Polycarbonate, also called PC resin, is widely used in transparent parts, electrical housings, lighting covers, medical devices, safety shields, automotive components, and high-performance engineering applications.
Many buyers and engineers search for the polycarbonate melting point when they need to evaluate heat resistance, molding temperature, or application limits. However, PC is different from many semi-crystalline plastics such as PP, PA6, PA66, POM, and PBT.
Polycarbonate does not have a sharp melting point in the same way as crystalline plastics. Instead, PC is an amorphous thermoplastic. Its most important thermal indicators are usually:
- Glass transition temperature, or Tg
- Vicat softening temperature
- Heat deflection temperature, or HDT
- Processing temperature
- Continuous use temperature
- Thermal degradation temperature
Understanding these values is important for correct material selection, mold design, injection molding setup, and final part performance.
1. Does Polycarbonate Have a Melting Point?
Strictly speaking, polycarbonate does not have a true crystalline melting point because it is an amorphous thermoplastic.
Unlike crystalline plastics, PC does not suddenly melt at one fixed temperature. Instead, it gradually softens as temperature rises. When the temperature is high enough, the material becomes rubbery, then viscous, and finally processable as a melt.
This is why the phrase polycarbonate melting point is commonly used in search and communication, but technically it is not the best term.
For PC resin, engineers should focus more on:
- Tg
- Vicat softening temperature
- HDT
- Melt processing temperature
- Service temperature
- Degradation temperature
Simple explanation
For practical engineering communication:
| Search Term | Technical Meaning |
| Polycarbonate melting point | Common search phrase, but not technically exact |
| PC melting point | Usually refers to processing or softening range |
| Polycarbonate Tg | More accurate thermal transition value |
| PC softening temperature | Useful for heat deformation risk |
| PC processing temperature | Important for injection molding and extrusion |
| PC heat resistance | Depends on Tg, HDT, part load, and application time |
So, if a customer asks, “What is the melting point of polycarbonate?”, a better answer is:
Polycarbonate is an amorphous thermoplastic, so it does not have a sharp melting point. Its glass transition temperature is typically around 145–150°C, and it is usually processed at much higher melt temperatures during injection molding or extrusion.
2. Why PC Is Different from Crystalline Plastics
To understand the thermal behavior of PC, it is useful to compare amorphous and semi-crystalline plastics.
Amorphous plastics
Amorphous plastics have a random molecular structure. They do not form large crystalline regions. As temperature increases, they soften gradually instead of melting sharply.
Common amorphous plastics include:
- PC
- PMMA
- ABS
- PS
- PSU
- PES
- PEI
Semi-crystalline plastics
Semi-crystalline plastics have both amorphous and crystalline regions. Their crystalline areas melt at a relatively clear melting temperature, usually called Tm.
Common semi-crystalline plastics include:
- PP
- PE
- PA6
- PA66
- PBT
- PET
- POM
- PPS
- PEEK
Comparison table
| Item | Amorphous PC | Semi-Crystalline Plastics |
| Molecular structure | Random, non-crystalline | Contains crystalline regions |
| True melting point | No sharp melting point | Has clear Tm |
| Main thermal transition | Tg | Tg and Tm |
| Softening behavior | Gradual softening | Clear melting of crystals |
| Shrinkage | Usually lower and more uniform | Usually higher and more directional |
| Transparency | Often transparent | Often opaque or translucent |
| Processing window | Controlled by viscosity and degradation | Controlled by melting and crystallization |
PC belongs to the amorphous group. This is why Tg and softening behavior are more meaningful than a single melting point value.
3. Key Thermal Terms for Polycarbonate
When evaluating PC resin, engineers should understand the following thermal terms.
3.1 Glass Transition Temperature, Tg
The glass transition temperature, or Tg, is the temperature range where PC changes from a hard, glassy state to a softer, rubbery state.
For standard bisphenol-A polycarbonate, Tg is commonly around 145–150°C.
Below Tg, PC is rigid and dimensionally stable.
Near or above Tg, PC starts to lose stiffness quickly.
Above Tg, PC becomes easier to deform under load.
Why Tg matters
Tg is critical for:
- Heat resistance
- Dimensional stability
- Part stiffness at elevated temperature
- Long-term service temperature evaluation
- Stress relaxation
- Post-mold deformation risk
- Assembly performance near heat sources
Engineering note
PC may still keep its shape near Tg if there is no load, but under load, stress, snap-fit force, screw torque, or assembly pressure, deformation risk increases as the temperature approaches Tg.
