Why does plastic get white when bent?

Dyes for plastics and resins

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 plastics, 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.

Plastic expands with heat

Nowadays, it is commonplace for vehicle plastic trim to be ordered factory-painted. However, certain ranges and series integrate some plastic elements, such as door trims or window trims, uncoated. These plastics are deep black in color and usually have a textured finish.

Thus, the black plastics lose their intense and eye-catching color, which becomes an uneven and dull whitish black, while the transparent optics yellow and lose transparency. This deterioration is caused by these three factors:

When using any of these products, it is advisable to disassemble the affected plastic, as this makes it easier to sand and beautify it. If this is not done, it will be necessary to mask and protect the adjacent areas and components. In addition, the necessary risk prevention measures must always be observed.

To apply a stain it is necessary to clean the plastic well and degrease it and then apply the product with a sponge making longitudinal passes that cover the entire length of the part. It is not necessary to sand the piece, although it is recommended.

Restoring sunburned plastics

Soft plastics: Use a microfiber cloth soaked in rejuvenating liquid and rub with gentle circular movements. If the plastic of your dashboard is rough, apply the cleaner using a cotton towel as it adapts better to the surface and cleans more thoroughly.

Engine compartment: This type of plastics are dirtier. Do the same as in the case of hard plastic, but when you apply the cleaner, leave it to act for at least five minutes. Make circular and soft movements, this way the product spreads better and you get to recover the original shine.

Soft, hard and engine compartment plastics: If once you have applied the rejuvenator you have not achieved sufficient shine, spread a thin layer of plastic wax with a chamois and rub gently to achieve a better result.

Homemade plastic reviver

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 plastics, 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.