PET Melt Temperature & Practical Processing Guidelines

Understanding PET Melt Temperature in Industrial Processing

Polyethylene terephthalate (PET) requires precise melt temperature control to achieve consistent flow behavior, mechanical strength, and surface finish. In injection molding and extrusion, the melt temperature typically ranges from 260°C to 290°C, depending on IV (intrinsic viscosity), moisture content, and equipment configuration. Maintaining this window ensures polymer chains remain intact and reduces issues such as degradation, yellowing, or excessive shear.

Key Factors That Influence PET Melt Temperature

Moisture Content and Its Impact

PET is highly hygroscopic, meaning it absorbs moisture easily. If processed without proper drying, water triggers hydrolytic degradation at melt temperature, reducing molecular weight and creating brittle parts. Drying PET to below 50 ppm moisture before melting is essential for stable melt behavior and strong end products.

Intrinsic Viscosity (IV) Variations

High-IV PET resins require slightly higher melt temperatures to achieve the same flow characteristics as lower-IV grades. Bottling-grade PET (0.76–0.84 IV) processes differently from fiber-grade or engineering-grade PET. Adjusting temperature settings based on IV helps ensure proper mold filling and cycle efficiency.

Shear and Residence Time

Excessive screw speed or long residence time increases melt temperature beyond the set points. This can degrade PET, generate acetaldehyde, and affect clarity. Optimizing screw design, back pressure, and screw rpm minimizes unnecessary heat buildup and preserves resin quality.

Recommended PET Processing Parameters

The following table summarizes typical processing conditions that help maintain proper melt temperature and reduce defects during PET molding and extrusion.

Processing Aspect	Typical Range	Notes
Melt Temperature	260°C–290°C	Lower for standard grades; higher for high-IV PET
Drying Temperature	160°C–180°C	Ensure moisture < 50 ppm
Mold Temperature	20°C–30°C	Higher mold temps improve clarity
Screw Speed	Moderate	Avoid excessive shear heating

Practical Tips for Maintaining Optimal PET Melt Quality

• Pre-dry PET thoroughly with desiccant dryers equipped with dew point control to avoid molecular degradation during melting.
• Monitor actual melt temperature using a needle probe rather than relying solely on barrel temperature settings.
• Use vented or vacuum-assisted screws when processing recycled PET to help remove residual moisture and volatiles.
• Keep residence time short to prevent darkening, yellowing, and acetaldehyde formation in bottle-grade PET.

Troubleshooting PET Melt Issues

Common melt-related problems such as splay, brittleness, haze, or color change often stem from improper temperature or moisture control. If defects appear, check moisture levels first, followed by melt temperature calibration, screw back pressure, and contamination sources. Maintaining consistent melt quality allows smoother production and longer mold life.