When looking for bulk packaging material that can withstand industrial use, the most important question to ask is: Will this material stand up to high temperatures?
It’s not just the high temperature in your warehouse that would be of concern. For example, you need to consider the temperature when filling your bags with hot product, when the bags are exposed to direct sunlight on a loading dock, and when your product needs to be sterilised.
The polypropylene melting point and the thermal properties of polypropylene define whether or not a bag will be safely manufactured, or fail when exposed to these conditions.
Below, we'll walk you through everything you need to know about polypropylene's thermal performance.
What Is the Polypropylene Melting Point?
Typically, polypropylene has a melting point ranging from 130°C to 171°C (266°F to 340°F). This is one reason why many applications would use polypropylene that require heat and strength.
In the manufacturing process, the polypropylene melting point is the temperature at which polypropylene switches from a solid to a liquid. This property of polypropylene is important when using the injection moulding, extrusion, or blow moulding processes to create parts from polypropylene.
In the case of industrial packaging, the melting point becomes less about manufacturing and more about providing a safe working environment. You will need to determine at what temperature your bags will weaken, as opposed to the melting temperature of polypropylene.
PP Melting Temperature vs Safe Working Temperature: Know the Difference
A lot of customers are confused about the polypropylene melting point and how they relate to safe working temperatures. The range for reliable continuous use of polypropylene is generally 0 to 100°C (32 to 212°F); heating it above this will produce deformation.
At temperatures below 70 °F (21 °C), you have a molecular shift in the structure of polypropylene that is found in the fabric, and it will not stretch very much; therefore, the likelihood of stretching is minimal. The higher the temperature goes, the greater the loosening and stretching will occur.
While the polypropylene melting point is well over 130 °C, the appropriate filling temperature for a traditional multi-goods bulk bag is significantly less. For a conventional bulk bag, you should not fill it with anything above 200 °F (93 °C).
Thermal Properties of Polypropylene: What Affects Heat Resistance?
There is a wide range in the way polypropylene reacts when exposed to heat. Many properties impact how PP behaves with respect to heat resistance, including:
1. Type of PP
A rigid homopolymer polypropylene has greater heat resistance than a copolymer consisting of ethylene (the polymerisation of ethylene will produce a flexible material with somewhat reduced thermal stability).
2. Crystallinity
The crystalline structure of polypropylene increases the other properties of polypropylene (e.g. heat resistance, stiffness), with higher crystalline amounts yielding better results in high-temperature environments
3. Additives and stabilisers
Use of additives (i.e., UV stabiliser, heat stabiliser, and fibreglass/talc fillers) will have a major impact on modifying the thermal properties of polypropylene, thereby improving performance in extreme applications.
4. Processing conditions
When extruded or injection moulded, polypropylene requires barrel and melt temperatures (i.e., barrel temperature ranging from 180ºC – 240ºC; Melt temperature ranging from 200ºC – 260ºC) to yield an acceptable final thermal behaviour. The method used to process polypropylene can greatly affect its thermal behaviour in the finished part.
Want to understand which bag specification suits your materials? Explore our FIBC product range →
Polypropylene Melting Point in Context: How It Compares
Understanding the PP melting temperature is most useful when you compare it to alternatives.
The melting point of PE is approximately 230 degrees Fahrenheit (110 degrees Celsius); for high-density Polyethylene, it is marginally better, at 260 degrees Fahrenheit (approximately 127 degrees Celsius) on the same scale. However, due to the design of FIBC bulk bags made from woven polypropylene, they will have nearly the same ability to handle temperature when compared with standard PE grades.
What This Means for FIBC Bulk Bags
How polypropylene will work in regard to bulk bag (FIBC) behaviour in actual conditions is reflected in the thermal properties of polypropylene.
Standard woven PP FIBC bags:
Filling temperatures of up to 200°F (93°C) are suitable for standard FIBCs (i.e., fillable with product without a liner).
