PROTA, Introduction to Fibres

PROTA 16, 2005. Plant Resources of Tropical Africa. vol. 16. Fibres. ed. by M. Brink & E.G. Achigan-Dako. Wageningen, PROTA Foundation - CTA. 659 p.

Choice of species

PROTA 16: ‘Fibres’ describes the wild and cultivated plant species of tropical Africa used for their fibres. Some of these are traded on the international market, but many are only used locally, for making tying material and clothes, for thatching, packing and filling, and for the production of baskets, mats, wickerwork, brooms and toothbrushes. Rattans of which the stems are used for tying and wickerwork are also included in this commodity group. Most species have several other, secondary, uses. PROTA assigns one primary use and, if relevant, one or more secondary uses to all plant species used in Africa. For instance, the primary use of Crotalaria juncea L. (sunn hemp) is as a fibre plant, and thus it is treated in PROTA 16, but it has several secondary uses, e.g. as a green manure, as a forage and as a medicinal plant. The fibres of Cocos nucifera L. (coconut) are also commonly used, but the primary use of this species is as an oil crop, and consequently it is described in PROTA 14: ‘Vegetable oils’.

In PROTA 16, some species are treated which, in addition to the primary use as fibre, also have another primary use and consequently are described in two PROTA books. These species are Ceiba pentandra (L.) Gaertn. (also in PROTA 7(1): ‘Timbers 1’), Corchorus olitorius L., Hibiscus cannabinus L. and Hibiscus sabdariffa L. (also in PROTA 2: ‘Vegetables’), and Linum usitatissimum L. (also in PROTA 14: ‘Vegetable oils’).

Comprehensive descriptions are given of 75 important fibres. These major fibre plants comprise mostly wild species, but also several cultivated or partly domesticated species. The accounts are presented in a detailed format and illustrated with a line drawing and a distribution map. In addition, accounts of 173 fibres of minor importance are given. Because information on these species is often scanty, these accounts are in a simplified format and usually do not include a drawing. For another 267 species the information was too scarce to justify an individual treatment and they have only been mentioned in the accounts of related species. Following the alphabetical treatment of the ‘primary use’ fibres, all ‘secondary use’ fibres are listed as ‘Fibres with other primary use’ and referred to other Handbook volumes.

Plant names

Family: Apart from the classic family name, the family name in accordance with the Angiosperm Phylogeny Group (APG) classification is also given where it differs from the classic name.

Synonyms: Only the most commonly used synonyms and those that may cause confusion are mentioned.

Vernacular names: Only names in official languages of regional importance in Africa are included: English, French, Portuguese and Swahili. It is beyond the scope of PROTA to give an extensive account of the names of a species in all languages spoken in its area of distribution. Checking names would require extensive fieldwork by specialists. Although regional forms of Arabic are spoken in several countries in Africa, the number of African plant species that have a name in written, classical Arabic is limited. Arabic names are therefore omitted. Names of plant products are mentioned under the heading ‘Uses’.

Origin and geographic distribution

To avoid long lists of countries in the text, a distribution map is added for all species. The map indicates in which countries a species has been recorded, either wild or planted. It should be realized that for many species these maps are incomplete because they are prepared on the basis of published information, the quantity and quality of which varies greatly from species to species. This is especially the case for wild species which are not or incompletely covered by the regional African floras, and for cultivated species which are only planted on a small scale (e.g. in home gardens). For some countries (e.g. Central African Republic, Chad, Sudan, Angola) there is comparatively little information in the literature. Sometimes they are not covered by recent regional or national floras and although species may be present there, this cannot be demonstrated or confirmed. For some major species, a distribution map has been omitted because there is too little information on distribution.

Properties

Information is presented on the morphological, chemical and physical properties of the fibre.

The main morphological properties determining the suitability of fibres for different uses are the length and width of the individual fibre cells (‘ultimate fibres’). Cell wall thickness and lumen diameter are generally less important. For the industrial production of fine textiles, a length:width ratio of over 1000 is generally required. Fibres with a length:width well below 1000 can only be used for coarser textiles and cordage. In papermaking the length:width ratio affects the paper's flexibility and resistance to rupture.

The chemical properties mainly concern the amounts of cellulose, hemicelluloses, pectin and lignin in the fibre. Cellulose is the main component of plant fibres, and the higher the cellulose content of a fibre, the greater its value. The term holocellulose refers to the entire carbohydrate fraction of the material, i.e. cellulose plus hemicelluloses, whereas a-cellulose is the fraction isolated by a caustic extraction procedure. It is generally considered to be pure cellulose, but it actually is 96–98% cellulose. The presence of hemicelluloses in material for paper making increases the pulp yield and the strength of the resulting paper, but hemicelluloses are not wanted in dissolving pulps for cellulose-based plastics. Pectin binds fibre cells together. Lignin increases the rigidity of the cell wall, makes it less susceptible to predation and less permeable to water. High-quality fibres contain less than 5% lignin. In paper making, removal or modification of lignin is essential for the production of quality papers.

Important physical properties of plant fibres include strength, elasticity, durability and colour. These characteristics usually vary widely within species, even between fibre strands within the same plant. They also depend on a range of other factors, including temperature, moisture content and test methods. The strength may be given by the tensile strength: the breaking load or force per unit area of cross-section, usually expressed in N/mm2. An older method of expression is the breaking length: the length at which the material, when hung up, will break under its own weight. It is usually expressed in km. Another useful characteristic is the elongation at break, which is a measure of the resistance of material to elongation. It is defined as the amount of extension when the fibre breaks, expressed as a percentage of the original length of the fibre. The Young’s modulus or modulus of elasticity is the ratio of the stress (force per unit area) or applied load to the strain or deformation produced in a material that is elastically deformed; the higher the value, the stiffer the material.

Description

A morphological characterization of the species is given. The description is in ‘telegram’ style and uses botanical terms. Providing a description for the general public is difficult as more generally understood terms often lack the accuracy required in a botanical description. A line drawing is added for all major and some lesser-known species to complement and visualize the description.

Management

Descriptions of husbandry methods including weeding, fertilizer application, irrigation, and pest and disease control measures are given under ‘Management’ and under ‘Diseases and pests’. These reflect actual practices or generalized recommendations, opting for a broad overview but without detailed recommendations adapted to the widely varying local conditions encountered by farmers. Recommendations on chemical control of pests and diseases are merely indicative and local regulations should be given precedence. PROTA will participate in the preparation of derived materials for extension and education, for which the texts in this volume provide a basis, but to which specific local information will be added.

Genetic resources

The genetic diversity of many plant species in Africa is being eroded, sometimes at an alarming rate, as a consequence of habitat destruction and overexploitation. The replacement of landraces of cultivated species by modern cultivars marketed by seed companies is another cause of genetic erosion. Reviews are given of possible threats for plant species and of the diversity within species, and reference is made to the IUCN Red list of threatened species where relevant. Information on ex-situ germplasm collections is mostly extracted from publications of Bioversity International (formerly the International Plant Genetic Resources Institute – IPGRI).

References

The main objective of the list of references given is to guide readers to additional information; it is not intended to be complete or exhaustive. Authors and editors have selected two categories of references; ‘major references’ are limited to 10 references (5 for minor species), the number of ‘other references’ is limited to 20 (10 for minor species). The references listed include those used in writing the account. Where the internet was used, the website and date are cited.

Editors

• M. Brink, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
• E.G. Achigan Dako, PROTA Network Office Africa, World Agroforestry Centre (ICRAF), P.O. Box 30677-00100, Nairobi, Kenya

Photo editor

• G.H. Schmelzer, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands