CARBONBLACK

CARBON BLACK

Among the reinforcing fillers used in rubber industry, a lion's share is constituted by different types of carbon blacks. They are essentially elemental carbon prepared by converting liquid or gaseous hydrocarbons into elemental carbon by partial combustion or thermal decomposition. Depending on the process adopted for the preparation, carbon blacks and lampblack. The furnance blacks, channel blacks and lamp blacks. The furnace blacks are produced by incomplete combustion of natural gas or heavy aromatic residue oils from the petroleum industries, in refractory lined steel furnaces and separating the carbon formed by means of cyclones and filter bags. Finally, they are pelleted and packed, In the thermal process, natural gas or oil is thermally decomposed at about 1300°C in the absence of free air, in cylindrical furnaces filled with an open checker work of slice bricks. The channel blacks are produced by feeding the natural gas or oil into thousands of small burner tips where the small flames inpinge either on to a large rotating drum or on to reciprocating channel irons. The black deposited is scraped out and collected. Lamp black is made by burning oil and allowing the black formed to settle out by gravity in a series of chambers.

EXTENDERS

Extenders

These are substances which are added to rubber compounds in lage quantities so that the cost of the compound can be reduced, without seriously affecting the final properties. Important among the commercially used extenders are the following.

PLASTICIZERS

PLASTICIZERS

Plasticisers are added in rubber compounds with the following objectives.
1.Increase plasticity and workability of the compound.
2.Aid in wetting and incorporation of fillers

3.Modify the properties of the vulcanised products.
4. Provide lubrication to improve extrusion, moulding or other shaping operations.
5. Reduce batch temperature and power consumption during mixing
Plasticisers are divided broadly into two classes:

1)chemical Plasticisers:-Chemical Plasticisers act as reducing the molecular weight of the rubber, by chain scission.

2)physical Plasticisers:- Physical platiciser not as intermolecular lubricants.

Chemical Plasticisers are used when:
a) The primary concern is for modifying the properties of the uncured stock rather than those of the vulcanisate.
b) The type of rubber being used is one which responds to such agents.
c) The other compounding ingredients and mixing conditions are right for maximum activity of the plesticiser
d) The cost is favourable in comparison with other methods of getting the same effect.

ANTIOXIDANT

Antioxidants & Antidegradants

Factors Contributing to Polymer Degradation:

• All polymers (saturated / highly unsaturated) are vulnerable to reactive degradation factors such as:

- Storage aging
- Oxygen
- Heat
- UV Light & Weathering
- Catalytic degradation due to the presence of heavy metal Ions (Cu, Mn, Fe etc.)
- Dynamic Flex - Fatigue
- Ozone (Static / Dynamic / Intermittent exposure)

• These factors degrade polymers causing substantial changes in the technical properties of the rubber products and ultimately lead to their failure during service or shorten the expected service life in the absence of Antioxidants.

Polymer Degradation Chemistry

• The formation of free radicals (R.) during polymerization, processing or service of the rubber product is the first stage of polymer degradation and is called as ‘Initiation’ of degradation process.

ACCELERATORS

ACCELERATORS: DEFINITION & CLASSIFICATION

•An accelerator is defined as the chemical added into a rubber compound to increase the speed of vulcanization and to permit vulcanization to proceed at lower temperature and with greater efficiency.

•Accelerator also Decreases the Quantity of Sulphur necessary for vulcanization thus improving 'aged' properties of the rubber vulcanizates.

•Over 150 different chemicals belonging to different classes of composition are known to function as accelerators for rubber vulcanizates of which around 50 accelerators are most commonly used by the Rubber Industry.

•The accelerators are generally classified as follows :

Chemical Composition Accelerators Vulcanisation Speed
Aldehyde Amines BA, HMT Slow
Guanidines DPG, DOTG Slow
Thiazoles ZMBT, MBT, MBTS Moderate
Thiophosphates ZDBP Semi-Fast
Sulphenamides CBS, TBBS, MBS Fast (delayed action)
Thioureas ETU, DPTU, DBTU Fast
Thiurams TMTM, TMTD, TETD, DPTT Very Fast
Dithiocarbamates ZDEC, ZDMC, ZDBC Very Fast

VULCANIZATION

Vulcanization is a cross linking process in which individual molecules of a polymer (such as rubber)
is converted into three dimensional network of interconnected polymer chains through a chemical cross link.
comparing with unvulcanized polymer the vulcanized polymer has

-High viscosity
-High modulus
-high tensile strength
-low elongation
-high hardness
-high resilience
-high abrasion resistance
-high elasticity
-high flex-fatigue

biodegradable polymers

BIODEGRADABLE POLYMERS

polymers are widely used in the form of packing material and throw away that bag.The plastic thrown away after use are not biodegradable.this produce a serious waste disposal problem.Scientist these days are carrying on researches to develope plastic which are capable of biodegradability over the period of time