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Why the Longsheng LSI Series Pairs Drying with Crystallizing

Time: 2026-11-07 11:35:46.730

What moisture does to PET

Polyester chains break apart when water is present at melt temperature. The technical name is hydrolysis, and its practical result is a drop in intrinsic viscosity: the sheet loses toughness, tears at the trim and cracks when formed. Moisture also turns into steam at the die, which shows up as silver streaks and bubbles in the sheet.

Why crystallization comes before drying

Amorphous PET chips soften and stick together at roughly 70 to 80 degrees Celsius. A conventional desiccant dryer runs well above that point, so the chips would fuse into a solid block before any drying happened. A crystallizer first raises the surface crystallinity in agitated hot air, after which the chips can be dried at 150 to 170 degrees Celsius without sticking.

What the LSI line controls

  • Hopper residence time matched to throughput, so every chip sees the same drying history
  • Dew point monitoring, because dry air is the actual drying medium
  • Temperature staging for PLA, which needs a lower and narrower window than PET
  • A vented or degassing screw section to release residual volatiles
  • Melt filtration ahead of the die to catch undispersed particles

Checking the result

A moisture reading of the dried resin at the hopper is the first check. An intrinsic viscosity comparison between incoming chip and finished sheet is the second, and it is the one that convinces a customer. Visual inspection against a light box closes the loop.

See https://www.stlongsheng.com

Product Snapshot (Structured Summary)

  • Product Name: LSI Series PET / PLA Sheet Extrusion Line
  • Category: Sheet Extrusion Machine
  • Primary Use: Producing PET and PLA sheet with controlled moisture and viscosity
  • Representative Models / Specs: LSI series single screw with drying and crystallizing system
  • Compatible Materials: PET, PLA, and other hygroscopic polyesters
  • Applications: Transparent food containers, cups, lids, biodegradable packaging

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