The Expanding Nature Of Plastic Under Heat: How Much?

Plastic is a material that can expand when heated, but it can also shrink. This phenomenon is known as negative thermal expansion (NTE) and is caused by the difference in thermal expansion on either side of the plastic creating an internal stress. When the temperature gets higher, the plastic goes softer and bends when it can no longer hold the stress. The amount of expansion depends on the manufacturing process, the material used and the thickness. For example, a 3m strip of UHMWPE or HDPE can grow by as much as 9mm for a 15° temperature change.

Plastic expands when cooled

When plastic is heated, it softens and bends. This is due to the difference in thermal expansion creating an internal stress. The plastic sheet bends when the temperature gets higher and the plastic goes softer, until the plastic structure is weakened to a point that it cannot hold the stress. This is particularly true of thermoplastic semi-crystalline materials, like Polyethylene, which has a low flexural modulus.

However, the expansion rates of plastics are not particularly high. A 3-metre strip of UHMWPE or HDPE can grow as much as 9mm for a 15° temperature change. Nylon and Acetal can grow as much as ten times that of your typical metals.

One example of plastic expanding when heated is the little plastic rings that are put on the top of drinks to seal them. When these are heated, they shrink.

Plastic shrinks when heated

It is a common misconception that plastic expands when heated. In fact, plastic shrinks when heated. This phenomenon is known as negative thermal expansion (NTE). When the temperature gets higher, the plastic goes softer and bends. This is due to the difference in thermal expansion creating an internal stress. The plastic structure weakens to a point where it cannot hold the stress, and the plastic sheet bends.

The amount of shrinkage depends on the manufacturing process, the material used, and the thickness of the plastic. For example, a 3-metre strip of UHMWPE or HDPE can grow as much as 9mm for a 15° temperature change. On the other hand, Nylon and Acetal can grow as much as ten times that of your typical metals.

It is important to note that not all plastics exhibit NTE. Some plastics may expand when heated, especially if they are heated unevenly. This can create internal stress, leading to bending or warping of the plastic.

Overall, the behaviour of plastic when heated depends on various factors, including the type of plastic, the manufacturing process, and the temperature change.

Plastic sheets bend when heated

Plastic sheets can bend when heated due to the difference in thermal expansion on each side of the sheet, which creates an internal stress. As the temperature increases, the plastic softens and weakens, and when it can no longer hold the stress, it bends. This phenomenon is observed in thermoplastic semi-crystalline materials like Polyethylene, which has a low flexural modulus.

The amount of expansion in plastics due to heating can vary depending on the material. For example, a 3-metre strip of UHMWPE or HDPE can expand by up to 9mm for a 15-degree temperature change. On average, Nylon and Acetal can expand up to ten times more than typical metals.

It is important to note that some plastics exhibit negative thermal expansion (NTE), meaning they shrink when heated and expand when cooled. This behaviour is also observed in other materials, including certain ceramic oxides, phosphates, cyanides, and graphite.

The expansion or contraction of plastic sheets upon heating depends on various factors, such as the manufacturing process, the material used, and the thickness of the sheet.

Plastic expands more than metal

A 3-metre strip of UHMWPE or HDPE can grow as much as 9mm for a 15° temperature change. Nylon and Acetal could grow as much as ten times that of your typical metals.

However, it is important to note that some plastics exhibit negative thermal expansion (NTE) and shrink when heated. This is due to the molecular bonds in the material.

Plastic changes state to liquid when heated

However, some plastics seem to shrink when heated. This is because the plastic softens and bends due to internal stress. This phenomenon is known as negative thermal expansion (NTE) and is seen in other materials besides plastics/polymers, such as many ceramic oxides (particularly molybdates and tungstates), phosphates, cyanides, and even graphite.

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