PVC is a fascinating material with many uses across various industries, whether you’re looking at semi-rigid injection compounds or rigid extrusion compounds. However, the way it reacts to temperature is fairly consistent across different formulations.
In this blog, we highlight what happens to PVC at different temperatures so that you can better understand how it should be used for maximum effectiveness.
Below Freezing
When temperatures are below 0°C, PVC becomes more rigid and brittle because the molecular motion within the polymer chains slows down, making the material less flexible.
If frequently exposed to these cold temperatures, PVC has the potential to become brittle and crack under stress. The thermal contraction that takes place under such sub-zero temperatures can also cause PVC to undergo subtle dimensional changes.
These contractions need to be taken into account where applications involving tight fittings or structural components are concerned.
Room Temperature
When PVC is subjected to room temperature, generally between about 10°C and 40°C, it exhibits a more stable mechanical state. This means it maintains a good balance between flexibility, durability, and strength.
At room temperature, PVC tends to perform optimally, making it suitable for a wide range of applications. Thermal expansion or contraction at these temperatures is virtually nothing, thereby ensuring dimensional stability for industrial or manufacturing uses.
Moderate Heat
When the temperature rises above 25°C, up to about 60°C, PVC becomes more flexible. The polymer chain gains mobility, which enhances the material’s flexibility. This is useful when developing products such as hoses or flexible tubing.
Although PVC will remain solid at these temperatures, prolonged exposure, particularly towards the upper limit of this temperature range, can cause the material to soften slightly.
In some cases, this can affect the material’s load-bearing capacity and shape retention capabilities when put under stress.
High Temperatures
When subjected to temperatures between 60°C and 100°C, PVC softens more significantly. In many cases, it might even deform under its own weight or external loads. This is owing to the increased molecular motion within the polymer chain, which reduces the intermolecular forces that hold the polymer chains together.
Certain formulations of PVC compounds allow them to withstand these temperatures better. However, for most common PVC compounds, these high temperatures cause the plasticisers and other additives to start migrating to the surface or volatilising, thus compromising the material’s integrity.
Extreme Heat
When subjected to temperatures above 100°C, PVC starts to soften and degrade through a process that includes dehydrochlorination, where hydrogen chloride gas is released, leading to the formation of a polyene structure. This can cause discolouration and loss of mechanical properties, and will start changing the shape of the product.
Above 150°C, PVC is also prone to igniting and burning, so it is generally not suited to these types of temperatures.
However, under highly controlled circumstances, usually at temperatures of around 160 – 200°C, PVC can become fully plasticised and ready for remoulding. Within this range, the polymer chains can be given enough mobility to allow the material to flow and be reshaped, making it ideal for recycling.
If you are looking for a company that can provide you with everything from a semi-rigid injection compound to a blow-moulding compound or a flexible extrusion compound, contact us at IPC.
Frequently Asked Questions
At what temperature does PVC soften?
Flexible PVC compounds begin to soften around 50°C to 60°C, depending on the Shore A Hardness, while rigid PVC compounds soften at 70-90°C. As the polymer chains become more mobile, structural strength and shape stability are reduced.
Although certain specially designed industrial-grade formulations can tolerate these conditions slightly better, most standard PVC compounds will deform if exposed to sustained heat within this range.
What causes PVC pipe to crack?
PVC can crack due to cold temperatures, mechanical stress, chemical exposure, or impact over time. When exposed to freezing conditions, the polymer chains lose flexibility and become brittle. Any added pressure at this stage, such as from internal water expansion or external force, can then cause cracking.
UV exposure and age-related degradation can also weaken the pipe, increasing the likelihood of fractures.
Is PVC toxic when heated?
When PVC is heated above 100°C, it can start to decompose, releasing hydrogen chloride gas and other harmful compounds. At even higher temperatures or during burning, this process accelerates and can produce toxic fumes.
Therefore, proper ventilation and temperature control are essential when processing or welding PVC materials.
Does PVC shrink when heated?
No. PVC expands when heated and contracts when cooled. However, repeated cycles of heating and cooling can cause slight dimensional changes over time. This is why tight fittings or assemblies using PVC should allow for minor movement to prevent stress or distortion during temperature shifts.
Does PVC release dioxins when burnt?
Yes. When PVC burns at uncontrolled temperatures, it releases dioxins, hydrochloric acid, carbon monoxide, and particulate matter. These emissions are hazardous to both humans and the environment. For this reason, PVC should never be incinerated outside regulated recycling or industrial settings.
How does temperature affect plastic versus metal piping options?
Plastic piping, including PVC, expands more rapidly under heat and becomes less rigid, while metals can tolerate higher temperatures before softening. That being said, metals corrode faster in moist or chemical environments. PVC offers stronger corrosion resistance and is lighter weight, but it’s not suited for sustained extreme heat or direct flame exposure.
How hot can PVC pipe get?
PVC pipe can handle water or air temperatures up to about 60°C under normal use. Beyond that, its mechanical strength and pressure rating drop quickly.
For environments that consistently exceed this range, a high-temperature alternative such as CPVC or metal should be considered.
Can PVC withstand heat?
PVC can handle moderate heat but is not designed for sustained exposure above 60°C. At these high temperatures, the structure begins to soften, and its rigidity declines. Although IPC can deliver specialised high-temperature PVC formulations, they are still limited compared to heat-resistant plastics or metals.
Is PVC heat-resistant?
PVC offers limited heat resistance. It performs well under mild thermal fluctuations but not under constant or intense heat. For applications that involve long-term exposure to hot fluids or ambient temperatures, materials like CPVC, PEX, or metal piping might be more suitable.
Is it safe to pour boiling water down the drain?
No. Boiling water, typically around 100°C, can warp, soften, or deform PVC drain pipes, especially if done repeatedly. It can also weaken pipe joints and seals; therefore, for clearing clogs, it’s safer to use warm water mixed with mild detergent or a suitable non-corrosive cleaning agent instead of boiling water.
