Plant Fibers - Biol 1300 Unit 11 PDF

**Biol 1300 Unit 11** **PLANT FIBRES** Plant fibres are long strands of cellulose, gathered from individual or groups of plant cells. Useful fibers can be interlaced, twined, or spun into yarns, threads, or ropes. The specific characteristics of each fibre, like surface roughness and elasticity, d...

**Biol 1300 Unit 11** **PLANT FIBRES** Plant fibres are long strands of cellulose, gathered from individual or groups of plant cells. Useful fibers can be interlaced, twined, or spun into yarns, threads, or ropes. The specific characteristics of each fibre, like surface roughness and elasticity, determine its use. Plant fibres are used to make cloth, canvas, ropes, mats, and paper, and must be extracted from the plant material in which they are embedded. Three major methods of fibre extraction are used: 1. **GINNING**: Invented in 1793, cotton gin mechanically removes seed hair fibres from cotton seeds. The extracted fibres are then cleaned and combed. 2. **RETTING**: Also known as bacterial rotting, retting is used to extract bast or soft-stemmed fibres. Plant stem fibres consist of cells with thick cellulose walls, making fibre cells much more resistant to microbial breakdown than other plant cells. Thus, freshly harvested plant material is decomposed in stagnant water (fastest retting method), leaving it on the ground after cutting (slower method), or by bailing and storing (dew retting-the dew contributes to decomposition). The decomposed material, containing intact cellulose fibres, is then washed, dried, and \"broken\" under rollers to extract the fibres, which are then straightened and intertwined by combing. 3. **Decortication**: This simple mechanical process extracts hard leaf fibres and some bast fibres (stems). Freshly harvested plant material, usually leaves, is crushed between rollers, and the non-fibrous material is scraped away to isolate the cellulose fibres. **SEED FIBRES** **COTTON (Gossypium hirsutum)** Numerous cotton species were independently domesticated in both the New and Old Worlds. Archaeological evidence shows woven cotton cloth from pre-Inca civilizations in South America and cotton cultivation in the Indus Valley (India) from about 7,000 years ago. Cotton is the most important plant seed fibre (in general as well) and the world\'s most profitable non-food plant commodity. Nearly all cotton grown today is *Gossypium hirsutum*, a species native to Central America. Agronomists have developed annual varieties of this short-lived perennial, which complete their life cycle in a single growing season. These varieties have short, uniform heights and synchronous flowering and fruiting, simplifying harvesting. Recall that monocultures that have seeds all at once are more efficiently harvested as farmers do not have to continuously harvest. The largest producers are China, India, the United States, and Pakistan, with an annual global production of about 100 million bales (each bale is 500 lbs or 227 kg). Each cotton fibre is a long, slender seed epidermal cell. Fibre length ranges from 1-6 cm, but most commercial cotton fibres are 2-3.5 cm long and 0.001-0.002 cm wide. Fresh cotton fibres are 91% cellulose and 8% water, with small amounts of waxes, pectins, and salts. Despite their small size, they bind and twist together to form longer, thicker threads, held together by natural mechanical forces. Mature cotton crops are sprayed with herbicide or harvested after frost. Cotton bols (mature fruit) are placed in a cotton gin to separate fibres from seeds. The fibres are mechanically plucked using specialized spikes and rollers to beat and clean them (to remove debris and insects). After cleaning, the fibres are combed or carded to align them parallel to one another and gathered into a loose thread known as a \"sliver.\" This sliver is then drawn, meaning it is stretched and twisted to form cotton yarn. The yarn undergoes a cleaning process by boiling it in a bath of caustic soda bleach, which whitens the fibres and removes any residual waxes and salts. Additional chemical processes enhance the durability and quality of cotton fabric. Mercerization, involving stretching the yarn under pressure and immersing it in cold caustic soda, increases luster and durability, and makes the yarn easier to dye. Sanforizing uses ammonia to reduce fabric shrinkage, while permanent pressing cross-links cotton fibres to help fabrics retain their shape better. High quality processes will ensure that the cloth does not shrink too much and maintains its shape. Most cotton is used to manufacture woven cloth. While initially used for fiber, cotton is now also harvested for oil. Additionally, cotton fibres can be used to produce high-quality, pure cellulose paper, known as \"100% rag content\" paper, which is very durable and resistant to decay. **KAPOK** (Ceiba pentandra) The kapok is a very large, fast-growing tree (60-70 m tall) native to northern South America. The mature fruit (kapok \"pod\") contains seeds that produce light, resilient fibres composed of cellulose and lignin. Individual fibres average 2 cm long and 0.003 cm wide. Unlike cotton, kapok fibres are brittle and therefore