its subsequent functionalization into cellulose derivatives for variety of applications. This was also demonstrated that these noxious weeds could also be managed by their utilization into products of commercial importance.

A wide variety of natural fibers can be applied as reinforcement or fillers in composites. Bast fibers, such as flax and hemp, have a long history of cultivation and use. They are characterized by low weight and excellent range of mechanical properties. The properties of bast fibers are influenced by conditions of cultivation, retting, and processing. Pretreatment and surface modification of bast fibers is conducted for optimization of the interfacial characteristics between fiber and matrix as well as improvement of their mechanical properties. Application of bast fibers as reinforcement to replace the glass fibers to composite manufacture brings positive environmental benefits.

Naturally abundant, biodegradable, and sustainable plant and wood fibres are composed of smaller and progressively mechanically stronger entities. These smaller structural load-bearing cellulosic fibrils, termed as micro- and nanocellulosic fibrils, can be separated by defibrillating the pulp fibres with either mechanical, chemical, enzymatic, and ultrasound sonication methods or a combination of these treatments. Engineered biopolymer, like cellulosic fibrils, and inorganic mineral composite structures have the potential to create new material properties and applications. This chapter deals with the production, characterisation, and application of cellulosic fibril-precipitated calcium carbonate structures in printing and writing paper. We enunciate a novel composite paper consisting of cellulosic fibrils and precipitated calcium carbonate as the backbone structure and reinforced with a minimal fraction of long fibres. However, recent research investigations show that cellulosic fibrils and their composites find wide application across different fields of manufacturing such as polymers and plastics, medicine, construction, and automotive industries.

Natural fibres have been the prime candidate to replace synthetic fibres for the production of composite materials. Major advantages associated with natural fibres include low cost, low density, high toughness and biodegradability. However, these intriguing properties of natural fibres do come at a price. The hydrophilic nature of natural fibres often results in poor compatibility with hydrophobic polymer matrices. Various surface treatments of natural fibres using chemicals have been developed to improve the compatibility between the fibres and the matrix, but large amounts of solvents are usually involved. In this chapter, greener surface treatments without the use of hazardous chemicals are reviewed. These include plasma treatments, the use of enzymes and fungi for the extraction and surface treatment of raw fibres or natural fibres and the deposition of bacterial cellulose onto natural fibres. These treatments are aimed at improving the interfacial adhesion between the fibres and the matrix, thereby improving the stress transfer efficiency from the matrix to the fibre. The effects of these treatments on the properties of natural fibres are discussed. In addition to this, the overall impact of these treatments on the mechanical properties of the resulting natural fibre reinforced composites is also addressed.

When subjected to acid hydrolysis or mechanical shearing, lignocellulosic fibers yield defect-free, rod-like, or elongated fibrillar nanoparticles. These nanoparticles have particularly received great attention as reinforcing fillers in nanocomposite materials due to their low cost, availability, renewability, light weight, nanoscale dimension, and unique morphology. Preparation, morphological features, and physical properties of nanocelluloses are discussed in this chapter. Their incorporation in nanocomposite materials including processing methods and ensuing properties such as microstructure, thermal properties, mechanical performances, swelling behavior, and barrier properties are also presented.

In recent years, there has been a resurgence of interest for the use of renewable materials such as plant fibers, also called “lignocellulosic fibers”, due to increasing environmental concerns along with the unique characteristics of these fibers. These include abundant availability, renewability, biodegradability, as well as low wear and tear of equipments, particularly when processing their composites. In comparison with today’s most used synthetic fibers such as glass fiber, lignocellulosic fibers offer the advantage of lesser health hazards and of course lower cost. In addition, they help in generating employment, particularly in rural sector, by leading to better living standards of the rural population. Thus, the utilization of these fibers has both short-term objectives, through the synthesis and characterization of composites, and long-term objectives, to use them as alternates for synthetic fibers and possible substitute for wood. This has driven the researchers to bring out data on the source and availability of all the useful lignocellulosic fibers, cataloging their available information on morphology and properties as well as current uses. A sound knowledge of the morphology of these fibers helps the understanding of their observed properties in terms of structural parameters, such as number, size, and shape of cells, chemical constituents, as well as the fracture mechanism in these fibers. Further, a careful examination of various properties of these fibers indicates that they are inconsistent probably due to the nonuniformity in dimensions and the defects in these fibers. The latter may be present either inherently or due to their processing. As a consequence, highly scattered properties are observed, which may be one of the drawbacks for their use as engineering materials. These limitations could, in principle, be overcome through an individual selection of fibers with approximately the same dimensions and properties by knowing the nature of correlation of fiber dimensions with a given property whereby the strongest fibers based on selection of their diameters could be separated. However, this may pose some problem with tedious work. Development of a scientific methodology does become essential to the selection of these fibers particularly for their application as reinforcements in various matrices to render them reliable, similar to synthetic fiber products.

