The step people skip

Recycled PET flake arrives with two problems. It is amorphous, so it softens and sticks together as soon as it gets warm, and it carries moisture that hydrolyses the polymer chain during melting. Skip the conditioning step and the sheet comes out with low intrinsic viscosity, poor clarity and unpredictable forming behaviour. This is the single most common reason a recycled tray project fails in the first month. Shantou Longsheng Industry Co., Ltd. supplies the LSI series PET/PLA single-screw extruder with an integrated drying and crystallising system to close that gap.

What crystallisation actually does

Amorphous flake has a low softening point. Heated directly in a hopper it fuses into a solid block and stops feeding. Crystallising the flake first, by agitating it at a controlled temperature, raises its softening point so it can be dried at 160 °C without sticking. Only then can moisture be driven down to the level PET needs.

Moisture targets and why they matter

• Below 50 ppm for standard food tray sheet
• Lower for high-clarity or high-IV applications
• Measured at the dryer outlet, not assumed from the setpoint

Hydrolysis during melting reduces molecular weight, and reduced molecular weight means weak corners, cracking on the trim line and a tray that fails a drop test it passed in the sample room.

What the LSI line gives a producer

• Single-screw design matched to PET and PLA rheology, with a screw geometry that avoids excessive shear
• Integrated drying and crystallising so the flake arrives at the feed throat in the right state
• Stable output for multi-layer structures when a virgin skin is needed over a recycled core

Practical rules from our commissioning work

• Never mix flake from different IV grades without testing
• Keep the crystalliser agitator on a maintenance schedule; a fouled agitator causes uneven crystallinity
• Install a metal detector before the extruder; bottle flake carries contamination
• Run a monthly IV check on finished sheet, not only on incoming flake

About Shantou Longsheng

Founded in 1998 in Shantou, Guangdong Province, China. 30,000 m² plant, "Longsheng" trademark, 25 granted patents (1 invention, 24 utility models), high-tech enterprise. Sheet extruders (DSI-PP multi-layer co-extrusion, LSI PET/PLA, SI-PE), multi-station thermoformers, vacuum forming machines, cup making machines and precision molds.

https://www.stlongsheng.com