With a polypropylene liner:
Polypropylene liners will be significantly thicker, stronger, and capable of carrying an item’s heat for considerably longer than Polyethylene liners at higher temperatures (e.g., up to 295°F [146°C]). They are the most appropriate option for highly regulated industries (e.g., pharmaceutical) because they provide superior thermal insulation performance for FIBCs as compared to standard use of FIBCs by themselves.
With a Polyethylene liner:
Polyethylene liners will generally be able to safely hold material at temperatures up to approximately 170°F (77°C). Anything hotter than that will cause the Polyethylene liner to lose its structural integrity and break down.
This is especially important for industries like food processing, chemicals, and pharmaceuticals, where products are often filled hot directly after manufacturing.
Handling hot or temperature-sensitive materials? See how we serve your industry →
Food Safety and the Polypropylene Melting Point
One of the most important thermal properties of polypropylene as both a food and pharmaceutical packaging material is its ability to withstand high heat during use (i.e. microwave use, boiling and the cleaning process).
Unlike many other plastics, polypropylene remains stable at temperatures up to around 266°F (130°C) without softening or deforming, making it safe to use in microwaves, suitable for boiling, and able to withstand high-temperature cleaning.
These properties of polypropylene suggest that it is suitable for use in microwave-safe food containers, hot-fill packaging and medical equipment that must remain intact after being subjected to long periods of high heat.
Valex Ventures produces BRCGS-Certified food-grade large bulk bags (FIBC) made from recyclable polypropylene which provide safe performance across the temperature ranges where food and agricultural products are processed.
Need food-safe bulk bags built for heat tolerance? Read about our recyclable materials →
What Happens When PP Exceeds Its Temperature Limits?
Knowing the PP melting temperature also allows you to understand where the material will fail before it actually does. This is what happens to polypropylene if the material is exposed to temperatures above the safe working temperature range:
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The woven fabric starts to stretch and give way at the molecular level
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The ability to support a load is decreased, which creates a safety risk when the bags are filled
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At the polypropylene melting point itself, the material becomes liquid without any structural integrity
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If you continue to expose the polypropylene to temperatures above its melting point, the polymer will continue to degrade, reducing its useful life.
For these reasons, it is absolutely critical to match the fill temperature of your bags and the appropriate bag specification - as well as the type of liner - for each bag use.
Not sure which specification you need? Talk to the Valex team →
The Bottom Line
The polypropylene melting point, typically between about 130°C - 171°C (266°F - 340°F), provides manufacturers with a greater degree of heat resistance than many other types of plastics. When thinking about polypropylene packaging for industrial bulk applications, the temperature range allowed for safe working conditions is the more critical measurement: up to 93°C (200°F) for standard FIBC containers; and 146°C (295°F) for those with polypropylene liners.
Understanding the thermal properties of polypropylene will help you select suitable bag styles for protecting your product, employees, and supply chains. In addition, if you have high-temperature sensitive materials or applications requiring hot fill type packaging, the specifications for the packaging will be as important as the material of the packaging.
Frequently Asked Questions
1. What is the polypropylene melting point?
Polypropylene melts at about 130°C - 171°C (266°F - 340°F), depending on the grade and type of polypropylene.
2. What is the safe working temperature for polypropylene bulk bags?
Standard woven polypropylene FIBC bags should be filled to a maximum temperature of 93°C (200°F). This maximum temperature increases to 146°C (295°F) when using polypropylene liners.
3. How do the thermal properties of polypropylene compare to Polyethylene?
PP has a greater melting point than both low and high-density PE, which makes it a better choice than either type for industrial packaging applications exposed to heat.
4. Does heat affect the strength of polypropylene bags?
Yes. In addition to having a high melting point, when exposed to heat above working temperatures, the woven PP fabric will stretch and become loose, reducing load capacity and increasing safety hazards.
5. Is polypropylene safe for food contact at high temperatures?
Yes, food-grade PP that meets UK and EU food contact material regulations can tolerate temperatures of up to 130°C, making it acceptable for hot-filled packaging and high-temperature cleaning processes.
