For previous reading, please refer to Plastics Materials (Part Six): In-Depth Analysis of ABS.
Polycarbonate (PC) is the most well-rounded of the five major engineering plastics, boasting high transparency, high impact resistance, and high heat resistance, earning it nickname "transparent metal." At room temperature, PC's impact strength is dozens of times that of ordinary plastics, its light transmittance is close to that of glass, and its heat resistance exceeds 130℃. It also possesses advantages such as dimensional stability, electrical insulation, and flame retardancy. With these unique properties, PC occupies an irreplaceable position in automotive lighting, electronics, optical lenses, architectural lighting, and medical equipment.

PC = Polycarbonate, a high-molecular polymer containing carbonate groups in its molecular chain. The most common type is bisphenol A PC:

Core Characteristics of PC: Benzene ring provides rigidity and heat resistance, while carbonate groups provide transparency and toughness. Balance between rigidity of molecular chain and free volume creates PC's unique comprehensive properties.
PC Molecular Structure and Performance Relationship

 

PC's superior performance stems from its unique molecular structure: Benzene ring structure → High rigidity, high heat resistance, high strength; Carbonate groups → High transparency, moderate polarity; High molecular chain rigidity with some degree of freedom → High impact resistance, high toughness; Amorphous structure → High transparency, dimensional stability
Main Classifications of PC

 

PC vs ABS vs PMMA: How to Choose a Transparent Plastic?

Selection Logic: For transparency and impact resistance, choose PC; for transparency and hardness, choose PMMA; for affordability and opacity, choose ABS.
Classified by General Purpose and Light-Stable Grades
General Purpose PC
Core difference between 2405 and 2447 lies in their viscosity/molecular weight: 2405: Low viscosity (MVR 20), good flowability, suitable for thin-walled parts and complex molds. 2447: Medium viscosity (MVR ~10), higher molecular weight, better strength and toughness, suitable for structural parts and thick-walled parts.
Numerical naming convention: The first two digits may represent series, and the last two digits may represent MVR or molecular weight grade.
Light-Stable/Weather-Resistant PC
AL = Anti-Light/UV Stable: AL2447 adds UV stabilizers and anti-yellowing agents to 2447, making it less prone to yellowing and aging in outdoor use, is the first choice for automotive exteriors and outdoor applications.
Note: Light stabilizers slightly reduce impact strength and light transmittance, but improve weather resistance; this is a necessary trade-off for outdoor applications.

PC's mechanical properties are quite unique among engineering plastics—it possesses high rigidity, high strength, and ultra-high toughness simultaneously.
Comparison of Typical Properties of Different Types of PC

Note: Above are typical ranges for materials of same grade. Specific values may vary depending on molecular weight, additives, and modification methods.
Yield-to-tensile strength ratio analysis
Yield-to-tensile strength ratio (yield strength / tensile strength) of PC has following characteristics: General grade: High yield-to-tensile strength ratio (~0.9~0.95), with obvious cold drawing and necking after yielding, and extremely high elongation at break (100~150%). Light-stabilized grade: High yield-to-tensile strength ratio (~0.9+), slightly lower elongation at break. Flame-retardant grade: High yield-to-tensile strength ratio, with a significant decrease in elongation at break. Glass fiber reinforced: Even higher yield-to-tensile strength ratio (~0.95+), direct brittle fracture. Engineering conclusion: PC is a typical tough material—it has a distinct yield point and undergoes large plastic deformation after yielding before fracture. At room temperature, elongation at break of PC can reach over 100%, which is source of its high impact resistance. However, at low temperatures, PC becomes brittle, and its impact strength decreases significantly.
Influence of Temperature on Performance
PC's properties are highly sensitive to temperature: Impact Strength: Extremely high at room temperature (60~80 kJ/m², partial fracture), decreasing to 10~15 kJ/m² (complete fracture) at -30℃, exhibiting a distinct brittle-ductile transition temperature (approximately -10~0℃). Stiffness: Decreases with increasing temperature, Tg approximately 150℃, modulus decreases significantly above 130℃. Creep: PC's creep resistance is relatively good among engineering plastics, but significant creep still occurs under long-term high-temperature loads.
PC is more difficult to mold and process than ABS and PP, requiring strict process control.
Key Process Parameters

