Agave fibres

Agave fibres       

                                                                                    

The growing environmental problems, the problem of waste disposal and the depletion of non-renewable resources have stimulated the use of green materials compatible with the environment to reduce environmental impacts. Therefore, there is a need to design products by using natural resources. Natural fibers seem to be a good alternative since they are abundantly available and there are a number of possibilities to use all the components of a fiber-yielding crop; one such fiber-yielding plant is Agave Americana. The leaves of this plant yield fibers and all the parts of this plant can be utilized in many applications. The “zero-waste” utilization of the plant would enable its production and processing to be translated into a viable and sustainable industry. Agave Americana fibers are characterized by low density, high tenacity and high moisture absorbency in comparison with other leaf fibers. These fibers are long and biodegradable. Therefore, we can look this fiber as a sustainable resource for manufacturing and technical applications.

Over the years there have been a number of natural fibres besides cotton, linen, and silk that have been used in the textile industry for various purposes. Nettle, Hemp, sugarcane, soy, and bamboo are some of them. One such natural source from which fibres can be extracted is from the cactus plants. With the debate on sustainable textile products and adapting environment friendly methods of manufacturing increasing among consumers, the use of natural and biodegradable fibres becomes inevitable.

Agaves are succulents with a large rosette of thick, fleshy leaves, with most species ending in a sharp terminal spine. The stout stem is usually short, the leaves apparently springing from the root. Along with plants from the related genus Yucca, various Agave species are popular ornamental plants in hot, dry climates, as they require very little water to survive.

Each rosette is monocarpic and grows slowly to flower only once. During flowering, a tall stem or "mast" ("quiote" in Mexico) grows from the center of the leaf rosette and bears a large number of short, tubular flowers. After development of fruit, the original plant dies, but suckers are frequently produced from the base of the stem, which become new plants.

It is a common misconception that agaves are cacti. They are not related to cacti, nor are they closely related to Aloe whose leaves are similar in appearance.

Agave species are used as food plants by the larvae of some Lepidoptera (butterfly and moth) species, including Batrachedra striolata, which has been recorded on A. shawii.

Textile fibres obtained from various kinds of the Agave species can be used in making vegetable silk, mats, as fillers, and even can be used as bio-composites, in substitute to glass fibres. The cactus silk, also known as organic or vegan silk, Agave silk or the more local name Sabra silk is a cruelty free fabric unlike mulberry silk. This silk is made in Morocco using vegetable dyes and the cacti used are found in the desert of Sahara. The cactus hails from the Aloe Vera species of the Agave family.

The fibres have high strength, are durable, and are known for its beauty. The manufacturing process of this vegetable silk remains traditional and ages old. After the cactus is collected from the Agave plant crushing of the long spiked leaves begins. Then the fibres are washed and hammered, and lastly the leaves are soaked in water to separate the fibres and filaments easily. Once this is done, the fibres are spun into threads for weaving and are later died in different colors. However, the production processes are a guarded secret within communities in Morocco and are passed on only from a father to the son. The royalty in Arabic countries wear gowns and wedding outfits made from this rare cactus silk.

Sabra silk is hand loomed in Morocco and hence is an expensive product. The silk is also woven with strips of camel wool, chenille, and cotton yarns to create different blends. The high elasticity of Sabra silk leads to wrinkle free fabrics. Carpets, rugs, table napkins, and cushions are made out of these. Since the process of making the silk is long, time-consuming, and hand woven, the fabrics and products are very costly and unique in nature.

Weber tequilana more widely recognized by the name of Blue Agave is essentially used to make tequila and a natural sweetener. The waste from making Mexico's national drink is used to make textile fibres, and not just that, but also used as animal feed, biofuel, and paper.

This look alike of the cactus plant is found in the semi-arid regions of Jalisco state of Mexico. The strong structures in the form of fibres found in the leaves have been used since the time of the Aztec civilization to make ropes and twines. The cottage industry and small scale artisans in the area have been using the fibres from the plant to make baskets, mats, hats, belt, and fillers in mattresses, handbags, and even to make accessories for apparels. The waste from making the tequila out of the Blue Agave, which is known as Bagazo, has been used for the use of making textile fibres.

