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日本語 Introduction
PBT polymer modification is widely used to improve the performance of polybutylene terephthalate for demanding engineering applications.
This guide covers the basic properties of PBT, common modification methods, compounding considerations, and the use of twin screw extruders in PBT modification.
What Is PBT Material?
PBT, short for Polybutylene Terephthalate, is a semi-crystalline thermoplastic polyester and a widely used engineering plastic. It is produced through the polycondensation of terephthalic acid and 1,4-butanediol.
The main polybutylene terephthalate properties include:
| Property | Typical Characteristics |
| Thermal Properties | Melting temperature of approximately 223–225°C and glass-transition temperature of around 40–60°C, depending on grade and test conditions. Many commercial PBT grades are processed at melt temperatures of approximately 250–275°C. |
| Mechanical & Processing Properties | Good rigidity, surface hardness, fatigue resistance, wear resistance, and relatively low friction. Rapid crystallization supports short injection-molding cycles and efficient processing. |
| Chemical & Environmental Resistance | Good resistance to many oils, greases, fuels, hydrocarbons, and common chemicals, with relatively low moisture absorption. However, PBT can undergo hydrolytic degradation under hot and humid conditions. |
| Electrical Properties | Good electrical insulation, making PBT widely used in connectors, relays, switches, coil bobbins, sensor housings, and other electrical and electronic components. |
| Moisture & Processing | PBT should be adequately dried before melt processing to prevent hydrolysis and molecular-weight loss. Some commercial grades specify residual moisture below approximately 0.04%, depending on the grade and supplier. |
PBT common applications include:
- Automotive Industry:Widely used in connectors, sensor housings, relays, fuse-box components, and EV electrical parts.
- Electrical and Electronics:Common applications include plugs, switches, circuit breakers, terminal blocks, coil bobbins, and lighting components.
- Industrial Machinery and Precision Engineering:Used in gears, pump impellers, valve parts, bearing cages, actuator components, and other wear-resistant machinery parts.
- Fibers and Brushes:PBT monofilament is used in toothbrushes, personal-care brushes, household-cleaning brushes, technical brushes, and industrial brushes.
- Modified PBT Compounds:Available in glass-fiber-reinforced, flame-retardant, mineral-filled, impact-modified, hydrolysis-resistant, and other grades for different engineering applications.
Why Does PBT Need Modification?
There are primarily the following five reasons:
- Pure PBT has low notched impact strength and high notch sensitivity, and often shows brittle fracture in notched specimen tests. Therefore, elastomer toughening or blending is commonly used to improve its toughness.
- Unreinforced PBT has a low heat deflection temperature and can deform under load at high temperatures.
- Standard PBT is flammable and has limited flame retardancy, making it unable to meet the requirements of some electrical applications.
- PBT has a relatively high molding shrinkage, and molded parts are prone to shrinkage and warpage, making dimensional stability difficult to control.
- The mechanical properties, flame retardancy, and heat resistance of pure PBT alone are difficult to simultaneously meet the demanding requirements of automotive, electrical, and electronic applications.