This chapter presents such a methodology involving some of the Brazilian fibers through statistical evaluation with the aim to select fibers of highest possible strength and to explain the strengthening mechanism responsible for the superior performance of these dimensionally selected fibers. Concluding remarks and suggestions are given at the end, indicating some future direction of work with a view to motivate the readers and researchers to explore the future potentials of these natural resources with proper selection of lignocellulosic fibers to develop new uses including composites for these fibers. In addition, this may help different industrial sectors, which are already using these fibers or may use them in the future.

Lignocellulosic fibers have been recognized as attractive fillers for different types of matrices in polymeric composites. Their advantages such as recyclability and renewability are unique characteristics for composites used as automobile components and building structural panels. In view of the hydrophobic behavior of most polymers and the hydrophilic nature of lignocellulosic fibers, poor adhesion is observed between lignocellulosic fibers and the polymeric matrix, which results in lower mechanical properties. Pullout tests have been successfully used to determine the interfacial shear stress in synthetic fiber-reinforced composites, but little has been reported in the case of lignocellulosic fiber–polymer composites. This chapter presents an overview on the determination of the interfacial strength of lignocellulosic fibers–polymer matrix composites including some obtained by the authors on Brazilian fibers such as curaua, ramie, and piassava, considered as reinforcement for composites. Concluding remarks and suggestions indicate some future works.

This chapter discusses the supermolecular structure and interphase phenomenon in composite-reinforced natural fibers. We analyzed the formation of the polymorphic forms in polypropylene (PP) matrix. It was found that in the composites with natural fibers, the hexagonal form arises when the fibers are in motion in relation to the polymeric matrix. of Moving temperature of the natural fibers was found to have a strong influence on the content of the hexagonal modification. If the temperature of the moving fibers is low, then the amount of β-PP significantly increases. The content of β-PP also depends on the rate of the moving of fibers; however, the chemical modification of the natural fiber’s surface reduces the content of this form. Also, the processing conditions play an important role for structural changes in PP matrix.

Further, this chapter provides a survey about the formation of a transcrystalline layer in the composite system. The occurrence of transcrystallization was found to strongly depend on the type of chemical treatment of the fiber surface. Predominant nucleation ability was found for unmodified fibers. However, chemical modification of fiber surface slightly depressed the nucleation of polypropylene matrixes.

The influence of physical and chemical treatment methods of natural fibers on mechanical properties was analyzed also. Additionally, the mechanical and other physical properties of the composite are generally dependent on the length, content, and dispersion of fibrous filler and processing parameters.

Pineapple leaf fibers (PALF) have long been known as textile materials in many countries. Despite being mechanically excellent and environmentally sound, PALF are the least-studied natural fibers, especially for reinforcing composites. This article presents a survey of research works carried out on PALF and PALF-reinforced composites. It reviews PALF extraction, fiber characterization, and PALF applications, modification of PALF, and manufacture and properties of PALF-reinforced composites. With increasing importance of pineapple and pineapple plantation area, value-added applications of PALF as reinforcing fibers in polymer composites must be developed in order to increase “resource potential” of pineapple and consequently energize the utilization of PALF.

Rice husks are an important by-product of the rice milling process and are a major waste product of the agricultural industry. Rice husks contain nearly 20 mass% silica, which is present in hydrated amorphous form. They have now become a great source of raw biomass material for manufacturing value-added silicon composite products, including silicon carbide, silicon nitride, silicon tetrachloride, magnesium silicide, pure silicon, zeolite, fillers of rubber and plastic composites, cement, adsorbent, and support of heterogeneous catalysts. The controlled burning or thermal degradation of the rice husks in air or nitrogen leads to the production of white rice husk ash (WRHA) or black rice husk ash (BRHA), respectively.