Other Molding Methods of PC
Extrusion: Sheets, Films, Tubes. Blow Molding: Bottles, Hollow Products. Thermoforming: Translucent Panels, Protective Covers. Injection Molding & Blow Molding: Water Bottles, Food Containers. 3D Printing: High-Strength, High-Heat-Resistant Printed Parts

PC has a wide range of applications, covering almost all fields requiring transparency, impact resistance, and heat resistance.
Automotive Applications

 

Automotive lighting is one of the largest application areas for PC. PC's high transparency, high impact resistance, and ease of molding make it preferred material for automotive headlight lenses. Light-stabilized PC (such as AL2447) can ensure that headlights do not yellow after long-term outdoor use.
Electronic and Electrical Applications

Optical Applications

 

 

Simulation modeling of PC requires special attention to rate dependence, temperature sensitivity, and internal stress.
Five Commonly Used Constitutive Models

 

PC failure modes have their unique characteristics, with stress cracking and abrasion/scratching being the most common problems.
Stress Cracking

 

Problem: Under combined action of stress and chemical media, PC products develop crazing and cracks, eventually leading to fracture. This is the most typical and common failure mode for PC.
Common Scenarios: Cracking after contact with alcohol, detergents, or lubricants; long-term cracking caused by assembly stress; spontaneous cracking caused by internal stress.
Solution:

Abrasion/Scratching
Problem: PC surface hardness is not high, making it easily scratched, affecting appearance and optical performance.
Common Scenarios: Scratched eyeglass lenses, scratched mobile phone cases, abrasion on the surface of transparent parts.
Solution:

Aging/Yellowing
Problem: Under long-term ultraviolet radiation, PC yellows, becomes brittle, and its light transmittance decreases. Benzene ring in PC is sensitive to UV radiation, and ordinary PC is not weather-resistant.
Common Scenarios: Yellowing of outdoor lighting fixtures, automotive exteriors, and building skylights after long-term use.
Solution:

Low-Temperature Brittle Fracture
Problem: At low temperatures, PC changes from ductile to brittle, resulting in a significant decrease in impact strength. Brittle-ductile transition temperature of PC is approximately -10~0℃.
Common Scenarios: Outdoor use in northern winters, cold chain transportation, and drops in low-temperature environments.
Solution:

Combustion/Thermal Degradation
Problem: PC itself has good flame retardancy (UL94 V-2), but it will burn and thermally degrade at high temperatures. Flame retardant grades are required for applications with high flame retardancy requirements.
Common Scenarios: Short circuits in electronic appliances, battery thermal runaway, and high-temperature environments.
How to solve:

Development Trends
Optical Grade PC: Higher light transmittance, lower haze, lower birefringence, meeting needs of high-end optics and displays. Weather-resistant PC: Long-lasting UV stability, resistant to yellowing, expanding outdoor applications. Flame-retardant PC: Halogen-free flame retardant, ultra-thin flame retardant (V-0 @ 0.5mm), high-flow flame retardant. Abrasion-resistant PC: Surface hardening, abrasion-resistant modification, replacing glass and PMMA. Bio-based PC: Some raw materials are bio-based, reducing carbon footprint. PC Alloys: Alloying of PC/ABS, PC/PBT, PC/PMMA, etc., for customized performance. Glass Fiber Reinforced PC: Higher rigidity, higher heat resistance, replacing metal structural components. Medical Grade PC: Sterilizable, high purity, biocompatible, increasing applications in medical devices. Recyclable PC: Breakthroughs in chemical recycling technology, closed-loop recycling improves quality. Optical Grade 3D Printing PC: High-precision, high-transparency 3D printing material.
For further reading, please refer to Plastic Materials (Part 8): In-depth Analysis of PC/ABS Materials.