PC/PBT Alloy: Properties, Processing & Applications
PC/PBT alloy is an engineering plastic blend produced by compounding polycarbonate
(PC) with polybutylene terephthalate (PBT). The material combines the rigidity and
toughness of PC with the chemical and thermal stability of PBT, delivering high
toughness, good chemical resistance, strong resistance to stress cracking,
excellent paintability, and low moisture absorption. It is widely used in
automotive bumpers, lighting technology, electronic components, and many other
fields.
# Key Properties
– **Heat Resistance: **PC/PBT alloy offers good heat resistance, retaining its
strength and stability at elevated temperatures, and can typically withstand
temperatures above 150°C.
– **Impact Resistance: **PC/PBT alloy delivers outstanding impact strength at room
temperature, making it suitable for parts and components that require impact-
resistant performance.
– **Chemical Resistance: **PC/PBT alloy has good resistance to a range of
chemicals, withstanding attack from certain solvents and chemical agents.
– **Electrical Insulation: **As a good electrical insulating material, PC/PBT
alloy is used in electronic and electrical applications to prevent current leakage
and ensure safe operation of equipment.
– **Dimensional Stability: **PC/PBT alloy resists dimensional change across a
range of temperatures, making it suitable for applications requiring precise
dimensions, such as medical equipment.
– **Good Surface Quality: **PC/PBT alloy can produce smooth parts with good
surface finish, suitable for applications with high appearance requirements, such
as consumer electronics.
– **Weatherability: **PC/PBT alloy maintains its performance and appearance over
long periods outdoors, making it suitable for automotive exterior trim and outdoor
lighting equipment.
– **Processability: **The addition of PBT gives PC/PBT alloy better processing
performance, including good flow, lower melt viscosity, and a wide processing
temperature window.
# 1. Effect of Processing Temperature on PC/PBT Alloy PropertiesIn these trials the twin-screw extruder speed was fixed at 450 r/min and the feed
rate at 100 kg/h.
## 1.1 Mechanical Properties
Variations in processing temperature have little effect on the tensile and
flexural properties of PC/PBT engineering plastic. At 250°C the notched Izod
impact strength reaches its highest value; as temperature rises further, notched
Izod impact strength declines. PC/PBT is a typical blend of an amorphous polymer
and a crystalline polymer, and its interfacial adhesion is poor, giving low impact
strength. When PC and PBT undergo a transesterification reaction, an intermediate
product is formed that promotes bonding at the PC/PBT interface and improves
performance. However, as temperature increases further (275°C and above), the
reaction becomes random and uncontrollable, and varying degrees of internal
degradation cause the notched impact performance to fall instead.
## Melt Mass-Flow Rate (MFR)
The melt mass-flow rate of the material increases as processing temperature rises,
mainly due to the transesterification reaction. Under dry conditions, the thermal
stability of PC is better than that of PBT, and the thermal degradation rate
constant of PBT is only on the order of about 0.0001/min. As temperature rises,
the degree of transesterification increases further; the average block length of
the resulting block copolymer gradually becomes shorter, which lowers the system
viscosity and improves flow.
## Heat Resistance
As temperature rises, the heat deflection temperature of the material decreases.
This is mainly because an increased degree of transesterification further reduces
the molecular weight of the material — particularly the PC, which provides heat
resistance and gradually degrades. When heated, the molecular chain segments move
more easily, so the heat deflection temperature falls accordingly.
# 2. Effect of Screw Speed on PC/PBT Alloy Properties
In these trials the twin-screw extruder feed rate was fixed at 100 kg/h and the
processing temperature set to 250°C.
## 2.1 Mechanical Properties
Change
s in screw speed have little effect on the tensile and flexural properties
of the material. However, as screw speed increases, the notched Izod impact
strength rises slightly. Higher screw speed increases the shear and dispersive
action of the extruder screw, so the PC resin, PBT resin, toughening agent, and
other components are distributed more uniformly in the barrel, giving bettermaterial performance.
## Melt Mass-Flow Rate (MFR)
As screw speed
increases, the melt flow rate of the material also rises
substantially. On one hand, higher screw speed strengthens the shear and
dispersive action of the extruder screw, so the PC resin, PBT resin, toughening
agent, and other components are dispersed more uniformly in the barrel, reducing
the material’s flow resistance.
