Bast Fibers and Their Composites

Natural fiber-based composites have made significant progress in recent decades due to their environmental friendliness, lightweight, and low cost. While there are numerous sources of natural fibers, this chapter focuses on bast fibers because they possess desirable characteristics for a variety of applications. These fibers are derived from the phloem that surrounds the stems of fibrous plants, primarily dicotyledonous. Bast fibers’ qualities are regulated by environmental conditions, maturity, extraction method, and processing. This chapter discusses various aspects of different types of bast fibers, their physical, chemical, and mechanical properties, and their applications in a variety of fields, intending to promote their use in advanced technology sectors.

The advantages of using lignocellulosic natural fibres from the plant bast, as compared with synthetic ones, namely in terms of environmental impact and availability for a number of industrial sectors, from textile to wood replacement and even to automotive or aerospace one, are counterbalanced by the need to extract them from the plant. In principle, the number of plants that are suitable to obtain bast fibres is considerable: some of the most popular are, among others, jute, hemp, flax, ramie, kenaf, nettle, etc., although this work aims also at giving a hint on the wider picture of the possible expansion of the market to other species. However, the quality of the fibre obtained depends on the extraction method employed, namely mechanical extraction, decortication or retting in different environments (water, dew, chemical) for the single species. Information on this aspect is not always consistent and very precise, although this chapter would like to underline the importance to consider and thoroughly describe the extraction method for every batch of bast fibre obtained to try to improve the general quality of the products and generally expand further the market for natural fibres.

Biocomposite materials are a newly established class of composites. They possess desirable properties for numerous applications. This chapter provides an extensive analysis to highlight the recent improvements in bio-composite materials, natural fibers, and their chemical treatments. The importance and novelty of natural fiber composites (NFCs) are specifically examined along with polymers and their classification, characterization, and treatments. The chapter further provides detailed explanations regarding the recent techniques and chemical treatments currently applied to process natural fibers. The various chemical treatments addressed in this chapter include alkaline, silane, benzoylation, and permanganate treatments. Multiple effects of chemical treatments influence various properties of natural fibers, especially; their mechanical properties, which further impact the mechanical performance of composites and matrices. Such effects have been sufficiently explored. The common applications and recent utilization of NFCs have been considered to subsequently highlight current prospects.

Among the naturally available biodegradable materials, bast fibres (BF) play a significant role in engineering applications. The key attributes of BFs are dielectric, hygroscopic and surface properties, insulation properties and mechanical strength. The properties are variable based on chemical composition and environmental conditions. This study exhibits the extraction of BFs and the effect of physical modification of BFs and their effects. BFs can be extracted from herbs such as flax, hemp, ramie and other wild plants. The common extraction processes are microbial retting, mechanical extraction and alkali extraction techniques. The outer bark or phloem of jute, kenaf flax and hemp plants are called cellulose fibres and it is annually renewable crops growing in 9–100 days. The modifications of these BFs through biodegradable and eco-friendly techniques such as plasma treatment, fungi, microbial and biochemical reactions of enzymes. The treatment of BFs using these techniques varies the properties of the material. In the textile industries, natural fibres extracted from the plants play a vital role in the production of cloths, fabrics and mats that are ecologically sound. Cultivators involved in the growth of the herbs, as well as the extraction and treatment of the fibres, may benefit from the BFs. Hence, researchers show interest in discovering novel fibre and focusing on the various techniques to modify the surface of the already-discovered fibre for industrial requirements. These modifications can be accomplished by various eco-friendly methods such as physical, chemical and physicochemical treatments. In this paper, we have discussed and reviewed the various physical, chemical and surface behaviours of BFs and various surface treatments to modify the surface behaviour of the extracted BFs.

The lack of fundamental knowledge in providing an eco-friendly surface modification of bast fibers for enhancing the composite’s properties is still a major challenge in creating next generation composite products. The remarkable characteristics of bast fiber composites, which are ideal for manufacturing innovative green materials, have piqued the interest of researchers. Unfortunately, the fibers’ chemically inert and smooth surface restricts their applicability. There has been much effort taken by the researchers to provide organic modification on fiber surface for enhancing the fiber-matrix interaction adhesiveness. In order to improve the chemical activity of the fiber's surface, reduce its hydrophilic character, and improvement in surface roughness, it is necessary to modify the fiber's surface. The major focus of this chapter is to briefly summarize the recent progress in surface modification of bast fiber in an eco-friendly approach and how far it affects the composite properties are being highlighted.

