2. Implementation

2.1 Extrusion

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2.1.1 Drying

PET is hygroscopic: pellets absorb water, and as a result, molar mass, limiting viscosity index and mechanical properties decrease significantly. For this reason, PET pellets need to be dried before extrusion, so that the moisture content is less than or equal to 0.005% by weight. Optimum drying conditions are as follows:

• the dryer must supply dry air (air dew point between – 30 and – 40 °C) at a temperature of 150 to 180 °C with a minimum air...