On the other hand, higher screw speed generates more shear heat; this heat
promotes the transesterification reaction, the average block length of the block
copolymer gradually becomes shorter, and material flow consequently improves.
## Heat Deflection Temperature
As screw speed increases, the heat deflection temperature of the material shows a
gradual downward trend. On one hand, the material undergoes slight degradation,
with chain segments becoming shorter due to increased shear; on the other hand,
the higher degree of transesterification lowers the molecular weight, so chain-
segment motion occurs more readily when the material is heated, causing the heat
deflection temperature to fall.
# 3. Scanning Electron Microscopy (SEM)
SEM images of the fracture surfaces of impact bars after brittle fracture,
prepared under different process conditions.
Temperature comparison: when the extrusion temperature is low, the PC and PBT
phases are distinct with a clear boundary, indicating poor compatibility between
the two. As the temperature rises to 300°C, the boundary between PC and PBT
becomes blurred — though still distinguishable — indicating that the compatibility
of PC and PBT is greatly improved at higher temperatures.
Screw-speed comparison: as the speed increases from low to high, the phase
boundary between PC and PBT also becomes less distinct, but less markedly than the
change seen from low to high temperature. The degree of reaction between PC and
PBT is influenced more by temperature than by shear intensity.
# 4. Summary of Findings
– The higher the processing temperature, the greater the degree of
transesterification, the better the material flow, and the poorer the heat
resistance.
– Temperatures that are too low or too high result in poor toughness; processing
temperature should be maintained at around 250°C.- Within the 300–600 r/min range, increasing screw speed improves dispersion and
gives better mechanical properties.
– Higher screw speed produces a greater degree of transesterification, increasing
flow and reducing heat resistance.
– From the SEM analysis, the degree of reaction between PC and PBT is relatively
less affected by shear; temperature plays the more decisive role.
## 4.1 Application Areas
### Automotive
– **Applications: **Automotive bumpers, grab handles, luggage racks, wiper
components, door handles, instrument panels, door interior trim, EV charging
stations, charging guns, and similar parts.
– **Role: **PC/PBT alloy offers excellent toughness, chemical resistance, heat
resistance, and dimensional stability, meeting automotive requirements for high
strength, impact resistance, wear resistance, and chemical-corrosion resistance,
while keeping precise dimensions and good appearance.
### Electrical & Electronics
– **Applications: **Electronic components, appliance housings, appliance handles,
connectors, electrical switches, and similar parts.
– **Role: **PC/PBT alloy has good electrical insulation and good resistance to
certain chemicals, withstanding attack from some solvents and chemical agents,
making it well suited for housings and internal components of electrical and
electronic products.
### Floor-Cleaning / Mopping Robots
PC/PBT alloy is suitable for structural and functional components in robotic
floor-cleaning and mopping devices, where toughness, dimensional stability, and
good surface finish are required.
### Medical Equipment
– **Applications: **PC/PBT alloy is also used to manufacture components for
medical equipment, such as instruments and parts requiring high chemical
resistance, heat resistance, and dimensional stability.
– **Role: **The all-round performance of PC/PBT alloy meets the demanding material
requirements of medical equipment, ensuring reliability and safety.Example: thin-wall handheld ultrasound devices benefit from PC/PBT alloy. The
relevant material is a thin-wall moulding grade of PC/PBT, which must offer
chemical resistance, weatherability, and high flow.
### Other Fields
– **Communication Equipment: **PC/PBT alloy can be used for the housings and
internal components of communication equipment, meeting requirements for high
strength, wear resistance, and chemical-corrosion resistance. Applications include
satellite-navigation equipment.
– **Aerospace: **In the aerospace field, PC/PBT alloy is also used to manufacture
parts that must withstand high-temperature and high-pressure environments.
## 4.2 Development Trends
PC/PBT alloy materials are evolving toward higher performance, expansion into
high-end applications, environmental sustainability, and growing market demand.
The material combines the rigidity and toughness of PC with the chemical and
thermal stability of PBT, offering high toughness, chemical resistance, and low
moisture absorption, and is widely used in automotive, electronics, and other
fields. As environmental awareness grows, demand is rising for eco-friendly
products such as halogen-free flame-retardant PC/PBT, particularly in fields with
high environmental and safety requirements such as new-energy-vehicle battery
systems. At the same time, development of the automotive industry is driving the
broad application of PC/PBT in interior and exterior trim, engine-surrounding
components, and more.