Bast fibres are natural fibres that are sourced from the stem region around plants. Bast fibres show great potential as fibre reinforcement in composites. The inherent characteristics of unmodified bast fibres such as being hydrophilic in nature resulting in low fibre-matrix interfacial adhesion, natural wax and impurities on the fibre surface cause poor surface wetting, hydroxyl groups and free water reduce the fibres adhesive characteristics with resins, swelling and plasticising due to high moisture absorption causing dimensional instability and poor mechanical properties and high crystalline regions preventing resins from penetrating the fibre. Various methods, modifying the structure and surface of fibres, improve their inherent characteristics. The surface modifications of bast fibres achieve varying improvement of fibre-matrix adhesion in fibre-reinforced composites depending on the method of treatment. Treated fibres offer increased strength, improved hydrophilic nature, reduce water absorption, and remove impurities from the fibre surface. Surface modification methods are characterized as physical methods, chemical methods and biological methods.

Each day, an increasing number of objects for several industries, including automobile, aerospace, biomedical, construction, and even electronics industry, are manufactured using bast fiber-based composites. Composite manufacturing depends on the matrix and reinforcement configuration. Many techniques can be used, and the selection depends on the final use or purpose of the composites. For example, it is possible to obtain simple laminates by casting or using a most expensive technique like compression molding. In this chapter, the main aspects of the processing techniques are discussed. Comments are provided on alternatives to improve the final quality of composites, and in some cases, aspects of how nanostructures can be included during composite manufacturing are introduced. The analyzed techniques are for polymer and cementitious matrices.

Bast fiber application as a reinforcing material in natural fiber composites is increasing day by day, which is currently a trending topic in the composites industry. Bast fibers are derived from the fibrovascular group located between the epidermis or bark surface and the inner woody core of dicotyledonous plants, known as bast (or phloem). It has a variety of advantages, including low cost, low density, excellent durability, acceptable explicit strength qualities, improved energy recovery, carbon dioxide sequestration, and biodegradability. However, in this study, the main focus is on the concerns surrounding bast fibers such as their low thermal stability. The major issue reviewed in this paper is the thermal stability of bast fibers reinforced composites. Compilation of recent literature is done along with state of art thermal characterization techniques. Improvement of thermal stability of bast fibers and their reinforced composites are also compiled.

The demand for biodegradable materials are increasing due to their environmentally friendly properties and for the replacement of petroleum-based products. Bast fibers are the most important renewable materials for many engineering applications. Bast fiber-based composites are receiving great attention due to their good mechanical properties, biodegradability, and non-toxic nature. These fibers consist of cellulose, hemicellulose, and lignin. The major drawbacks associated with bast fibers are their low thermal stability, low water barrier, and low hygroscopicity. To improve the functional properties of bast fibers, it is generally modified with several physical and chemical agents. The current chapter is designed to give an overview of some of the important bast and leaf fibers, their modifications, and water barrier properties.

Bast fibre composites offer tremendous properties to material science such as lightweight, sustainability and cost effectiveness. Ramie, Jute, Hemp, and Flax are the major bast fibres which are extracted from the stem of the plant. Rheology is the science which deals with the flow behaviour of the material and plays a major role for the fabrication of bast fibre composite materials. It deals with changing viscosity and non-Newtonian behaviour of the molten polymer sample. Complex viscosity, storage modulus, and loss modulus are the key parameters to be studied in this field. Proper understanding and analysis of rheological properties are very important to develop improved quality bast fibre composites having diverse applications.

