Rubber
| Infobox on Rubber | |
|---|---|
| Example of Rubber |  |
| Facts | |
| Origin | - |
| Stowage factor (in m3/t) |
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| Humidity / moisture | - |
| Ventilation | - |
| Risk factors | See text |
Rubber
Contents
Description / Application
Natural rubber, also called India rubber or caoutchouc, as initially produced, consists of suitable polymers of the organic compound isoprene with minor impurities of other organic compounds plus water. Forms of polyisoprene that are useful as natural rubbers are classified as elastomers. Currently the rubber is harvested mainly in the form of the latex from certain trees. The latex is a sticky, milky colloid drawn off by making incisions into the bark and collecting the fluid in vessels. This process is called "tapping". The latex then is refined into rubber ready for commercial processing. Natural rubber is used extensively in many applications and products, either alone or in combination with other materials. In most of its useful forms it has a large stretch ratio, high resilience, and is extremely waterproof.
The use of rubber is widespread, ranging from household to industrial products, entering the production stream at the intermediate stage or as final products. Tires and tubes are the largest consumers of rubber. The remaining 44% are taken up by the general rubber goods (GRG) sector, which includes all products except tires and tubes.
The major commercial source of natural rubber latex is the Pará rubber tree (Hevea brasiliensis), a member of the spurge family, Euphorbiaceae. This species is widely used because it grows well under cultivation and a properly managed tree responds to wounding by producing more latex for several years.
Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as easily as the Pará rubber latex does; some of them require more elaborate processing to produce anything like usable rubber, and most are more difficult to tap. Some produce other desirable materials, for example gutta-percha (Palaquium gutta) and chicle from Manilkara species. Others that have been commercially exploited, or at least have shown promise as sources of rubber, include the rubber fig (Ficus elastica), Panama rubber tree (Castilla elastica), various spurges (Euphorbia spp.), lettuce (Lactuca species), the related Scorzonera tau-saghyz, various Taraxacum species, including common dandelion (Taraxacum officinale) and Russian dandelion (Taraxacum kok-saghyz), and guayule (Parthenium argentatum). To distinguish the tree-obtained version of natural rubber from the synthetic version, the term gum rubber is sometimes used.
Rubber exhibits unique physical and chemical properties. Rubber's stress-strain behavior exhibits the Mullins effect, the Payne effect, and is often modeled as hyperelastic. Rubber strain crystallizes.
Owing to the presence of a double bond in each repeat unit, natural rubber is susceptible to vulcanisation and sensitive to ozone cracking.
There are two main solvents for rubber: turpentine and naphtha (petroleum). Because rubber does not dissolve easily, the material is finely divided by shredding prior to its immersion.
An ammonia solution can be used to prevent the coagulation of raw latex while it is being transported from its collection site.
Shipment / Storage / Risk factors
Rubber is shipped in sheet, block, crepe or crumb form, packed in pressed bales, in cases, or for crumb rubber in bales inside crates. Damage caused by exposure to rain prior to, or actually during loading, can frequently occur, because rubber is produced and transported to the loading port in countries where there is frequent and heavy rainfall. Wet bales may well dry out externally when exposed to the sun and the water staining left may not be obvious except on close scrutiny by an experienced person.
Bales of rubber are from time to time found to be damaged in way of dunnage marks. This may occur in the vessel if damp or ‘green’ timber has been used as dunnage. It can occur prior to shipment from the same causes and also, even if the bales are stowed on dunnage which is initially dry, if the ground below is damp or wet – the water can be drawn up through the dunnage and affect the underside of the bale in contact with the dunnage.
In sheet rubber where mould is dry and well developed and there are secondary growths of mould, e.g. brown coloured moulds over green, the damage can be said to be of considerable standing. However, moisture can be retained in rubber for a very long period after the initial penetration. Therefore, it cannot be assumed that because moisture is present the damage is of recent origin.
With sheet or crepe rubber if free moisture only is present, particularly in the outer parts of the bale, and if there is only minor growth of mould, the damage is more likely to be of recent origin. The effect of water on sheet rubber, in addition to producing mould, is to discolour and ‘bleach’ it. Confusion may arise in this respect because sheet rubber, when subject to comparatively low temperatures, become rather lighter in colour. A check can be made on this by warming a section of the discoloured sheet. If the colour does not return then it would appear that the discolouration has been cause by water damage.
With crepe rubber considerably more penetration of damage as a result of capillary action occurs than in sheet rubber, as a bale of crepe rubber acts as a sponge.
There is a greater range of colours in mould on crepe rubber than in sheet. These colours can very from crimson through yellow, blue and green to black. These moulds should not be confused with natural streak.
