Handbook of Green Materials

The following sections are included:

• Contents
• List of Corresponding Authors

“Bionanomaterials: Separation Processes, Characterization, and Properties” is topic of the first volume of a set of four in Handbook of Green Materials. This first volume consists of 14 chapters starting with the state of art of the structure and physical properties of cellulose, followed by potential and used raw materials sources for nanomaterials separation. The volume covers also the most important chemical pretreatments and separation technologies as well as functionalization of the nanomaterials for different uses. The properties and characterization methods are described in detail. Also, other green nanomaterials such as starch are taken up in one of the chapters. In the last chapters, the industrial point of view of manufacturing of nanocelluloses, their availablility, and uses especially in the paper industry is presented.

Cellulose is biosynthesized as slender crystalline nanofilaments deposited on existing cell wall to concentric layers in plant constituting the main biomass. Native cellulose takes crystalline allomorphs that are drastically different from regenerated cellulose obtained from solution (cellulose II) or after amine treatments (cellulose III). Although hydrogenbonded molecular sheet is an invariant among native celluloses, hydrophobic interaction is major driving force of molecular assembly. Two crystallographic surfaces with interchain distances of 5.4 and 6Å are considered to be dominating the exposed surfaces by analogy to model cellulose samples. The crystalline order extends to a length of the order of 100nm along the chain, with only small region of disorder, which makes it an exception compared with regenerated cellulose or semicrystalline synthetic polymers. The tensile modulus of this crystalline element in ramie fiber along the chain direction is estimated to be of the order of 130GPa, while the crystal modulus perpendicular to the chain direction is estimated to be a magnitude lower. The thermal expansion coefficient is the highest in the direction perpendicular to the pyranose plane, and very low or slightly negative along the chain direction.

Huge amounts of potential raw material sources for isolation of bionanomaterials have been identified. These are wood, especially waste from forest industries, and agricultural crops, as well as waste from food and marine production. Bionanomaterials can also be extracted from algae and sea animals and synthesized by bacteria. A number of studies about the isolation of bionanomaterials from many of the above-mentioned sources have been published. It has been shown that bioresidues are suitable for production of cellulose nanomaterials and that the extracted nanofibers and crystals have similar structure and properties compared with the nanomaterials extracted from primary resources, but can be produced at lower cost. This chapter covers an introduction to bioresources such as wood and plant fibers and their main characteristics in terms of chemical composition and physical properties. Also, some examples of different sources and their nanomaterials are discussed.

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation is one of the advantageous and characteristic chemical reactions of native cellulose as a pretreatment for preparation of nanocelluloses, in which significant amounts of carboxylate groups can be formed selectively and densely on crystalline cellulose microfibril surfaces under aqueous conditions. Three TEMPO-mediated oxidation systems have been reported as green chemistry: TEMPO/NaBr/NaClO at pH 10, TEMPO/NaClO/NaClO₂ at pH 5 or 7, and TEMPO electro-mediated oxidation at pH 7 or 10. Differences in oxidation mechanism, reaction conditions, and properties of the oxidized products between the three oxidation systems are comprehensively summarized. The oxidized celluloses prepared under adequate conditions are convertible to mostly individualized TEMPO-oxidized cellulose nanofibers (TOCNs) by mechanical disintegration treatment in water. The mechanisms to obtain TOCNs and fundamental properties of self-standing TOCN films and TOCN containing composite materials are reviewed on the basis of recently published papers. In conclusion, the abundant sodium carboxylate groups present on TOCN surfaces, ultrafine and homogeneous TOCN widths of 3–4 nm, high aspect ratios, and high crystallinities are the key characteristics for TOCNs to be used as new biobased and functional nanofibers in wide application fields.

The separation of cellulose nanofibers (CNFs) from the original plant fiber is a rather complicated process, often involving several steps of chemical or enzymatic and mechanical treatment. In an ideal method, it is possible to produce large amounts of low-cost CNFs with uniform size distribution without degrading the properties of cellulose and using only a low amount of energy in the processing. Currently, there are various mechanical methods available which can be used in the isolation of nanocellulose. The most commonly used methods are the ultrafine grinding and homogenization techniques. This chapter will discuss these methods, as well as techniques which are not as common but have been tested for fiber separation. We will show examples of how the different methods affect the fibrillation efficiency, energy consumption, and size distribution of CNFs. Also, different chemical, enzymatic, and mechanical pretreatments to make the separation process more efficient are discussed briefly, as they are often an important part of the CNF production process.

This chapter describes the state of the art in the cellulose nanocrystals preparation in terms of existing cellulosic sources, reaction protocols, size, morphology, stability, and separation of these exceptional nanoparticles. It also covers the various activities about large-scale production of these nanomaterials all over the world.

Fossil energy depletion and growing environmental concerns have brought up increasing interest in biobased eco-efficient and high technology materials. Among them, starch nanocrystals (SNCs) consist of crystalline nanoplatelets produced from the hydrolysis of starch granules and are mainly used as nanofillers in polymeric matrices. New applications have brought up the need for scaling-up the SNC preparation process.

This chapter reports the most relevant aspects related to the isolation and purification of a native cellulose-producing strain belonging to the genus Gluconacetobacter. Specifically, a Colombian strain of a newly discovered bacterial species named Gluconacetobacter medellinensis was characterized phenotypically and genotypically. The main factors to enhance the production of bacterial cellulose (BC) by this bacterium were investigated. In addition, the structural characteristics of cellulose nanoribbons produced under different culture conditions are revealed. Energy-rich agroindustrial wastes were used as culture media with the aim of enhancing the production of BC on a large scale. The main properties of the BC produced by the Colombian G. medellinensis strain in these media are presented.