3.2 Vicat Softening Temperature
The Vicat softening temperature measures the temperature at which a flat-ended needle penetrates the plastic specimen under a defined load and heating rate.
For PC, Vicat softening temperature is often close to its Tg range, but the exact value depends on test method, load, grade, filler, and supplier datasheet.
Why Vicat matters
Vicat softening temperature helps evaluate:
- Surface softening risk
- Dimensional change under heat
- Short-term thermal resistance
- Product comparison between resin grades
- Heat performance under light mechanical load
Vicat is useful for comparing grades, but it should not be used alone to define final application temperature.
3.3 Heat Deflection Temperature, HDT
The heat deflection temperature, or HDT, measures the temperature at which a plastic specimen deflects under a specified load.
HDT is very important because it links thermal resistance with mechanical load.
For PC resin, HDT depends strongly on:
- Test load
- Grade type
- Molecular weight
- Reinforcement
- Annealing condition
- Molded specimen quality
- Residual stress
Why HDT matters
HDT helps engineers evaluate:
- Whether a part can keep shape under heat and load
- Whether a housing can resist deformation near electronics
- Whether a component can pass thermal performance tests
- Whether a reinforced PC grade is needed
HDT versus Tg
| Item | Tg | HDT |
| What it measures | Molecular transition | Deformation under load |
| Load involved | No direct mechanical load | Yes |
| Use | Material thermal transition | Engineering heat resistance |
| For PC | Around 145–150°C typical | Depends on load and grade |
| Best for | Understanding softening behavior | Designing loaded parts |
For real parts, HDT is often more practical than Tg because many components are used under mechanical stress.
3.4 Processing Temperature
The processing temperature of polycarbonate is much higher than its Tg. During injection molding or extrusion, PC must be heated until it flows properly.
Typical PC injection molding melt temperatures are often in the range of 260–320°C, depending on grade, part design, machine, flow length, and supplier recommendation.
However, too high a temperature or too long residence time can cause thermal degradation, discoloration, bubbles, black specks, molecular weight loss, and mechanical property reduction.
Why processing temperature matters
Processing temperature affects:
- Melt flow
- Filling ability
- Weld line strength
- Surface quality
- Optical clarity
- Yellowing risk
- Degradation risk
- Cycle time
- Internal stress
For PC molding, it is not enough to set a high barrel temperature. Engineers must control both melt temperature and heat history.
3.5 Continuous Use Temperature
The continuous use temperature describes the temperature range where the material can perform for long-term use.
This value depends on:
- Grade
- Additives
- Flame retardant system
- Reinforcement
- Mechanical load
- Exposure time
- UV exposure
- Chemical environment
- Safety requirement
Continuous use temperature is usually lower than Tg, Vicat, or HDT. It is more application-focused and should be checked from the resin supplier datasheet.
3.6 Thermal Degradation Temperature
Thermal degradation means the polymer chain begins to break down under excessive heat or long heat exposure.
For PC, degradation may cause:
- Yellowing
- Browning
- Black specks
- Gas generation
- Bubbles
- Splay marks
- Lower impact strength
- Poor optical quality
- Lower molecular weight
- Brittle parts
Thermal degradation is controlled not only by temperature, but also by residence time, oxygen exposure, moisture, shear heat, contamination, and hot runner design.
4. Polycarbonate Thermal Data Reference Table
The following values are general reference ranges. Actual values must be confirmed from the specific supplier datasheet.
| Thermal Item | Typical PC Reference Range | Engineering Meaning |
| True melting point | No sharp melting point | PC is amorphous |
| Glass transition temperature, Tg | About 145–150°C | Main softening transition |
| Vicat softening temperature | Often around 145–155°C | Softening under defined load |
| HDT | Grade and load dependent | Heat deformation under load |
| Injection molding melt temperature | About 260–320°C | Melt flow processing range |
| Mold temperature | Often about 70–120°C | Affects stress, surface, shrinkage |
| Drying temperature | Often about 110–125°C | Moisture removal before processing |
| Continuous use temperature | Grade and application dependent | Long-term heat performance |
| Degradation risk | Increases with high temperature and long residence time | Causes yellowing and property loss |
These values are not a substitute for a technical datasheet. PC resin grades from different suppliers may have different processing windows and heat resistance levels.
5. Polycarbonate Tg: Why It Matters More Than Melting Point
For PC resin, Tg is one of the most important thermal indicators.
When temperature approaches Tg, PC changes from a rigid glassy material to a softer state. This does not mean the part instantly melts. But stiffness, dimensional stability, and load resistance may drop significantly.