With increasing use and research in the field of natural fibers and their reinforced composites, it is important to explore the potential of these novel materials in diverse fields. Bast fiber is an important category of natural fibers consisting of mainly jute, ramie, hemp, kenaf, etc., extracted from the stem of the plant. Extensive work has been done on the mechanical properties of these fibers and their reinforced composites, but the dielectric property aspects of these materials have been less explored. Dielectric properties like dielectric constant, resistivity, conductivity, etc., decide whether the material is useful in insulation or conducting products. Bast fibers with low resistivity have a high tendency to allow the flow of electric current. Lignocellulosic with these bast fibers have (OH) hydroxyl groups that affect the dielectric constant. Moisture content of the material is also responsible for the dielectric properties. This study compiles the work done on dielectric aspects of natural fiber, especially bast fiber-reinforced composites in order to improve the understanding of commercialization aspects of these materials in the production of electrical and electronic goods.

Recently, the using of plant-based fibers especially bast fibers has been investigated as substitutes for the synthetic fibers such as aramid, carbon, and glass in the polymers composites as reinforcement because of their lightness, biodegradability, low cost, and high mechanical behaviors. Biodegradable composites are defined that a biodegradable polymeric matrix is reinforced with biodegradable fibers. Biodegradable polymers are known as the polymers degraded with enzymes. In order to produce a biodegradable composite, plant-based fibers are frequently used. The behaviors of these composites are fundamentally dependent on the fiber kind, aspect ratio, orientation of fibers in the matrix, volume fraction, and adhesion of fibers and matrix. Especially, fiber properties affect the biodegradable composite behaviors. The plant-based fibers are mainly categorized into grass bast, leaf, seed, and straw fibers. In plant-based fibers, bast fibers are obtained in the bast of plant and it is known that these fibers have been utilized by earlier civilization. Common examples of bast fibers are jute, ramie, kenaf, flax, hemp, and bagasse. Because these plants are annual crops, they are getting rising interest in a variety of biodegradable composite production processes. This chapter, it is reported an overview of the current investigation of biodegradable materials. These consist of some developments substantiated in the field of biodegradability, biodegradable polymers biodegradable composites, bast fibers, and biodegradability testing methods. This chapter could help in the investigation of this area and using of composites in industries.

Fiber-reinforced composites have been widely used in industries for their enhanced stiffness and damping characteristics. Recent advancements in the use of biodegradable or natural fiber reinforcements in composites have gained acceptance worldwide because of their biodegradability and as well as favorable mechanical and vibration properties. This article reviews the free vibration characteristics of various bast fibers (jute, flax, hemp, kenaf, ramie, roselle and banana) incorporated composites. The natural frequencies of composites reinforced with these fibers have been studied under various weight percentages, fiber treatments, fiber layering patterns, fiber orientation, and hybridization with secondary reinforcements and so on. Notable improvements in both natural frequency and damping have been observed by many authors on varying the mentioned parameters. This chapter gives an insight into the selection of composite constituents for better vibration characteristics.

Natural fiber reinforced composites (NFRC’s) are novel materials whose demand is increasing day by day due to their unique advantages like sustainability, ecofriendly nature, availability of raw material, diverse applications, etc. Bast fiber composites are sub-category of these NFRC’s in which natural fiber is extracted from the stem of the plant. Flax, kenaf, hemp, jute, and ramie are the major bast fibre plants. Extensive work has been done on the composites developed with these bast fibers during the last decade. Being hydrophilic in nature the adhesion of bast with hydrophobic matrix is the key issue that has drawn the attention of the scientific community. Surface treatment methodologies of bast fibers like chemical treatment (alkali, silane, acetylation, etc.), physical treatment (corona, plasma), and biological treatment (enzyme, algae) have been applied to these bast fibers to overcome these issues [5]. Nano reinforcements are also providing phenomenal changes in the field of composite as well as material science. In nano reinforcement a little quantity of nano material is mixed with a variety of bast fiber composites which can enhance the performance and quality of bast fiber composites drastically. Scientists have used different types of Nano clays like montmorillonite, closite, garamite, and various nano fillers mainly Nano SIO₂, CNTs, etc., and other nano reinforcements in bast fiber reinforced composites for enhancement in performance. Characterization with sophisticated analysis equipment for the performance evaluation after the addition of these nano reinforcements is a very important aspect of commercialization and comparison of these novel materials with synthetic fiber reinforced composites. Present compilation reviews of state of art characterization techniques by advanced analysis equipment like mechanical testing, dynamic, water absorption, Thermogravimetric analysis (TGA), XRD, FTIR, etc.