Artificial fibre works
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Artificial Fibre Works as a class are subject to co-ordination as outlined in the relevant Practice Note to this Section.
2.1 General
Artificial fibre works are usually large industrial hereditaments, often situated on extensive sites and incorporating many items of specialist plant.
See the relevant Practice Note for background information relating to the state of the industry as at the appropriate valuation date.
2.2 Principal artificial fibres
The principal artificial fibres produced in the United Kingdom and the raw materials involved in their manufacture are as follows:
Fibre |
Main Raw Material |
Final Composition |
Viscose Rayon |
Wood pulp |
Cellulose |
Acetate Rayon |
Cotton Linters or wood pulp |
Cellulose acetate |
Nylon |
Benzene |
Polyamide |
Polyester |
Para-xylene |
Polyester |
Protein |
Lactic Casein or vegetable |
Modified protein |
Protein |
||
Plythene |
Ethylene from oil |
Polyethylene |
Alginate |
Seaweed |
Calcium alginate |
Terylene |
Ethylene and para-xylene |
Polymer |
These fibres are produced in the following forms:
- continuous filament, ie a thread consisting of one or several continuous filaments requiring no further conversion to yarn before weaving or knitting;
- staple fibre, ie filaments cut into short lengths for spinning into yarn on normal spinning machines. Such yarns are known as “spun yarns”;
- tows, ie a collection of a large number of continuous filaments for conversion by either tow-to-top or tow-to-yard machinery.
2.3 Outline of processes
An outline of some of the processes used in the manufacture of artificial fibres is given below: a. Regenerated cellulosic fibres
Viscose
The starting material is timber, usually spruce, which is chipped and treated with calcium bisulphite. The treated chips are cooked with steam under pressure, after which the mass is diluted with water and subsequently concentrated to 30% cellulose content, bleached with hypochlorite and converted into paper board. The sheets of board which contain 90-94% pure cellulose are conditioned by storing in a room at a specific humidity and temperature, and are then steeped in a solution of caustic soda. The excess alkali is pressed out by hydraulic rams and the moist mass of soda cellulose passed into a shredding machine. The shredders break the mass into fine crumbs which are “aged” in vessels by the application of oxygen under pressure. After “ageing” the crumbs are introduced into churns and are churned with carbon disulphide, forming a jellified mass. This is passed to mixers where it is stirred with diluted caustic soda in a cooled vessel. The resulting liquid is known as viscose, but is still too impure, too aerated and too “young” to spin. It is transferred to a secondary blender where the viscose is stirred and moved about, to dissolve any remaining fibres. The viscose is then stored from four to five days at 10-18 degrees centigrade during which time it ripens. When the solution is ripe it is forced by compressed air through spinning heads. The spinning bath into which the filaments are projected is of sheet lead, containing a solution of 10% hydrochloric acid and sodium sulphate. As the viscose solution passes through the jets into the bath it solidifies into filaments, owing to the regeneration of the cellulose.
Cellulose acetate
The starting materials are cotton linters and wood pulp which are steeped in glacial acetic acid and loaded with acetic anhydride into enclosed vessels with powerful stirrers. Sulphuric acid is then added and the mixture conditioned at between 20 degrees and 30 degrees centigrade. This forms a jellified mass. This mass is converted into acetone “dope” by hydrolysis. The dope is fed from a feed tank to spinning cabinets where it is squeezed out of jets, and dried by means of hot air into filaments.
Alginate fibres
The starting material is dried milled seaweed. This is treated with solutions of sodium carbonate and caustic soda. The alginic acid is chemically extracted from the solution, generally by precipitation, and the remaining sodium alginate, having been sterilised chemically, is filtered and passed to the spinning machines. Jets discharge the sodium alginate into a coagulating bath with a small amount of hydrochloric acid.
Regenerated protein fibres
Casein fibres
The starting material is casein which is the dried curd of milk. The casein is carefully blended and dispersed in caustic soda solution. The solution is clarified and extruded through jets into a coagulating bath containing a weak solution of hydrochloric acid with fomaldehyde, and glucose. The resultant fibre is collected as tow.
