In the world of transparent plastics, polycarbonate and acrylic (PMMA) stand out as popular choices for various applications. This comprehensive comparison will help you make informed decisions about which material best suits your specific needs.
Physical Properties Comparison
Strength and Impact Resistance
Polycarbonate
- Impact strength: 250 times stronger than glass
- Virtually unbreakable
- Tensile strength: 9,500 psi
- Flexural strength: 13,500 psi
Acrylic
- Impact strength: 17 times stronger than glass
- Brittle under impact
- Tensile strength: 10,200 psi
- Flexural strength: 16,500 psi
Optical Properties
Polycarbonate
- Light transmission: 88%
- Refractive index: 1.586
- Yellows with UV exposure
- Slightly hazier appearance
Acrylic
- Light transmission: 92%
- Refractive index: 1.491
- UV resistant
- Crystal clear appearance
Manufacturing Characteristics
Machining Properties
Polycarbonate
- CNC Machining
- Feeds: 300-800 IPM
- Speeds: 3000-15000 RPM
- Easy to machine without melting
- Requires sharp tools
- Drilling
- Standard twist drills work well
- Lower speeds recommended
- Less likely to crack
Acrylic
- CNC Machining
- Feeds: 200-600 IPM
- Speeds: 2000-10000 RPM
- Prone to melting if overheated
- Very sharp tools required
- Drilling
- Special plastic drills recommended
- Higher speeds possible
- More prone to cracking
Thermoforming
Polycarbonate
- Forming temperature: 380-400°F
- Wider forming temperature range
- More forgiving in processing
- Better deep-draw capabilities
Acrylic
- Forming temperature: 290-320°F
- Narrower forming temperature range
- Requires more precise temperature control
- Limited deep-draw capabilities
Cost Considerations
Material Costs
Polycarbonate
- Base cost: 20-40% higher than acrylic
- Higher processing costs
- Better durability may offset initial cost
Acrylic
- More economical initial cost
- Lower processing costs
- May require replacement more often
Processing Costs
- Machining
- Polycarbonate: Higher tool life, faster processing
- Acrylic: More careful handling required, slower processing
- Forming
- Polycarbonate: Higher energy costs due to higher forming temperatures
- Acrylic: Lower energy costs, but more scrap due to narrower processing window
Application-Specific Considerations
Indoor Applications
Polycarbonate
- Best for high-impact areas
- Security glazing
- Machine guards
- Interior structural elements
Acrylic
- Display cases
- Signage
- Furniture
- Decorative elements
Outdoor Applications
Polycarbonate
- Must be UV coated for outdoor use
- Greenhouse panels
- Security barriers
- Industrial roofing
Acrylic
- Naturally UV resistant
- Outdoor signage
- Building glazing
- Outdoor furniture
Processing Guidelines
Cutting Parameters
Polycarbonate
- Sawing
- Blade speed: 3000-5000 FPM
- Carbide-tipped blades
- Cooling recommended
- Routing
- RPM: 18000-24000
- Feed rate: 200-400 IPM
- Two-flute end mills preferred
Acrylic
- Sawing
- Blade speed: 2000-4000 FPM
- Fine-tooth blades
- Minimal cooling needed
- Routing
- RPM: 12000-18000
- Feed rate: 150-300 IPM
- Single-flute end mills preferred
Surface Finishing
Polycarbonate
- Mechanical Polishing
- Requires special compounds
- More difficult to achieve high gloss
- More resistant to scratching
- Flame Polishing
- Not recommended
- Can cause crazing
- Surface degradation likely
Acrylic
- Mechanical Polishing
- Standard buffing compounds work well
- Easily achieves high gloss
- More prone to scratching
- Flame Polishing
- Excellent results possible
- Quick edge finishing
- Requires skill but effective
Chemical Resistance
Polycarbonate
- Resistant to:
- Vulnerable to:
- Alkalines
- Ketones
- Aromatics
Acrylic
- Resistant to:
- Most weather conditions
- Dilute acids
- Natural gases
- Vulnerable to:
- Solvents
- Alcohols
- Strong acids
Design Considerations
Tolerance Guidelines
Polycarbonate
- Standard tolerance: ±0.005 in/in
- Thermal expansion: 3.75 x 10^-5 in/in/°F
- More flexible in design
Acrylic
- Standard tolerance: ±0.004 in/in
- Thermal expansion: 4.1 x 10^-5 in/in/°F
- Requires more rigid design
Joint Design
Polycarbonate
- Mechanical fastening preferred
- Solvent bonding possible
- Ultrasonic welding effective
Acrylic
- Solvent bonding preferred
- Mechanical fastening requires care
- Ultrasonic welding limited
Sustainability Aspects
Recyclability
Polycarbonate
- Recyclable (Code 7)
- More energy-intensive recycling
- Limited recycling facilities
Acrylic
- Recyclable (Code 7)
- Can be reformed multiple times
- Wider recycling acceptance
Environmental Impact
Polycarbonate
- Higher production energy
- BPA concerns
- Longer service life
Acrylic
- Lower production energy
- No BPA issues
- Shorter service life
Conclusion
The choice between polycarbonate and acrylic depends heavily on the specific application requirements. Polycarbonate excels in high-impact, structural applications where strength is paramount, while acrylic is the superior choice for optical clarity and UV resistance. Understanding these differences allows for optimal material selection in any given application.
Selection Guide Quick Reference
Choose Polycarbonate When:
- Impact resistance is critical
- Operating temperatures are high
- Deep forming is required
- Structural strength is needed
Choose Acrylic When:
- Optical clarity is paramount
- UV resistance is needed
- Cost is a major factor
- Aesthetic finish is critical
This comprehensive comparison should serve as a valuable reference for engineers, designers, and manufacturers in making informed material selections for their specific applications.