The present review is an attempt to consolidate and critically analyze the research work carried out so far on the processing, properties, and application of rice husks and the products of its thermal degradation in various laboratories and also highlight some results on the processing and characterization of rice husk ashes (RHAs) and reactive silica obtained in the author’s laboratory. In this connection, the composition, structure, and morphology of the raw rice husks (RRHs) and the products obtained from its thermal degradation in an oxidative or inert atmosphere are described in detail. The controlled burning or pyrolysis of the RRHs in a fluidized-bed reactor is shown to be the most perspective method. The products obtained might successfully be used as fillers of polypropylene (PP) and tetrafluoroethylene-ethylene copolymer (TFE-E) composites, rubbers, and other polymer composites and to replace the expensive synthetic additive as Aerosil, for instance. The physicochemical and physicomechanical characteristics of the obtained composites are described. The RHA-polymer composites can lead to the futuristic “organic–inorganic hybrid materials” with specific properties. Due to the high pozzolanic activity, the rice husk silica also finds application in high strength concrete as a substitute for silica fume.

The abundance of waste from paddy milling industry as well as its interesting complex of behaviors are prerequisites for success in obtaining cheap and valuable products and stipulate new alternatives for its applications. The production of value added materials from rice husks not only facilitates utilization of an abundantly available agro waste but also reduces the environmental pollution and solves a serious ecological problem.

The development of high performance natural fiber composites (NFC) in the last few decades saw a significant growth in the industries as well as academia. These natural fiber reinforced composites exhibit numerous advantages such as high mechanical properties, low weight, low cost, low density, high specific properties, good thermal and acoustic insulating properties when compared with other composites. There has been a dramatic increase in the use of natural fibers for composites based on thermoplastics polymers such as polyvinyl chloride (PVC), polypropylene (PP), and high-density polyethylene (HDPE). A large number of natural fibers including flax, hemp, jute, kenaf, and sisal are being used for this purpose. In development of these composites, incompatibility between the natural fibers and polymer matrix and the tendency of the fibers to form aggregates are the two important issues. Additionally, the composites exhibit poor dimensional stability due to moisture absorption. Some of these issues/problems can be solved by the use of coupling agents, use of compatibilizer and treatments of fibers using peroxide, permanganate, and plasma.

In this chapter, the preparation and properties of polyolefin-based NFC with special reference to the types of fibers, compatibilization, processing methods, mechanical properties, and some applications will be discussed.

The use of cellulosic fibers as load bearing constituents in composite materials has increased over the last decade due to their relative cheapness compared to conventional materials such as glass and aramid fibers, their ability to recycle, and because they compete well in terms of strength per weight of material. All-cellulosic based composites prepared from cellulose derivatives based matrices and microcrystalline cellulosic fibers made by direct coupling between fibers and matrix present interesting mechanical and gas permeation properties, thus being potential candidates for packaging materials. Both the cellulosic matrix and the reinforcing fibers are biocompatible and widely used in the pharmaceutical industry, which is very important for the envisaged application. In addition to their biocompatibility, cellulosic systems have the ability to form both thermotropic and lyotropic chiral nematic phases, and the composites produced from the latter show improved mechanical properties due to fiber orientation induced by the anisotropic matrix. The preparation and characterization (morphological, topographical, mechanical, gas barrier properties) of all-cellulosic based composites are described in this chapter.

The increasing amount of synthetic polymers above the permissible limits is causing a lot of environmental pollution and is one of the greatest threats to the modern world. There is a growing demand for biodegradable polymeric materials derived from nature and is being seen as a solution for solid waste management. Biodegradable materials have been found to show a pronounced impact in case of environmental protection. Such biodegradable and eco-friendly materials have got diversified applications including sustained drug delivery devices, gene therapy, soft-tissue engineering, biomedical engineering, pharmaceuticals, artificial organ design, etc. Biodegradable materials have been found to possess good elasticity and impact strength because of which they have got potential applications in replacement of heart valves and kidneys. Moreover, such materials have been found to exhibit selective absorption toward saline water and are of great importance in petroleum industry as well as in desalination of water. Recently, such materials have been found to show electrical stimulus sensitivity both under the influence of AC and DC. These polymers have been found to be stimuli responsive and could be of great significance for drug and pesticide/fungicide delivery devices. Such materials are also pH sensitive toward different media and are of potential industrial usage in packaging and nursery plantation as well as in tissue culturing.

