Zeus
TECHNICAL
NEWSLETTER
Crystallinity in Plastics
Introduction
In previous Technical Newsletters, we mentioned the effect of crystallinity in plastics but never delved deeper into this topic. This Technical Newsletter will more closely consider crystallinity in plastics: what it is, and more importantly, how it affects the properties of plastics.
Most people are familiar with crystals only because of salt and perhaps growing crystals as part of a school science project. Therefore, talking about crystals and plastics together is a new concept to many people. In reality, polymers are not like salt, which is totally crystalline, but are semi-crystalline. Unlike crystals like salt, polymers have only short-range order and a much looser organization.
Crystallinity is one of the great divisions of the complete family of plastics. Amorphous polymers (those with no significant degree of crystallization) behave very differently than crystalline polymers (those with a significant degree of crystallization). Understanding crystallization and the effect it has on the properties of polymers can make understanding the behavior of polymer families much easier.
Amorphous and crystalline polymers:
Amorphous polymers
Amorphous polymers are those where the polymer chains have no well-defined order in either the solid or liquid states. The model that is most often associated with this characterization is a bowl of cooked spaghetti, where the long strands of spaghetti are both flexible and slide over one another. This is similar to a molten amorphous polymer as it is being processed. If the hot spaghetti is tipped into a bowl, then it will take the shape of the bowl, just as a plastic does when it fills a mold. After the spaghetti has cooled, the long strands tend to stick to one another, which is very similar to the behavior of an amorphous polymer after it has cooled.
The classic two-dimensional representation of an amorphous polymer is shown below:
Page
NEWSLETTER
Crystallinity in Plastics
Introduction
In previous Technical Newsletters, we mentioned the effect of crystallinity in plastics but never delved deeper into this topic. This Technical Newsletter will more closely consider crystallinity in plastics: what it is, and more importantly, how it affects the properties of plastics.
Most people are familiar with crystals only because of salt and perhaps growing crystals as part of a school science project. Therefore, talking about crystals and plastics together is a new concept to many people. In reality, polymers are not like salt, which is totally crystalline, but are semi-crystalline. Unlike crystals like salt, polymers have only short-range order and a much looser organization.
Crystallinity is one of the great divisions of the complete family of plastics. Amorphous polymers (those with no significant degree of crystallization) behave very differently than crystalline polymers (those with a significant degree of crystallization). Understanding crystallization and the effect it has on the properties of polymers can make understanding the behavior of polymer families much easier.
Amorphous and crystalline polymers:
Amorphous polymers
Amorphous polymers are those where the polymer chains have no well-defined order in either the solid or liquid states. The model that is most often associated with this characterization is a bowl of cooked spaghetti, where the long strands of spaghetti are both flexible and slide over one another. This is similar to a molten amorphous polymer as it is being processed. If the hot spaghetti is tipped into a bowl, then it will take the shape of the bowl, just as a plastic does when it fills a mold. After the spaghetti has cooled, the long strands tend to stick to one another, which is very similar to the behavior of an amorphous polymer after it has cooled.
The classic two-dimensional representation of an amorphous polymer is shown below:
Page