However Agave fibres are rigid and coarse and hence need to be blended with a softer yarn for application in textile fabrics and garments. Creating a blend with cotton yarn and 10 to 15 percent Agave fibres and developing such a combination of textile fabrics can result into saving atleast ten percent of cotton and move a step ahead towards sustainability. Moreover, Agave fibres enhance the quality and performance of such fabrics.

The most popular fibre provided by the Agave is Sisal. Sisal fibres, procured from Agave Sisalana, are an eco-friendly substitute to glass-fibres to be used in furniture, automobiles, boats, water pipes, and tanks. The fibre can be employed in geo-textiles, for instance sisal fibre can add strength when mixed with cement concrete in alternative to asbestos. The major manufacturers of sisal are Brazil, Tanzania, and Kenya. China is a large producer as well as consumer of the fibre. Just like most other fibres derived from all kinds of varieties of plants of the Agave family, sisal is hundred percent bio-degradable.

The Agave plant has an age span of seventy long years. The plant needs little water and external inputs, and can be grown in other semi-arid regions. Different kinds of Agave plants are used to obtain fibres like Sisal, Henequen, and Tampico which are used to make products like ropes, mats, and brushes respectively. Agave as a fibre is strong, highly durable, and has high affinity to humidity. But by research and development of such natural fibres and creating interesting blends, the environment can be greener and the textile industry can be turned into a sustainable place.

Agave Fiber Extraction

Agave plants are stemless perennials that contain fibers. You can remove these fibers with either a machine or by hand. This removal process involves crushing or beating the leaves with a rotating wheel that has blunt edges. The crushed leaf particles are then washed, brushed and dried, creating the agave fiber. You can grade the agave fiber by the size of the plant and by the quality of the resulting fiber.


Chemical Method

Chemical fiber extraction involves the use of acids, alkali and enzymes. The use of acids in cellulosic fiber extraction hydrolyses lignin and hemicellulose into shorter chain pentose molecules. Acid treatment results in the formation of reactive groups and causes fibers to fibrillate, revealing a higher degree of crystallinity of fibrils. Alkali used in fiber extraction dissolves the lignocellulosic material between fibers and separates structural linkages between lignin and cellulose, which leads to increased surface area as well as a degree of polymerization and lowers the breaking strength of fibers. In enzymatic process of fiber extraction, there is degradation of lignocellulosic component in fibers by enzymes resulting increased fiber swelling and lowers the degree of polymerization. Fibers extracted by using enzymes are more pliable and softer.

 Retting Process

Retting is a well studies method of extraction of fibers by a natural microbial process. Retting involves the degradation of non-fibrous matter which acts as glue between the fibers in woody plant parts and fibers without damaging the fiber cellulose. This process allows easy separation of individual fiber strands and the woody core. Since retting is a biological process, it requires both moisture and a warm temperature for microbial action to occur .
 Natural Retting

It is a preferential rotting process to separate the fiber from lignocellulosic biomass without damaging the fiber cellulose. Retting is the microbial freeing of plant fibers from their surroundings . The process takes up to three weeks. Retting microbes consume the non-fibrous cementing materials mainly pectin and hemicellulose. This gradually softens the leaves by the destruction of the less resisting intercellular adhesive substances. When fermentation has reached the appropriate stage, the fibers can be separated quite easily from the leaves. If retting process is allowed beyond this point, fibers decline in quality. Under-retting causes incomplete removal of gummy materials such as pectin substances, and extraction of fiber becomes difficult. Hence, the progress of retting must be observed carefully at intervals to avoid fiber damage. Though the natural retting takes more time, the process is economical.
There are two traditional types of retting include water retting and field or dew retting. In water retting, plant leaves are immersed in water (river, pond or tanks). In field or dew retting, the crop is spread in the field where rain or dew provide moisture for retting. Water retting produces fibers of greater uniformity and higher quality than fibers extracted by field retting.

