The concept of 'green' economy is supported by energy efficiency, renewable feed stocks in polymer products, encouraging industrial processes that reduce carbon emissions and producing recyclable materials. The popularity of natural fibres is undeniably based on the fact that natural fibre is not only good for skin, but it is also good for the environment. As a matter of fact, growing one tonne of jute fibre requires less than 10 percent of the energy used for the production of polypropylene, a plastic polymer.
Earlier, Sisal was widely used in ropes, general cordage and twines, but product varieties gradually increased, as companies started using sisal to manufacture paper, buffing cloth, dartboards, handicrafts, Macram, carpets, geotextiles, wire rope cores and mattresses. Other sisal-inclusive products now range from steel cable yarn to twisted thread, and general yarn to knitted art crafts.
The use of sisal in non-woven textile is also of prime significance, as sisal is an environmentally friendly strengthening agent to replace asbestos and fibre glass in composite materials. This has led to increased employment of sisal fibre in the automobile industry. The use of sisal fibre depends on its grade.
Sisal is broadly categorized under three grades, which are lower, medium and high grades. Manufacturers in the paper industry use lower-grade fibre due to significant portion of hemicelluloses and cellulose found in that variety. Handled by the cordage industry, medium-grade fibre mostly is diverted to the production of binder twine, ropes and baler. These products are primarily used for agricultural, marine and general industrial purposes. The third quality, a high-grade variety of sisal, is put in the works by the carpet industry to manufacture yarns. In case of carpets, sisal is used by itself or in blends with wool and acrylic for a softer hand.
Sisal fibre is made from the process of decortications. Under this process, leaves of sisal plant are compressed and trampled by a revolving wheel set. The set contains blunt knives, so that only fibres remain. The remaining parts of the leaf are washed away by water. The decorticated fibres are also cleaned by water before drying in the natural heat or by the artificial process of hot air. The grade of fibre is decided on the basis of the moisture content so appropriate drying is imperative. Artificial drying is preferred for better grades instead of natural sun drying. After drying, the fibres are untangled via machine and categorised into grades. Another process used to separate fibre from the leaves is retting followed by scrapping. Under the retting process, a combination of bacteria action and moisture is taken into effect for rotting of plants. The process gets rid of cellular tissues and gummy substances around bast-fibre bundles, helping the fibre to separate from the stem.
Sisal fibre in cross-section consists of about hundreds of fibre cells, which are smooth, straight and yellow in colour. The main feature of sisal fibre is its strength, which gives it a rough and rigid appearance. Properties like strength, durability, ability to stretch and resistance to deteriorate in saltwater, are some of the reasons that sisal is used in making ropes and similar stuff.
The texture of the fibre ensures that it absorbs dyes easily and offers the widest range of dyed colours among all the other natural fibres. In comparison to pineapple and banana fibre, sisal fibre-polyester composites are likely to give high work of fracture because of high toughness.
The fibre is extremely tough and is low on maintenance with minimal wear and tear. However, sisal fibre is still not used by the garment industry and is also not apt for wet areas. The sisal leaves are also often treated with natural borax for fire resistance properties. Sisal is used commonly in the marine industry for fastening small craft, lashing, and handling cargo. It is also surprisingly used as the core fibre of the steel wire cables of elevators.
In rare cases, sisal fibre replaces silk during summer. However, the process to soften the rugged fibre is lengthy and expensive. It requires a high degree of beating and pulping that gives a fabric that is light enough to be worn in the hottest weather. The amount of work to process the sisal into this sheer fabric implies that the cost of the resultant fabric is extremely high.
Global sisal production is estimated at 223.000 tonnes. Brazil, East African region, Asia (particularly China) are the highest producers of sisal fibre. Continuous research and development going on in use of sisal fibre has ensured that in coming years the use of the fibre will be many. The sisal fibre is a sustainable renewable resource for its cordage, woven and pharmaceutical products. The synthetic substitutes of sisal fibre have created havoc to the environment and threatened the very existence of the earth. Thus, the ecological appeal of sisal must be utilised to ensure that there are positive developments in future prospects of this natural fibre.