Nivel de conocimiento que tiene el docente en el ámbito de la gestión del

75 2.2.9 Bifenthrin spray preservatives

In Australia, a water-based bifenthrin preservative has been developed to improve the insect resistance of timber. As this preservative is applied by spray, it only penetrates the outer 2 mm of the timber cross-section. Concerns have been raised as to whether this thin-envelope system will provide protection against insects in the longer term, particularly when exposed to sunlight for extended periods. (Bill-Meyer, 2003).

2.2.10 Fire retardant treated wood

This treated wood utilizes a fire retardant chemical (example formaldehyde) that remains stable in high temperature environments. (Bill-Meyer, 2003).The fire retardant is applied under pressure at a wood treating plant like the preservatives described above, or applied as a surface coating.

2.2.11 Oil-born preservatives

These include pentachlorophenol and creosote. They are toxic, have an unpleasant odour and are generally not used in consumer products.

2.2.12 Coal-tar creosote

Creosote is a tar-based preservative that has been commonly used for telephone roles and railroad ties (http://www.tpaa.com.au/creosote.htm). Creosote is one of the oldest wood preservatives, and was originally derived from a wood distillate. These days virtually all creosote is manufactured from the distillation of coal tar. It often collects inside chimneys and may cause a fire hazard. Creosote is regulated as a pesticide. It is still used for railroad ties and utility poles. It is a deterant against insect attack and possesses flame retardant property.

76

I, CH₂OOCR^III, R^I, R^II and R^III. This indicated that about three different species of acids are present. Fixed oil is usually referred to as non volatile oil and is readily vaporized by heat.

Sometimes, fixed oil are usually characterized by a spit when dropped on a paper, most of them are liquid at 100^oC while others are solid at the temperature of 200^oC. Consequently, the solid form designates fats, though; most of the fats undergo a change from solid to liquid and vice versa on a slight change in temperature (Ajiwe et al., 2004., Nwafor, 1995). Fixed oils are sourced mainly from the seeds of plants. Fixed oils can be obtained from the vegetable tissues but this requires lots of techniques. The commonly used technique is that in which the seeds obtaining the oils are usually subjected to great and intense pressures. This can be done without necessarily applying heat but is more frequently facilitated and hot-pressed instead of cold-pressed. (American Society for Testing and Material, 1985), At present, the machine press method is preferred and is widely in use. This particular machine press has a rotating screw, whose function is to press the ground seals under high pressure through a large cylinder. The oil is therefore squeezed through the openings in the cylinder. This procedure has a comparative advantage over the other method because it is continuous and the machine need not be stopped from loading. The third method of obtaining the oil from the plant tissues is by employing various methods of refining deodorization and deoxidation respectively.

Alternatively, the soxhlet-solvent extraction method is applicable using petroleum ether (60-80^oC) followed by the expression of oil from the plant tissues. Oils are classified into four group namely drying, semi-drying, none drying and vegetable oils. Drying oils refer to those which on exposure to air form a tough elastic film. Their iodine values are normally above 130.

They contain unsaturated acid like anoleic acid. Examples of such oils are tung oil and linseed oil. They are used for making paints. Non-drying oils denote those oils that do form films on exposure to air and remain liquid at ordinary temperature. They have high content of oleic acid and have iodine value too. They are generally edible. Examples of non-drying oils are castor oils, cocoa butter, melon, and coconut as well as teas seed. Semi drying oils are intermediate in nature between non-drying oils and drying oils. Their iodine value range is 90-140. The principal semi-drying oils are cotton seed oil, Soya bean, corn oil and Pachystela brevipes seed oils etc. Drying and semi-drying oil belong to the group of oils often classified as hard and soft oils. The drying oils are hard oils, while semi-drying oils are soft oils, Fats and oil play vital roles in industrial production of paints, liquid soap, shampoo, varnish, and polish, binders in paints, plasticizers for plastics, paints, and cosmetics, textile, paper and lubricants (Ajiwe et al.,1995., Nwafor, 1995., Ajiwe et al., 1996., Njikan, 1995).

77

CHEMICAL CHARACTERIZATION OF OIL EXTRACTED FROM WOOD 2.3.1 IODINE VALUE

This is indicates the main unsaturation present in the oil and usually expressed as the number of grams of iodine absorbed by 1.0g of oil. The higher the unsaturation of the oil, the better the drying quality of the oil (Kirk, 1965)

2.3.2 Saponification value

This is determined as the number of milligram (mg) of potassium hydroxide (KOH) required changing 1g of fat completely to glycerol and the potassium soap. Oils that are composed of long chain, high molecular weight fatty acids have low saponification number while low molecular weight short chain fatty acids have high acid value (American society for testing material, 1985. (Spammuth, 1949).

2.3.3 Acid value

This is defined as the number of milligram of potassium hydroxide (KOH) required neutralizing the free fatty acid present in 1g of sample. It is also a measure of the amount of free acid present in an oil or fat sample (Bernfeld, 1987).

2.3.4 Fatty Acids

This denotes a large group of aliphatic monocarboxylic acid occurring mainly in glyceride in natural fats and oils.The general formula of fatty acid is as follows

Which indicated that carboxyl group;-COOH is attached to a radical that consists of an open chain of carbon atoms, which may either be saturated or unsaturated with respect to hydrogen.

With regards to unsaturated acids beside the chemical formula, the position of the double bonds is equally indicated by the position of the preceding carbon atom as in linoleic and oleic acids.

In most fat, about two or three categories of fatty acids exist: the mixed fatty acid which consists of normal straight chain and the unsaturated acid with an even number of carbon atom, that is, C6O24

per molecule. They can be saturated or unsaturated and can be used as food. The unsaturated fatty acids are mainly limited to those having one, two or three double bonds, for example: linoleic, oleic etc. Those with more than one double bond normally have them in the

78

isolated position in which a CH₂ interposed. Consequently, in saturated series, myristic, palmatic, stearic and lauric are the most wide spread. Generally, the proportion of different kinds of fatty acids, depend on the length of the molecules, geometric isomerism in the unsaturated acids, degree of unsaturation and the position of the double bonds with respect to carboxylic groups and to each other respectively. But when there is a substituting group, such also influence in the property of the acid. (A.O.C.S, 1990, Kirk,1965). Fats and Oils are lipids, which are the naturally occurring compound which is soluble in organic solvent but sparingly soluble in water. They are compounds of glycerol and various organic acids and they occur in the proportion of approximately 95% fatty acid and 5% glycerol respectively; they are therefore termed glycerids or glyceryl ester. Oils are unsa turated while fats are saturated. So, a typical molecule has the structure below, in which R, R¹, R¹¹ indicate long saturated chains (A.O.C.S, 1960., Bernfeld, 1987).

(Fats or Oil)

The fatty acids radical constitute the greater part of the glycerol molecule and the reactive portion, hence the chemical and physical properties of oil determined by the properties of its component fatty acids. The chief saturated acids are myristic, stearic and lauric acids. On the other hand, the chief unsaturated are oleic and linoleic. Palmatic acid is the most abundant of the saturated acid such as palm oil. Glycerids are named according to the nature of the acids present and it is said to be simple when all the acid are the same and mixed when the acids are different, for example, steroid. Animals and vegetable fats are mainly composed of triglycerides of fatty acids such as stearic, palmitic and oleic, a molecule of such a triglyceride being derived by the combination of one molecule of glyceride; three fatty acid molecule.

When the average molecular weight of the fatty acid increased, fats progressively have melting points and more easily solidifies. (A.O.C.S.,1960., Lillian, 1982).