ABSTRACT
Tannins are polyphenolic substances present in plant, which has the ability to convert the putrefiable hide or skin into imputrescible leather. Chemical action of vegetable tannins on hides and skin involves associating the polyphenolic hydroxyl group of tannins with the peptide bond of amino acids of animal collagen using hydrogen bond. The effect of Neem plant bark extract (Azadirachtaindica), on leather tanning was determined in this project, by using the extract to tan animal hide.Neem bark and “Bagaruwa” seed dried, grinded, soaked in water allowed to stand for 48hours to get their extract. The Cow hide underwent the following; Pre-tannin processes: soaking, liming/dehairing, defleshing, deliming, bating, pickling, to give a swollen de-haired pelt. Tanning processes to give leather. And post-tanning processes;samming, splitting, dyeing, greasing, drying and finishing, to give a leather of characteristic colour and flexibility. The Neem bark extract-tanned leather and “Bagaruwa” extract-tanned leather, after their exposure to atmospheric pollution and moisture. The results showed that Neem plant bark extract leather resisted microbial growth but showed little cracks on bending, while there were whitish microbial growth on “Bagaruwa” extract leather with little cracks on bending. Comparing Neem bark extract leather and “Bagaruwa” extract leather proved Neem bark extract to be another local tanning material with additional property to “Bagaruwa”.
CHAPTER ONE
1.0 INTRODUCTION
Leather is a durable and flexible material created by the tanning of animal raw hide and skin, primarily cattle hide. It was extensively used from the primitive times and is widely used today (Convington, 2009).
In prehistoric times man was concerned mainly with eating or collecting the food, clothing did not exist. The desire for the clothing is dedicated towards hunting. The primitive man realised that animal he hunted was not only for food but can also be used for their clothing purpose. Hence they started using animal skins to satisfy their clothing needs. Animal skin was first worn by the people in the Paleolithic period. Later on man realised that the skins rapidly putrefied and thus became useless. They needed a way to preserve the hides,(Marion and Roy, 2006). People found that the quality of the leather could be improved so they started preserving the hides/skins by rubbing them with fats and animal brains, these primitive people also preserved the skin bythe smoke of wood fire but this procedure had a limited preserving and softened action. Later on tannin from the bark of certain trees was used to convent raw skins into soft material, today which is known as “vegetable tanning (Convington, 2009).
Tannins are polyphenolic substances which convert the putrefiable hide or skin into imputrescible leather, (Whiteet al.,1956). This process is achieved by associating the hydroxyl groups of tannins with the peptide bonds of amino acids present in animal protein, known as collagen (Haslam, 1966). Based on the earlier ideas of white, tannins are classified as water soluble phenolic compound having molecular weight between500 and 3000, and besides giving the usual phenolic reactions, they have special properties such as the ability to precipitate alkaloids, gelatine and otherproteins (Bate et al., 1962).
This higher plant secondary metabolites are scientifically and terminologically described as plant polyphenol (Haslemet al., 1998). In generalthe term tannin includes mixture of polyphenolic substances that have limited solubility in water and tend to form supersaturated solution.
Modern tanning method makes use of salt of chromium (iii), presently used to tan about 90% of the world’s product. However as a result of the carcinogenic effect of sparingly soluble chromate salts, regulatory authorities has mounted so much pressure on tanners to limit dischargers of chromium (iii) into the environment.
From environmental standpoint, the obvious option is a low chrome offer tanning process. However, this is only a partial solution to the problem, because although there can be a greater than commensurate decrease in waste chromium by reducing the offers, this requires an increased level of process control and there is a practical lower limit to the chromium offer; to maintain shrinkage temperature above 100oc, the lowest chromium offer is 0.75% Cr2O3, so the health hazard associated with burning tanned waste is not diminished.
The unique feature of chromium (III) as a simple tanning agent is that it confers high hydrothermal stability to the leather, whilst this is not essential for all leather goods purpose, it is critical for most applications, particularly for shoe upper leather, which is likely to encounter stringent conditions during the manufacturing of shoes.
Currently, there is only one established tanning method that can match this aspect of leather performance and that in semi-alum tannage, comprising tanning with natural polyphenolic plant extracts (vegetable tanning) and re-tanning with aluminium (III) salts. Semi-alum tanning is not new, it has been used but not understood, from as long as 6000 years ago (Haslam et al., 1998). This conventional technology has two drawbacks: first it is usually at two stage process, in which the first stage is vegetable tanning, conferring typically characteristics to the leather, second, it involves aluminium (III) salt which, for a variety of reasons are perceived to be environmentally unacceptable.
To avoid the above problem, vegetable tanning has been identified, and extracted from a natural plant bark such as Acacia nitotica (Bagaruwa). And to further address this problem, the aim of this project is focused on the potential of Neem tree bark (Azadirachtaindica) extract as a leather tanning material.
1.1Objectives: To extract tannin from the stem bark of Neem plant (Azadirachtaindica) and to determine the effect of Neem plant bark extract on leathertanning.
1.2Significance: To encouragethe use of Neem bark extract as another local tanning material if it has a positive effect on leather tanning.
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