Practical meaning of PC Tg
| Temperature Zone | PC Behavior |
| Far below Tg | Rigid, strong, dimensionally stable |
| Near Tg | Stiffness decreases, stress relaxation increases |
| Above Tg | Softening and deformation risk increase |
| Much above Tg | Material becomes suitable for melt processing when heated further |
Common engineering risks near Tg
- Part deformation under load
- Loss of snap-fit holding force
- Dimensional drift
- Warpage after heat exposure
- Stress relaxation around screws
- Poor performance in hot assemblies
- Failure in thermal cycling tests
For this reason, engineers should not use PC near Tg under high mechanical load unless the grade, design, and testing support the requirement.
6. Polycarbonate Softening Temperature: What Engineers Should Know
The softening temperature of PC is often discussed through Vicat softening temperature or Tg. These values help determine when the material starts to lose hardness and stiffness.
However, softening is not the same as melting.
A PC part can soften before it flows. It may deform under load long before it becomes a liquid-like melt.
Softening risk depends on:
- Temperature
- Load
- Part thickness
- Molded-in stress
- Assembly stress
- Exposure time
- Reinforcement
- Grade selection
- Annealing condition
Example
A PC electrical cover may keep its shape at a certain temperature when placed freely in an oven. But the same cover may deform at a lower temperature if it is fixed by screws, clipped into a frame, or exposed to continuous stress.
This is why heat resistance should be evaluated with real part geometry and real load condition, not only by material data.
7. Polycarbonate Processing Temperature for Injection Molding
PC resin usually requires a relatively high processing temperature because of its high viscosity and strong molecular structure.
Typical injection molding temperature areas
| Processing Area | Function |
| Rear barrel zone | Starts resin heating and plasticizing |
| Middle barrel zone | Builds melt uniformity |
| Front barrel zone | Final melt temperature control |
| Nozzle | Controls melt delivery into sprue or hot runner |
| Hot runner | Maintains melt flow before cavity filling |
| Mold | Controls cooling, surface quality, and residual stress |
Typical PC injection molding considerations
- PC must be dried before processing.
- Melt temperature should be high enough for filling.
- Melt temperature should not be too high.
- Residence time should be controlled.
- Screw speed should avoid excessive shear heat.
- Back pressure should be moderate.
- Mold temperature should be stable.
- Packing pressure should be controlled to reduce sink marks and stress.
- Cooling time should be enough to reduce warpage.
Why higher temperature is not always better
Increasing barrel temperature can improve flow, but it also increases degradation risk. For PC, high temperature may cause:
- Yellowing
- Burn marks
- Black specks
- Gas
- Bubbles
- Splay
- Lower impact strength
- Poor optical clarity
The correct approach is to use the lowest melt temperature that still achieves stable filling, good surface quality, and acceptable weld line strength.
8. PC Drying Temperature and Its Relationship with Heat Problems
PC resin is moisture-sensitive. Moisture in PC pellets can cause hydrolysis during high-temperature processing. This may reduce molecular weight and cause appearance and mechanical defects.
Moisture-related defects include:
- Bubbles
- Splay marks
- Silver streaks
- Brittleness
- Poor optical clarity
- Lower impact strength
- Surface defects
Typical drying control points
| Item | Why It Matters |
| Drying temperature | Removes moisture without unnecessary heat damage |
| Drying time | Ensures moisture reaches safe level |
| Dryer dew point | Shows drying air quality |
| Hopper sealing | Prevents moisture re-absorption |
| Regrind drying | Prevents wet regrind defects |
| Material residence in hopper | Avoids long exposure to humidity |
Drying temperature should not be confused with melting point or processing temperature. Drying is for moisture removal before processing, while melt processing temperature is for plasticizing and injection.
9. Heat Resistance of Polycarbonate in Real Applications
PC has good heat resistance compared with many general-purpose plastics. However, the real application limit depends on the load, time, environment, and grade.
PC heat resistance is affected by:
- Tg
- HDT
- Vicat softening temperature
- Part thickness
- Mechanical load
- Continuous or short-term exposure
- UV exposure
- Chemical contact
- Flame retardant additives
- Reinforcement
- Molded-in stress
- Annealing
- Color and pigment system
Application examples
| Application | Heat Resistance Concern |
| LED lighting cover | Heat aging, yellowing, optical clarity |
| Electrical housing | HDT, flame rating, dimensional stability |
| Automotive lens | Heat, UV, impact, transparency |
| Medical device housing | Sterilization resistance, dimensional stability |
| Safety shield | Impact strength and thermal deformation |
| Battery component | Flame retardancy, heat deformation, electrical insulation |
| Industrial cover | Hot environment and mechanical load |
For high-temperature or long-term heat exposure, engineers should confirm supplier data and perform application testing.
