The selection of plastic parts should consider the following aspects to determine whether they meet the needs of use or not.
- The mechanical properties of the plastic: such as strength, rigidity, toughness, elasticity, bending properties, impact properties and sensitivity to forces.
- The physical properties of plastics: such as adaptability to changes in temperature of the use environment, optical properties, the degree of insulation or electrical insulation, finishing and appearance of the degree of perfection.
- Chemical properties of the plastic: such as resistance to contact materials (water, solvents, oils, pharmaceuticals), the degree of hygiene and safety in use, etc.
- The necessary precision: such as the size of the shrinkage rate and the difference in shrinkage rate in each direction.
- Molding processability: such as plastic flow, crystallinity, heat sensitivity, etc.
These requirements for plastics are often selected and compared by the properties of the plastic. It is better to make a prototype mold according to the idea formed by the experiment, and then confirm the target value by the test article produced by the prototype mold, which will make the selection of plastic material more accurate.
Now we compare the characteristics and selection principles of polypropylene (PP) and high-density polyethylene (HDPE).
Polypropylene has more excellent properties than HDPE, such as good gloss and good appearance.
Advantages of polypropylene（PP）：
1. Shrinkage: PP shrinkage rate is smaller than HDPE, making fine parts of good clarity, the surface can be made into leather patterns, etc.. But HDPE shrinkage rate is larger, the surface of the product is difficult to make the fine treatment of molding.
2. Transparency: PP has better transparency than HDPE, so products that require transparency, such as syringes and other medical instruments, blow-molded containers, etc., are made of PP.
3. Dimensional stability: PP has better dimensional stability than HDPE, so it can be used to make thin-walled products with larger planes.
4. Heat deformation: The heat deformation temperature of PP is higher than HDPE, so it can be used to make heat-resistant tableware.
Advantages of high-density polyethylene (HDPE)：
a.Impact resistance and low-temperature toughness: HDPE has better impact resistance than polypropylene and is also tougher at low temperatures, so HDPE is suitable for manufacturing products for use in cold regions in cargo boxes or cold rooms.
b. Climate adaptability: HDPF has better climate adaptability than PP, so plastic products like beer bottle crates, outdoor garbage bins, etc. are suitable for manufacturing with HDPE.