PET (Polyethylene Terephthalate) is extremely challenging to recycle and pelletize due to its inherent susceptibility to hydrolysis and thermal degradation.

Core Challenges:

Hydrolysis: Trace amounts of moisture at high temperatures can cause the molecular chains of PET to break, leading to a significant decrease in intrinsic viscosity (IV).

Thermal degradation: Excessive processing temperatures or prolonged residence time can also result in a reduction in IV and an increase in the yellowing index.

Oxidative degradation: Oxygen in the air can exacerbate thermal degradation.

Key Processes:

1. Deep pre-drying: A dehumidifying dryer must be used to reduce the moisture content of the flakes to below 50 ppm (typically required to be below 30 ppm). The drying temperature is usually between 160°C and 180°C.

2. Crystallization and pre-crystallization: For amorphous PET flakes, pre-crystallization or crystallization equipment is required before they enter the plastic granulator machine to prevent agglomeration and caking at high temperatures.

3. Efficient venting and vacuum system: A two-stage vented screw with a large length-to-diameter (L/D) ratio is used, and a high vacuum (e.g., above -0.095 MPa) is applied at the vent port to vigorously remove residual moisture and low-molecular-weight compounds.

4. Gentle plasticization concept: The “low temperature, high shear” approach is no longer suitable. Instead, a “medium temperature, low shear” screw design should be adopted to minimize melt temperature and reduce the residence time of the melt in the barrel.

5. Application of melt pump: Installing a melt gear pump at the end of the screw can stabilize output pressure, eliminate screw pulsation, ensure more uniform IV, and reduce screw backpressure, thereby saving energy.

Why Choose Purui Machinery:

With over 25+ years of expertise and a footprint in over 100 countries, Purui Machinery continues to lead the way in plastic regeneration.

Purui Machinery is a high-tech enterprise specializing in the R&D and manufacturing of plastic recycling machinery. Its product portfolio includes plastic pelletizing lines, washing lines, and crushing equipment. Purui is dedicated to providing global customers with the most efficient, reliable, and intelligent plastic regeneration systems.

Contact Us to Get Your Customized Recycling Solution:

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