Repsol YPF
Ruta
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HDPE Characteristics
Characteristics
The main characteristics of Hdpe in order to determine its use in different applications are:
- Viscosity depends on the average length of the macromolecules that is controlled in the reactor by means of the inclusion of a hydrogen stream, the temperature and the catalytic system. The simplest method to determine the viscosity is the melt flow index (MI), the lower that the melt flow index is, the greater the viscosity.
- Density is another important parameter of control. Density has an influence on the stiffness of the container, its resistance to impact and its resistance to cracking. Density is controlled through the concentration of the comonomer (buthene or hexene) in the reactor.
- Swelling: After extrusion through a scylindrical nozzle to form the parison, the molecules of polymer try to recover their original shape, which is called elastic memory, for which reason it swells upon leaving the nozzle. This phenomenon will determine the weight of the container and the length of the parison, thus the swelling in the small opening will be an essential constant to optimise in the production of the containers.
