Polypropylene (PP) is the most widely used plastic in automobiles, accounting for approximately 40% of the total plastic usage in a vehicle. From bumpers to dashboards, from door panels to battery casings, PP is almost ubiquitous.

 

Polypropylene is a semi-crystalline thermoplastic polymer formed by polymerization of propylene. PP used in automobiles is primarily modified PP.

PP's Five Core Advantages: Low density (0.90 g/cm³), chemical resistance, easy processing, high cost-effectiveness, and recyclability.

 

PP is a semi-crystalline polymer. Its stress-strain curve shows a clear yield point → necking → cold drawing process.
Comparison of Performance of Three Types of PP

Yield Strength Ratio (Yield Strength / Tensile Strength)
The lower yield strength ratio, the greater safety margin after yielding, and the stronger impact resistance: Homopolymer PP: Yield strength ratio ≈ 0.8~0.9 (Slightly brittle); Impact copolymer PP: Yield strength ratio ≈ 0.6~0.8 (Medium); TPO modified PP: Yield strength ratio ≈ 0.4~0.6 (Toughest).
Engineering Conclusion: For safety components such as bumpers, choose TPO with a low yield strength ratio; for structural components such as dashboards, choose filled PP with a high yield strength ratio.
Other Key Performance Characteristics: Melting Point: 155~170℃; Heat Deflection Temperature (0.45MPa): 80~110℃; Continuous Use Temperature: Approximately 80~100℃; Water Absorption: < 0.01% (Almost no water absorption, no pre-drying required before molding); Flame Retardant Rating: UL 94 HB (pure PP), flame retardant modification is often required for automotive parts

 

Over 80% of automotive PP parts are injection molded.
Key Process Parameters

Four Key Process Points: No Drying Required: PP has extremely low water absorption; new material can be used directly. Anti-Degradation: Significant degradation occurs above 280℃; avoid prolonged exposure to high temperatures. Controlled Shrinkage: Pure PP has a shrinkage rate of 1.5~2.5%, which decreases to 0.8~1.2% after filling; pressure holding is crucial. Weld Lines: PP weld lines have low strength; avoid their appearance in stress areas.

PP usage in a single vehicle can reach 50~80 kg, covering interior and exterior trim and functional components.

 

 

Functional Components

PP is a viscoelastic-plastic material; simulation cannot simply use linear elasticity. Choosing right model is very important.
Five Commonly Used Constitutive Models

Typical Simulation of Automotive PP Components

Three Modeling Reminders. Temperature Must Be Considered: PP performance is extremely sensitive to temperature. Summer exposure to 80-100℃ significantly reduces stiffness and strength. Rate Effect Cannot Be Ignored: Strain rate must be considered in collision impact problems; static models will underestimate strength. Data Must Be Measured: Different batches/colors of same grade may vary; for key items, actual measurement and calibration are recommended.
Development Trends. High Flow PP: Supports thin-walled, large-scale, and short-cycle production. Low VOC/Low Odor: Standard for interior trim, meeting in-vehicle air quality regulations. Paint-Free PP: Metallic texture/pearl effect, saving painting processes. Long Glass Fiber Reinforced PP (LFT): Replaces metal for front-end modules and seat frames. Micro-foamed PP: 20-30% weight reduction, better sound and heat insulation. Recycled PP: Improved quality of recycled materials, increased application in non-critical components.