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

Classifications of polymers

Polymers can be classified in number of ways

1)classification based upon source

polymers can be classified based upon source are

a)Natural polymers:- these are the naturally occurring polymers such as starch cellulose nucleic acids and natural rubber.natural rubber is a polymer of isoprene(2-methyl buta 1,3-diene)
b)Synthetic polymers:- these are man made polymers such as poly vinyl chloride (PVC),Bakelite,nylon,polystyrene etc

2)CLASSIFICATION BASED ON SYNTHESIS

based on the method of synthesis polymers can be classified as follows
a)Addition polymers:-these type polymers are formed by the repeated additions of monomeric unit .the monomers involved are unsaturated compounds and are usually the derivatives of ethene

eg:-polypropylene, PVC,polythene,etc belongs in this type

b)Condensation polymers:-these are formed by a series of condensation reaction between two monomers each monomers having two functional group.during condensation simple molecule like H2O,HCl,NH3 etc are eliminated.The reaction is called condensation polymerisation

eg nylone66

CLASSIFICATION BASED ON INTERMOLECULAR FORCES

based on the inter molecular forces polymers can mainly classified in to 4
a)Elastomers :-the polymers that have elasticity, like rubber are referred to as elastomers.the polymer chain in elastomers are held together by the weakest intermolecular forces.they have ability to be elongated under stress and regain their former shapes when the stress is removed

b)Fibers:-these are thread like polymers which can be woven into fabric.they have high tensile strength and high modulus.this is due to strong inter molecular forces like hydrogen bond.
eg:- cotton,wool,silk,nylon and Dacron etc

c)Thermoplastic:-The inter molecular forces of attraction in the thermoplastics polymers are intermediate between those of elastomers and fibres .As a result thermoplastic polymers when heated became melt and can be molded again in different forms.
eg:- polyethylene polypropylene and polystyrene

d)Thermosetting plastic:- These polymers are prepared from low molecular mass semifluid polymers .thy cannot be reshaped on heating because the polymer chain under go extensive cross linking resulting in the formation of three dimensional network of inter connected polymer chain

eg:- Bakelite,melamine etc

polymers

polymers are macromolecules formed from same or different type of small molecule.the term polymer is a Greek word(poly=many,mer=part ).The smallest molecules that form the repeating unit in polymer are known as monomer unit.The process by which a polymer is produced from monomers known aspolymerization.
for example consider the polymerization of ethylene monomers to form poly ethylene.
n(CH2=CH2)-> -(CH2-CH2-CH2-CH2)-n