Pelletising
A process where the polymer powder is homogenised, addiviated and made to pellets. The polymer melt coming from the extruder is pressed through dies in a die plate and cut to pellets by knives under water (underwater pelletising) or cooled to solid strands and then cut to pellets (strand pelletising).

Permeability
Material constant characterising gas penetration, like water vapour, oxygen or carbondioxide.

Polymerisation
Polymerisation is a chemical reaction where polymer is synthesised from monomers.

Polypropylenes
Polypropylenes are thermoplastic polymers consisting mainly of propylene (C3H6), come frome a low pressure process based on catalysts and have generallya linear polymer chain.

Productivity
A property of the catalyst which indicates how much the catalyst has produced polymer in the process (kg polymer/g catalyst).

Prepolymerisation
A process where polymerisation is started to increase the activity of the catalyst getting over the induction time of the catalyst and not to overheat the catalyst particle by to sudden onset of polymerisation.Prepolymerisation will also help in ensuring more even polymerisation on the catalyst particles reducing the probability of creating a high fraction of fines in the later reaction steps.

Peroxide
Peroxides are a group of compounds that contain the O22- ion. It is used to initiate the polymerisation for high-pressure free radical polymerisation processes.

Polydispersity
Broadness of the molecular weight distribution. A commonly used measure, polydispersity index, is defined as the ratio of weight average molecular weight to the number average molecular weight.

Processability
A concept to describe the behaviour of the polymer in a converting process, such as blow moulding machine and film line. A good processability means a stable behaviour in the process and a high processing speed.

Puncture
In certain packaging applications film is stretched and wrapped around multiform items which can have sharp corners or other protrusions causing high point loading for the film. Puncture test is used to simulate this kind of film loading. Puncture resistance is measured by pressing a specially shaped probe through a clamped film sample. The maximum force, force at break, penetration distance and energy to break are determined.

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