PC/PBT Resin Plastic Material Blend (polycarbonate / polyester blend) is a thermoplastic alloy of amorphous polycarbonate and semi-crystalline polyester (either polybutylene terephthalate or polyethylene terephthalate). PC/PBT provides a combination of chemical resistance, temperature resistance, and mechanical strength.
Our polymer compounding technology allows us to prepare alloys of Polycarbonate (PC) and Polyesters (either PBT or PET).
PBT Material Properties
Polycarbonate (PC) is used in many applications because PC provides excellent toughness, high rigidity, and good heat resistance. Polycarbonate does have a weakness with resistance to organic chemicals. Polyesters such as PBT plastic and PET have a very high resistance to organic chemicals because they are semi-crystalline. These materials are also rigid and can hold up to high temperatures. The crystallinity of polyesters causes them to have both high specific gravity and high shrinkage values. Polyesters such as PBT and PET also have very low notched Izod impact values.
With our compounding extruders, Polymer Resources can blend PC and either PBT material or PBT into polymer alloys that combine the desirable properties of both PC and the polyester, and that minimize the less desirable properties. These alloys offer the toughness of PC along with the chemical resistance of the polyesters. Chemical resistance can be “fine-tuned” by varying the ratio of PC to polyester. Specific gravity and shrinkage of these alloys are less than that of polyesters and greater than that of PC.
The properties of our PC/PBT alloys can be further enhanced by the addition of additives during compounding. Impact modifiers can be added to provide products with a very good low-temperature impact. Flame retardants can be added to provide products with UL 94 V-0 ratings. Glass fibers can be added to provide products with high flex strength. Stabilizers can be added to improve resistance to UV radiation and to improve thermal stability. Also, colorants can be added in order to provide a specific property profile in any given color.
Additives, Modifiers, and Reinforcing Agents:
- Additives – UV stability, easy release (mold releases), colorants, and other stability additives
- Modifiers – Flame retardants, impact modifiers, flow enhancers
- Reinforcing Agents – Glass fibers, mineral filler
What is Polybutylene Terephthalate (PBT)?
Polybutylene Terephthalate (PBT) is a semi-crystalline engineering thermoplastic material. It has similar properties and composition to polyethylene terephthalate (PET). It is a member of the polyester family of polymers.
PBT has gained commercial interest due to its wide range of applications. These range from automotive, electrical and electronics, medical, and many more.
The PBT product range includes a wide variety of grades which are great for injection molding. These include:
- Reinforced
- Filled
- Impact-modified, and
- Flame-retardant
The unfilled PBT grades have a wide range of melt viscosities. This helps to provide processing latitude in injection molding and extrusion techniques. These techniques include melt-blowing of PBT fibers to the production of rod and slab, fiber optic buffer tubes, or brake cable liners.
Flame-retardant PBT and lubricated PBT versions are also available in both filled and unfilled grades. When compared to non-reinforced resins, glass-reinforced PBT grades exhibit increased mechanical properties. This means a 2 to 3-fold increase in tensile, moduli, flexural, and compressive strengths.
The broad use of PBT is also shown by the numerous regulatory approvals held by various grades. These include:
- VDE or UL approvals for the electrical and electronics market
- FDA approval for the nutrition and medical market.
What are the properties of PBT?
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- Physical properties – PBT provides dimensional stability and low moisture absorption characteristics. It gives good durability under thermal stress and/or harsh chemical environments. Can be particularly seen in automotive underhood applications.
- Mechanical properties – PBT delivers high strength, toughness, and stiffness. All over it shows a good practical impact. It provides good creep resistance over steady and elevated temperatures.
- Thermal properties – PBT has a high heat-deflection temperature and high-temperature index rating. It helps components withstand both short-term thermal excursions and long-term heat exposure.
- Electrical properties – PBT protects electrical and electronic components against discharge. It provides high electrical resistance and dielectric strength. It also guards the components against leakage and breakdown in power circuitry. The low dielectric loss minimizes energy absorption in high-frequency electronic uses.
- Chemical resistance – PBT has robust chemical resistance to a wide range of chemicals. These include diluted acids, alcohols, aromatic hydrocarbons, ketones, solvents, oils, and greases. Suitable to produce plastic parts exposed to organic solvents, gasoline, and oils. It also avoids erosion after a period of time. It exhibits good resistance to UV radiation and stain.