In the recent years, biobased products have raised great interest since sustainable development policies tend to expand with the decreasing reserve of fossil fuel and the growing concern for the environment. Consequently, biopolymers, i.e., biodegradable polymers, have been the topic of many researches. They can be mainly classified as agro-polymers (starch, protein, etc.) and biodegradable thermoplastic homo or copolyesters (polyhydroxyalkanoates, poly(lactic acid), etc.). These latter, also called biopolyesters, can be synthesized from fossil resources but main productions are obtained from renewable resources. Unfortunately for certain applications, biopolyesters cannot be fully competitive with conventional thermoplastics because some of their properties are too weak. Therefore, to extend their applications, these biopolymers have been formulated and associated with lignocellulose fillers, which could bring a large range of improved properties (stiffness, crystallinity, thermal stability, etc.). The resulting “biocomposites” have been the subject of many recent publications.

This chapter is dedicated to this class of materials, which are elaborated from different natural fibers and biopolyesters. These systems based on renewable resources nowadays show strong developments in different fields, including automotive and packaging industries.

The present chapter considers the possibilities of reinforcing thermoplastic matrix materials with cellulose man-made fibers, in particular high performance rayon tire cord yarn. Mechanical properties of the composites such as tensile strength, stiffness, and impact properties are in the focus of interest. Composite and fracture surface morphology is accessed by scanning electron microscopy (SEM) and the quality of fiber–matrix adhesion is revealed. Advantages and disadvantages of using coupling agents are discussed. Thermoplastics both from fossil and from renewable resources are used as matrix materials. From the first group, polypropylene is the most important example and is considered in detail while polyethylene, polybutene-1, impact modified polystyrene, ABS are briefly sketched. On the bio-based side, the emphasis is on poly(lactic acid) (PLA) as the most easily commercially accessible inexpensive bioplastic. Polyhydroxyalkanoates (PHA) are also considered but in less detail. Composites are manufactured by a specially developed melt compounding method on twin screw extruders and shaped by injection molding. In general, rayon reinforcement proves to be superior to natural fiber reinforcement, in particular in terms of impact strength. For PP–rayon the properties are even comparable to those of short glass fiber reinforced polypropylene (GFPP) and PC/ABS with advantages in terms of impact strength compared to GFPP. With 30% rayon in PP, tensile strength is tripled, modulus is doubled, and notched impact strength is doubled at room temperature and quadrupled at −18°C. For the bio-based thermoplastics, rayon is an ideal reinforcement since the bio-based character is preserved. Strength and modulus always increase, and at the same time, impact strength is increased dramatically for brittle products such as PLA. This is true in particular for a specially designed fiber–matrix interphase using a decoupling agent.

The primary objective for development of cellulose-based polymer composites is to create a material with acceptable environmental degradability in order to reduce the increasing ecological risk by so-called nonbiodegradable polymers. It is believed that cellulose may act as biodegradable part in the composite, which is preferably consumed by microorganism leaving behind disintegrated polymer fraction that may enter in bio-cycle in a systematic manner and ultimately convert into biomass and carbon dioxide. The present chapter is focused on the biodegradation behavior of cellulose-based composites under different circumstances.

In the twenty-first century, major changes are coming and materials will be a key enabling technology. Fuel economy, consumption, and demand for high-performance light-weight materials are pressurizing the industrialists. The maximum possible use of renewable resources is gaining attention as an alternative to petroleum resources. On the other hand, reinforcement of polymers with nanoscale particulates has gained a massive attraction from the researchers in academia and industries, because of the exponential improvement in physical, mechanical, and thermal properties with smaller amount of incorporation. For a global commercialization of these materials, the environmental concerns such as raw materials, energy use, recycling, and disposal (especially via biodegradation) are also to be envisioned. Thus, this chapter is intended to review the recent research activities in the area of nanocomposites using biopolymers that include polymers derived from renewable resources. General preparation methods, structure–property relationships, and biodegradability of these nanocomposites have been discussed in the context of environmental benignness.