 Enzymatic Retting

Enzymatic retting is the process in which the pectin materials surrounding the fiber bundles are degraded by industrially produced enzymes. Enzymatic retting is faster than natural fermentation retting and results into softer fibers. It has the potential to simplify and reduce fiber extraction costs. Enzymatic retting is expected to offer greater process control, increased fiber yield and shorter processing time. Enzyme solution used in retting can be recycled several times, which makes the process eco-friendly and cost effective .
Pectinases and xylanases are the enzymes which can be used for retting plant portions for fiber release. The enzyme can be used at higher concentrations to speed up the retting process. For example: 1.5 gpl (grams per liter) of water or 3.0 gpl of water or 5.0 gpl of water can be used. The enzyme cellulase should be avoided in any enzymatic retting process of cellulosic fibers, since this will reduce the strength of the fibers .

 Mechanical Method

Historically, hand decortication was done by rural folk whereby the leaves were pounded and the pulp was scraped away with a knife . Hand decortication is time consuming and needs a lot of manpower. Nowadays, decortication can be done efficiently by using mechanical decorticator. In the mechanical decoration process, leaves are crushed and beaten by a rotating wheel set with blunt knives, so that only fibers remain . Some decorticators are fed by hand and the pulp is first scraped from half of a leaf, the leaf is withdrawn, and then the opposite half is inserted for scraping. In some machines, the whole leaf is decorticated in single insert .
Figure 2 gives a sectional view of the most important parts of fiber stripper/decorticator. Agave Americana plant leaf is fed through the mouthpiece, then it passes through the fluted feed rollers, which hold the leaves as they are fed in against a stationary bar, while the stripping drum is beating out the vegetable matter as the leaf passes between it and the beater bar. The stripping drum diameter, width and speed vary according to different makes. The drum, scraping against the leaf, held in position by the beating bar and feed rollers beats off the bulk of the vegetable matter and leaves the fibers somewhat roughened and with a residue of vegetable matter remaining upon it .
After completion of decortication and washing, the fibers are dried either with mechanical driers or in the sun. The operations of fiber removal, washing and drying must be done promptly after the leaves are cut, otherwise the gums in the leaves harden, causing the pulp to adhere with the fibers and making it difficult to clean the fibers properly . Mechanical extraction methods are not efficient in the removal of cementing compounds (mostly waxes, hemicelluloses, lignin and hydrocarbons) between fibers .

 Fiber Morphology

The below Figure depicts the longitudinal  and cross-section  views of an agave Americana fiber. By examining Agave Americana fibers with an SEM (Scanning Electron Microscope), we can observe longitudinal streaks which are characteristics of long vegetable fibers. The fiber has a composite structure. Ultimate fibers (Figure 3c) are held together by sticky and waxy substances such as lignin, pectin and hemicelluloses. The fiber surface is also covered with these substances. Due to this natural coating, Agave Americana fibers present a high resistance when they are exposed to the influence of some external factors like weak chemical agents such as acids and alkalis, as well as to UV (108 h). Agave Americana fibers occur as a technical fiber, having oval and irregular sections with a large lumen and appears as a helical structure of square shape spires. These fibers can be characterized by two parameters: the average length of a spiral side which is about 10.1 μm and the average diameter which is equal to 3.1 μm. The average diameter is very small compared to other natural fibers such as flax, sisal and alfa. This particular structure will be used to explain the mechanical behavior of the technical fibers.

 Fiber Length

Agave Americana fibers are somehow longer than sisal fibers. The bundles have a long effective length. If fiber is removed from the full length of leaf sheaths by hand stripping, the fiber strands from the middle sheaths may run as long as 2.8 m.

Fiber Diameter
 

The Agave Americana fibers appear as in bundles, which contain many ultimate fibers imperfectly held together by some sticky and waxy substances. The thickness of the fiber when determined using projection microscope, it was in the range of 100–150 μm. Agave Americana fibers are relative thick fiber as a result of the numerous cell ultimates that form the fiber bundle .

Moisture Absorption Properties
 

The fiber shows hydrophilic properties. This fiber absorbs more water than its own weight. Moisture content as well as moisture regain of Agave Americana fiber is found to be around 8%–9%, which is comparable to other cellulosic fibers .

Visual and Hand Evaluation

In visual and hand evaluation of Agave Americana fibers, the observation of fiber shape, color, surface texture are visually evaluated .

