Friday, July 8, 2011

TEXTILE CATALYSTS

        A perfectly pure olefin acid ester oxidises comparatively slowly . The rate of oxidation is influenced very greatly by the presence of catalysts and can be increased a millionfold in this way Almost all oils prepared from natural sources contain oxidising catalysts . The most powerful catalysts are compounds of those metals copying the lowest points on the atomic volume curve . Even I mole . ferric oleate per 10,000,000 moles . Ethyl oleate has a detectable effect on the mickey test .

When metallic catalysts ans fatty acids are both present their combined effect is very great. Exposure to light has also an important catalytic effect not altogether due to the formation of peroxides.
All catalysts seem to act primarily by greatly increasing the rate of peroxide formation. the author considers that metals act as activating agents and light and heat act be supplying activation energy fatty acids are known to be more easily activated than esters . In the case of metals if C is the metal compound and a the activation energy then C+a Ca : Ca + M to Ma + C: C+ a to Ca ,etc
In the case of light either the catalysts or the fatty acid ester may become activated directly I,e M+bv to Ma : C + bv to Ca.

TEXTILE OILS

The first line of this post is concerned with the reactions which take place when an ester of an unsaturated fatty acid of the kind occurring in many suitable textile oils is oxidised by air or oxygen . For the sake of simplicity such an ester may be represented as R1 C H:C H-R 2 COOR 3 an example being ethyl oleate.

When a saturated carbon chain is oxidation takes place mainly at elevated temperatures such as occur in the Mackey  test or in vapour phase oxidation or due to bacterial action.

The most common type of oxidation is attack on the double bond which takes place rapidly even at normal room temperatures . The first stage is peroxide formation by addition of a molecule of oxygen at the double bond the subsequent stages may be shown diagram manically as follows


                                                                 splitting products
                                               MO
                                                                 condensation products
When monophthongs fatty acids E g Leica acid are involved the condensation products will be limited to dimers which will be soluble in the oil. This is what happens in a non drying oil.
          When diethenoid fatty acids E g Linotype acid are involved the possibility of trio or higher polymers arises as Linotype may form a double peroxide and each such compound con condense with two othe peroxides . In the case of Linotype acid such condensation products are likely to be relatively simple and will at first from dispersion or microscopically small aggregates in the mass of unoxidised oil.
As oxidation becomes more extensive these aggregates may link up to form al loose structure which will be viscous and sticky .If the oxidation has taken place on a textile fibre the oil. will not readily split up into small droplets during scouring and will be difficult to scour out .This is a description of the behaviour of a semi drying oil E g cotton seed oil.