Polypropylene (PP) and Acrylonitrile Butadiene Styrene (ABS) are two of the most widely used thermoplastics in manufacturing. While they overlap in some applications, their fundamental differences in mechanical properties, thermal behavior, and cost make each suitable for distinct use cases. This guide provides a detailed comparison to help you select the right material for your application.
1. Material Overview
Polypropylene (PP): A semi-crystalline thermopolymer made from propylene monomer. The most widely used polyolefin after polyethylene.
- **Density:** 0.90-0.91 g/cm³ (lightest common thermoplastic)
- **Price range:** $1.0-1.5/kg (commodity grade)
- **Key traits:** Excellent chemical resistance, low density, good fatigue resistance, easy processing, recyclable
ABS (Acrylonitrile Butadiene Styrene): An amorphous terpolymer combining the properties of three monomers.
- **Density:** 1.04-1.07 g/cm³
- **Price range:** $2.0-3.5/kg
- **Key traits:** High impact strength, excellent surface finish, good dimensional stability, paintable, bondable, easily electroplated
Fundamental Difference: PP is semi-crystalline (organized molecular structure) while ABS is amorphous (random molecular structure). This difference drives most of their property differences.
2. Mechanical Properties Comparison
Tensile Strength: - PP: 25-35 MPa (homopolymer), up to 40 MPa (copolymer) - ABS: 40-50 MPa - Winner: ABS — 30-40% higher tensile strength
Impact Strength (Izod, notched): - PP: 2-5 kJ/m² (neat), >50 kJ/m² (impact modified) - ABS: 20-40 kJ/m² (standard grades) - Winner: ABS (neat comparison) — inherently tougher without modification
Flexural Modulus (stiffness): - PP: 1000-1500 MPa - ABS: 2000-2700 MPa - Winner: ABS — significantly stiffer
Elongation at Break (ductility): - PP: 100-600% (very ductile, living hinge capable) - ABS: 10-50% (moderate ductility) - Winner: PP — much higher ductility, enables living hinge designs
Hardness (Rockwell R): - PP: R80-100 - ABS: R100-120 - Winner: ABS — harder surface
Summary: ABS wins on strength, stiffness, and hardness. PP wins on ductility and can be modified for high impact. PP with 20% elastomer modification approaches ABS impact strength at lower cost.
3. Thermal Properties
Heat Deflection Temperature (HDT @ 0.45 MPa): - PP: 100-110°C (homopolymer), up to 155°C (GF reinforced) - ABS: 90-105°C - Winner: PP — slightly higher, especially reinforced grades
Continuous Use Temperature: - PP: 0-100°C (homopolymer), up to 135°C (copolymer) - ABS: -20 to 80°C - Winner: PP — wider temperature range
Vicat Softening Point: - PP: 145-155°C - ABS: 100-110°C - Winner: PP — higher softening temperature
Low Temperature Performance: - PP: Becomes brittle below -10°C (neat), impact modified grades to -20°C - ABS: Maintains impact strength to -20°C (standard grades) - Winner: ABS — better low-temperature toughness without modification
Coefficient of Thermal Expansion (CTE): - PP: 100-150 × 10⁻⁶/°C - ABS: 70-90 × 10⁻⁶/°C - Winner: ABS — lower CTE means better dimensional stability with temperature changes
Summary: PP excels at high temperatures; ABS performs better at low temperatures and has better dimensional stability.
4. Chemical and Environmental Resistance
Chemical Resistance: - PP: Excellent resistance to acids, bases, and solvents. Virtually immune to most chemicals at room temperature. Absorbs <0.01% moisture. - ABS: Good resistance to weak acids and bases but attacked by strong acids, esters, ketones (acetone dissolves ABS), and some chlorinated hydrocarbons. - Winner: PP — dramatically superior chemical resistance
UV Resistance: - PP: Poor without UV stabilizers. Degrades rapidly in sunlight (surface chalking, embrittlement). - ABS: Moderate. Better than unstabilized PP but still requires UV protection for outdoor use. - Winner: ABS (marginally) — both require UV stabilization for outdoor applications
Moisture Absorption: - PP: <0.01% (practically zero) - ABS: 0.2-0.5% (requires pre-drying for processing) - Winner: PP — no drying required, better for wet environments
Recyclability: - PP: Recycle code #5, widely recycled, good secondary properties - ABS: Recycle code #7 (other), less commonly recycled, can be ground and reprocessed - Winner: PP — more established recycling infrastructure
Summary: PP dominates chemical resistance and moisture resistance. Both need UV protection outdoors.