In this book chapter, we highlight the potential of the chemical functionalization to tailor the polarity of cellulose nanofibers (CNFs) in order to elaborate functional materials with tunable properties. Three different utilizations have been envisaged for CNF, namely as reinforcing agents, films, and porous materials.

Rheology is of great importance to understand the structure and properties of nanocelluloses. The dependence of flow behavior and viscoelastic properties of nanocellulose suspensions on the shape, dimension, and surface properties of particles as well as solvents and additives are discussed in this chapter.

Comprehensive characterization of cellulose nanomaterials (CNs) is needed to advance our understanding of these materials and enable material designers, models, and manufacturers to make informed decisions in the development of new products and materials based on CNs. This chapter summarizes several characterization methods as they pertain to CNs, in particular to characterize CN morphology, structure, mechanical properties, and surface chemistry.

Nanocelluloses, nanosized starches, and nanostructured chitins are among the most abundant renewable biobased nanomaterials. Due to their unique, nanospecific properties, they are promising materials for improving the performance of many future products. However, at the moment, it is not well known how the nanospecific properties affect the safety of the biobased nanomaterials, as they depend on many, still poorly understood factors, such as their interactions with cells and living organisms, as well as on the exposure routes. Generally, biobased nanomaterials are considered safe, due to their natural origin and the benign nature of their bulk forms. Results published so far on the safety of biobased nanomaterials have shown that nanomaterials are not generally toxic to humans or to the environment. However, they are not inert either and may have interactions with their surrounding environment. In addition, due to the great variation in the properties of biobased nanomaterials, the toxicity test results obtained are valid only for the samples tested. More research and knowledge of nanomaterials' interactions with living organisms are needed before results from toxicity testing can be generalized, and currently, the safety of biobased nanomaterials must be assessed case by case.

The aim of this chapter is to present an extended review about the use of cellulose nanofibers (CNFs) for paper applications. This review confirms the recent interest of the paper research and industry. This work is based on a selection of more than 60 relevant references published very recently, including scientific publications (31), international conference proceedings (11), and patents (18). The chapter is divided into two different sections. One section deals with the bulk addition of CNFs while the other describes the surface treatment with CNFs or CNF blend coating. We think that surface treatment with CNFs offers the highest potential in comparison to the bulk addition of CNFs. Irrespective of the strategies involved, CNFs are more effective once combined with other materials because of synergetic effects in which CNFs play the role of a carrier or a binder. At the end of each section, a table summarizing the references according to the strategies involved and presenting the main findings or parameters is provided. With the benefit of this hindsight, this chapter proves that CNFs will replace existing materials or help develop new functional materials in coming years. In order to conclude about the potential uses of CNF in the paper industry, a SWOT (strengths/weaknesses/opportunities/threats) analysis is presented.

This chapter covers the multiple commercialization approaches identified by the major players that produce nanocellulose material. For each of the nanocellulose family, several aspects such as the production (technical, environmental) and marketing (oil industry, public acceptance, market penetration) issues as well as the potential applications will be covered. This chapter is concluded with a tentative prospect on the perspectives and challenges of the nanocellulose industries.

The following section is included:

• Index

The following sections are included:

• Contents
• List of Corresponding Authors

The second volume of the Handbook of Green Materials focuses on bionanocomposites or renewable nanocomposites, their processing methods, characterization, and most important properties. The volume contains 17 chapters covering not only processing technologies for thermoset and thermoplastic bionanocomposites but also green chemistry of nanocellulose modification for composite applications. Specific composites materials such as advanced bacterial cellulose nanocomposites, all cellulose composites, and responsive nanocomposites are discussed. Properties of cellulose nanocomposites such as toughness, strength, stiffness, and optical transparency are described in detail. Moreover, the reinforcing efficiency of cellulose in nanocomposites will be assessed in one of the chapters. The last chapters cover potential applications of bionanocomposites in medical devices, such as blood vessel replacements, as substrates for printed electronics, and additives in wood adhesives.

The hydrophilicity of cellulose, arising from the presence of large number of hydroxyl groups, reduces its potential in nanocomposites containing nanocellulose (typically <10 wt%). In order to manufacture nanocomposites containing nanocellulose with improved properties, chemical modification is often needed. This chapter summarizes the chemical modification of nanoscale cellulose and its impact on the fiber–matrix interface, as well as the mechanical performance of the resulting polymer nanocomposites. We start with the discussion of conventional esterification of nanocellulose via acetylations reaction with acetic anhydrides and carboxylic acids. Methods for direct and indirect quantification of the fiber–matrix interface are reported. Green(er) esterification reactions in the gas phase and utilizing ionic liquids as the solvent and catalyst for the modification of nanocellulose are also discussed. In addition to this, this chapter also discusses the recent work on the carboxymethylation of nanocellulose and the deformation mechanism of bacterial cellulose networks within a composite.

