There were only really two ways forward: to make a move to special high grade technical or pharmaceutical white oils with less than 1% aromatics or to develop a whole new vegetable oil package for jute batching.
During the early 1990's it was not possible to interest jute mills in experimental batching oils which cost between 4 and 5 times as much as their cheap low grade mineral oil. However, as a result of the IJO meeting in 1998 to discuss the proposals by the IOCCC and CAOBISCO to reduce the presence of mineral oil hydrocarbons in jute sacks, interest began to develop.
The use of vegetable oils immediately threw up problems:
1. Problems of oxidative stability (rancidity) vs. melting points
2. Problems on cost
3. Technical problems with emulsification and in the batching process.
1. The rate at which a vegetable oil becomes rancid is directly related to the degree of saturation of the basic molecule. Unsaturation in this case refers to a situation where two C atoms are linked by a double bond which can then be broken by a reaction such as oxidation
Vegetable oils are a mixture of various fatty acids the most common being:
Capric Acid C10 Saturated - MP 30C - Expensive - found in small quantities in Coconut oil and Palm Kern Oil
Lauric C12 - saturated - MP 46C - anti-microbial - found in Coconut and Palm Kern Oil
Mysteric C14 - saturated - Small quantities in Palm oil
Palmitic C16 - saturated - MP 54C - quantities in Palm oil - Palm Kern Oil and Coconut Oil
Stearic C18 - saturated - MP 70 - varying quantities in most oils
Oleic C18 - mono-unsaturated - MP 15C - varying quantities in most oils
Linoleic C18 - poly(2) unsaturated - MP -7C - Sunflower oil, Olive oil, Rice bran oil, Corn oil
Linolenic C18 - poly(3) unsaturated - Rapeseed, Soya, Corn
Eicosenic C20 - mono-unsaturated
An approximate idea of how fast an oil will oxidise can be obtained from the Iodine Value of the oil (the amount of Halogen, in terms of Iodine, that can be absorbed by 100 gms of oil). An Iodine value in excess of 80 will indicate that an oil is likely to be unstable. The use of the correct antioxidants, at permitted food levels can increase the resistance to oxidation by 400-500%
Diagram 1 shows the trade-off between melting point and Iodine Value. Coconut oil has a lower melting point because it contains short chain (C12 TO C16) saturates whereas in all the other oils the saturated component is mostly stearic (C18).
The rate at which an oil oxidises is governed by the degree of saturation and the level of natural antioxidants (tocopherols). The more saturated the oil: the more stable it will be.
Unfortunately the fully saturated oils have melting points which render them unsuitable for the purposes of batching jute. The melting points also increase with the length of the C chain. Oils below C16 can be ruled out on cost. In addition Lauric oils seem to have anti-microbial qualities which are a hinderance to the jute maturing process.
The result is that an oil must be found which is a combination of Stearic and Oleic acids - while keeping the linoleic and the highly unstable linolenic acids to a minimum : the particular blend depending upon the ambient temperature at which the oil will be used.
Most jute mills run in temps. between 24C and 35C. If the ambient temperature falls lower than this the oleic content but not the linoleic content must be increased (linoleic oxidises 10 times faster than Oleic)- at considerable cost. Because mono-unsaturated Oleins are used rancidity poses a risk.
The conditions of emulsification and spreading at almost molecular
thickness on jute fibres, combined with the maturing process mentioned earlier is asking for rancidity problems.
There are three approaches to this problem:
a. Use an oil with the lowest possible unsaturated content in the ambient temperature prevailing
b. Use man made antioxidants
c. Concentrate the natural antioxidant tocopherols present in vegetable oil in the oil used.
Option a. A number of vegetable oils have been developed recently using selective plant breeding (not GM) which have high oleic acid content and lower linoleic than natural oils. These are important where low temperature application is required.
Option b. is straightforward - there are a number of food grade antioxidants available.
Option c. would seem to be a sensible approach - the unsaponifiable part of vegetable oils naturally contain between 0-1000ppm of tocopherols - this amount can be increased through processing to around 5000ppm with great benefit to oxidative stability, unfortunately the overall increase in unsaponifiables might compromise the ability of the oil to meet the IOCCC criteria, nevertheless research work done by the Umass Lowell labs in the USA suggests strongly the vitamin A complexes such as tocopherols have positive health benefits.
2. Cost
When vegetable oils were first proposed for the jute industry they were rejected on grounds of cost. Neptune Chemicals did much work with Alan Burgess at the Filtisac mill in the cote D'Ivoire to see if the batching process could be modified to offset the increased costs.
It was found that provided the right emulsifiers and oils were used the oil content of the emulsion could be reduced to 10% from the usual 25% and that application of the emulsion should be made at 30%.
The oil used is thus reduced from the normal 5% to 3%. Maturing times have also reduced from an average of 3 days to 36 hours. If the maturing times were left as before then the jute becomes too soft and falls off the rollers.
3. Technical Issues
a. Unsaturated vegetable oils can be quite difficult to emulsify using the small amounts of emulsifiers that our customers are used to buying (around 0.25%- 0.5% of the emulsion consists of emulsifiers).
b. Historically Nonyl-Phenol ethoxylates have been used as emulsifiers. These should not be used but currently we are unaware of industry scrutiny here. Neptune's oils & emulsifier blends all have food contact approval for use with food packing materials.
c. In addition there are a number of simple mill procedure changes and maintenance issues which need to be addressed. Neptune will, of course, advise their customers on these changes.
d. Inconsistency of lab. results - Neptune's oil / emulsifier blends have been tested for unsaponifiables by a number of reputable laboratories and the results have been good. ( That said independent lab results can still differ on "same samples"). Neptune's base oils have a max. unsaponifiable content of 0.6% and we know that our additives and emulsifiers can add a maximum further 2.5% - so the maximum total unsap. content of our complete oil / emulsifer blend is approx. 3%. Applied at 3% on the jute we expect 900ppm added unsaponifiables in the sacks. It is interesting to note that a major recent survey of 1600 "hydrocarbon - free" sacks from all over the world has shown the following results:
35% below 1250 ppm
13% 1250 - 2000 ppm
38% 2000 - 5000 ppm
14% over 5000 ppm
Neptune's Further Research / Conclusions:
a... concerns the degree to which the unsaponifiable content of jute fibre itself varies. (Neptune's tests have shown unsaps as high as 650ppm on un-oiled jute).
b... whether dust is being washed out and measured..
Thus far: Neptune has been instrumental in securing changes made to the original Caobisco criteria. The unsaponifiable limit has been changed from 1000ppm to 1250 ppm and it is arguable whether this should be adjusted again. The original test methods (IUPAC WG/90) were also flawed. We have ensured that this was brought to the attention of the industry and changed.
Ultimately mills must ensure that their chosen vegetable oil / emulsifier blend does not bow to the unsap criteria at the expense of mill efficiency. They must achieve both.
Neptune has been at the forefront of research into the correct (though delicate) balance between: rancidity; temperature; cost; mill efficiency; and the need to meet the current unsap criteria (et al ) for food contact.
To date its products are being used successfully throughout the spinning world, and sacks which use Neptune's products have emerged as most acceptable by the food industry. Neptune's technical director: Mr Alex Heron has recently (04/2001) lectured at Nestle on the company's reseach and continues a useful dialogue with the industry in order to provide both jute & sisal spinners with the experience gleaned in the hard fibre industry since 1864.