5. Processing Comparison
Injection Molding: - PP: Melt temp 200-250°C, mold temp 20-60°C. No drying required. Very fast cycle times due to rapid crystallization. Low shrinkage (1.0-2.5%). Can be challenging for thin walls due to high crystallization shrinkage. - ABS: Melt temp 220-250°C, mold temp 50-80°C. Requires drying (80-85°C, 2-4 hours). Moderate cycle times. Shrinkage 0.4-0.7%. Excellent flow for thin-wall parts.
Surface Finish: - PP: Matte to semi-gloss. Difficult to paint (low surface energy requires treatment). Cannot be electroplated. - ABS: High gloss to satin. Excellent paint adhesion. Easily electroplated for metallic finish. Can be vapor polished for mirror finish. - Winner: ABS — far superior surface quality and finishing options
Welding and Bonding: - PP: Ultrasonic and vibration welding work well. Difficult to bond with adhesives (requires surface treatment). Living hinge designs unique to PP. - ABS: Excellent ultrasonic welding. Bonds well with ABS-specific solvents (acetone welding, cyanoacrylate). No living hinge capability.
Summary: PP is easier to process (no drying) with faster cycles. ABS offers superior surface finish and bonding options.
6. Cost Analysis
Material Cost: - PP: $1.0-1.5/kg (standard), $1.5-2.5/kg (copolymer/impact modified), $2.0-3.0/kg (reinforced) - ABS: $2.0-3.5/kg (standard), $3.0-5.0/kg (flame retardant), $3.5-6.0/kg (high heat)
Processing Cost: - PP: Lower — no pre-drying, faster cycles, lower energy (lower melt temp) - ABS: Higher — drying required, longer cycles, higher melt temperature
Total Cost per Part (typical 100g part): - PP: ~$0.15-0.20 (material + processing) - ABS: ~$0.30-0.45 (material + processing)
When PP is More Cost-Effective: - High-volume commodity applications - Living hinge or fatigue-resistant designs - Chemical exposure environments - When weight reduction is critical (PP is 15% lighter)
When ABS Justifies Its Premium: - Premium appearance requirements (gloss, paintability) - Applications requiring dimensional stability - Assemblies with tight tolerances - Consumer electronics housings where aesthetics matter
7. Application Guide
Choose PP for: - Living hinge applications (toolboxes, flip-top caps) - Chemical containers and tanks - Food packaging and containers (FDA compliant grades) - Automotive under-hood components - Reusable containers and crates - Pipe fittings and plumbing - Textile (woven bags, ropes, carpets) - Cost-sensitive consumer goods
Choose ABS for: - Consumer electronics housings (keyboards, monitors, printers) - Automotive interior trim (instrument panels, consoles) - Luggage and protective cases - Toys (LEGO bricks are ABS) - Medical device housings - Pipe and fitting systems (ABS cement-weldable) - 3D printing filament (FDM) - Prototyping (good machinability)
When Modified Grades Bridge the Gap: - Impact Modified PP can replace ABS in bumper applications at 40% lower cost - Glass Fiber Reinforced PP matches ABS stiffness at lower weight - Flame Retardant ABS is needed when both impact and V-0 are required - ASA (acrylic-styrene-acrylonitrile) replaces ABS when UV resistance is needed
Need Help Deciding? Contact YicaiPlas application engineers for material recommendations tailored to your specific requirements. We supply both PP-based and ABS-based compounds and masterbatch solutions.