As a result of high specific surface area and energy, cellulose nanocrystals (CNCs) usually have a strong tendency for aggregation. This makes it difficult to produce nanocomposites with polymers in which these filler particles are homogeneously dispersed and form percolating networks. This chapter summarizes recent efforts to create such nanomaterials by applying sol-gel processes. One particularly useful method, dubbed the “template approach”, relies on the formation of a three-dimensional network through self-assembly of originally well-individualized nanofibers, and subsequently filling the template with a polymer of choice. The template is made by first forming a homogeneous aqueous CNC dispersion, followed by gelation through solvent exchange with a water-miscible solvent. The resulting CNC organogel is subsequently imbibed with a matrix polymer by immersion into a polymer solution. The process is broadly applicable and has allowed for the fabrication of several CNC-based nanocomposites. It is particularly useful for the fabrication of otherwise inaccessible nanocomposites of immiscible components, such as the polar CNCs and hydrophobic matrix polymers.

Solution casting is the oldest technology to make plastic films and was developed in the 19th century to produce photographic films by Eastman Kodak. Solution casting is an easy and versatile method to produce nanocomposite thin films/sheets in laboratory scale. In the solution casting of polymer nanocomposites, the polymer phase is dissolved in water or a non-aqueous volatile solvent and mixed with nanosized reinforcements in the same solvent medium prior to casting on a flat surface. The solvent phase is removed by evaporation and thereafter the dried film is released from the substrate. This chapter discusses the solution casting process of nanocomposites where biobased nanofibers or crystals are used as the reinforcing phase. The effect of processing route on the composites morphology and mechanical properties is discussed.

Compounding of nanocomposites using twin-screw extrusion is a process whereby nanocellulosic materials are mixed with a polymer melt. The process can be scaled up to produce cellulose nanocomposites for industrial-scale use. This process method may also allow nanocomposites to be easily injection molded or compression molded. Our aim has been to develop a cellulose nanocomposite processing method using two specific processing routes: (i) liquid feeding of the nanomaterials into the extruder and (ii) preparation of a master batch which is diluted to the desired concentration during a compounding process. The prepared nanocomposites have usually been compression molded to sheets or injection molded to samples. The studies on nanocomposite structure and properties have enabled optimization of the process as well as improved performance. Depending on the extent of separation of cellulose nanocrystals or nanofibers in the liquid medium and the interaction of nanocelluloses with the polymer matrix, different types of nanocomposites have been obtained: composites with aggregated nanocelluloses, partially dispersed nanocellulose, or fully dispersed nanocelluloses. Ultimately, the objective of these studies has been to produce nanocomposites with good mechanical properties, thermal stability, and transparency and at the same time develop an energy-efficient and cost-effective processing methodology.

Bionanocomposites are a class of composites where both the polymer matrix and nanofillers are derived from renewable resources and/or based on biodegradable polymer matrices. Nevertheless, processing such systems faces many obstacles mainly related to interfacial incompatibility between the most industrially appealing biobased polymers that are hydrophobic and the most naturally abundant nanofillers that are hydrophilic. Among the methodologies developed to overcome this challenge, in situ polymerization constitutes one of the most viable and promising approaches because good filler dispersion and enhanced interfacial adhesion with the surrounding matrix can be achieved. This chapter collates key advances realized in the field of in situ polymerization of bionanocomposites, particularly based on polylactide and polycaprolactone as matrices while the fillers are nanoclays and nanocelluloses, and their related properties.

This chapter summarizes several techniques that have been used in the characterization of cellulose nanocomposites, in particular cellulose nanomaterials (CNs) dispersion, distribution, and orientation within polymer matrixes. The microscopy techniques described are optical microscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Also, the use of X-ray diffraction for quantification of CN orientation is discussed. The characterization of bionanocomposites is challenging because these materials are soft, moisture sensitive, non-conductive, and usually both the matrix phase and the reinforcement phase primarily consist of low atomic number elements (making differentiation difficult). Different sample preparation techniques for CN composite materials are also discussed.

This chapter addresses the challenges and approaches to obtaining detailed and accurate information on the nature and mechanics of interfaces in cellulose nanofiber–based nanocomposites. Covering the nanofiber types of nanocrystals, nanofibrils, and bacterial cellulose, the chapter directs the reader to issues governing the mechanics of nanocomposite materials in general. The chapter also introduces a number of techniques that have been used to follow the micromechanics of cellulose nanocomposites, namely, Raman spectroscopy, X-ray diffraction, and Förster resonance energy transfer imaging.

Cellulose nanopaper in the form of nanofiber networks show superior mechanical performance and new functional characteristics compared with the brittle paper and fiberboard materials and thermoplastic biocomposites, which are commercially available. The chapter analyzes the potential to combine toughness and strength in polymer matrix nanocomposites based on cellulose nanofiber networks.

Cellulose nanofibers (CNFs) have been shown to offer good reinforcement in polymer composites. The recent advancements in combined processing techniques have lowered the energy requirements to produce these nanosized celluloses advancing both the availability and commerciality of these biobased materials. Here, we focus on the current status of the mechanical properties of reinforced polymer nanocomposites. A comparison is made of the reinforcing efficiency of CNF composites by back-calculating a reinforcing efficiency parameter using established micromechanical models. Included is a brief review of the factors affecting reinforcing efficiency such as the sources and production methods of CNF as well as the matrices and methods used to manufacture nanocomposites from them. Some comparisons are made to current reinforced polymer composites, such as glass fiber composites. Highlighted are some of the issues that need addressing if these materials are to be used as structural applications.

