Introduction
- Have you ever wondered why insulation is used to keep buildings cool when a building is heated in summer or how a computer or electronic device is protected from overheating? All this is done with the help of thermal properties.
- Thermal properties are also used a lot in blown film extrusion; we will discuss further how thermal properties are used in blown film extrusion.
Table of Contents
What Are Thermal Properties?
- If understood in simple words, thermal properties describe the interaction of any material with heat. Meaning, how a material will absorb, store, conduct, or resist heat—it all depends on its thermal properties.
- When heat is applied to a material, the kinetic energy of its molecules starts increasing, due to which it can expand, transfer heat, or even resist. All these properties are different in different materials and also affect their applications.
Main Types of Thermal Properties:
Thermal Conductivity:
- Thermal conductivity tells how easily a material can transfer heat.
- Materials with high conductivity (like copper and aluminum) transfer heat fast, while materials with low conductivity (like wood, rubber, and plastic) resist heat.
Fourier’s Law:
Where:-
- q = Heat transfer rate (W/m²)
- k = Thermal conductivity (W/m·K)
- dT/dx = Temperature gradient
Heat Capacity:
- Heat capacity is the property that tells how much heat a material can store without increasing its temperature too much. Materials with high-specific heat can absorb more heat without getting warm too quickly.
- Heat capacity tells how much heat energy a material can store. Materials with high heat capacity (such as water) take time to heat up but can hold the heat for a long time.
Thermal Expansion:
- When a material gets hot, the temperature of that material increases, so its molecules vibrate more, causing it to expand.
Example:-
- Expansion joints are provided in railway tracks and bridges so that the tracks are not damaged and the structure is not damaged due to thermal expansion in heat.
- Glass and ceramics do not expand much, so they are used in heat-resistant cookware.
Thermal Resistance:
- Thermal resistance measures a material’s capability to inhibit heat movement. Insulators (e.g., fiberglass, polystyrene) have high thermal resistance, so they work to block heat.
Role & Applications of Thermal Properties in Blown Film Extrusion
- Extrusion is an important plastic processing technique used to make thin plastic films for packaging, agriculture, and industrial applications. Thermal properties are directly impacted in this process because heat transfer, cooling rate, and material selection all depend on thermal behavior.
- Let’s understand in detail the key applications of thermal properties in blown film extrusion.
Application in Blown Film:
1. Thermal conductivity: cooling rate and film quality
- If a material has high thermal conductivity, it will pass heat quickly and cool quickly.
If a material has low thermal conductivity, it will retain heat and cool slowly. - LDPE (low-density polyethylene) has low thermal conductivity, so it allows gradual cooling and helps in forming smooth and uniform films even at low cooling.
If you need a material for thermal insulation, LDPE is the better choice because LDPE has lower thermal conductivity. - LDPE → Low thermal conductivity → Slow cooling → Flexible film (best for packaging & stretchability).
- Nylon (PA) has comparatively higher thermal conductivity, so a fast cooling system is required. If you need a material that can handle moderate heat transfer while also providing mechanical strength compared to LDPE, nylon is the better option.
- Nylon → Slightly higher thermal conductivity → Faster cooling → rigid film (best for strength & durability).
- Desired properties can be achieved by controlling the cooling rate.
Conclusion:
Proper understanding of thermal properties in blown film extrusion is very important for process efficiency, film quality, and application suitability.
- Thermal conductivity: Thermal conductivity controls cooling and film thickness.
Specific heat capacity helps in energy consumption and process optimization. - Thermal expansion: Thermal expansion controls film shrinkage and warping.
- Thermal diffusivity: Thermal diffusivity helps in uniform heat distribution and defect-free production.
- Heat resistance: Heat resistance defines material durability for packaging and industrial applications.
Note: Do you want read more about thermal properties?
FAQ of ThermalProperties in Blown Film Extrusion
Why is Thermal Conductivity (𝑘) Important in Blown Film Extrusion?
Thermal conductivity decides how quickly the polymer melt will cool down. If the conductivity is high, the film will cool down quickly and become hard. If it is low, slow cooling will give a flexible and uniform film.
Which material transfers heat faster between LDPE and nylon?
Nylon’s thermal conductivity is slightly better than LDPE, so it passes more heat and cools faster. LDPE retains more heat, which helps it cool slowly and maintain flexibility.
Which material gives better heat resistance?
- High-Heat Resistant Films: Nylon (PA), PET, EVOH, Polyimide
- Low-Heat Resistant Films: LDPE, LLDPE, EVA
If a film is needed for high-temperature applications, it is better to use a multi-layer structure (such as Nylon-EVOH-PE combination).
