Rope-making fibres - manila hemp and sisal

What is Manila hemp?

Manila hemp is the fibre extracted from the leaves of abaca, (Musa textilis) a plant related to the banana. It is widely distributed in the hot humid tropics of the western hemisphere.

What does the abaca plant look like?

When mature, the giant herbaceous plant consists of a series of twelve to twenty overlapping leaf-sheaths, which form a pseudostem, surmounted by large oval leaf blades. The true stem is an underground rhizome from which the pseudostems arise. The stalk bearing the inflorescence grows up through the centre of the pseudostem. After pollination (usually by bats) green fruits are produced which look like bananas but are in fact inedible.

What are Manila hemp fibres?

The fibres, which are extracted from the surface layers of the leaf sheaths, are long slim cells forming part of the supporting structure of the leaf associated with the water and food-transporting systems (xylem and phloem respectively) of the plant. The fibre strands, which can be up to 3 m in length, are composed of many single fibre cells bound together. These long flexible pale-coloured bundles are used in rope and textile manufacture whilst individual fibre cells can be teased out from these bundles for paper-making.

How is abaca grown?

The plant is propagated from seeds, from suckers (new above ground shoots) or from rhizomes (the underground stems). It grows best in a fertile well-drained soil and a hot humid climate with year-round rainfall. When new plantings reach four to five years of age, they produce a full crop of mature stalks yielding up to 1 tonne of dry fibre per acre. Maximum production continues until the plants are seven to eight years old.

How is abaca processed?

The larger pseudostems are harvested before the flowers are due to appear to ensure a good yield of fibre. The pseudostem of rolled leaves is cut down and the palm-like fronds of leaves at the tope of the plant are cut off and discarded. The leaves are 2-4 m long, and heavy and unwieldy to handle, so most of the processing is done in the field. It takes 100 kg of fresh leaves to produce 13 kg of fibre. The surface layer of the sheath is stripped within twenty-four hours of harvesting to prevent deterioration. Strips from the inner and outer leaf sheaths in the pseudostem are kept separate because they contain fibres of different qualities. Fibre from the outer sheaths is coarser and stronger and can be graded for use as rope-making fibre; that from the inner sheaths is paler and finer, more suitable for paper-making. The leaf strips are decorticated to separate the fibres from the surrounding tissues. This is frequently done by hand using sharp knives to scrape the 'tuxies' along their length to reveal the fibres. Decorticating can also be performed mechanically using a battery-driven 'hagotan' with a whirling set of eight knives or by using a large decorticating machine to clean the fibres. After stripping and decorticating, the fibre strands are hung across drying poles in the open. Drying may take from a few hours to a couple of days.

How is Manila hemp used?

Manila hemp is spun into yarn to be used for the manufacture of ropes and coarse cloth for sacking. The ropes are frequently used as ships' rigging and other marine cables. The paper-making industry in the developed world continues to buy and use Manila hemp pulp which is a source of long strong fibres. Papers produced from the pulp are highly porous, that is, they allow easy passage of water. This property is especially suitable for the manufacture of stencil papers, tea-bags and sausage skins in the developed countries. Brown envelopes made from the pulp are known as Manila envelopes after the capital of the Philippines.

Why is abaca important?

Abaca is an important crop in the Philippines and Ecuador, where its cultivation, harvesting and processing are major sources of employment. Before European textiles arrived in the Philippines, woven Manila hemp fibre was the chief source of clothing. In 1980 the Philippines and Ecuador exported 87% (75,000 tonnes) and 12% (10,100 tonnes) respectively of the total world production of the fibre to a world-wide market, with 60% of the fibre being converted to pulp for specialised paper-making.

Sisal

Desert plants with succulent leaves may seem unlikely sources of useful fibres, but such plants in the genus Agave and several closely related genera provide fibres suitable for making ropes, twines, netting and coarse sacking. Their long narrow leaves contain the so-called 'hard fibres', which are in fact bundles of fluid-conducting cells (xylem) surrounded by a sheath of individual fibre cells. Originating in Central america and Mexico, the sisal plant (A. sisalana) is a major source of cordage fibre. The fibre is named after the port in Yucatan through which it was first exported. It was introduced to East Africa in the 1890s as a crop suitable for the hot dry conditions of the coastal plains. The bulk of world sisal production now occurs in Tanzania. Sisal is a hardy plant that can withstand very dry conditions with rainfall as low as 250375 mm rainfall per year and it is able to grow on dry rocky soils.

What does the sisal plant look like?

Shoots consisting of a short thick stem with a rosette of leaves arise from an underground rhizome. The dark bluish-green leaves have a waxy surface to reduce water loss. They are long, narrow and pointed and have a sharp terminal spine. Once a certain number of leaves have been produced, a flowering shoot, known as the pole, develops. This can be up to 9 m in height and, near the top, bears branches carrying the greenish-white flowers. Although seeds are rarely produced, bulbils, each a viable small plant, arise in the axils of the individual flower stems and these are used for propagation. After flowering the plant dies.

Sisal fibres

Seventy-five percent of the fibre bundles in the sisal leaf have a mechanical function; they are located just below the leaf surface and provide support for the leaf so that it remains upright. Such mechanical fibres vary in length from a few centimetres to 1.5 m. Other fibre bundles, known as ribbon fibres, are found in the centre of the leaf and extend into the terminal spine. The ribbon fibres are weaker than the mechanical fibres and tend to become badly damaged or lost during processing.

Processing and use

Sisal leaves are cut by hand, leaving enough leaves on the plant for it to continue growing. The leaves are decorticated as quickly as possible to reduce fibre deterioration, the fibres being extracted by a crushing and scraping process. The pulp is washed away, a process requiring up to 45,000 litres of water per hour, and returned to the fields as fertiliser, supplying nutrients and improving the soil structure. The coarse cream-coloured fibres are made into agricultural twines (1 kg sisal produces 440 m of binder twine or 150 m of baler twine) and coarse fabrics, such as sacks and nets.