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| POLYPROPYLENE AND TECHNOLOGY: |
Physical properties:
Density - 0.905
Melting point - 155-162°C
Bulk density Kg/m3
Giulio Natta is credited with the discovery of stereospecific polymerization, the positioning of monomers in space to add to a growing polymer. Simultaneously, Karl Ziegler worked wlth catalysts to obtain high molecular weight, crystalline polypropylene polymers. These two discoveries permitted the polymerization of isotactic polypropylene that could be formed into a textile fiber. Natta and Ziegler received the Nobel prize in 1962 for these significant findings in polymer chemistry.
| Moisture regain | <0.1 % |
| Coefficient of refraction NnD23 | 1.49 |
| Heat of fusion | 21 cal/g |
| Specific heat | 0.46 cal/gC |
| Density of melt at 180°C | 0.769 g/cc |
| Heat of combustion | 10.778 cal/gr |
| Oxygen index | 17.4 |
| Decomposition temperature range | 328-410°C |
| Dielectric constant (0.1 M Hz) | 2.25 |
| Dissipation factor (0.1 M Hz) | <0.0002 |
| Specific volume resistivity | >1016.cm |
CHEMICAL SPECIFICATIONS OF POLYPROPYLENE
Propylene is a hydrocarbon with three carbon atoms. When it polymerizes in a step chain reaction, it forms a polymer in which methyl groups extend from the polymer backbone. Three different polypropylene polymers-isotactic, syndiotactic and atactic- are formed. These polymers differ in position of the methyl groups in three dimensional space. In the isotactic polypropylene, all the methyl groups are positioned on one side of the polymer. In the syndiotactic polypropylene, the methyl groups alternate from side to side; in the atactic polypropylene, they are in random positions. Only the isotactic polypropylene is useful to form textile fibers.
PRODUCTION OF POLYPROPYLENE
Polypropylene was first produced in Italy in 1957. USA production began in 1962. Polypropylene is made from a raw material, propylene, which is a byproduct from the cracking process in the petroleum industry. Propylene is polymerized at 10 atmospheres of pressure at <80°C. Oxygen must be excluded due to the sensitivity of the polymer to oxidative degradatlon. Low heat is necessary to permit maximum polymer length to be achieved. Special catalysts control the orientation of the monomers in space, so stereospecific polymerization takes place, and the methyl groups all end up on one side of the polymer backbone. Stabilizers are added to polypropylene to provide meet extrusion stability, long term thermal stability at normal use temperatures and stability to ultraviolet light.
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