Polybutylene Terephthalate (PBT) - Kehui Mold Co., Limited

What is PBT?

PBT (Polybutylene Terephthalate) is a semi-crystalline thermoplastic polyester known for its excellent mechanical strength, chemical resistance, and electrical insulation properties. It belongs to the same polyester family as PET (Polyethylene Terephthalate) but offers faster crystallization and better processability, making it ideal for injection molding and high-performance engineering applications.

Key Characteristics of PBT:

High stiffness & dimensional stability
Good resistance to heat (up to ~150°C continuous use)
Low moisture absorption (better than Nylon)
Excellent electrical insulation (used in connectors, switches)
Resistant to oils, fuels, and solvents

Key Properties & Advantages

Property	Value/Description
Melting Point	~225°C (437°F)
Tensile Strength	50-60 MPa (GF-reinforced: up to 120 MPa)
Chemical Resistance	Resistant to fuels, oils, solvents, and weak acids
Electrical Properties	Excellent dielectric strength & arc resistance
Moisture Absorption	Low (~0.1-0.2%), better than Nylon

Why Choose Polybutylene Terephthalate?

Fast cycle times (due to rapid crystallization)
Good creep resistance (maintains shape under load)
Flame-retardant grades available (UL94 V-0 compliance)
Good fatigue resistance (suitable for moving parts)

Common Applications of Polybutylene Terephthalate

Connectors, sensors, ignition components
Under-the-hood parts (e.g., throttle bodies, fuel system components)
Circuit breakers, relays, switches
Insulating housings for power tools
Kitchen appliance parts (e.g., blender housings）
Zippers, snap-fit fasteners
Pump components, gears

PBT vs. Other Engineering Plastics

Property	PBT	PET	Nylon (PA6/PA66)	POM (Acetal)
Strength	High	Higher	Very High	High
Moisture Absorption	Low	Low	High	Low
Chemical Resistance	Excellent	Good	Good	Excellent
Processing Ease	Easy	Moderate	Moderate	Easy

Key Takeaways:

PBT vs. PET: PBT has better flow properties and faster molding cycles, while PET has higher strength and thermal resistance.
PBT vs. Nylon: PBT absorbs less moisture, making it more dimensionally stable in humid conditions.
PBT vs. POM: POM has better wear resistance, but PBT offers superior electrical insulation.

Typical values of PBT

Mechanical Property
Elongation at Break	5-300%
Elongation at Yield	3.5-9%
Flexibility (Flexural Modulus)	2-4 GPa
Hardness Rockwell M	70-90
Hardness Shore D	90-95
Stiffness (Flexural Modulus)	2-4 GPa
Strength at Break (Tensile)	40-50 MPa
Toughness (Notched Izod Impact at Room Temperature)	27-999 J/m
Toughness at Low Temperature (Notched Izod Impact at Low Temperature)	27-120 J/m
Young’s Modulus	2-3 GPa
Electrical Property
Arc Resistance	124-190 sec
Dielectric Constant	2.9-4
Dielectric Strength	15-30 kV/mm
Dissipation Factor	10-200 x 10^-4
Volume Resistivity	14-17 x 10¹⁵ Ohm.cm
Physical property
Shrinkage	0.5-2.2%
Water Absorption 24 hours	0.1-0.2%
Density	1.3-1.4 g/cm³
Glass Transition Temperature	55-65°C
Thermal Property
Coefficient of Linear Thermal Expansion	6-10 x 10^-5 /°C
Thermal Insulation (Thermal Conductivity)	0.21 W/m.K
Fire Resistance (LOI)	20-24%
Flammability UL94	HB
Service Temperature
Ductile / Brittle Transition Temperature	-40°C
HDT @0.46 MPa (67 psi)	115-150°C
HDT @1.8 MPa (264 psi)	50-85°C
Max Continuous Service Temperature	80-140°C
Min Continuous Service Temperature	-40°C

PBT is a versatile engineering plastic that balances mechanical strength, chemical resistance, and electrical properties. Its fast processing and reliability make it a top choice for automotive, electronics, and industrial applications.