Bacterial cellulose (BC) is one of the strongest materials produced by nature, possessing high modulus and strength, estimated to be 114GPa and in excess of 1500MPa, respectively. It has been shown to be an effective nano-reinforcement for polymers to produce lightweight and mechanically strong nanocomposites when high loading fractions of BC were used. This chapter discusses the applications of BC in advanced polymeric materials. These materials include optically transparent nanocomposites and BC-reinforced, natural fiber-reinforced hierarchical composites. We also discuss the use of BC in the so-called “all-cellulose nanocomposites” and biomimetic BC-reinforced nanocomposites. The application of BC simultaneously as stabilizer and nano-reinforcement to produce macroporous polymers by mechanical frothing of acrylated epoxidized soybean oil is also discussed in this chapter.

Flexible circuit boards are currently ubiquitous in electronic products, and eventually the substrate of image displays will soon be made of flexible materials as well. Plastics are prospective candidates due to their inherent flexibility and optical qualities but they also present large thermal expansion. The expansion of the substrate has to be compatible with those of the active layers deposited on it, to avoid damages during the thermal cycles involved in the display manufacture. One way to reduce the thermal expansion of plastics is to reinforce them with nanofibers, without losing transparency. Nanofibers are available in large amounts in the form of cellulose and chitin in nature, being produced by plants and animals. Here, some of the researches to produce optically transparent composites based on natural nanofibers for use in flexible displays are presented and discussed.

The outstanding mechanical properties of nanocellulose, added to its wide availability, biodegradability, and wide number of alternatives for chemical modification, have been the driving force for its utilization as reinforcement in responsive polymers. In particular, segmented polyurethanes (SPUs) with shape memory behavior have been utilized in the production of nanocellulose-reinforced responsive composites. Additionally, the hygroscopic nature of cellulose has led to the investigation of nanocomposites with water-responsive behavior, displaying a dramatic reduction of the material rigidity in the presence of the liquid or switchable swelling behavior. More recent developments in the area of nanocellulose responsive materials were addressed to growing active polymers or functional nanoparticles on the surface of cellulosic crystals or fibrillar structures. These developments are opening new roads for activating different material responses by indirect or non-contacting methods.

The area of self-reinforced polymer composites is one of the fastest growing areas in engineering polymers, but until now, these materials have been mainly developed on the basis of thermoplastic fibers of moderate performance. In this work, we review a new type of self-reinforced composites based on cellulosic fibers to produce all-cellulose composites or all-cellulose nanocomposites, in which both the fibers and matrix are cellulose. Natural cellulose boasts a high elastic modulus and high tensile strength, implying that cellulose possesses the potential to replace glass fibers. The concept of all-cellulose composites allows for the production of composites with higher fiber contents than traditional fiber-reinforced plastics. Moreover, since the matrix and reinforcement phases of these biocomposites are completely compatible with each other, all-cellulose composites allow for efficient stress transfer and adhesion at their interface. Under optimized processing conditions, the mechanical and thermal properties of the cellulose fibers in these all-cellulose composites can be retained, while the excellent interface can bring optical transparency to these composites. Fabrication, structure, and properties of such all-cellulose composites are reviewed.

Bacterial nanocellulose (BNC) represents an important green nanomaterial and, in particular, a promising natural biomaterial. It is produced biotechnologically from low-molecular-weight sugars like d-glucose by using non-pathogenic bacteria such as Gluconacetobacter species. In this process, BNC is generated as a dimensionally stable hydrogel. The unique valuable properties of BNC are mainly based both on the collagen-like hierarchical three-dimensional nanofiber network structure and its exciting controllability and design directly during biosynthesis. The great potential for medical applications ranges from wound dressings up to innovative implants for visceral and cardiovascular surgery. This chapter assembles initially the current knowledge in biocompatibility, bioactivity, and mechanical properties of BNC. The following are examples for the in situ design of channeled BNC membranes and of BNC tubes, the latter as bioactive implants for small-diameter (≤5mm) blood vessels. Using a matrix technology, the walls of these BNC tubes consist of several layers, firmly connected and arranged rotationally symmetric around the longitudinal axis of the tubes — similar to natural blood vessels. As substitutes of the carotid artery of sheep, such tubes with a length of 100mm show good surgical feasibility and functional performance during the evaluation period of 3 months. They are specifically colonized with endothelial cells, smooth muscle cells, and fibroblasts.

During the last decade, printing technique was essentially used for several pages of book, magazines, and newspaper, so-called graphic printer. Nowadays, due to its achievement on rapid, accurate, and reliable concept, it was widely encouraged for electronic community. The use of printer for electronic purpose has been increasing exponentially. The emergence of this concept was strongly evident in many applications such as diode, transistor as well as radiofrequency identification. In this chapter, the overview of printed electronics and its significance and finally, the role of this technique in many applications area are discussed.

Adhesive bonding is one of the key steps in the production of modern wood composite products. Improvements in wood adhesion are desirable in terms of performance improvement, adhesive savings, or both. The brief overview of the state of the art given in this chapter demonstrates the feasibility of wood adhesive modification through the addition of nanocellulose. Highly significant positive effects of nanocellulose addition on mechanical bond stability in both wet and dry conditions are reported. The effects are consistent for brittle thermosets such as urea–formaldehyde as well as comparably soft thermoplastics such as polyvinylacetate. It is shown that both solid wood adhesion and wood composite production can benefit from the addition of only a few percent of nanocellulose to the adhesive.

