Structure:PE = flexible, low-temp resistant
PP = rigid, heat-resistant
Processing:PE suits film & blow molding；PP excels in injection molding
Applications:PE for packaging, pipes, cold chain；PP for containers, auto parts, appliances
Performance:PE = tough & soft；PP = strong & stable
Have you ever noticed that? PP (polypropylene) and PE (polyethylene) plastic products are everywhere in both industry and daily life. However, it is so confusing to identify these two raw materials for newcomers to the field. We are so close to them while we actually have no idea of them.
Let's take a little time, step by step, to get a closer look at our "old friends".
🔵 PE (polyethylene) has a simple molecular structure with weak intermolecular forces, allowing its molecular chains to rotate and align easily — which explains why it's often used for flexible packaging materials.
There are HDPE (High-Density Polyethylene) with high strength, LDPE (Low-Density Polyethylene) with excellent flexibility, and LLDPE (Linear Low-Density Polyethylene) with both strength and flexibility.
🔵 PP (polypropylene), on the other hand, has methyl side groups that make the molecular chains stiffer and reduce rotational freedom. As a result, PP has higher stiffness and heat resistance than PE.
Another difference is that PP is more non-polar, which makes it difficult to bond or print on. Surface treatments such as corona discharge are usually needed to improve its surface polarity.
| Property | PE | PP |
|---|---|---|
| Melt Flow Index (g/10min) | 0.3–50 | 1–40 |
| Heat Deflection Temperature (°C, 0.45MPa) | 50–85 | 100–110 |
| Impact Strength | Higher, good at low temperature | Lower, brittle at low temperature |
| Tensile Strength | Moderate | Higher |
| Electrical Insulation | Excellent | Excellent (with stronger heat resistance) |
Overall, PP is more suitable for applications that require rigidity and heat resistance, while PE is better for products that demand flexibility and impact strength.
| Process Parameter | PP | HDPE | LDPE |
|---|---|---|---|
| Injection Temperature (°C) | 200–270 | 180–280 | 160–260 |
| Mold Temperature (°C) | 40–80 | 30–70 | 20–60 |
| Extrusion Temperature (°C) | 190–250 | 160–230 | 120–200 |
PP generally shrinks less during cooling, producing parts with better dimensional accuracy. PE, in contrast, experiences greater shrinkage, so molds usually allow extra tolerance. For transparency, PP can be clarified with nucleating agents, whereas PE typically appears milky or opaque.
| Application Field | Main Uses of PP | Main Uses of PE |
|---|---|---|
| Packaging | Microwave food boxes, yogurt cups, pharmaceutical packaging | Shopping bags, cling films, bottles |
| Automotive | Bumpers, dashboards, battery cases | Fuel tanks, cable protection tubes |
| Construction | Ventilation ducts, tanks, valves | Water pipes, gas pipes, cable sheaths |
| Household | Storage boxes, tableware, chair backs | Cutting boards, cleaning bottles, toys |
| Medical | Syringes, instrument trays | Medicine bottles, protective films, IV bags |
Now that we've gone through the differences between PP and PE, how do you actually choose the right one?
You can refer to the applications listed above and also consider the following factors — they'll help clear up most of your doubts:
Since 2009, Suzhou Standard Polymer Materials Co., Ltd. has specialized in masterbatch colorant solutions based on PP and PE resins, with customers in over 50 countries worldwide.
