olycarbonate (PC) – Properties, Processing, and Applications
Polycarbonate (PC) is a high-performance polymer containing carbonate groups in its molecular chain. Based on ester group structure, it can be classified into aliphatic, aromatic, and aliphatic-aromatic types. Among the five major engineering plastics, PC is currently the fastest-growing general-purpose engineering material.
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Advantages and Disadvantages of PC
PC is colorless, transparent, heat-resistant, impact-resistant, and inherently flame-retardant (UL94 V-0 without additives). It has excellent mechanical properties within normal temperature ranges, a high refractive index, and good processability.
However, PC has limitations:
•Low hydrolysis resistance
•Notch sensitivity
•Limited resistance to organic chemicals and scratching
•Tendency to yellow under prolonged UV exposure
•Poor wear resistance (surface treatments are required for wear-critical applications)
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Processing Conditions for PC
PC is ideal for producing precise, complex-shaped parts that bear light loads or low impact. Processing requires careful control of raw material drying, injection temperature, and mold temperature.
1. Raw Material Drying
PC is highly sensitive to moisture at high temperatures. Even trace amounts can cause degradation, CO₂ release, discoloration, and reduced performance. Moisture content must be ≤0.02%. Improper drying can lead to defects such as silver streaks, bubbles, or cracks.
2. Injection Temperature
PC has high thermal stability and a wide molding temperature range, but viscosity is highly temperature-dependent.
•Too low: Poor filling, shrinkage, wrinkles, dull finish
•Too high (>320°C, prolonged): Severe degradation, discoloration, surface defects, bubbles
3. Mold Temperature
PC has high viscosity and low flowability.
•Too low: Incomplete filling, high shrinkage, surface defects, residual stress
•Too high: Slow cooling, longer cycles, poor release, deformation
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Injection Pressure & Holding Time
Holding time affects product density and dimensional stability:
•Too short: Shrinkage, voids, vacuum bubbles
•Optimal: Increased density, stable dimensions
•Too long: High internal stress, cracking risk
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Applications of Polycarbonate
PC is widely used in construction, automotive, medical, aerospace, electronics, packaging, and optics.
1. Construction Industry
PC sheets offer excellent light transmission, impact resistance, UV stability, and processability, outperforming traditional glass.
2. Automotive
PC’s impact resistance, heat resistance, weatherability, and hardness make it suitable for headlights, dashboards, heater parts, defrosters, bumpers, and PC-alloy components.
3. Medical Devices
PC withstands steam sterilization, cleaning agents, heat, and radiation without yellowing or losing properties. Applications include dialysis devices, surgical masks, disposable dental tools, blood separators, and high-pressure syringes.
4. Aerospace
PC is used extensively in aircraft and spacecraft. For example, a Boeing aircraft may contain 2,500 PC parts totaling ~2 tons, including fiber-reinforced PC components and astronaut protective gear.
5. Packaging
Reusable, sterilizable PC water bottles are common due to their light weight, impact resistance, and transparency.
6. Electronics
PC’s insulating properties, flame resistance, and dimensional stability make it ideal for tool housings, appliance components, refrigerator drawers, vacuum cleaner parts, and computer/TV parts.
7. Optical Lenses
Optical-grade PC is widely used for camera, microscope, telescope, projection lenses, laser printer optics, prisms, and mirrors. In eyewear, PC is popular for children’s glasses, sunglasses, safety goggles, and high-performance lenses.
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