The crystallinity rate is a measure of the proportion of crystalline material in the sample studied.
There are three types of crystallinity rate:
mass, noted ϰm, defined by the ratio of mass of the crystalline phases to the mass of the sample
volumetric, noted ϰv which, in the same way as the preceding one, is defined by the ratio of volume of the crystalline phases to the volume of the sample
and finally, molar defined by the ratio of the number of moles of crystalline phases to the number of moles of the sample
A crystallinity rate can vary between 10% and 80%. A higher crystallinity rate is only possible with molecules with low molar mass and/or specially annealed samples.
Thus, here are some examples of polymers with different crystallinity rates:
- Polyoxymethylene (POM copolymer); 75% crystallinity
- Polybutylene terephthalate (PBT); 40%-50% crystallinity
- Polyethylene terephthalate (PET); Crystallinity 30%-40%.
The crystallinity of a polymer depends on several factors: the cooling conditions, the additives used, the flow conditions during solidification and finally, the fillers mixed with the polymer.