What is the Difference Between HDPE and PP?

HDPE (High-Density Polyethylene) and PP (Polypropylene) are both thermoplastic polymers with overlapping uses, but they have distinct differences in terms of their physical properties, applications, and costs. Here are the main differences between HDPE and PP:

Density: HDPE has a lower density (0.944 - 0.965 g/cm³) compared to PP (0.905 g/cm³). This difference in density makes HDPE more rigid and PP more flexible.
Strength-to-Weight Ratio: HDPE has an excellent strength-to-weight ratio, making it suitable for applications that require strength and lightweight properties.
Chemical Resistance: Both materials offer good chemical resistance, but HDPE has a slight advantage in this area.
UV Resistance: PP requires stabilization with additives to improve its UV resistance, while HDPE has inherent UV resistance.
Applications: HDPE is widely used for water tanks, food packaging, and piping. PP, on the other hand, is used for single-use plastic applications, such as food packaging, and it also has excellent fatigue resistance.
Manufacturing Processes: HDPE can be manufactured using extrusion, injection molding, and rotomolding, while PP can be manufactured using blow molding, injection molding, and extrusion.
Cost: HDPE can be bought at $0.98-1.56 per kilogram, whereas PP is slightly more expensive, ranging from $1.00-3.00 per kilogram.

In summary, HDPE and PP are both versatile materials with overlapping uses, but their differences in density, strength-to-weight ratio, chemical resistance, and UV resistance make them suitable for different applications. When choosing between HDPE and PP, consider the specific requirements of your project and the material's properties to determine the most suitable option.