Polypropylene PP is a semi-crystalline commodity polymer that comes in three main variations:
- PP Homopolymer (PPH): The simplest and most commonly used PP grade. It is slightly stiffer and stronger than copolymer.
- PP Copolymer (PPC): A small portion of PE has been compounded to PPH. This makes the material a little softer while increasing impact resistance. Resistance against stress-cracking is improved as well.
- PP Random-Copolymer (PP-RC): During the polymerization process, the polymer chains are randomly arranged. This makes the material transparent and improves visual properties.
- (High crystalline PP (hcPP))
Let’s start with PPH and then see why you should or should not prefer PPC or PP-RC instead.
PP Homopolymer or PP in general
Why choose it?
- The utilization of living hinges (e.g. packages.)
- Low density, floats in water
- Fairly ductile, especially when impact modified
- Excellent chemical resistance
- Common food-grade plastic
- Easy to process (if the tendency to warp is eliminated with proper design)
- Common material, easy to find reference cases
Why not choose it?
- PP-H can not be considered transparent
- Low strength and modulus compared to most other plastics
- Low thermal resistance.
- Poor UV resistance.
- Turns brittle in sub-zero temperatures (depends on grade)
- Plastic tableware
- Plumming joints
Why choose PPC over PPH?
- Better impact resistance
- Due to compounded PE, remains ductile in sub-zero temperatures
Why not choose?
- Strength and modulus slightly lower
- Snow shovels
- Hose couplings
- Plastic chairs
Why choose PP-RC over PPH or PPC?
- Improved gloss
Why not choose?
- Even at its best, the transparency is slightly milky. If you need crystal clear clarity, you have to look at amorphous plastics (keeping in mind their weaknesses).
- Storage boxes