company news about Modified PBT: Common Problems and Solutions

  Polybutylene Terephthalate (PBT) is a semi-crystalline engineering plastic valued for its excellent electrical properties, chemical resistance, fast crystallization rate (leading to short molding cycles), and good mechanical strength. However, when modified—especially with glass fibers—several common challenges arise. 

1. Warpage in Glass Fiber Reinforced PBT:

Cause: The primary cause is anisotropic shrinkage. Glass fibers align in the flow direction during injection, restricting shrinkage along that axis. Shrinkage across the flow direction is higher. This differential shrinkage causes warping, especially in flat or long parts.

Solutions:

Material: Add mineral fillers (like talc) which are more isotropic in shape to balance shrinkage. Blend with a low-shrinkage amorphous polymer (like ASA or PC) using a suitable compatibilizer to reduce overall and differential shrinkage.

Processing: Optimize the mold temperature (higher temps can reduce warpage). Adjust gate location and size to manage flow patterns. Use a higher mold temperature to allow more uniform cooling.

2. Floating Fiber on the Surface:

Cause: Similar to other reinforced plastics, exposed glass fibers ("floating fibers") on the PBT surface result from poor interfacial adhesion between PBT and the fiber, shear-induced separation during flow, and the "fountain flow" effect that pushes fibers to the mold surface.

Solutions:

Material: Use coupling-agent-treated glass fibers for better bonding. Incorporate compatibilizers and processing aids to improve wetting and adhesion.

Processing: Increase mold and melt temperatures to delay fiber freeze-off and allow the polymer to better encapsulate fibers. Use higher injection speed and pressure. Polish mold surfaces to a high gloss.

3. Hydrolysis Resistance:

Cause: PBT contains ester bonds that can break in the presence of heat and moisture (hydrolysis), especially at temperatures above its glass transition temperature. This leads to a severe drop in molecular weight and mechanical properties.

Solutions: Use hydrolysis-resistant PBT grades stabilized with additives like carbodiimides, which