Today we are going to talk about polycarbonate (PC). A polymer that accounts for about 2–3% of global polymer consumption. But what a special percentage it is! A share that sets itself apart from most other polymers. It is my love, my dearest, my very breath. Why? Let’s find out together.
Structure and Transparency
Polycarbonate has two aromatic rings in its repeating unit along with a carbonate group (-O-(C=O)-O-). These rigid rings give it an amorphous structure, allowing light to pass through, making it both amorphous and transparent.
Its light transmittance is about 86–89%, ranking it among the most transparent engineering plastics (PMMA is slightly higher at ~92%). That’s why whenever transparency is needed in an engineering-grade polymer, polycarbonate is one of the top candidates.
Mechanical Properties
- Tensile strength: ~55–75 MPa (compared to ~30 MPa for ABS, PP, or PE in good grades). This means PC is about 2–3 times stronger.
- Impact strength: ~50–80 kJ/m² (Izod/Charpy, notched). For comparison: PP ~10–15, ABS ~15–25. This outstanding toughness is why PC is often described as virtually unbreakable.
Thermal Properties
- Heat deflection temperature (HDT, 1.8 MPa load): ~128–135 °C.
For comparison: - Polypropylene (PP): ~80 °C
- ABS: ~90–95 °C
- Polystyrene: ~95 °C
- Polyethylene (PE): ~50 °C
This makes PC an excellent choice for high-temperature applications, where dimensional stability and thermal resistance are critical.
Cost Consideration
PC is more expensive than commodity plastics:
- Polyethylene: ~$1000/ton
- Polycarbonate: ~$1800–2000/ton
This higher price is justified by its superior optical, mechanical, and thermal properties.
Flame Resistance
Unmodified polycarbonate typically meets UL-94 HB or V2 classifications. However, flame-retardant grades with additives can reach UL-94 V0, making PC widely used in electrical and electronic housings. When ignited, it emits black smoke and leaves a carbonized residue.
Applications
Electrical junction boxes, connectors, and housings are common applications where PC provides:
- Transparency and aesthetics
- Thermal stability
- Mechanical strength
- Flame safety
Limitations
- Transparency vs. PMMA: PMMA is slightly clearer (92% vs. ~88% for PC).
- Chemical resistance: PC is weaker against solvents due to its polar carbonate groups and amorphous structure. That’s why PC is often blended into alloys such as PC/ABS, PC/PBT, and PC/ASA to improve performance.
- Scratch resistance: Lower than PMMA. Coatings or blending with PMMA can improve this property.
- Processability: Due to rigid chains, PC has high melt viscosity. Even at MFI 10–20, it flows less easily than PE or PP, requiring higher pressures during extrusion and injection molding.
- Moisture absorption: PC absorbs 0.2–0.3% water. It must be dried before processing to prevent hydrolysis, loss of properties, and surface defects.
Conclusion
Polycarbonate is a polymer that balances transparency, toughness, thermal resistance, and safety better than most engineering plastics. Despite its higher cost and processing challenges, it is a prime choice for high-performance applications in electronics, automotive, optical devices, and consumer products.
