How To Learn rubber : Natural Rubber(India Rubber),Treatments to improve and modify natural rubber properties,Reclaimed Rubber,Synthetic Rubber,Rubber flooring materials for general purposes
It is essentially an elastic material and is obtained both as natural and as synthetic material.
Natural Rubber (India Rubber).
Natural rubber is present as an emulsion in the latex of certain plants growing in Ceylon, Singapore, Malaya and Mexico etc. Latex is the milky colloidal fluid oozing from vertical grooves having an upward inclination cut around the trunk of the rubber trees. Pots are tied to the trunk of trees for collection of lates. Crude rubber is obtained from the latex by its coagulation with acetic acid, alcohol, alum or lime etc. Coagulation of latex is achieved even by heating. In certain cases the latex is mixed with appropriate compounding materials and then precipitated directly from the solution to the shapes required. More modern methods are used these days for obtaining Natural rubber rubber from the latex.
Treatments to improve and modify Natural rubber properties
Crude rubber becomes hard and brittle in winter and soft and sticky in summer. Treatments to improve and modify natural rubber properties is therefore subjected to following treatments to improve and modify natural rubber properties.
To crude rubber are added certain compounds to modify natural rubber properties. The compounds that are added are vulcanizing agents, plasticize rs, accelerators, fillers, hardeners, reinforcing agents and pigments.
Vulcanizing agents are substances like sulfur which when added to crude rubber reduce its plasticity while maintaining its elasticity. These are essential for vulcanization of rubber.
Plasticize rs are materials like vegetables oils, rosin and wax etc. that soften the crude rubber.
Accelerators are substances like white lead, lime, magnesia etc. which when added hasten the process of vulcanization and reduce the requirements of sulphur.
Fillers are substances like lamp black, oxide of iron or zinc, china clay, magnesia, and silica etc. that modify the properties of rubber and at the same time reduce its cost. Substances that increase tensile strength of rubber are called reinforcing agents. Lamp black and zinc oxide are both fillers and reinforcing agents.
Hardners are substances like barium sulphate, calcium carbonate and sealing wax that give hardness to rubber and increase its tensile strength. Hard rubber withstands high temperature better.
Pigments are substances like ferric oxide, lithophone and lead chromate etc. that are added to give desired colour to rubber. Compounded rubber is hard, tough, weather and water resistant.
(ii) Calendering is the operation of passing rubber between large steel rollers kept at controlled temperatues and pressures. The rollers press rubber into sheets of desired thicknesses and sizes.
(iii) Vulcanization treatment of rubber with sulphur or compounds resulting in a change in the properties of rubber is known as Vulcanization. Vulcanization renders it useful for all seasons. Vulcanization with 1 to 5 per cent sulphur produces soft rubber whereas with 30 per cent sulphur produces hard rubber. Increasing sulphur gives harder and less flexible product. Full vulcanization requiring about 45 per cent sulphur will give rise to a fully rigid product known as Ebonite.
Sulphur is absorbed by rubber when they are heated together at 135ºC to 160ºC. To accelerate the process of vulcanization acclerators may be used. Vulcanization makes natural rubber much less sensitive to changes of temperature, more elastic and strong, more durable and resistant to action of water, base and dilute acids. It is a bad conductor of heat, resistant to abrasion, tough and shock absorbent. It can be moulded to any shape.
Rubber waste and worn out rubber articles are treated for reuse and the rubber so obtained is called reclaimed rubber. Worn out rubber and rubber waste is cleared of all metal or other matter and heated with alkali solution in closed steel vessels. Separate fabric contents and free sulphur. The treated rubber is washed with clean water and then dried to get what is called the reclaimed rubber. Reclaimed rubber may be mixed with some raw rubber. Reclaimed rubber is cheaper, is of uniform composition, more durable, more easily compounded, vulcanized and moulded. However it has low elasticity, low tensile strength and poor resistance to friction.
It is had by adding sodium-bicar bonate during vulcanization. Small pores are left on evaporation of moisture from within the rubber. This rubber has better heat and sound insulating properties.
Important varieties of synthetic rubber are obtained from petroleum, coal tar and alcohol. Properties of synthetic rubber, though similar to those of natural rubber can have wider variations. Synthetic rubber has better resistance to light rays, weather, acids, oils and greases etc. Synthetic rubbers are getting more popular than natural rubbers and has wider uses.
Rubber flooring materials for general purposes.
Rubber flooring materials is well suited for covering floors of domestic and public buildings. cinemas, hospitals, large stores, ships, transport vehicles etc. Toppings of these floors may be plain or marbled and ribbed or fluted. Backings may be fabric backing or fabric insert, sponge rubber backing or plain rubber backing. The rubber flooring materials should be satisfactorily vulcanized, free from sulphur bloom and objectionable odour and blisters, cracks and embedded foreign matter. The colour of rubber flooring materials should not be affected by cleaning with water and washing soap or floor polish.
Sizes of tiles are 200×200 mm, 300×300 mm and 500×500 mm. Sheets are 900 mm wide and of lengths 5, 3.5 or 2.5 m. Thickness varies for 2.5 to 6.5 mm.
The rubber floor coverings are used in the public and industrial buildings, buses and ships because of their fair weather resistance quality, resiliency and reduction in noise.
For details refer to IS : 809-1970.