What Is Polybutylene Terephthalate (PBT)?
Polybutylene terephthalate (PBT) is a thermoplastic polyester that is one of the engineering plastics.
It is usually abbreviated as PBT (Poly Butylene Terephthalate) and also known as polytetramethylene terephthalate (PTMT).
PBT has a structure in which the number of carbons in the alkyl chain of polyethylene terephthalate (PET) has been increased from 2 to 4, and it has the same properties as PET.
Basically, it is a relatively easy material to handle because of its high stability and lack of known toxicity.
Uses of Polybutylene Terephthalate (PBT)
Polybutylene terephthalate (PBT) is used as a material for a variety of products because of its good mechanical properties, high heat resistance, high chemical resistance, and good processability. In the US, polybutylene terephthalate is mostly used in the automotive field, while in Japan it has been mainly used in the electrical and electronics fields. In recent years, the use of this material has been increasing in the automotive field, particularly due to its lightweight characteristics.
1. Automotive Field
- Ignition coils
- Wiper arms
- Distributors
- Switches
- Headlight housings
- Motor parts
- Valves
- Gears
- Exhaust and safety related parts
2. Electrical and Electronic Fields
- Switches
- Connectors
- Sockets
- Relays
- Housings
- Motor parts
3. Others
Food packaging, camera parts, watch parts, gears, cams, bearings, etc.
Characteristics of Polybutylene Terephthalate (PBT)
Polybutylene terephthalate (PBT) has a melting point of 225°C, a deflection temperature under load of 65°C (1.8 kPa), a tensile strength of 56 kPa, and a flexural strength of 81 kPa. Polybutylene Terephthalate (PBT) is often used as a composite material. For example, PBT composites with 30% glass fiber can significantly increase mechanical properties, with a deflection temperature of over 200°C, tensile strength of 127 kPa, and flexural strength of 186 kPa, while maintaining the same electrical properties and dielectric constant.
In addition to its excellent mechanical properties, polybutylene terephthalate (PBT) also offers electrical properties, chemical resistance, heat resistance, abrasion resistance, low water absorption, and excellent dimensional stability. In addition, because it is made from relatively inexpensive raw materials, 1,4-butanediol and terephthalic acid, it offers an excellent balance between cost and performance, making it competitive enough against other engineering plastics.
Other Information on Polybutylene Terephthalate (PBT)
How Polybutylene Terephthalate (PBT) Is Produced
Polybutylene terephthalate (PBT) is produced by direct polymerization, which is an esterification reaction of 1,4-butanediol and terephthalic acid, or by DMT, which is an ester exchange reaction of 1,4-butanediol and dimethyl terephthalate.
1. Direct Polymerization Method
Bis-hydroxybutyl terephthalate (BHT) is synthesized by reacting 1 mole of terephthalic acid with 2 moles of 1,4-butanediol at 150~230℃ for 60~120 minutes under normal pressure. Polybutylene terephthalate (PBT) is then obtained by setting the temperature to 250~270°C and reduced pressure conditions below 133 Pa, and proceeding with polymerization while removing the 1,4-butanediol and tetrahydrofuran that are produced. Titanium-based catalysts are often used as catalysts for esterification.
2. The DMT Method
BHT is synthesized by reacting 1 mole of dimethyl terephthalate with 2 moles of 1,4-butanediol at 150~200℃ for 60~120 minutes under normal pressure, similar to the direct polymerization method. The reaction is carried out while removing methanol that is produced during the reaction.
The amount of 1,4-butanediol is 2 moles of dimethyl terephthalate, but the reaction time depends on this amount ratio, and the smaller the molar ratio, the faster the ester exchange rate can be increased. Polybutylene terephthalate (PBT) is obtained from the generated BHT in the same way as in the direct polymerization process.
Polybutylene terephthalate (PBT) obtained by polymerization is blended with glass fiber to make glass fiber-reinforced grades, or with additives such as flame retardants to increase flame retardancy, and is then commercialized.