The following section is included:

• Index

The following sections are included:

• Contents
• List of Corresponding Authors

This third volume of the set of four in the Handbook of Green Materials focuses on self- and directed-assembled and structured materials based on nanocellulose, their preparation methods, characterization, and most important properties. The volume consists of 15 chapters covering thin films and layer-by-layer deposition; chiral nematic nanocellulose colloidal dispersions and resultant solid films; bicomponent structures from cellulose derivatives, etc. In addition, it contains contributions in the area of surface functionalization by using click chemistry and production of lightweight foams and aerogels based on nanofibers and nanocrystals. The applications of these systems take advantage of a number of functional properties, relevant to protective barrier films, membranes, biosensors, flexible electronics, and advanced materials. In the description of the science and technology of bionanomaterial assemblies, some of the methods to probe their most critical properties are also introduced.

In this chapter, we present a summary of some advances aimed at assembling nanocellulose as ultrathin films, including the main techniques used for the deposition of coating layers of cellulose nanocrystals (CNCs). The Langmuir–Schaefer (surface lifting) method is introduced as a suitable way to produce thin films with tunable surface packing density. Results from recent efforts to align CNCs under convective and shear-assisted assembly. The orientation of the component nanoparticles has been shown to be sensitive to external electric fields, which allow additional control of film structure and morphology. Some physical and electromechanical properties of the produced CNC films are briefly introduced. Continuous films obtained by phase-separation of bicomponent solutions of cellulose derivatives are also discussed. Detailed description and examples of self- and direct-assembly for the formation of nanocellulose structures are described in detail elsewhere in this volume. However, this introductory chapter attempts to highlight the use of cellulose as a platform for the fabrication of functional coatings and as an enabling material to facilitate a number of novel applications.

Chemical functionalization of cellulose is often required to achieve more advanced applications beyond paper and textiles. Among the diverse repertory of functionalization strategies, the click chemistry approach and particularly the Cu¹-catalyzed azide–alkyne cycloaddition (CuAAC) has sparked an increased attention because it is one of the few reactions that occurs between chemically stable functional groups and also allows heterogeneous reactions in aqueous media. This chapter introduces different pre-functionalization strategies to afford “clickable” cellulose substrates. Furthermore, numerous examples demonstrating the use of CuAAC reaction in the production of cellulose-based materials, such as hydrogels, dendrimers, and composites are presented.

Cellulose nanocrystals (CNCs) are rod-shaped colloids that have inherent liquid crystalline properties and form chiral nematic phases under certain conditions. Here, we discuss the factors that influence chiral nematic phase formation and the parameters that modulate pitch, such as aspect ratio, ionic strength, sonication energy, and temperature. We describe how the orientation of CNCs in suspension can be preserved in solid films. Emphasis is placed on the techniques used to characterize chiral nematic CNC suspensions and films, and on the applications of these liquid crystals, including as iridescent pigments, alignment media for protein NMR, and templates for mesoporous carbon, silica, and hydrogel materials.

The formation of nanometer-thin films of cellulose nanofibers (CNFs), polyelectrolytes, and/or nanoparticles has opened up new possibilities of manufacturing interactive devices with controlled mechanical properties. By controlling the charge of the CNF and the charge and 3D structure of the polyelectrolytes, it is possible to control the buildup, i.e., the thickness, the adsorbed amount, and the immobilized water of layer-by-layer (LbL) films of these materials. The charge balance between the components is not the only factor controlling the LbL formation. The structure of these adsorbed layers in combination with the properties of the constituent components will in turn control how these layers interact with, for example moist air. The mechanical properties of the LbLs can be tuned by combining the high-modulus CNF with different components. This has been shown by using a microbuckling technique where the mechanical properties of ultra-thin films can be measured. In combination with, for example, moisture-sensitive poly(ethylene imine) (PEI), the Young's modulus of CNF/PEI films can be changed by one order of magnitude when the humidity is increased from 0% RH to 50% RH. The incorporation of high-modulus nanoparticles such as SiO₂ particles can also be used to prepare LbLs with a higher modulus. Examples are also given where it is shown that the color of an LbL film can be used as a non-contact moisture sensor since the thickness is related to the amount of adsorbed moisture. By chemical modification of the CNF, it is also possible to tailor the interaction between the CNF and multivalent metal ions, enabling a specific interaction between multivalent for example metal surfaces in water and modified CNF.

Cellulose nanocrystals (CNCs) align in suspension when subjected to external forces, such as electric and magnetic fields and shear stress. In this chapter, we discuss how orientation in suspension can be locked into solid films by solvent casting, spin coating, solution dipping, convective shear assembly, and Langmuir–Blodgett/Schaeffer deposition. The nature of the nanoparticle organization depends on the type and manner in which the external force is applied, for example magnetic fields produce films with either long-range nematic or chiral nematic order, whereas electric and shear forces generally give films with uniaxial order. In most cases, CNCs align with their long axes parallel to the direction of the applied force, except in magnetic fields, where CNCs orient perpendicular to the field. Aligned CNC films have many potential applications, including as model cellulose surfaces and tissue engineering substrates. Furthermore, the directed-assembly methods presented here may be used to prepare CNC-based composites with enhanced mechanical performance.

The layer-by-layer (LbL) assembly technique has been used for two decades as a simple, versatile, and robust tool to build thin polymer films with a tunable architecture. In the framework of the development of functional biobased coatings, the LbL technique was further extended for the production of nanocomposite thin films made of alternated layers of cellulose nanoparticles and polymers. First, in this chapter, the preparation and structural properties of cellulose nanocrystals/polymer LbL films are presented. Then, the influence of different parameters and the relationship between the architecture of the films and the interaction forces involved are discussed. Finally, the optical and mechanical properties of such multilayer films are reported.