- Other benefits – PBT has excellent heat aging behavior and machining characteristics. It enables efficient use of material to reduce weight and cost. It is compliant with many agency and regulatory approvals for food, medical, and potable water applications.
How can material properties be tailored?
Material properties can be tailored during compounding. This is done by incorporating fillers, reinforcers, and additives to meet end-user requirements.
For example, a benzotriazole-type UV stabilizer is generally used with PBT. It offers low initial color and good color stability.
What happens when PBT alloys with other thermoplastics?
Deliver engineering properties in a ductile, chemically resistant resin.
Give designers the ability to provide toughness. They do not compromise on mechanical performance and /or environmental resistance.
Remain ductile down to -40°C yet retains functional stiffness in a hot car interior. Specialty grades withstand the difficult performance requirements of safety equipment. These types of equipment include airbag doors and containers.
They show high electrical resistance, dielectric strength, and ductility. They also provide good chemical resistance to oils, greases, and fuels. These properties combine to meet demanding heat shock criteria. Possible use in under-the-hood power distribution boxes and distributor-less ignition systems, etc.
Perform (weatherable grades) in outdoor electrical applications, such as splice cases. Polyester flame-retardant technology can also be used in these alloys.
Polycarbonate/Polybutylene Terephthalate (PC/PBT) Blend
Polycarbonate and PBT have comparable tensile strength and flexural strength.
- The polycarbonate component adds resistance to impact, heat, and stiffness.
- The polybutylene terephthalate component provides chemical resistance.
Polycarbonate/polybutylene terephthalate blends retain their toughness even at low temperatures. They offer improved resistance to fuel and weather. The polycarbonate suppresses the moisture sensitivity of crystalline polybutylene terephthalate in the blend.
- PC blends show a higher modulus than that of PC alone.
- Blending a small quantity of polyester can improve the flexural modulus of PC.
- The impact strength of PC is higher. This property considerably improves for all polyester-rich blends.
PC/PBT blends have poor miscibility as compared to other PC/polyester blends.
- Automotive/transportation – Bumpers, tailgate outer panels, door handles, tractor hoods
- Household/consumer goods – Chain saw housings, power drill housings, and
- Others – Electrical enclosures, Double glazing spacer bars, etc.
Polyethylene/Polybutylene Terephthalate (PE/PBT) Blend
When PBT blends with 15-25% low density polyethylene, the following changes can happen:
- The processing can increase.
- The mechanical properties can enhance.
- The moisture consumption can reduce.
What are the benefits of PBT over other thermoplastics?
- Lower melting point
- PBT: (223°C [433°F])
- PET: (255°C [491°F])
- Lower strength and rigidity
- Lower glass transition temperature
- Better impact resistance
PBT is often preferred over Polyethylene Terephthalate (PET). It has excellent flow in the molten state combined with its rapid crystallization. This benefit makes it more cost-effective in injection molding applications.
In some areas, PBT is replacing other crystalline thermoplastics. These include polypropylene, nylon and acetal for improved performance. PBT can compete with many amorphous engineering materials such as polysulfone and polycarbonate.
What are the methods for processing PBT?
PBT grades are processed mainly by injection molding at 230°C to 270°C temperature range. They can also be processed by extrusion and blow molding. Unreinforced PBT is also used in special extrusion and fiber spinning processes.
A variety of PBT grades are also offered for other processes. These processes include profile, tube, and monofilament extrusion. They are also produced by melt-blown and spun-bond processes.
An optimum cooling temperature of 250-275°F for 2-4 hours will produce the best results.
Injection Molding Conditions
- Before injection molding, pre-drying is recommended to control moisture content below 0.02%
- Mold Temperature: 40-80°C
- Mold Shrinkage: Higher the mold temperature, greater the shrinkage
- Unfilled: 1.4-2.0%
- Glass-fiber Reinforced: 0.4-0.6%
- Injection Pressure: 100-140 MPa / 1000-1400
- Bar Screw: Graded three-zone screw with L/D ratio of 15-20 & compression ratio of 2.5-3.0
PBT can be joined together in a number of different ways. These include ultrasonic, hot plate, friction, and hot gas welding. PBT also can be joined by two-component adhesives.
What are the limitations of PBT?
- High mold shrinkage
- Poor resistance to hydrolysis (sensitive to hot water)
- Prone to warping due to high differential shrinkage
- Unreinforced PBT is notch sensitive
- Low HDT @ 60°C (140°F) compared to competitive materials
