Hard Bast

From without inward the following tissues make up f. v. bundles. Protophloem / Hard Bast— long tenacious bast fibers. 

Vegetable fibers are classified according to their source ia plants as follows (/) the bast or stem fibers, which form the fibrous bundles ia the inner bark (phloem or bast) of the plant stems, are often referred to as soft fibers for textile use (2) the leaf fibers, which mn lengthwise through the leaves of monocotyledonous plants, are also referred to as hard fibers and (J) the seed-hair fibers, the source of cotton (qv), are the most important vegetable fiber. There are over 250,000 species of higher plants however, only a very limited number of species have been exploited for commercial uses (less than 0.1%). The commercially important fibers are given ia Table 1 (1,2). 

Phormium. The Phormium tenax plant yields a long, light-colored, hard fiber also known as New Zealand hemp or flax, although it has none of the bast fiber characteristics. The plant is a perennial of the Agavaceae with leaves up to 4 m long and 10 cm wide. The fibers are recovered by mechanical decortication. 

In general, natural fibers are subdivided as to their origin, coming from plants, animals, or minerals (Fig. 2). Plant fibers usually are used as reinforcement in plastics. The plant fibers may be hairs, fiber sheafs of dicotylic plants, or vessel sheafs of monocotylic plants (bast and hard fibers). 

Bast is the inner bark of a plant, composed of the phloem and other fibrous cells. Hard fiber, which comes from leaves, is used mostly for cordage (rope, twine, cord) and the rough fabric used for making sacks and other containers. Soft fiber, which comes from plant stems, is used to make thread and finer fabrics like linen, cotton, and woven hemp. 

The electrical properties of this epoxy coal-tar system hardly changed due to contact with Middle Bast (Kuwait) crude oil ... 

The synthesis is easier than it may seem since Friedel-Crafts acylation of phenols is bast done by first making the phenolic ester and rearranging this with AlClj. In this case, the ester needed is (14) which hardly needs to be made since it is aspirin. No doubt this Salbutamol synthesis was planned with this cheap starting material in mind. 

Natural fibers can be classified as seed fibers (such as cotton), bast fibers (like flax, hemp, jute, kenaf, ramie), hard fibers (like sisal), fi-uit fibers (like coir), and wood fibers. The chemical composition and dimensions of some common agro-fibers are presented in Table 5.21. The origin of wood fibers can be sawmill chips, sawdust, wood flour or powder, cutter shavings, pulp or wood residues. As binders for these fibers, both thermosetting (like phenolic, epoxy, polyester) resins and thermosetting matrices [such as polyethylene (LDPE, HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS)j can be used. Thermoplastic composites are, however, less expensive to process than thermosetting composites, in addition to their ability to be manufactured into complex shapes. 

Flammability Tests Burning wool smells like burnt horn, burning silk smells like burnt egg-white, and burning cellulose fiber smells like burnt paper. Polyamide and polyester fibers melt before they burn polyacrylonitrile fibers, upon burning, leave a residue of hard, black spherical particles. On heating the dry fibers in a test tube, wool, silk, and polyamides develop alkaline vapors, while cotton, bast fibers, and regenerated cellulose (rayon) develop acidic vapors (test with moistened universal indicator paper). 

Natural fibres can be subdivided into plant, animal, and mineral fibres. All plant fibres (cotton, jute, flax, hemp, etc.) are made of cellulose animal fibres are made of protein (wool, silk, hair). Based upon their origin, plant fibres are subdivided into bast and hard fibres. Bast fibres are derived fix)m the stems or stalks of plants hemp, jute, ramie, and flax, for example, belong to this category. Hard fibres, on the other hand, are derived from leaves, leaf sheaths, or fruit sisal and coconut belong to this category ... 

Natural fibers are classified based on their origins, whether they are plant, animal or mineral fibers. All plant fibers are composed of cellulose while animal fibers consist of proteins (hair, silk, and wool). Plant fibers include bast (or stem or soft scleren-chyma) fibers, leaf or hard fibers, seed, fruit, wood, cereal straw, and other grass fibers [1]. Over the last few years, a number of researchers have been involved in investigating the exploitation of natural fibers as load bearing constituents in composite materials. The use of such materials in composites has increased due to their relative cheapness, their ability to be recycled, and because they can compete well in terms of strength per weight of material [2]. Provided below is the classification of natural fibers based on origin ... 

There are several different classifications in terms of plant fibers. While the classification of Nishino [59] includes seven groups as bast (soft) fibers (flax, hemp, jute), leaf (hard) fibers (sisal, abaca, pineapple, etc.), stem fibers (bamboo, banana stalk, corn stalk), fruit fibers (coconut), seed fibers (cotton, baobab, kapok), straw fibers (rice, wheat, corn), and others (seaweeds, palm), that of Faruk et al. [3] has six groups bast fibers (jute, flax, hemp), leaf fibers (abaca, sisal and pineapple), seed fibers (coir, cotton and kapok), core fibers (kenaf, hemp and jute), grass and reed fibers (wheat, corn and rice) and all other types (wood and roots). 

Natural fibers are basically derived from three natural resources, which are plants, animals, and minerals. Fibers from plants can be obtained from leaf (sisal fibers), bast (nettle fibers), seed (cotton), fruit (coconut) and wood (hard and softwood). Silk, wool and feathers are examples of animal fibers. Natural fibers from plants are widely used in fabrication of biocomposites for various applications [5]. 

All bast (stem) fibers (flax, kenaf, ramie, nettle, hemp, jute) as well as hard fibers (caroa, sisal) are suitable as for reinforcing fibers for natural fiber reinforced polymer composites, if they have a high tensile modulus and sufficient tensile strength. In addition to cultivation site, type and harvest, the properties of natural fibers depend significantly on the fiber extraction method. An extraction to technical fiber grades, i.e. production of bundles with different number of single fibers, is generally sufficient for use in plastics composites. The properties of such extracted fibers may be described as follows ... 

Technical bast fibers are obtained by mechanical extraction [1]. These methods are based generally on fibers initially decorticated on the field. Next they are extracted stationary by converting the decorticated aggregates to technical fiber grades. The hard (leaf) fibers are extracted by traditional methods. After harvesting, the leaves are depulped, the fibers are washed, diyed and combed by rotating brushes. 

Nature in its abundance offers us a lot of material that can be called fibrous fibres are found in plant leaves, fraits, seed covers and stalk. Fibres from these plants can be considered to be totally renewable and biodegradable. Bast fibres are soft, woody fibres obtained from stems of dicotyledonous plants (flowering plants with net-veined leaves). Such fibres, usually characterized by fineness and flexibility, are also known as soft fibres, distinguishing them from the coarser, less flexible fibres of the leaf, or hard , fibre group. This chapter will discuss bast fibres from flax, hemp, jute, ramie, kenaf and abaca. 

The fibres used for natural geotextile products are plant or vegetable fibres, although some research and development studies have considered the use of very low grade sheep s wool and wool waste. Figure 11.1 shows a classification of well known natural fibres. However, the only ones that meet with the technical requirements, cost effectively, are the bast fibres jute, hemp, kenaf and flax (also called soft fibres because they are from the softer region of the plants), and the hard (or leaf) and fruit fibres sisal and coir. Others of the remaining fibres, e.g. wood fibres, are sometimes used as fillers within the textile structure. 

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