What is PBT? Definition, Types, Properties

Global companies are constantly seeking innovative solutions to reduce costs and enhance efficiency. One effective strategy is to utilize lighter and more affordable materials and components, where PBT becomes essential.

PBT (Polybutylene Terephthalate) is a crystalline linear saturated polyester. PBT resin is widely used in fields such as electronics, automotive, machinery, instrumentation, and household appliances due to its excellent mechanical properties, electrical properties, thermal resistance, and processing capabilities, particularly its overall superior performance.

In this article, we will delve into these advantages and discuss why many manufacturers prefer PBT over other materials. Additionally, we will examine the key properties of PBT to highlight the value it brings to diverse applications.

What is PBT material?

Polybutylene Terephthalate (PBT) is a polyester made by the polycondensation of terephthalic acid and 1,4-butanediol. It is an important thermoplastic polyester and one of the five major engineering plastics.

Polybutylene Terephthalate is a milky white, translucent to opaque, semicrystalline thermoplastic polyester with high heat resistance. It is not resistant to strong acids and strong bases, but it can withstand organic solvents. It is flammable and decomposes at high temperatures.

Blended PBT Material

The mechanical properties of pure PBT resin are general, and after modification by adding other substances, it can not only maintain the original advantages of chemical resistance and processability of PBT resin, but also greatly improve its mechanical properties.

PBT+Glass Fiber (PBT GF20, PBT GF30)

PBT has good impact toughness, by adding 20%-30% glass fiber reinforcement, its density increased, while various mechanical properties doubled, under the same conditions than POM, PC, and PPO various strengths are better.

PBT has a low glass transition temperature, typically around 30°C, and it crystallizes quickly. The heat distortion temperature of PBT is 60°C, but this value significantly increases when reinforced with glass fibers. PBT reinforced with 30% glass fibers has a heat distortion temperature of 200-210°C, allowing it to be used safely at conditions around 140°C for long periods. These characteristics make PBT perform better than PA and other reinforced plastics in high temperatures and harsh environments.

Flame retardant-modified PBT

PBT resin is flammable and difficult to carbonize, and it tends to melt and drip continuously when burned, leading to a risk of fire spread. In the case of glass fiber-reinforced PBT, the addition of glass fibers improves the mechanical properties of PBT and introduces the “wick effect,” which makes the material in the flame zone less prone to melting droplets (anti-drip effect). However, this also leads to heat accumulation, thereby increasing the difficulty of flame retardancy for glass fiber-reinforced PBT. To address this issue and ensure the safety of PBT resin, flame retardants are typically introduced to glass fiber-reinforced PBT for flame-retardant modification.

Alloy modified PBT

PBT is a linear saturated resin that crystallizes easily. Additionally, the anisotropy caused by the orientation of glass fibers during processing makes plastic products prone to warpage and deformation. PBT has good compatibility with other resins, and due to the short development cycle and low cost of blending modification, blending is widely used for its modification both domestically and internationally. The polymers commonly blended with PBT for modification include PC, PET, ABS, PP, and elastomers.

PC/PBT Alloy

Polycarbonate (PC) has excellent properties and can be melt blended with PBT at any ratio under temperatures exceeding PC’s glass transition temperature of 150 °C. The resulting PC/PBT alloy can overcome the shortcomings of PC’s processing properties and wear resistance while compensating for PBT’s deficiencies in notch impact strength, impact resistance, and heat resistance. 

PET/PBT Alloy

Polyethylene terephthalate (PET) shares similar solubility parameters with PBT and has a similar chemical structure, resulting in good compatibility in their mixed system, which only exhibits a single glass transition temperature. 

ABS/PBT Alloy

Acrylonitrile-butadiene-styrene (ABS) has excellent mechanical properties and good resistance to chemicals, wear, heat, and low-temperature impact, making it a widely used engineering plastic for impact modification. Blending PBT with ABS not only reduces the shrinkage rate of the PBT finished product but also allows the rubber phase in ABS to enhance the notch impact strength of PBT. Research indicates that by appropriately adjusting the structure of ABS and increasing the rubber phase content to 50%–60%, the toughening of PBT under low-temperature conditions can be achieved. Furthermore, increasing the grafting rate of ABS can enhance the impact strength of ABS/PBT alloys.

PP/PBT Alloy

Polypropylene (PP) is inexpensive, readily available, and possesses excellent processing performance, making it an important general-purpose resin. Compared to ABS/PBT alloys, PP/PBT alloys offer better heat resistance and chemical corrosion resistance.

PBT Blended with Elastomers

Using elastomers for toughening is a primary method of modifying PBT to enhance its toughness. Typically, PBT is blended with nitrile rubber, ethylene-propylene-diene rubber, butyl rubber, or polyisobutylene rubber to improve its impact performance. To ensure a uniformly dispersed granular structure when blending PBT with rubber elastomers, a suitable amount of compatibilizers is added during blending. 

PBT Blended with Other Polymers

In addition to the aforementioned materials, several other compatibilizers, such as PU, SBS, EPDM, POE, ASA, and EVA, have been explored for melt blending modification of PBT. Future research on PBT modification should focus on reducing costs and meeting environmental requirements, while also further improving performance indicators to diversify functionalities, create a range of products, and maximize added value.

What are the properties of PBT plastic material?

Mechanical Properties:

PBT plastic has excellent mechanical properties, featuring high strength, stiffness, and resilience. Its tensile strength and elastic modulus are relatively high, allowing it to maintain stable performance under complex stress conditions, making it resistant to deformation or cracking. In addition, PBT material also exhibits good impact resistance, making it less likely to crack upon external force impact, thereby protecting the integrity of the encapsulated objects.

Thermal Properties:

PBT material has good thermal stability and heat resistance, capable of maintaining stable physical properties at elevated temperatures. Its heat deflection temperature is quite high, making it less prone to softening or deforming in high-temperature environments, which makes it suitable for applications requiring high-temperature stability. Furthermore, PBT material also exhibits good heat aging resistance, allowing it to maintain stable performance over long periods in high-temperature conditions.

Insulation Properties:

PBT material has excellent insulation properties, effectively blocking the conduction of electric current, making it suitable as an insulating material in the electronics and electrical appliance fields. Its insulation performance is stable, not easily affected by moisture or aging, allowing it to maintain good insulation properties over time, ensuring the safe and reliable operation of equipment.

PBT Limitation:

• Not resistant to strong acids and strong bases.
• Has moisture absorption properties, which can lead to dimensional changes and reduced mechanical performance. Therefore, controlling the moisture content during the manufacturing and using PBT products to maintain its excellent performance.
• Compared to other common plastic materials, such as polypropylene (PP) and polyethylene (PE), PBT is relatively expensive. 

Is Material PBT right for your project?

PBT is a versatile engineering plastic that offers an optimum combination of mechanical strength, heat resistance, and electrical insulation. If you need components that will perform well under varying thermal conditions or need insulated function, PBT is worth considering.