Biobased nanofibers are from abundant natural resources, and present interesting properties such as high strength, high aspect ratio and surface area, and ability to form networks through interfibril interactions. This makes them attractive for preparation of high porosity cellular foams and fibrillar aerogels. This could be achieved by drying aqueous nanofiber suspensions while maintaining a high porosity. In this chapter, the processing–structure–property relationship in highly porous biobased materials (mainly from cellulose and chitin) is discussed. Using freeze drying, nanofiber foams with an ice-templated cellular structure may be obtained and these have pores above the micrometer and a relatively low surface area. Other drying methods of nanofiber suspensions such as tert-butanol freeze drying and supercritical drying give high surface area aerogels with a fibrillar structure. The material structure in turn influences its mechanical properties. At a similar porosity, high surface area materials present weaker interfibril interactions and a softer and more ductile behavior. The present materials permit property tailoring after functionalization and this considerably increases the range of properties and applications for porous materials.

Aerogel is gaining increasing attention in the field of nanoporous materials. In addition to inorganic materials, organic polymers are emerging as aerogel scaffold with their variety of structure and properties with potential controllability. This chapter describes the research on aerogels based on cellulose and chitin, the important structural elements in living organisms, with their unique nature of nanobased gel formation.

This chapter discusses the use of nanocellulose, mainly cellulose nanocrystals, as a reinforcing material in the construction of 3D fiber structures. Specifically, it illustrate the effect of nanocellulose in the synthesis of non-woven fiber mats after electrospinning aqueous and organic polymer solutions. The main properties of the composite fibers are presented, emphasizing the benefits of nanocellulose reinforcement and some promising applications.

Emulsions typically consist of two immiscible liquids stabilized by surfactants and have various applications in foods, personal care, construction, medicine, and many other industries. It is long known that colloidal particles are excellent emulsifiers. Particle-stabilized emulsions, also known as Pickering emulsions, have gained significant interest in recent years. Cellulose has joined the long list of colloidal particles used as emulsifiers due to its ability to adsorb at the fluid–fluid interface and its renewability, biodegradability, and wide availability. This chapter discusses the application of nanocellulose as particulate emulsifiers, with the advantage being that cellulose is one of the most abundant organic materials on earth, thus surface-active particles based on nanocellulose can offer sustainable and potentially low cost replacement of surfactants for emulsion stabilization applications. The fundamentals of particle-stabilized emulsions are first briefly discussed in this chapter. Particles of modified nanocellulose have already been used in emulsion formulations in food and personal care products. The relationship between the hydrophobicity of nanocellulose particles and the types of emulsions formed is reviewed. In addition to this, this chapter also discusses the effect of particle size and surface charges of cellulose on the stability of the resulting Pickering emulsions.

This chapter provides an overview of recent progress made in the area of cellulose-based nanocomposites for sensing application. Since nanocellulose shows high tensile strength and good water dispersibility and hydrophilic properties, it has been used to improve mechanical and dispersibility properties of the materials. Porous structure of the hydrolyzed polymeric cellulose minimizes barriers to mass transport between the analyte and immobilized indicator decreases the response time. The applications and new advances covered in this chapter are the use of nanocellulose in ion exchange membrane, glucose biosensor, actuators/strain sensor, and heavy metal ion sensor. This chapter will also include the application of cellulose nanocrystals with high surface area and negative charge in biosensor application and separation technologies. The high energy interaction between binding site on the cellulose nanocrystal film and the cationic species combined with the permselective properties make the cellulose film prime candidate for application in sensor devices and permselective membranes.

Nanoscaled cellulosic materials have an inherent tendency to form films upon drying. These films have unique physical properties: they are strong and they can appear as translucent or even fully transparent depending on the overall dimensions of the individual fibrils. They possess good thermal stability, smoothness, density, and chemical reactivity which make them as attractive templates for bioinspired functional materials. Since the topic in question is broad, this chapter concentrates on describing the characteristic features of films prepared using plant-derived cellulose nanofibers (CNFs). Other nanocellulosic materials, i.e., bacterial cellulose as well as cellulose nanocrystals are only cited with relevant references. The characteristic features described here include the mechanical behavior, surface roughness, and reactivity of nanofibrillated cellulose films. The larger attention is paid not only for the films' ability to act as oxygen and moisture barriers but also for their peculiar behavior in the presence of water molecules. Few relevant approaches to control the water sensitivity of the films are discussed.

The moisture and gas barrier properties of cellulose nanocrystal (CNC)-based thin films are highly dependent on some film characteristics such as roughness, porosity, interaction of the crystals with water, film configuration, and nanocrystal surface chemistry. This chapter briefly describes the most commonly used methods for measuring the moisture and gas barrier properties of CNC thin films and explains the film characteristics that affect barrier properties.

This chapter gives an overview of the membranes based on biobased nanomaterials, viz, nanocellulose and nanochitin and their application in water treatment and gas separation. Cellulose nanofibers having nanoscaled diameters are capable of forming highly porous and stable network structures that can be used as filtration layers. Cellulose nanocrystals have negative surface charge with a potential to interact with positively charged metal ions and adsorb them on the surface by chemical or physical adsorption. Chitin nanocrystals have an inherent ability to interact with metal ions due its amino functional group and have antibacterial properties as well. All these nano-entities have high specific surface areas, which is a huge advantage in membrane technology and the functionalization of these nanoparticle surfaces can further enhance the membrane efficiency.

