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.

Different chemical Plasticisers and are available which are quite different from one another and are effective under different conditions. Some are listed below:
1. Certain accelerators (eg. MBT & DPG) have mild Plasticising action on NR.
2. Aromatic mercaptans (eg. Thionaphthol & Xylyl mereaptan) have strong softening effect on NR and reclaim.
3. Phenyl hydrazine salts-strong in NR & SBR.
4. Thiuram disulphides - Strong in neoprenes.
5. Benzami dodipheny1 disulphide - effective only at high temperature.
6. Certain petroleum sulophenol, especially its zinc salt, is powerful in NR and at high temperature in SBR.

It is important to note that in the absence of a chemical plasticiser NR breaks down most rapidly at low mill temperatures and that the chemical plasticisers work most effectively at high temperatures. For this reason, the compounded should use a fully effective quantity of the chemical plasticiser and masticate at high temperatures or else leave it out altogether and masticate at as low a temperature as possible.

Physical plasticisers are used when:
a) Modification of the vulcanisate properties is also desired
b) Processing required the lubricating, tackifying and other special properties that can be obtained with different physical softeners.
c) Cost is favourable in comparison with other approaches.

In general, the main factors considered for selection of physical plasticisers are as follows:
1. Compatibility
2. Cost
3. Efficiency
4. Staining characteristics
5. Low temperature properties
6. Effect on vulcanization and ageing characteristics of the rubber

Most of the important physical plasticisers come from any one of the following sources.

1. petroleum (mineral oils, resins, waxes, asphalt)
2. pine tree (Pine tar, pitch, resins)
3. Coal tar (coal tar oil, pitch, resins)
4. Natural fats & Oils (Vegetable oil, blown Oils, fatty acids, fictive)
5. Synthetic organic compounds (Ester Plasticiser, liquid polymers etc.)
Petroleum oils are the most common among the above.