Ardil
This is a vegetable protein fibre, the starting materials being ground nuts. The skin on the nuts is removed and the proteins are isolated by dissolving nut-meal in diluted alkali. This solution is extruded into a coagulating bath containing a solution of sodium sulphate and hydrochloric acid, and the filaments collected. A subsequent process of hardening is necessary, in a bath containing a saturated saline solution and hydrochloric acid.
Soya bean fibre
Soya beans are flaked, the oil is removed and the flakes treated with a solution of sodium sulphite to dissolve the protein. Hydrochloric acid is added and the protein precipitates as a curd. This is dissolved in acqueous caustic soda and the resultant solution is aged or matured. It is then extruded into a coagulating bath similar to that used in casein fibre.
a. Synthetic Fibres
Nylon
It is sometimes said that nylon is made from coal, air and water. Phenol is a coal-tar derivative, the hydrogen necessary in the reduction processes can be obtained from water and the ammonia from the nitrogen in the air and from hydrogen. Phenol is reduced by passing its vapour together with hydrogen gas over a catalyst. Alternatively it may be reduced in the liquid stage in an autoclave.
The product is called cyclohexanol. This is oxydised with concentrated nitric acid to form adipic acid which is one of the compounds for making nylon. The adipic acid is caused to react with ammonia to give the amide which is dehydrated over a suitable catalyst to give a nitrile which is then reduced with hydrogen in the presence of a cobalt or nickel catalyst in an autoclave. The resultant compounds are dissolved in methanol, and on mixing these solutions a precipitate “nylon salt” is thrown down. The nylon salt is melted in an atmosphere of nitrogen, air being excluded. Water is split off from the salt as polymerisation proceeds and is allowed to escape as vapour. A temperature of 280 degrees centigrade for four hours is normal. The molten polymer is then extruded through a slot in ribbon form and is quenched with cold water as soon as it solidifies to reduce the crystal size.
The ribbon is broken into chips which are fed through a hopper into the spinning vessel. In this they fall onto an electrically heated grid which melts the chips into a pool. From the pool the molten nylon is extruded, and on cooling in the air forms filaments. The filaments are subsequently drawn, which increases their strength due to changes in the orientation of the molecules. The supply of benzene (from which the phenol is derived) from coke ovens is limited, and two alternative sources are available. One is from petroleum by-products and the other from various cereal husks and by-products.
Terylene
Terylene is a polymeric-ester obtained by condensing terephthalic acid with ethylene glycol. Ethylene glycol is made in several ways one of which starts with ethylene, a petro-chemical product. This is oxydised with air in the presence of a catalyst, and the ethylene oxide is hydrated to ethylene glycol. Terephthalic acid is made from petroleum by-product paraxylene, which is oxidised with nitric acid. The raw materials are polymerised at a high temperature in a vacuum and the resultant polymer is spun direct from the melt. It is subsequently drawn in the same way as nylon to increase the strength of the filament.
3.1 Basis of measurement
The basis of measurement for this class is Gross Internal Area. Reference should be made to the VO Code of Measuring Practice for Rating Purposes in England and Wales.
3.2 Plant and machinery
Many of the manufacturing processes to produce artificial fibres, being chemical processes, require a considerable quantity and variety of plant. In the most modern artificial fibre works the plant is very similar to that found in major chemical works where such materials are manufactured. Reference should be made to [Rating manual section 6 part 5 [(https://www.gov.uk/guidance/rating-manual-section-6-chhallenges-to-the-rating-list/part-5-plant-and-machinery)for further guidance.
In most cases it will be appropriate to value artificial fibreworks on the rentals basis.
In the absence of direct rental evidence it should be possible, after making due allowance for age, location, etc, to value office and production accommodation by reference to other large factories within the locality. Separately valued plant and machinery will be valued on the contractors basis in accordance with the VO Cost Guide.
Where the contractors basis method has previously been adopted for valuation purposes and it is considered that the premises are so specialised that a valuation on the comparative rentals basis is inappropriate, then the contractor’s basis should continue to be used.
Comparisons based on output or capacity will be inappropriate because of the wide range of products that are manufactured.