Cellulose nanofibers and their composites offer a highly attractive research line in recent times. Cellulose nanofibers have generated a great deal of interest as a source of nanometer-sized fillers because of their sustainability, easy availability, and the related characteristics such as a very large surface-to-volume ratio, outstanding mechanical, electrical, and thermal properties. This chapter describes the many processes to produce nanocellulose from different cellulosic sources and how to increase the compatibility between cellulosic surfaces and a variety of plastic materials. Furthermore, it provides knowledge of different nanocelluloses and nanocomposites and provides updated information on their properties and also deals with fascinating high-tech applications, especially in the medical field.

The natural resources of the World are depleting very fast due to the high rate of exploitation and low rate of restoration, leading to an increase in global warming and pollution hazards. In recent years, there has been increasing interest in the substitution of synthetic fibers in reinforced plastic composites by natural plant fibers such as jute, coir, flax, hemp, and sisal. Sisal is one of the natural fibers widely available in most parts of the world; it requires minimum financial input and maintenance for cultivation and is often grown in wastelands, which helps in soil conservation. Advantages of sisal fiber are: low density and high specific strength, biodegradable and renewable resource, and it provides thermal and acoustic insulation. Sisal fiber is better than other natural fibers such as jute in many ways, including its higher strength, bright shiny color, large staple length, poor crimp property, variation in properties and quality due to the growing conditions, limited maximum processing temperatures. In recent years, there has been an increasing interest in finding innovative applications for sisal fiber-reinforced composites other than their traditional use in making ropes, mats, carpets, handicrafts, and other fancy articles. Composites made of sisal fibers are green materials and do not consume much energy for their production.

The characteristics of composites depend on different parameters such as extraction of fiber, surface modification and the synthesis of composites. During synthesis, fiber length, orientation, concentration, dispersion, aspect ratios, selection of matrix, and chemistry of matrix have to be considered to achieve the required strength. Inorganic fibers have several disadvantages, including their nonbiodegradability, the abrasion in processing equipments, high cost and density, and the health problems caused to workers during processing and handling. Commonly used composites, these days are, glass, aramid, carbon, and asbestos fibers filled in thermoplastic, thermoset, or cement composites. Yet natural fiber composites with equivalent characteristics to synthetic fibre composites are not available. Most of the plant fibers are hydrophilic in nature and water absorption may be very high. This may be controlled by different methods of interfacial surface modification. Because of the low density and high specific strength and modulus. Sisal fiber is a potential resource material for various engineering applications in the electrical industry, automobiles, railways, building materials, geotextiles, defense and in the packaging industry. Present chapter discuss about the research work on sisal cultivation, fiber extraction, processing, sisal fiber characteristics, and the use of sisal fiber in thermoplastic and thermoset polymer composites for various engineering applications.

Natural fibre-reinforced composites have recently received much attention because of their attractive properties such as lightweight, non-abrasive, combustible, non-toxic, low cost and biodegradable. This chapter examines the applications of natural fibre-reinforced composites and nanocomposites in automotive structural applications. Various applied and promising natural fibre-reinforced composites and nanocomposites including flax, hemp, kenaf, wood, pineapple, banana and sisal are presented. Key determinants to performance-specific properties of natural fibre-reinforced composites are discussed in detail. These include fibre–matrix adhesion, fibre mechanical properties, moisture, impact and fatigue, thermal stability and preparation of fibre-reinforced composites. The chapter further looks into lightweight component manufacturing techniques including their potentials and limitations. Examples of current applications are given, and future trends are outlined while addressing the main drawbacks faced by these composites to lightweight components or vehicle manufacturing.

Jute and allied fibers have gained interest as reinforcing materials in the composite industry for low-cost housing applications. Their advantages have been increasingly recognized with the major motivation being the environmental friendliness, low cost, renewability, and high specific strength and stiffness. In this chapter, an overview of efforts made during the previous decades on natural fiber composites is presented. Research and development carried out at CBRI on natural fiber composites with reference to jute is outlined. A three cornered approach: surface treatment of fibers, matrix resin modification, and selection of an appropriate processing technique for designing innovative building products have been adopted to develop dimensionally stable products. Based on these findings, various products such as composite panels, roofing sheets, door shutters, frames, and shuttering plates alternative to plywood have been prepared. Industrial trials for the manufacturing of standard size panel products are also carried out to know their commercial viability. The suitability of these products was assessed as per existing standard specifications for use as alternate building materials.