EXTRACTION OF TANNIN FROM INDIGENOUS WOOD SPECIES

ABSTRACT

A general analysis of bark and leave of some indigenous wood species was carried out with the aim of establishing whether their percentage tannin content is high enough to be of commercial value. The results obtained from the four species examined, show the percentage tannin to be 12.7%, 7.1%, 5.3% and 8.4% for the bark of four species pterocarpus osun, pterocarpus soyauxii, Burkea Africana and khaya senegalensis respectively. Also from the leaves, the percentages obtained where 3.2, 2.8, 4.4 for pterocarpus osun, pterocarpus soyauxii and khaya senegalensis respectively. These results are comparable with the empirical data and so are enough to be of commercial value.

CHAPTER ONE

1.0     INTRODUCTION

The tissue of wood, bark and leaves of trees contain a great variety of chemical substances of considerably scientific interest and some of the practical values. Tannin is a generic name for widely occurring group of substances of vegetable origin.

Tannins from the bark, wood and leaves of certain species of plants is one of the most important commercial extractives which also form the basis of some important industries. The main local source of obtaining industrial vegetable tannin in Acacia nilotica pods, obtained principally around Kano and Maiduguri. Due to ever increasing demand for this materials by the producers of particle boards and leathers, there has grown a scarcity which normally manifest itself in the cost of materials.

Even in the southern parts of Nigeria where new leather industries are developing, the problem of obtaining transporting and storing these pods cannot for too long be overlooked there is therefore the need for a search into other alternatives in order to avoid a heavy drain on foreign exchange because of the importation of synthan (synthetic phenolic polymers).

Again the mangrove (Rhizophora species) found largely in most tropical coast lines contain reasonable amount of tannin. But when used in the heavy tanning industries. They a re known to produce an extract which has the major set back because of its hard red colour, which is prone to further darkening on exposure to sunlight during drying Fasina (1974) suggested that after full tannage is achieved, that the leather or particle board is bleached and then retanned using a light coloured fast penetrating vegetable tannin extract. But one cannot over look here, the cost factor, since an industry is usually profit motivated.

This project is therefore an investigation carried out the determine other sources of vegetable tannin of commercial importance and which can sustain the available tanners industries in the country that is the species (bark and leaves) investigated were Pterocarpus Osun Pterocarpus Soyauxii. Burkea africana and Khaya senegalensis.

1.1     STATEMENT OF PROBLEM

For too long, there has been the importation of synthan (synthetic phenolic polymers) which is a heavy drain on foreign exchange. The importation adds much to the cost factors of the materials which tannin can be used for, thereby decreasing the profits of the products. This factor lowers the growth of some tanning industries, since industries are usually profit oriented.

Again, mangroves Rhizophora species contain a reasonable amount of tannin which has a major set back, even cacia nilotica pod is a good source of tannin but it is very for away. That is Kano and Maiduguri.

Due to ever increasing demand for this material (tannin) by the producers of particle board and leather there has grown a scarcity which normally manifest itself in the cost of this materials especially around Southern parts of Nigeria.

Therefore, there is need for a search into other indigenous wood tree species that has a lot of tanning in them to minimize the problems of obtaining, transporting and storing this pods from other wood species that contain tannin.

1.2     AIMS

  1. To educate students on how to use tannin in production of hides and skin.
  2. To educate students on how to use a local indigenous source to manufacture goods instead of foreign ones.

1.3     OBJECTIVES

The main objectives is to investigate into other wood species that has a greater percentage of tannin in them. Since there are other indigenous wood species that contain tannin eg focus (Ogbu) bark, cashew (Anacardium occidentale) bark etc, but they contain a lower percentage of tannin in them. This to avoid wastage of time and money pterocarpus Osun, Pterocarpus Soyauxii Burkea africana, Khaya Senegalensis are indigenous wood species that were investigated to contain a greater percentage of tannin.

1.4     LIMITATION AND DELIMITATION

The higher percentage of tannin in wood/trees depends on the condition of the climate upon which the tree species grow, it must be a fertile land, tropical region.

Poor laboratory equipments for extraction lowers the percentage of tannin extracts.

Extraction with a polar solvent extracts materials like glucosides, tannins, salts etc.

1.3     HYPOTHESIS

A good tannin of commercial importance must be soft.

It must have acceptable colour of light straw to dark reddish brown or colourless on purification.

It must tan rapidly when in contact with hides and skin (protein of the skin gelatine) and particles of wood (wood residuals “sawdust”).

It must be non crystalline colloidal particle.

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