What happens to a plastic when heated?

It is bad to heat food in plastic

It is an everyday image that we have seen a thousand times: a bottle of water (empty, of course) that twists and melts at high temperatures. We often encounter a series of physical or chemical phenomena that, because they are commonplace, often go unnoticed. For example, have you ever stopped to think why some polymeric materials, such as the polyethylene in plastic bags or rubber, are flexible, while others, such as PVC or methacrylate, are rigid? (I use the term ‘polymeric materials’ and not ‘plastics’ because, although all plastics are polymers, other polymers are not plastic, as is the case with rubber or natural products such as cellulose or proteins).

The reason lies in a physical quantity called glass transition which, although not exclusive to these materials, is typical of them due to their peculiar internal structure. The glass transition is the change from a flexible to a rigid state, or vice versa. It is a phenomenon associated with amorphous or glassy solids, hence its name, and does not occur in crystalline materials. Let us see why.

Eating plastic has consequences

The study was done with mice and the initial objective was to demonstrate how negative BPA is for them. Their surprise was that, when they were put in contact with alternative plastic materials, the effects were almost as harmful. These substitutes affected the reproduction of these animals in the same way.

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A good way to avoid using plastic to heat food is to replace our plastic lunch tupperware we take to work with a glass one. We will have to carry a little more weight in our bag or backpack, but it will be worth it.

Sometimes, however, we find foods that are only sold in plastic wrapping in the supermarket. In that case, we can take them out of that packaging and transfer them to a plate or a glass, porcelain or ceramic container. And from there to the microwave, while we throw the plastic into the yellow container.

Diseases caused by plastic

If they are heated or exposed to high ambient temperatures, they run the risk of decomposition of the plastic covering them and the formation of undesirable substances such as dioxins and other toxins that can migrate into the food.

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The EXPLANATION: The air inside the bottle reduces its pressure as the temperature drops, and the pressure outside the bottle reduces the volume and balances the internal and external pressures.

When you remove the plastic you will see that the two liquids will come together. What happens is that hot water is less dense than cold water. Therefore, the hot water tends to rise and the cold water ends up being below it. This phenomenon occurs mainly due to the activity of the molecules.

When a plastic burns, we are faced with a thermo-oxidative reaction that reduces the carbonaceous chains of the polymer to monomers or groups of monomers of low molecular weight and these, in turn, to CO2, water and other combustion products of lower molecular weight than the original polymer.

What happens if I put plastic in the microwave

Water molecules in a liquid state are arranged chaotically. The reason for this is that the hydrogen-bridging bonds are not very strong. However, at 0°C the hydrogen bridging bonds reach a stable point and, as a result, the molecules adopt a three-dimensional hexagonal crystalline conformation. In other words, in ice, the water molecules are completely ordered and separated from each other at the same distance. Thus, in ice there are fewer water molecules in a certain volume, i.e. water expands when it freezes.

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It should be noted that water expands when it cools and contracts when it warms between 4 degrees Celsius and 0 degrees Celsius. With metals for example, it is the other way around, when a metal is heated, it expands and if it is cooled, it contracts.

Water expands by 9% to 10% of its volume when it freezes. The curious thing is that materials and elements in nature expand when heated and contract when cooled. Therefore, if we fill a bottle with water and freeze it, it can break.