Physical Shape
 

The fiber is long, round and generally taper to a point, having one side thicker. The fibers from the lower side of the leaf are particularly finer.

Color
 

The color of the Agave Americana fiber ranges from off-white to yellowish, which is depending upon the processing technique and the processing time used for fiber extraction. The retted fiber was darkened, which can be discolored with a naturally looking light brown color, which is due to bacterial action.

Luster
The fibers are semi dull in appearance and one has a reason to believe that this is due to the fact that they have the uneven surface and cross-sectional shape. A fiber with an irregular cross-section scatters light in all directions, resulting in a dull appearance with few high lights. Whereas properly extracted fibers appear lustrous.

Texture

The fiber feels strong and durable. The dry Agave Americana fiber is stiff, harsh, coarse and hard-surfaced, which is typical characteristic of all the leaf fibers. However when fibers are wet, they become flexible, smooth and slippery.

Burning Test

When the fiber sample was brought near the flame, it burnt brightly. In the flame the fiber continued burning readily with a yellow-bright flame and continued burning even after removal of flame. The smell of burning Agave Americana fiber is like burning paper. Agave Americana fiber becomes very fragile when exposed to high temperature of up to 108 C. The burning behavior of Agave Americana fibers is similar to that of other natural cellulosic fibers .

Tensile Properties
 

Mechanical Behavior

Tenacity of Agave Americana fiber is in the range of 16–41 cN/tex. The elongation of fiber at rupture is in the range of 2%–4%. This implies that Agave Americana fiber can perform well where instantaneous forces act on the fibers during the use of end product. Higher values of tensile properties of these fibers indicated that it is strong enough to be a textile fiber. It is thought that its strength is due to high degree of cellulose polymerization and crystallization processes that may be due to many years of growth. This tensile strength implies that Agave Americana fiber can function well for furnishing fabrics, carpets, floor mats, rugs, upholstery fabrics as well as in nonwovens and fiber reinforced composites.
The tensile properties of Agave Americana fiber are not uniform. This can be explained by the fact that it is a natural fiber and natural fibers are subject to growth irregularities to the extent that fibers from the same plant are not uniform in size and properties. The outer leaf sheaths produce the strongest fibers while the inner sheaths produce the weakest fibers. The innermost fibers have a high fracture strain while the peripheral fibers have lower tensile strength . The outermost fibers have more elongation before breaking than inner fibers. The fibers are difficult to extend. This means Agave Americana fiber is rigid and has low elongation. The fiber is having lower elongation at break values. Therefore the end product manufactured using this fiber will be rigid one. The wet strength of fiber is lower than that of dry fiber. However, elongation of the break is higher when the fiber is in wet conditions.

 Chemical Properties 

Chemical Composition
Agave Americana fibers can be considered as naturally occurring composites consisting mainly of cellulose fibrils embedded in a lignin matrix. The main constituents of these fibers are cellulose, lignin and hemicellulose. However constituents like pectin, waxes, water-soluble substances, etc. are also present in small quantities. The chemical composition of natural fibers like Agave Americana depends on various factors such as type of soil used, weather conditions, age of the plants, etc. The property of each constituent contributes to the overall properties of the fiber. Table 2 exhibits the chemical composition of Agave Americana fibers .

 Chemical composition of Agave Americana fibers.
Composition                            Amount (%)
Cellulose                                  68–80
Hemicellulose                            15
Lignin                                         5–17
Wax                                            0.26
Moisture                                    8.0

Effect of Different Chemicals on Agave Americana Fibers

 
Agave Americana fibers are stable in weak acids and weak alkalis, and has no effect on structure and tenacity of Agave Americana fibers. Therefore these fibers can be safely treated with bleaches, detergents and dyes which are weak basic or weak acidic in nature. However, in strong acids and strong bases, fibers were dissolved or distorted. The bonds connecting the subunits (i.e., ultimate fibers) are unstable to acid, which leads to loss in tensile strength of fibers. Reaction with concentrated sodium hypochlorite results in the bleaching of fibers, but after prolonged exposure, the fiber looses its strength and disintegrates. This indicates that oxidizing solutions like sodium hypochlorite should only be used when cold, diluted and according to instructions given by the manufacturer. Therefore, chlorine bleaches should be used for a short period of time and must be rinsed out thoroughly to avoid further damage to the fiber.
 