The following section is included:

• Index

The following sections are included:

• Contents
• List of Corresponding Authors

The fourth volume of the Handbook of Green Materials focuses on green composite materials, including some interesting new raw materials, composites processing as well as properties and some applications. The volume contains 17 chapters covering natural fibers and their characterization methods. Furthermore, some interesting new biobased raw materials such as lignin-based carbon fibers, biobased polymers including hemicelluloses, lactate polymers, natural rubber, and biobased polyurethanes are discussed in this volume. Processing technologies for elastomer, thermoset, and thermoplastic composites are described in detail. Examples of few important technologies are compounding, extrusion, compression molding, and liquid composite molding. Preforms of natural fibers and foaming technology are also discussed to manufacture lightweight composites. Finally, natural fibers composite applications, especially for automotive industry, are exemplified. The last chapter discusses the principles of life cycle analysis of natural materials.

The objective of this chapter is to present experimental methods that are suitable for characterization of cellulose fibers. An overview of different techniques to obtain and analyze fiber strength distribution is presented. The differences of internal structure and mechanical behavior between natural and synthetic fibers, applicability and validity of experimental methods, as well as test conditions are discussed. Some of the techniques developed for synthetic fibers can be directly applied to the characterization of natural fibers, while others should be modified in order to adapt for the specific limitations of reinforcement with natural origin.

An overview of the production of carbon fibers based on lignin is presented. The structure, isolation, and properties of lignin are first discussed in the context of their effects on carbon fiber production. A general overview of carbon fiber manufacturing is then presented to provide background for a discussion of previous and current research on lignin-based carbon fiber. Current research on fiber spinning, thermostabilization, and carbonization of lignin is reviewed and directions for future research are discussed. Finally, emerging new opportunities for lignin-based carbon fiber in non-structural applications are presented, highlighting recent research from our laboratory on the production of sub-micron and nanometer scale carbon fibers by electrospinning of lignin.

Lactic acid-based polymers have attracted much attention as biomaterials and packaging materials during last few decades. Lactic acid polymers are biodegradable, low toxic, and bioresorbable in human body as well as in nature. Poly(lactic acid) is claimed to be the first commodity plastic produced from renewable resources. The environmental benefits provided by lactic acid-based polymers make its future brighter in selected areas of application. This chapter discusses about the different synthesis pathways of polymer from lactic acid and their general properties. Production of lactic acid through chemical and fermentative method and synthesis of its polymers through polycondensation and ringopening polymerization are shortly described here. Lactic acid polymer-based materials found their applications mainly in the field of biomedical and as packaging materials for short-term use. However, the mechanical property of the poly(lactic acid) and its thermal stability is limited which restricts its use in applications demanding high performance. Hence, to satisfy the increasing demand of market, the product should be engineered for better performance and the production of polymer should be hiked according to the demand.

A renewable packaging material which provides barrier properties against oxygen, grease, and aromas can be produced from the natural polysaccharide xylan. In addition, the material forms an efficient barrier to volatile migrants from recycled fibers when applied onto recycled paper or board. Xylan can be extracted from agricultural by-products such as grain husks. This raw material is available in large amounts and is a low value by-product which is not used for food production. After the extraction process, xylan was mixed with water and additives. The barrier can be applied onto paper, board, and plastics by dispersion coating using conventional coating techniques. After coating, the wet barrier coating is dried using IR or hot air to remove water. To achieve a homogenous barrier layer, a pre coating is often needed to prevent water penetration into the paper or board. The pre-coating can be optimized on the current substrate giving the right prerequisites for formation of a homogenous xylan-based barrier layer. In this chapter, material properties and application methods will be described and application onto different substrates as well as suitable end-uses within packaging will be highlighted.

In view of environmental and carbon emission concerns about increasing use of fossil fuels, there has been a greater emphasis on the use of biomass in polyurethane (PU) products, particularly in automotive and building applications such as cushions and insulation. Biobased PU is mostly made from petroleum-based isocyanates and polyols derived from vegetable or plant oils. Such PU offers similar performances to conventional PU, but in fewer footprints and better biodegradability exhibiting an eco-friendly environment.

The bioplastics industry underwent a fundamental change in 2010, when a new plant was able to deliver a new biobased plastic, bio-polyethylene, at a scale never seen in this industry. The introduction of bio-polyethylene helped the bioplastics industry evolve from a niche to full-scale biobased materials. This chapter presents the history of biopolyethylene and provides basic information about its properties, uses, and manufacturing process.

Natural rubber (NR) is a green polymer as far as its origin is concerned. It exhibits a wide range of elastomeric properties which makes it applicable in almost all areas of industry and technology. Biofibers are an important class of materials which are eco-friendly as well as biodegradable for reinforcement in rubber matrix. Such fibers are well known in imparting better strength to NR composites. This chapter is aimed at giving a basic understanding of the mechanical and thermal properties that biofibers provide to the green polymer, NR. The biodegradation studies of such composites are also explained in detail.