Common PBT Modification Methods and Materials
Glass Fiber Reinforcement
| Aspect | Details |
| Materials Used | Glass fiber, commonly at contents of approximately 10%, 15%, 20%, 25%, 30%, 35%, 40%, and 50%. |
| Performance Improvements | Significantly improves tensile and flexural strength, stiffness, heat deflection temperature, creep resistance, and dimensional stability, while reducing molding shrinkage and warpage. |
| Suitable Applications | Automotive connectors, sensor housings, relay frames, coil bobbins, circuit breaker components, appliance structural parts, industrial machinery parts, and electrical and electronic components. |
Flame-Retardant Modification
| Aspect | Details |
| Materials Used | Halogen-free phosphorus-based flame retardants, hypophosphite/phosphinate systems, phosphorus-nitrogen synergistic systems; compliant halogenated flame retardants and synergists are still used in some applications. |
| Performance Improvements | Improves flame-retardant performance and can enable certain PBT formulations to achieve ratings such as UL 94 V-0 at specified thicknesses and under applicable certification conditions. |
| Suitable Applications | Connectors, relays, switches, coil bobbins, charging equipment, electrical housings, home appliances, and other electrical and electronic components. |
Toughening Modification
| Aspect | Details |
| Materials Used | POE-g-GMA, E-MA-GMA, EMA-GMA, acrylic rubber, core-shell impact modifiers, selected TPU grades, or other reactive elastomers. |
| Performance Improvements | Improves notched impact strength, low-temperature impact toughness, and crack resistance while reducing notch sensitivity. |
| Suitable Applications | Automotive parts, power tool housings, impact-resistant electrical and electronic components, low-temperature parts, and materials requiring both flame retardancy and toughness. |
Mineral-Filled Modification
| Aspect | Details |
| Materials Used | Talc, mica, wollastonite, calcium carbonate, kaolin, barium sulfate, glass beads, and other mineral fillers. |
| Performance Improvements | Improves stiffness, dimensional stability, shrinkage control, and warpage control. Some fillers can also help reduce material costs, such as lower-cost talc and calcium carbonate. |
| Suitable Applications | Automotive, appliance, industrial, and building-material components requiring dimensional stability, cost control, stiffness, and low warpage. |
Polymer Blending Modification
(e.g., PBT/PC, PBT/PET, PBT/ABS, and PBT/elastomer blends)
PBT/PC
| Aspect | Details |
| Materials Used | PC, compatibilizers, impact modifiers, stabilizers, and other additives. |
| Performance Improvements | Improves impact toughness, low-temperature impact performance, and heat resistance while retaining the chemical resistance and processability of PBT. Drying, processing temperature, residence time, and transesterification reactions need to be controlled. |
| Suitable Applications | Automotive parts, power tool housings, electrical and electronic components, impact-resistant housings, and functional parts. |
PBT/PET
| Aspect | Details |
| Materials Used | PET, compatibilizers, chain extenders, impact modifiers, nucleating agents, and other additives. |
| Performance Improvements | Adjusts heat resistance, crystallization behavior, flow properties, cost, and overall processing performance. Improvements in impact toughness and warpage are not necessarily achieved in every formulation. |
| Suitable Applications | Engineering polymer blends, automotive and electrical components, and modified recycled polyester materials. |
PBT/ABS or PBT/Elastomer Blends
| Aspect | Details |
| Materials Used | ABS, SEBS, TPU, POE-type elastomers, compatibilizers, and other additives. |
| Performance Improvements | Can improve toughness, processability, or surface appearance, while heat resistance, chemical resistance, flame retardancy, and compatibility need to be balanced according to the specific formulation. |
| Suitable Applications | Power tool housings, consumer electronics housings, automotive interior parts, and components with moderate impact-resistance requirements. |
PBT Modification Compounding Process
Step 1: Raw Material Preparation
Prepare the required raw materials, including PBT resin, reinforcing materials such as glass fiber, flame retardants, toughening agents, fillers, and other additives.
Step 2: PBT Drying
PBT is hygroscopic, and moisture can cause hydrolytic degradation, so it must be thoroughly dried before processing. The dried material should be fed while still hot to prevent moisture reabsorption. After drying, the moisture content of PBT should be controlled at a sufficiently low level to reduce the risk of hydrolysis during subsequent processing.
Step 3: Formulation and Feeding
Meter PBT, fillers, toughening agents, and other materials according to the formulation, and feed them into the compounding equipment, such as a twin screw extruder.
Step 4: Melting
Heat and melt the materials in the extruder so that the PBT and additives form a melt. The barrel temperature should be controlled above the melting temperature of PBT, for example around 230–250°C in the relevant processing zones, to achieve proper plasticization.
Step 5: Filler/Additive Feeding
Glass fiber is typically introduced through a side feeder. Feeding glass fiber downstream through the side-feeding port helps reduce fiber breakage caused by excessive shear.