Water or moisture, whether it is acquired or present at the time of packing, causes physical deterioration of rubber and subsequent difficulties and extra costs in putting it into production. The extent of the deterioration varies considerably with the degree of damage and the grade of rubber involved, although properties can be restored if the rubber is completely dried. Since natural rubber contains hardly any inherent moisture, processing formulas are generally geared to the original dry state of the rubber with the necessary quantities of sulphur and accelerators, etc., being calculated. The presence of water, apart from causing problems during processing, e.g. dispersion of fillers, will disturb the whole mixture. Moisture retained after processing can cause porosity in the vulcanized rubber. Generally speaking, distortion and pressure on bales of sheet rubber as a result of superimposed weight in stowage should not have any material effect when the rubber is finally used. This is provided that the bales are not misshapen to an extent that they will not pass through the ‘gallows’ at the factory. Should this happen they then have to be cut by hand, involving extra costs.
If loaded particularly soft after lengthy exposure to the sun or subject to excessive weight in stowage, bales of crepe and sheet will ‘mass’ and adhere to one another. Separation on out-turn will involve considerable costs.
Splinters from dunnage which has become embedded may adhere to rubber, particularly crepe. This will cause problems in production and has to be removed by wire brushing or cutting off of the affected rubber.
The higher grades of baled pale crepe, and also sole crepe, are susceptible to heating and can sustain damage in this respect. Heating of crepe results in it becoming tacky and massing occurs both between the individual sheets in the bales and between the bales themselves. Sometimes the affected rubber may be trimmed off. Excessive pressure in stowage and heating, either individually or in combination, causes pale crepe sheets to fuse and become semi-opaque. In this grade of crepe the sheets must be capable of separation by hand pressure, therefore if they are fused the rubber has to be downgraded.
Contact with copper sulphate will cause rubber to degrade to a sticky state, and the initial contact with the sulphates sets up a form of disease which will continue unless arrested by the removal of the damaged portion. Certain paints contain copper sulphate. If a covering which has been previously marked with a paint containing copper sulphate comes into contact with rubber then it is sufficient to set up the process which will degrade it. Contact with other copper-containing materials should also be avoided. Oil will swell and/or dissolve rubber. Rubber shipped in the form of crumb or large compressed granules and packed in polythene wrapped blocks in crates is most vulnerable to water damage and heat, which causes deterioration and loss.
Additional information
India rubber or caoutchouc
Clean and dry containers are essential and care must be taken not to let unpacked rubber become contaminated by other cargo such as ore, copra, Palm Kernels, rice, or by dunnage, rust, paint and water. The quality of rubber greatly deteriorates in contact with oil . The stowage recommendations relate to South East Asia and are as follows:
- Bales must be stowed on their bulging side; prevents the rubber from sticking together. The bales must be carefully powdered with Omyah BSH-20 powder, on all sides. This powder can be obtained at Singapore. Particularly in the lower tiers and between parcels, powder should be used liberally.
- Omyah BSH-20 must be stored perfectly dry.
- All rubber and particularly "Crepe" must not be stowed next to heated tank tops, heated bulkheads and other sources of heat.
- Native rubber (from Thailand and Borneo mostly) readily sticks together.
- SMR (Standard Malaysian Rubber) and SIR (Standard Indonesian Rubber) frequently comes in paper bags, but also in crates. In connection with their weak packing, care must be taken when packing containers. Crates always to be stowed accurately on top of each other. The strong smell of rubber may taint other cargoes
- For solid stowage, plywood boards can be used between tiers.
- Contamination of rubber from any foreign matters must be avoided.
Palletizing of rubber
Crepe rubber lend itself perfectly to palletizing. On the pallet and between tiers, plastic foil to be used, liberally powdered with Omyah BSH-20 powder. In order to prevent contamination, plastic foil should also be put on the top tier. Palletized bales of crepe rubber are to be stowed on their flat side, strapped horizontally on the top tier with band-iron, whereafter two vertical straps must also be applied. Because of the rubber sinking down in the crates a void space will eventually develop in the upper side of the crate, weakening the top considerably. The crates cannot stand high pressure; therefore in order to limit damage, following guidelines must be adhered to:
- Crates not to be stowed more than 3-high.
- Dunnage, or plywood boards to be used between each tier, provided they are placed not to interfere with forklift access.
Sheet rubber
Because of it's tendency to deform, sheet rubber is not very well suited for palletizing. If offered as such, deformity of sheets should be expected and this particularly applies to so-called "jumbo bales", weighing over a ton. No weight to be stowed on top and if lifting use broad nylon web slings which do not cut into the sheets. Box pallets and crates will give no problems.
Rubber cloth
Usually packed in cartons and/or cases. Adversely affected by heat, moisture, oil and pressure. Deterioration and tendency to perish may not necessarily be due to heat in transit, but to inferior quality and manufacture.