Banana and Plantain Wastes 2: Fiber and other products from the pseudo-stem
Published Date: 17th August 2020
Synthetic fibers like nylon, rayon, aramid, glass, polyester, and carbon have gained extensive application, starting from the time of industrial revolution up to the present time, because of their lightweight, low water absorption, high stiffness, and strength. However, these petroleum-derived materials have been proven to be unsustainable and prone to environmental hazards due to their non-degradable nature. There has also been a rapid unsustainable increase in the exploitation of wood fiber derivable resources in recent times, through unregulated logging activities in many tropical forests. This has resulted in the recent global concerns about the fate of most tropical forests, and the need to identify alternative fiber sources. There is therefore an increasing global call for a change to renewable bio-based economies that engender sustainable utilization of natural resources. This change to a bio-based economy requires substitution of common raw materials currently produced from fossil (petrochemical) or mineral resources, with products produced from renewable (plant and animal-based) resources. A major effort towards achieving this has been to research rational methods of utilizing agricultural and forest residues as sources of fiber.
Li and coworkers in 2010 estimated the global annual production of lignocellulose fiber from plants at about 4 billion tons, with agricultural residues accounting for 60 percent, and the remaining 40 percent coming from forest residues. Their ubiquitous nature combined with the ease of their processing, low cost, low density, biological degradability, renewability, good mechanical properties, and non-toxicity makes lignocellulose fibers important potential substitutes for synthetic or petrochemical-based fibers. Many of the plant fiber sources, such as jute, flask, sisal, pineapple, okra, coir, banana, and palmyra among others are increasingly being exploited for industrial production of yarns, ropes, paper, mats, and mattings, as well as in making articles like wall hangings, table mats, handbags, and purses. Plant fibers extracted from cotton, banana, and pineapple are also used in making fabrics, in addition to being used in the paper industry.
Characteristics of banana pseudo-stem
After the banana fruit has been harvested, the trunk or pseudo-stem is discarded as agricultural waste by most banana producers, especially in Africa. It has been estimated that one hectare of the banana farm could produce approximately 220 tons of biomass wastes made of leaves, midrib, dried leaf sheath, pseudo-stem, and inflorescent flower. Annual banana waste estimates for Bangladesh for example has been put at 3,740,096 tons from which valuable fibre could be extracted, indicating that major African producers are generating larger quantities of banana wastes. In Africa, these wastes are usually left in the farm to decay or are disposed simply by burning. In large plantations, the disposal of large quantities of banana wastes can be costly, and constitute a major operation in order to avoid environmental damage and litigations. Several research reports have shown that the banana pseudo-stem can be processed into cellulose fiber for textiles, paper, and other value-added products.
The banana pseudo-stem consists of a soft central core and tightly wrapped 14 - 18 leaf sheaths, as shown in figure 1. As the banana plant grows, these leaf sheaths unwrap from the stem, and transform into banana leaves. The outermost 4 – 6 leaf sheaths are made up of course fiber, while the next 6 – 8 sheaths are made up of soft, lustrous fiber. The rest of the sheaths are made up of soft fiber, while the stem may also have a core depending on the stage of maturity. Each sheath also consists of three layers, an outer epidermis containing bundles arranged in a soft tissue background, the middle layer containing water transporting fiber vascular tissue, and an inner layer of soft cellular tissue.
The outer layer is the toughest, and it is usually used for weaving items, while the middle layer is used chiefly in making ropes or in weaving thick fabrics. The inner layer, which is the silkiest fibers, is used for spinning yarns used in making fine clothing and undergarments. It is equally possible to blend the banana fiber with other plant fibers like jute or cotton in certain ratios to produce composite and laminated fabrics.
Characteristics of banana pseudo-stem fibre
The banana pseudo-stem fiber is a multicellular fiber similar to other vegetable fibers. Its appearance is similar to that of bamboo and ramie fiber; however, banana fibre has better fineness and spin ability. It has a shiny appearance depending on the extraction and spinning process. It has very strong fiber with 3 percent elongation, and lightweight. The physicochemical composition of banana fibers has been reported to be 50 – 60 percent cellulose, 25 – 30 percent hemicellulose, and 12 – 18 percent lignin, while pectin and water soluble substances such as fat/wax, and minerals make up the rest. The fiber is, therefore rich in cellulose and low in lignin when compared with hardwood fiber. It absorbs and releases moisture easily, and can be spun by different techniques such as ring spinning, open-end spinning, bast fiber spinning, and semi-worsted spinning. Most importantly, banana fiber is bio-degradable and is therefore categorized as eco-friendly fiber.
