Polybutylene Terephthalate

Symbol: PBT
Crystallinity: Crystalline*
Trade Names: Valox, Celanex


PBT Car Bumper Fotolia_2838503_S.jpgPBT is a thermoplastic polyester that is semi-crystalline*. In contrast with PET, which is stronger with higher use temperature and lower cost, PBT is very stable, has high lubricity and surface gloss. PBT also has good chemical resistance, electrical properties and low moisture absorption. PBT will crystallize rapidly. Mold cycles are short and molding temperatures can be lower than for many engineering plastics. PBT is available with reinforcement, both GF and MF.

Processing Considerations:

  • Residence Time: Residence time is typically 2 to 4 minutes.
  • Back Pressure: Back pressure is 150 PSI (1500 plastic pressure) or less.
  • Heat Profile: Although semi-crystalline, it must be processed at higher temperatures to achieve strength characteristics of crystalline.
  • Drying: PBT material must be dried.
  • RPM: RPM can range from 30 to 100.

Screw Design Based on:

  • Low Compression Ratio (Can use CR up to 2.5:1.)
  • Medium Transition Length
  • Medium Meter Channel Depth

Other Information:

  • Mixer: A low shear mixer, like Reiloy Westland Corporation’s Eagle mixer, can be used in processing PBT.
  • Barrier: A barrier screw is not recommended when processing PBT.
  • Custom Design: A custom screw designed to process PBT will produce better results than a general purpose screw.
  • Recommended Valve: The recommended valve for processing PBT is a 3-piece free flow.
  • Screw & Barrel Material Recommendation: The screw and barrel used in processing PBT can be manufactured from standard material.

*Semi-crystalline material.

Various additives and/or fillers can have an effect on a resin’s process behavior. For more detailed information, please contact Reiloy Westland Corporation.

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Industry Applications - Resins

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