10. PC Heat Resistance vs Other Engineering Plastics
Polycarbonate offers a strong balance of transparency, impact strength, and heat resistance. However, it is not always the best choice for every high-temperature application.
Comparison table
| Material | Thermal Behavior | Key Strength | Typical Limitation |
| PC | Amorphous, Tg around 145–150°C | Impact strength, transparency, heat resistance | Moisture-sensitive, yellowing risk |
| ABS | Amorphous | Easy processing, good appearance | Lower heat resistance than PC |
| PMMA | Amorphous | Excellent optical clarity | Lower impact strength |
| PA66 | Semi-crystalline | Strength, wear resistance | Moisture absorption, dimensional change |
| PBT | Semi-crystalline | Electrical properties, chemical resistance | Lower impact than PC |
| PET | Semi-crystalline | Dimensional stability, chemical resistance | Processing and crystallization control |
| PPS | Semi-crystalline | High heat and chemical resistance | Higher cost, lower toughness |
| PEI | Amorphous | Very high heat resistance | Higher cost, higher processing temperature |
PC is often selected when the application needs:
- High impact resistance
- Transparency
- Better heat resistance than ABS or PMMA
- Good dimensional stability
- Good electrical insulation
- Balanced performance and cost
For higher heat resistance, materials such as PEI, PPS, PPA, or PEEK may be considered depending on cost and performance requirements.
11. Why PC Parts Deform Below the “Melting Point”
Many users ask why PC parts deform even though the temperature is far below the processing temperature.
The reason is simple: part deformation does not require melting.
A PC part can deform when:
- The temperature approaches its Tg
- The part is under mechanical load
- Residual stress is high
- Wall thickness is uneven
- Screw or snap-fit stress is present
- The part is exposed to heat for a long time
- The design has poor support
- The wrong grade is used
Example
A PC housing may be injection molded at around 280–300°C, but it can still deform at a much lower application temperature if it is loaded, stressed, or poorly designed.
Processing temperature is for melt flow.
Service temperature is for final part use.
They are not the same.
12. How to Select PC Resin for Heat Resistance
When selecting PC resin for a heat-resistant application, do not only ask for “melting point.” Instead, ask for technical data related to real use.
Important data to request
- Tg
- Vicat softening temperature
- HDT at specified load
- Continuous use temperature
- Tensile strength at elevated temperature
- Flexural modulus at elevated temperature
- Heat aging performance
- Yellowing index after heat exposure
- UV stability
- Flame retardant rating
- Processing temperature range
- Drying recommendation
- Mold temperature recommendation
- Mold shrinkage
- Application test data
Grade selection direction
| Requirement | PC Grade Direction |
| Transparent part | Optical-grade PC |
| Outdoor part | UV-stabilized PC |
| Electrical housing | Flame-retardant PC |
| High dimensional stability | Reinforced PC or PC blend |
| Thin-wall molding | High-flow PC |
| High heat aging resistance | Heat-stabilized PC |
| Low yellowing | Optical or heat-stable PC |
| Impact-critical part | High-impact PC |
| Chemical exposure | Check PC chemical compatibility or consider blend/coating |
Correct PC grade selection can reduce molding defects, heat deformation, yellowing, and field failure risk.
13. Troubleshooting Heat-Related PC Molding Problems
The following table connects thermal misunderstanding with real molding defects.
| Problem | Possible Heat-Related Cause | Corrective Direction |
| Yellowing | Melt temperature too high, long residence time | Lower temperature, reduce residence time |
| Bubbles | Moisture vapor or degradation gas | Improve drying, reduce overheating |
| Splay marks | Moisture, gas, shear heat | Dry resin, reduce screw speed/back pressure |
| Warpage | Uneven cooling, molded-in stress | Balance mold temperature and cooling |
| Sink marks | High local shrinkage, poor packing | Optimize holding pressure and cooling |
| Burn marks | Trapped gas and high temperature | Improve venting, lower injection speed |
| Brittle parts | Hydrolysis or degradation | Dry resin, reduce heat history |
| Poor clarity | Moisture, overheating, contamination | Dry, purge, control temperature |
Heat-related problems are often connected. For example, high melt temperature may improve flow but also increase yellowing and gas marks. Better troubleshooting requires a balanced approach.
14. Practical Checklist for Engineers
Before setting up PC molding or approving PC resin for a heat-related application, check the following items.
Material checklist
- Confirm exact PC grade.
- Check supplier datasheet.
- Confirm Tg.
