PC vs PA66: Which High-Performance Plastic Wins?

Which Material Should You Choose?Choose PC (Polycarbonate) if:Transparent enclosures, safety equipment, optical components, electronic housings, applications requiring impact resistance at low temperatures and dimensional stability without...

Polycarbonate (PC) and Nylon (PA66) represent two fundamentally different classes of engineering thermoplastics: amorphous vs semicrystalline. This structural difference drives every aspect of their performance — optical properties, mechanical behavior, chemical resistance, moisture sensitivity, and processing. The choice between them is rarely ambiguous: if you need transparency or impact resistance, PC wins; if you need mechanical strength, wear resistance, or fuel resistance, Nylon wins.

When to choose Polycarbonate: PC is the standard for any application requiring transparency combined with impact resistance. Its 87-91% light transmission and 600-900 J/m notched Izod impact strength make it irreplaceable for: safety equipment (hard hats, safety goggles, face shields), transparent enclosures (machine guards, display cases), optical components (LED lenses, light pipes, optical instrument windows), and electronic device housings where internal component visibility matters (medical devices, instrumentation). PC's amorphous structure provides excellent dimensional stability — it absorbs only 0.15% moisture, meaning parts maintain tolerances regardless of humidity. PC's HDT of 130-140°C (at 1.82 MPa) exceeds Nylon's dry HDT (75-90°C), giving PC better short-term heat resistance for unreinforced grades. PC is also the standard for bullet-resistant glazing (laminated PC sheets) and riot shields, where its combination of transparency and virtually unbreakable impact performance is unmatched.

When to choose Nylon PA66: Nylon is the standard for mechanical components operating under load — gears, bearings, bushings, fasteners, clips, and structural brackets. Its semicrystalline structure provides 20-30% higher tensile strength than PC (82 vs 60-70 MPa dry), superior fatigue resistance (critical for cyclically loaded parts like gears and snap-fits), and excellent wear and abrasion resistance (critical for bearing and sliding applications). Nylon's chemical resistance to fuels, oils, and hydrocarbons makes it the standard for automotive fuel system components (fuel rails, quick-connect fittings, filter bodies) — PC is attacked by gasoline and many solvents, making it unsuitable for fuel contact. Nylon GF30 (30% glass fiber reinforced) offers 180-210 MPa tensile strength and 245°C HDT — far exceeding PC GF30's 100-130 MPa and 140°C HDT. For under-hood automotive applications and high-temperature structural components, Nylon GF30 is the clear choice.

Critical limitations to consider: PC has two significant weaknesses: (1) Environmental stress cracking — PC is susceptible to sudden brittle failure when exposed to certain solvents (gasoline, acetone, methylene chloride, toluene) under tensile stress. A PC part that is perfectly impact-resistant can crack catastrophically if splashed with solvent while under load. (2) UV degradation — PC yellows and embrittles with UV exposure, requiring UV stabilizers for outdoor applications. Nylon's main weakness is moisture absorption — at 50% RH equilibrium, Nylon 66 absorbs 2.5% water, causing 0.7% linear dimensional swelling, 30-40% reduction in tensile strength and modulus, and 50-100% increase in impact toughness. This means Nylon parts designed at dry-as-molded properties will be oversized (swollen) and weaker (but tougher) in service. Designers must account for moisture-conditioned properties, not dry properties, for any Nylon part that will see ambient humidity.

Comparison at a Glance

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org