Polypropylene (PP) is a widely used thermoplastic polymer with a melting point that typically ranges between 130°C and 171°C (266°F to 340°F), depending on its grade and composition.
This broad melting range gives polypropylene excellent heat resistance, making it suitable for demanding applications such as hot-fill packaging, automotive components, medical devices, and FIBC bags.
In addition to its thermal stability, polypropylene offers outstanding chemical resistance, moisture resistance, and fatigue strength, while remaining lightweight and durable.
Its ability to withstand sterilization processes, combined with low density and flexibility, makes polypropylene a versatile material for films, containers, non-woven fabrics, and a wide range of consumer and industrial products.
What Is Polypropylene (PP)?
Polypropylene is a semi-solid thermoplastic polymer which is produced using propylene monomers using a polymerization reaction. It is a member of the polyolein family including polyethylene.
Key characteristics of polypropylene:
- Lightweight yet strong
- High fatigue resistance
- Excellent chemical resistance
- Good electrical insulation
- Melting point is very high in relation to most plastics.
These characteristics render polypropylene suitable to be used in challenging industries.
Polypropylene Melting Point – Exact Temperature Range
The melting point of polypropylene generally falls within the range of:
- 160°C to 170°C (320°F to 338°F)
However, polypropylene does not have a single fixed melting point like metals. Instead, it melts over a temperature range, which depends on:
- Polymer structure
- Crystallinity
- Copolymer composition
- Additives and fillers
This melting property enables polypropylene to be subjected to effective process by different techniques of manufacturing plastics.
Why Polypropylene Has a High Melting Point
Polypropylene has a relatively high melting point because of its semi-crystalline molecular structure.
Key reasons:
- Strong carbon–carbon backbone
- Large crystallinity degree.
- Compact polymer chains.
- Isotactic molecular structure (in homopolymers)
Increased crystallinity brings about:
- Higher melting temperature
- Better mechanical strength
- Improved heat resistance
Types of Polypropylene and Their Melting Points
There are varying grades of polypropylene which are used in different uses. Their melting points vary accordingly.
1. Homopolymer Polypropylene
- Melting Point: 160°C – 165°C
- Highest stiffness and tensile strength
- Superb resistance to chemicals.
- Used in:
- FIBC bags
- Woven sacks
- Rigid packaging
- Industrial containers
2. Copolymer Polypropylene (Impact Copolymer)
- Melting Point: 135°C – 160°C
- Improved impact resistance
- Ethylene content results in slightly low melting point.
- Used in:
- Automotive components
- Industrial crates
- Storage bins
3. Random Copolymer Polypropylene
- Melting Point: 140°C – 150°C
- Better clarity and flexibility
- Food contact good heat resistance.
- Used in:
- Food containers
- Medical packaging
- Transparent packaging
Softening Temperature vs Melting Point
Softening temperature is confused with the melting point by many people.
| Property | Temperature Range |
|---|---|
| Heat Deflection Temperature | 90°C – 110°C |
| Softening Begins | ~130°C |
| Melting Point | 160°C – 170°C |
Polypropylene can creep then form, however, it will not melt away like low-melting plastics.
Processing Temperature of Polypropylene
The process of manufacturing is directly related to the melting point.
Typical Processing Temperatures:
- Extrusion: 200°C – 240°C
- Injection Molding: 220°C – 280°C
- Blow Molding: 180°C – 230°C
These temperatures are kept above the melting point to ensure smooth flow and proper shaping without degradation.
Importance of Polypropylene Melting Point in Manufacturing
1. Product Performance
- Identifies final product heat resiliency.
- Precludes deformation during high temperature applications.
2. Manufacturing Efficiency
- Manages power consumption.
- Provides stability in quality of products.
3. Safety & Compliance
- Significant with food-grade products and medical items.
- Avoids a tearage of materials in use.
Polypropylene vs Other Plastics (Melting Point Comparison)
| Plastic Material | Melting Point |
|---|---|
| Polypropylene (PP) | 160–170°C |
| HDPE | 120–130°C |
| LDPE | 105–115°C |
| PVC | 75–105°C |
| PET | 250–260°C |
| Nylon (PA6) | ~220°C |
Polypropylene offers an excellent balance of heat resistance and cost-effectiveness.
Industrial Applications Based on Melting Point
Due to its high melting, and the fact that it has a high melting point, polypropylene is used in:
Packaging Industry
- FIBC bags
- Woven sacks
- Chemical packaging
- Fertilizer bags
Chemical Industry
- Containers for acids & alkalis
- Liners and protective sheets
Automotive Industry
- Interior panels
- Battery casings
- Under-the-hood components
Medical & Food Industry
- Syringes
- Food storage containers
- Sterilizable packaging
Does Polypropylene Melt in Boiling Water?
No.
The temperature at which water boils is 100°C and this is way lower than the melting point of polypropylene.
However:
- Long exposure can result in mild softening.
- Shape remains intact under normal conditions
This is one of the reasons why polypropylene can be used in hot-fill.
Thermal Degradation of Polypropylene
Though polypropylene melts at a temperature of approximately 160–170°C, thermal degradation begins at a significantly elevated temperature.
- Degradation begins: ~300°C
- Combustion: Above 350°C
Proper temperature control during processing prevents degradation and maintains material strength.
Environmental & Recycling Perspective
- Polypropylene is 100% recyclable
- There are numerous recycling steps with a melting point.
- Recycling temperature: ~230°C
The melting point is high thus giving it durability even after reuse.
Advantages of High Melting Point Polypropylene
- Better heat resistance
- Longer product life
- Higher load-bearing capacity
- Suitable for harsh industrial environments
- Safe for food and medical use
Conclusion
High melting point (160°C–170°C) of polypropylene is one of the most important reasons why polypropylene is very dominant in packaging, industrial, automotive and medical application.
It is one of the best plastics in the market today because of its capability to withstand elevated temperatures without losing its structural integrity.
The selection of the appropriate grade of polypropylene depending on the melting point guarantees more performance, safety, and longevity of any application.