- Confirm Vicat softening temperature.
- Confirm HDT under required load.
- Confirm processing temperature range.
- Confirm drying recommendation.
- Confirm UV, FR, optical, or heat-stable requirements.
- Confirm allowed regrind ratio.
- Confirm color masterbatch compatibility.
Processing checklist
- Dry resin correctly.
- Monitor dryer dew point.
- Keep dried resin sealed.
- Use proper barrel temperature.
- Measure actual melt temperature.
- Avoid long residence time.
- Reduce excessive screw speed.
- Avoid high back pressure.
- Maintain stable mold temperature.
- Control cooling time.
- Purge degraded material.
Application checklist
- Check real service temperature.
- Check short-term and long-term heat exposure.
- Check load at elevated temperature.
- Check assembly stress.
- Check screw torque and snap-fit stress.
- Check UV exposure.
- Check chemical exposure.
- Perform real part heat aging test.
15. Common Mistakes When Discussing Polycarbonate Melting Point
Mistake 1: Treating PC like PP or PA66
PC is amorphous. It does not have a sharp melting point like semi-crystalline plastics.
Mistake 2: Using processing temperature as service temperature
PC may be processed above 260°C, but that does not mean a molded PC part can be used at that temperature.
Mistake 3: Ignoring load
A part may resist heat without load but deform under load at the same temperature.
Mistake 4: Ignoring moisture
Wet PC can degrade during high-temperature processing, causing bubbles, splay, and brittleness.
Mistake 5: Ignoring residence time
Even if barrel temperature is within range, long residence time can still cause yellowing and degradation.
Mistake 6: Using only Tg for material approval
Tg is important, but HDT, Vicat, continuous use temperature, and real part testing are also needed.
16. FAQ: Polycarbonate Melting Point and Heat Resistance
Q1: What is the melting point of polycarbonate?
Polycarbonate does not have a sharp melting point because it is an amorphous thermoplastic. Its glass transition temperature is typically around 145–150°C.
Q2: Does polycarbonate melt at 150°C?
No. Around 145–150°C, PC reaches its glass transition range and starts to soften. It does not flow like a melt at this temperature.
Q3: What temperature does polycarbonate soften?
PC softening is commonly evaluated by Tg and Vicat softening temperature. Standard PC often softens near the 145–155°C range, depending on grade and test method.
Q4: What is the processing temperature of PC resin?
Typical PC injection molding melt temperature is often about 260–320°C, depending on grade, part design, machine, and supplier recommendation.
Q5: Why is PC molded at such a high temperature if Tg is only around 150°C?
Tg indicates the glass transition, not melt processing flow. PC needs much higher temperature to reach suitable melt viscosity for injection molding or extrusion.
Q6: Can PC be used above 120°C?
Some PC grades may be used near elevated temperatures depending on load, exposure time, grade, and design. Engineers should check HDT, continuous use temperature, and real part testing.
Q7: Why does PC yellow during molding?
PC yellowing is often caused by excessive melt temperature, long residence time, high shear heat, contamination, degraded regrind, or unsuitable colorant.
Q8: Is PC more heat-resistant than ABS?
Yes, PC generally has better heat resistance than standard ABS. However, exact performance depends on grade, load, and application conditions.
Q9: Is PC suitable for LED lighting covers?
PC can be used for LED lighting covers when impact strength, transparency, and heat resistance are needed. For long-term light and heat exposure, UV-stabilized or heat-stable optical PC grades should be considered.
Q10: What data should I check instead of asking only for PC melting point?
Check Tg, Vicat softening temperature, HDT, continuous use temperature, processing temperature range, drying condition, heat aging data, and application test results.
Conclusion
The term polycarbonate melting point is widely used, but it is not technically precise. PC resin is an amorphous thermoplastic, so it does not have a sharp crystalline melting point. Instead, engineers should focus on Tg, Vicat softening temperature, HDT, processing temperature, and long-term heat resistance.
For standard PC resin, Tg is typically around 145–150°C, while injection molding melt temperature is usually much higher, often around 260–320°C. These two values describe different things. Tg explains softening behavior. Processing temperature explains melt flow during molding.
In real applications, PC heat resistance depends on grade, load, wall thickness, residual stress, exposure time, UV, chemicals, and part design. For injection molding, correct drying, controlled melt temperature, stable mold temperature, and limited residence time are essential to avoid bubbles, splay marks, yellowing, brittleness, and dimensional problems.
For buyers and engineers, the best approach is simple: do not approve PC resin only by asking for “melting point.” Request the full thermal data, confirm processing recommendations, and test the molded part under real application conditions.