Step 6: Mixing and Dispersion
The screw provides shear and mixing to uniformly disperse fillers, flame retardants, toughening agents, and other additives in the PBT melt. Process parameters such as screw speed, feeding rate, and vacuum level can affect the mixing and dispersion results.
Step 7: Venting and Devolatilization
Venting and vacuum degassing can help remove residual moisture and volatile components during processing. However, proper pre-drying of PBT remains essential to minimize hydrolytic degradation.
Step 8: Extrusion
The molten material is extruded through the die to form strands.
Step 9: Cooling
The extruded strands are cooled and solidified in a water bath.
Step 10: Pelletizing
The cooled strands are cut into pellets using a pelletizer, followed by drying, screening, and packaging.
Why Is a Twin Screw Extruder Commonly Used for PBT Modification?
Reason 1: Better Suited for Multi-Component PBT Formulations
Twin screw extruders are widely used for filled modification, rubber-plastic blending, polymer alloys, glass-fiber reinforcement, flame-retardant masterbatch, and other multi-component formulations. Their good mixing, plasticizing, and conveying performance makes them well suited for PBT modification systems containing multiple components.
Reason 2: Flexible Feeding of Fibers, Fillers, and Additives
The modular barrel design allows the use of main feeders, side feeders, liquid injection ports, and loss-in-weight feeding systems, making it possible to arrange the feeding positions of different materials more flexibly.
Glass-fiber-reinforced PBT is a typical example: PBT can be melted first, and the glass fiber can then be added downstream. This reduces the shear history experienced by the fibers and helps minimize excessive fiber breakage while maintaining good distribution.
Reason 3: Devolatilization Capability for PBT Processing
Twin screw extruders are widely used in venting and devolatilization processes and can be equipped with venting and vacuum degassing sections. This helps remove moisture and volatile substances during PBT processing.
Reason 4: Modular Configuration for Different PBT Modification Processes
Different PBT formulations have different requirements for mixing intensity, temperature, residence time, feeding, and venting. Twin screw extruders use modular screw and barrel designs, allowing the screw configuration and functional zones to be adjusted according to the specific formulation. This provides greater flexibility in controlling shear and material heat history while meeting mixing and dispersion requirements.
What Should Be Considered During PBT Modification Extrusion?
1. Dry PBT and other hygroscopic materials thoroughly
Follow the resin supplier’s moisture requirements before processing, as excess moisture can cause hydrolytic degradation.
2. Control melt temperature, shear, and residence time
PBT processing temperature typically depends on the resin grade, formulation, screw configuration, and residence time. In many applications, the melt temperature is controlled in the range of approximately 250–270°C, but the actual processing window should follow the resin supplier’s recommendations.
3. Reduce fiber breakage in glass-fiber-reinforced PBT
Optimize the feeding position and mixing conditions to maintain good fiber distribution while limiting excessive breakage.
4. Balance processing conditions in polymer blends
When PBT is blended with other polymers, the processing conditions should meet the requirements of all components. For example, in PBT/PC blends, PC generally requires a higher processing temperature, while PBT is more sensitive to excessive heat.
Beyou PBT Modification Extrusion Solutions
For PBT compounding, equipment configuration should be selected according to the formulation, filler content, target output, and required material properties. Recommend suitable twin screw extruder specifications based on the formulation, filler content, and target output.
- Configure main feeding, side feeding, liquid addition, vacuum venting, and other systems as required.
- Select suitable screw configurations and wear-resistant components for different formulations.
- Provide downstream systems for cooling, pelletizing, and related processing.
Recommended Models: CTS-D Series Twin Screw Extruder
The CTS-D Series is suitable for PBT modification and compounding applications, including reinforcement, filling, flame-retardant modification, and polymer blending. Its modular screw and barrel design allows the processing configuration to be adjusted according to different formulations and production requirements.
