Polybutylene terephthalate (PBT) is a synthetic semi-crystalline engineered thermoplastic with similar properties and composition to polyethylene terephthalate (PET). It is part of the polyester group of resins and share similar characteristics to other thermoplastic polyesters. Additionally, it is a high performance material with high molecular weight and is often characterized as being a strong, stiff, and engineerable plastic. Color variations of PBT range from white to bright colors.
Use of PBT
PBT is present in everyday life and is common in electrical, electronic and automotive components. PBT resin and PBT compound are the two types of products that are used across various applications. PBT compound is comprised of various materials that can include PBT resin, fiber glass filing and additives, whereas the PBT resin only includes the base resin. The material is often used in mineral or glass filled grades.
For use outdoors and in applications where fire is a concern, additives are included to improve its UV and flammability properties. With these modifications it is possible to have a PBT product that can be used in numerous industrial applications.
PBT resin is used to make PBT fiber as well as electronic parts, electrical parts and auto parts. TV set accessories, motor cover sand motor brushes are some examples of the use of PBT compound. When reinforced, it can be used in switches, sockets, bobbins and handles. The unfilled version of PBT is present in some brake cable liners and rods.
When a material with high strength, good dimensional stability, resistance to various chemicals and good insulations is needed, PBT is a preferred choice given its excellent characteristics. The same is true when bearing and wear properties are determining factors in material selection. For these reasons, valves, food processing machinery components, wheels, and gears are also made from PBT. Its application in food processing components is largely due to its low moisture absorption and its resistance to staining. It also does not absorb flavors.
Advantages of PBT
Some of the major advantages of PBT are evident in its resistance to solvents and low shrinkage rate when forming. The material also has good electrical resistance and due to its fast crystallization is easy to mold. It also has excellent heat resistance for up to 150oC and melting point reaching 225oC. The addition of fibers enhances its mechanical and thermal properties allowing it to withstand higher temperatures. Other notable advantages include:
- Excellent stain resistant
- Excellent machining characteristics
- High strength
- Excellent stiffness-to-weight ratio
- Resistance to environmental changes
- Excellent machining characteristics
- Better impact resistance compared to PET
- Excellent dimensional stability
- Blocks UV radiation
- High electrical insulation properties
- Good variety of grades available on the market
Disadvantages of PBT
Despite the numerous advantages of PBT it does have disadvantages that limit its application in some industries. Some of these disadvantages include:
- Lower strength and rigidity than PET
- Lower glass transition temperature than PET
- Prone to warp when glass is used as a filler
- Does not present satisfactory resistance to acids, bases and hydrocarbons
Future of PBT Plastics
The demand of PBT has regained footing after the economic crisis in 2009 caused various industries to lower production of certain materials. With the growing population in some countries and new innovations in the automotive, electrical and electronic industry, the use of PBT will steadily increase for the future. This reality is more apparent in the automotive industry given its increasing need for lighter, more resistant materials that require little maintenance and are cost competitive.
The use of engineer-grade plastics such as PBT will increase due to issues surrounding corrosion of metals and exorbitant costs to implement measures that minimize of eradicate this problem completely. Many designers are looking for alternatives to metals and are turning to plastic as the solution. A new grade of PBT that offers better results in laser welding has been developed thus providing a new solution to welded parts.
Asia-Pacific is the leader in the use of PBT and this reality has not shifted even after the economic crisis. In many Asian countries PBT is mostly used in the electronic and electrical markets. This is not the same in North America, Japan and Europe where PBT is mostly used in the automotive industry. It is believed that by the year 2020, the consumption and production of PBT in Asia will considerably increase compared to Europe and the USA. This reality is reinforced with the numerous foreign investments in the region and the need to have materials at a lower production cost which is not feasible in many Western countries. The closing of the Ticona PBT facility in the USA in 2009 and the absence of new facilities to undertake the production of PBT resin and compounds in Europe are contributing reasons for the decline and low production of PBT in the Western world. China and India are two emerging countries that promise to show evident increase in their consumption of PBT.