Applications of Agave Americana Fibers
Agave Americana fibers exhibit high tensile strength and have low density. Because of this, historically, they were used in manufacturing twines and ropes for fishing and agricultural purposes. Further, these fibers can be used for the production of nets, carpets, rugs, doormats, bags, sacks, fish stringers, furniture webbing, drapes, upholstery padding, saddle pads, cushion stuffing, brush brittles, baskets, bracelets, headbands, sandals, decorative items, clothing and other woven objects. Papers also have been made from lower grade Agave Americana fibers. Agave Americana fibers are also used for embroidery of leather in a technique known as piteado
Research findings showed that Agave Americana fiber can also be utilized for other industrial purposes. There can be a potential application of Agave Americana fibers in composites as well as in nonwovens. Bio-plastics, geotextiles, carpets, fiber boards, dart boards and molded furniture can also be manufactured using Agave Americana fibers.

Environmental Benefits of Agave Americana Plant and Fibers
Agave plants have four times more cellulose than the fastest growing eucalyptus tree, and it effectively captures CO2 from the atmosphere. When properly maintained, it requires irrigation only three to four times per year. Agave Americana fibers have minimal environmental impact. The production does not need agricultural chemicals. During processing of Agave Americana fibers, only organic waste is produced which can often be reused. The by-products after the processing of the agave takes the form of bio-degradable organic matter which can be used as “compost” or as an organic material to be returned to the land and as fuel for biogas production. In this way, they enhance soil fertility. Unlike synthetic fibers, Agave Americana fiber is 100% biodegradable during its lifetime and Agave Americana ropes and other products can be recycled as paper. The plants can be also used as an effective hedge to protect crops and land from predators and the extensive root system helps to reduce soil erosion in arid areas. This is truly a “no waste” plant. The “zero-waste” utilization of the plant would enable its production and processing to be translated into a viable and sustainable industry .

Agave Americana fibers can be used in technical applications such as reinforced composite materials, paper making, non-woven fabrics, geotextiles, etc. The “zero-waste” utilization of the plant would enable its production and processing to be translated into a viable and sustainable industry.

 Properties  of Agave fibres

                                

 

 

                              Stress-strain curves of tested agave fibers

                                                                     Agave fiber mechanical properties 

	Tenacity (cN/tex)	Extension (%)	Initial modulus (cN/tex)	Energy (J)
X min	15.556	29.359	20.11	0.023
X mean	28.290	49.646	61.01	0.046
X max	41.078	62.36	145.49	0.076
CV%	22.92	12.5	55.67	30.14
LPE (95%)	6.5	3.55	15.8	8.47
± IC (95%)	1.843	1.763	9.65	0.0039

Agave Fiber Products

Traditionally, indigenous people, including the American Indians, used agave fiber to make twine. Today, manufacturers commonly use agave fiber in the textile industry. Additionally, companies that produce green products such as washcloths, artisan crafts, slippers, belts and spa products commonly use agave fiber. Other applications for agave fiber include wall coverings and yarns made for specialty products such as durable carpets and rugs.

Industrial Products

Different industries use agave fiber to replace the harsh chemicals and toxicities found in synthetic fibers. Manufacturers use agave fiber as a strengthening agent for asbestos and fiberglass in composite materials. There are three different grades of agave fiber used in industrial applications. Manufacturers use the low grade to produce paper products. The cordage industry uses the medium grade of agave fiber to make ropes and twines. Finally, manufacturers use the high grade of agave fiber to produce fine yarns and threads.

Types of Agave Fiber

The specific varieties of agave plants have different characteristics and produce different fiber variations. Sisal is an agave plant variety that will grow almost anywhere and has a strong, stiff fiber commonly used to make twine and ropes. Henequen is another agave plant variety that produces a hard and wiry fiber used to produce binder and durable mats that have luster and resist stains. The agave plant istle has short and coarse fibers used to make brushes and low-cost twine products.

 References

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