Banana fiber extraction
The banana fiber can be extracted by a cumbersome manual method, or by a more modern mechanized method. In the manual fiber extraction method, the pseudo-stem is initially cut into pieces of about 60 cm length and 7.5 cm width and then scraped with a scraper or a flat blunt blade to separate the fibers. This method is slow and laborious, with a skilled operator managing to produce only 500 – 600 g of dry fiber in an eight-hour working day. In a semi-automated fiber extraction method, a cutter machine which facilitates speedy splitting of pseudo-stem into sheets is used. The sheets are then passed through the extracting machine, known as mechanical decorticator, and the fibers automatically extracted. The mechanical decorticator comprises a pair of feed rollers and a beater, through which the split sheets are passed so that water and non-fibrous elements are removed from the bottom of the machine. The extracted fibers are subsequently treated with bio-enzymes to clean, and improve their quality in terms of length, softness, strength, color, and shine. They are then sun-dried and knotted before separation. Knotting involves clamping a bunch of fibers on a stick to facilitate segregation according to fiber sizes. This is repeated until bunches of un-knotted fibers are finished to form a long continuous strand. The fiber so produced can be used in making different types of bio-products.
The spinnability of banana fiber, fineness, and tensile strength makes banana fibers usable in making different types of textile materials of different weights, and thicknesses, depending on the part of the banana pseudo-stem the fiber was extracted from. Banana fiber is widely used as blending material in textile industries in Asian countries, where it is routinely blended with jute and cotton fibers. Variety of industrial products such as gunny bags, doormats, carpets, yarn, ropes, geo-textiles, trivialities, luggage carriers, interior decorative crafts paper, tissue paper, paper bag, stockings, and gloves among others are now routinely made from banana pseudo-stem fiber. The fiber is also being used as natural sorbent, a base material for bioremediation and recycling, and as a natural water purifier.
Other potential applications of components of banana pseudo-stem
In addition to being an excellent plant fiber, banana pseudo-stem can be processed into different products (Figure 2) such as paper pulp, or converted by vermicomposting into bio-fertilizer. Its high content of cellulose and starch makes it a good candidate for animal feed production. Again, it contains certain proteins, which can possess antimicrobial products. The central core has been sure to produce snacks and confectionaries such as pickle, candy, and soft drink, while the sap can be converted into liquid fertilizer and mordents for fixing colors. Banana pseudo-stem sap is also being used to improve the fire retardancy of cotton fiber-based textile materials.
Production of paper pulp: During the fiber extraction process, a substantial amount of wastes is generated, which are mainly non-fibrous components. These wastes and even the extracted fiber can be processed into pulp for paper production, or ensiled and fed to animals. The pulp is a fibrous material derived from intricate manufacturing processes that involve the chemical and/or mechanical treatment of different types of plant material, especially wood. The pulp is a highly abundant raw material used predominantly in the manufacture of paper and paperboard, as well as other applications in the textile, food, and pharmaceutical industries. Indeed, the fairly low amounts of lignin and ash, as well as high levels of cellulose and hemicellulose in the banana pseudo-stem lends it to pulping for paper production. It has been observed that pulping of banana fiber processing waste produces pulps with better chemical and physical properties than pulps from intact pseudo-stem. Ogunsile and coworkers compared the quality, and yield of the pulp produced from different types of banana by-products, and found that the leaves (midrib part), pseudo-stem, and fruit stalk produced 34 – 49 percent of pulp, and the yield was heavily influenced by the pulping parameters such as pH, temperature, and pulping time. Paper made from banana pulp are reported to have very low water absorption capacity, making it more water-resistant, and stronger than wood-pulp paper. It is therefore used in making cardboards, notepads, envelops, postcards, tea bags, degradable shopping bags, and packaging material among others.
Vermicomposting of banana pseudo-stem: Whole banana pseudo-stem or the wastes generated from fiber extraction can be converted to vermicomposts by adding other essential components like animal dung in order to improve its fertilizer value. Excellent organic manure has been produced by composting banana pseudo-stem waste, and cattle dung at a ratio of 70:30. Studies have shown that such vermicomposts are comparable to other bio-composts in sustaining soil health in banana and sugarcane plantations.
Central core-based products: The central core of banana plant is the most tender portion of the pseudo-stem. Different edible products such as candy, soft drinks, and pickles can be made from it. The candy produced from the central core has been shown to contain substantial amounts of iron and vitamin B vitamins. The sugary syrup generated during the candy preparation, or those extracted directly from the central core sap have also been used to prepare soft drinks fortified with flavorings and colorants. Again, pickles have been produced from mixtures of bleached central core and fruits or vegetables.
Pseudo-stem sap-based products: Banana sap can be converted into liquid fertilizer and nutrient spray solution for vegetable, and other forms of gardening. The fresh sap can be enriched with essential plant nutrients, and growth-promoting substances to enhance its efficacy in vegetative gardening. Banana sap extracts has been used as liquid fertilizer for banana, pawpaw, sugarcane, and vegetable production to save between 20 and 40 percent of fertilizer requirements.
ConclusionMillions of tons of banana pseudo-stem discarded as wastes by farmers in banana producing countries may accumulate because of difficulties in disposing them, and may constitute environmental problems. However, every part of the banana pseudo-stem can be converted into useful products. Simple techniques, and technologies used in turning such banana wastes into value-added products however exist and can be exploited by banana producers in Africa to generate extra income. This can also create lots of employment opportunities, especially for rural woman and unemployed youths, thereby improving their socio-economic wellbeing. A video on banana pseudo-stem processing can be viewed at https://youtu.be/wbQ3dM9H-w8
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