cannot be spun into a thread, so it cannot be used for clothing. Kapok fibre was once used as a filling in mattresses and upholstery, and as an insulating material. Today synthetic materials are used instead, since kapok fibre is highly flammable. The largest producer is Indonesia. **BAST OR STEM FIBRES** Bast or stem fibres consist of hundreds of cells and may be up to 2 m in length. They are normally removed from plant material by bacterial retting. The following bast fibre plants are of major economic importance: **JUTE** (Corchorus capsularis) Jute is an herbaceous annual plant that grows up to 5 meters tall and is native to India and West Asia. It is the most economically important bast fiber, growing quickly and producing easily extractable fibers known as hessian. These coarse fibers are used to manufacture canvas, carpet backing, twines, and burlap. Jute is primarily grown in India, Bangladesh, and Pakistan. **FLAX** (Linum usitatissmum) Cotton and flax were the earliest plant fibres used for cloth. Flax fibres, extracted by retting, are smooth, straight, and 2-3 times stronger than cotton but are difficult and expensive to extract. The best quality linens come from hand-retted flax fibre. Flax fibres are used for linens, cigarette paper, and high-quality writing paper. Most fibre flax is grown in Europe and China, with a variety also grown as oilseed. **HEMP (Cannabis sativa)** Hemp, obtained from the cannabis plant native to Central and East Asia, has been cultivated for thousands of years as a natural fibre source. It produces coarse fibres used for cordage, rope, canvas, and sailcloth. Originally, Levi\'s jeans were made from hemp (today, most jeans are made from cotton). Recently, there\'s been a resurgence in using hemp for clothing. Fibre hemp, which has virtually no THC (it is a different variety), is mainly grown in Russia, India, China, and parts of Canada, including Manitoba. **RAMIE** (Boehmeria nivea) Ramie is an herbaceous perennial species native to East Asia (mainly China) and belongs to the nettle family, (Urticaceae). It produces long, silky and exceptionally strong plant fibres. However, ramie is difficult to harvest, and the fibres are not easily extracted. Ramie is grown mainly in China, where it is used to manufacture upholstery, canvas and cloth. **KENAF** (Hibiscus cannabinus) Kenaf is an herbaceous annual plant, 1.5-3.5 meters tall, native to East Asia. Its coarse fiber is used to manufacture canvas, twines, and burlaps. Kenaf fibre also produces durable newsprint paper, which is less polluting than wood pulp and yields a high-quality product. It\'s mainly grown in India, Southeast Asia, China, and the southern United States. **LEAF OR HARD FIBRES** Most leaf or hard fibres are obtained from rapidly growing tropical monocot species. Such fibers are easily and inexpensively extracted from plant leaves by decortication. Two leaf fibres are of considerable economic importance: **SISAL** (Agave sisalana) Sisal fibre comes from the sisal agave, a perennial monocot species native to Central America. Mature agave leaves are cut at the base, fed into rollers, and the fibres are extracted, and sun-dried. Sisal is a coarse fibre used to make mats and ropes. Major production areas include Africa and Central America, particularly Mexico. **MANILA HEMP (Musa textilis)** Manila hemp, also known as abaca, is a banana relative whose fibres are used for making cordage and fine paper products like paper money, tea bags, and envelopes. The fibres are hand-peeled from the leaves. As the name suggests, it is native to the Philippines, where its commercial production is concentrated. **CELLULOSE FIBRE** Cellulose fibre is made from regenerated natural cellulose. Bamboo fibre, used for durable sheets and towels, is obtained from regenerated cellulose extracted from bamboo stalks. Rayon, a common cellulose fibre developed in the late 1800s and early 1900s, is sourced from various plants. Most other manufactured fibres, like nylon, polyester, acrylic, polyamide (e.g. Kevlar), and polyurethane, are derived from non-renewable petroleum. **WOOD FIBRE** The extraction of cellulose fibre from wood, known as pulping, involves mechanical and chemical processes. Wood\'s main components are cellulose and lignin, with lignin binding the cellulose fibres (acting as a polymer). The pulping process breaks down wood to isolate cellulose fibres for paper manufacturing. Wood is chipped, chemically treated to denature lignin and other binders like hemicellulose, and then processed using the kraft or sulfate method, which uses strong alkali (e.g. sodium hydroxide, sodium sulfide) at high temperatures. The sulfite acid process can also be used but produces weaker fibres. The cellulose fibre slurry is mixed, poured onto a fine screen, and processed into matted pulp, which is then rolled, pressed, and dried. The resulting material is brown and must be bleached for higher quality paper. Fillers (e.g. clay and alum) and sizings (e.g. starch, resins) may be added to enhance the paper\'s smoothness and resistance to ink. Effluent from pulp mills can be environmentally polluting and may contain harmful chemicals like carcinogenic dioxins.