There is a growing interest in natural fibers as sustainable reinforcement for composites. For easy processing, a preform with stabilized fiber architecture is important. However, due to the limited length of the natural fibers, the processing from fiber to reinforcement is different than with synthetic fibers. With natural fibers, the first step is to make a continuous yarn-like structure. The necessary spinning leads to misorientation of the fibers in the preforms. This misorientation has a direct influence on the mechanical properties of the preforms. There is also an indirect influence of the spinning on the amount of crimp in the preforms. The influence of spinning on the performance of the composites is discussed within this chapter, together with some other properties of preforms. At the end, some new developments are presented.

This chapter addresses the volumetric composition of composites in general, and with special emphasis on green composites consisting of natural fibers in a polymer matrix. The governing equations of the relationship between the gravimetric composition (i.e., weight content of fibers and matrix) and the volumetric composition (i.e., volume content of fibers, matrix, and porosity) of composites are presented. Next, the principles of the gravimetric method for determination of the volumetric composition are presented, together with the involved measurements and calculations. Focus is put on the special precautions required to be taken for natural fiber composites. Finally, an analysis of the uncertainty of the determined volumetric composition is presented. Throughout the chapter, examples of experimental data for natural fiber composites are given, together with data for conventional glass fiber composites for means of comparison. Altogether, the chapter intends to provide the theoretical background for the practical use of the gravimetric method to determine the volumetric composition in composites.

This chapter discusses special considerations that must be taken into account to improve the understanding of natural fibers variability such as moisture content and chemical composition and some specific needs for compounding equipment set up. Another challenge industry is facing today is the lack of technology, to feed natural fibers gravimetrically into the extruder with a uniform feeding rate. Natural fibers are having different forms when supplied and that also demands the different feeding concepts and machine designs. The low bulk density is causing problems in feeding when conventional processing machines are used. Entrained air, together with other undesirable volatiles and moisture, removal need degassing during the compounding process. The chapter also gives examples of equipments, which can be used to solve the feeding challenges and to remove undesired gases and volatiles. Pelletization of the fibers is one option explored in overcoming the feeding challenges. Diverse techniques for feeding and pelletization are also described.

The compression molding is an established and proven technique for the production of extensive and lightweight green composite materials. The advantages of this process are lightweight construction, deformation resistance, lamination ability, depending on the overall concept, and also price. On the contrary, the disadvantages include limited shape and design forming, scraps, and cost disadvantages in case of high part integration in construction parts. Process optimizations are in progress, in order to reduce certain problem areas such as scraps and to recycle wastage. It is known that green composite materials usually have lower mechanical and thermal properties compared to conventional composite material. The performance of the green composites such as strength and rigidity is strongly dependent on their thermal histories, which is directly interrelated with their processing method and the processing parameters, e.g., time, temperature, and pressure. The fabrication method should be selected where the fiber properties are maintained and not degraded during the processing. Among the wide variety of processing methods that have been used for green composites manufacturing, compression molding is the mostly practiced manufacturing process, especially in automotive sector till date. The thermoforming process has not been practiced extensively for green composite materials, but day by day, their acceptance is growing because of their specific advantages.

Wood fiber/plastic composites (WPCs) have attracted considerable attention in the construction, furniture, automotive, electronics, packaging, and aerospace industries. However, their shortcomings such as high density, low ductility, and low impact strength have limited their utility in many applications. These shortcomings can be effectively compensated for through the foaming of WPC. Foaming technology is a family of different processing methods that can produce WPC parts with numerous bubbles created by a blowing agent. However, it is not easy to obtain fine and uniform cell structures, which are critical to the maintenance of mechanical properties when the density is reduced. This chapter reviews recent advances in WPC foams, especially focusing on their processing technologies. First, we recapitulate the fundamentals of foaming process, and then review three types of foam processing technologies, i.e., (i) batch foaming processing, (ii) extrusion foaming processing, and (iii) injection foam molding processing.

Liquid composite molding (LCM) is a means of manufacturing composites with high fiber volume fraction and with layups tailored to the end product's structural requirements. In the chapter, advances in the use of LCM, in particular, resin transfer molding and vacuum infusion, with natural fibers are reviewed. Differences between LCM process of natural fibers and man-made fibers are highlighted and the consequences these have on measurement and modeling. By taking into consideration the differences between natural fibers and man-made fibers, considerable improvement in the mechanical properties of the natural composites can be achieved.

This chapter presents an overview on the compounding and processing techniques of natural rubber compounds. The introductory portion deals with different types of rubbers and principles of rubber compounding. The primary and secondary fillers used in rubber systems and vulcanization agents are discussed. The different processing techniques used in rubber-based green composites are elaborated. Recent studies based on the compounding and processing of natural rubber-based composites are also discussed.

Natural fiber composites are generally well known for their environmental benefit. However, the reasons why natural fibers are used in industrial applications are due to the economic and technical benefits in addition to their green image. This chapter deals with compression-molded natural fiber thermoplastics for different automotive applications. The production line for non-woven products as well as examples of applications produced using natural fiber composites are described in detail.

Life cycle assessment (LCA) is widely used tool to assess the overall environmental impacts of a product or service. The results are used, for example, for policymaking, product development, and environmental communication. Biobased materials have specific features that brings challenges to the LCA methodology, like the balance of biobased carbon and reuse, recycling, or energy recovery. Furthermore, the sensitivity of the results to other assumptions behind the calculations deserves special attention. Typically, the environmental performance of products based on renewable raw materials is superior to those made of non-renewable materials. However, LCA brings out also cases of opposite consequence and helps avoiding burden shifting from one life cycle stage to another.

The following section is included:

• Index