Topic: Investigation of thermal material properties
Determination of the Crystallinity of Plastics
Problem
The product has an undesirably high level of brittleness and is therefore unsuitable as a packaging material. The aim is to identify the causes of the brittleness and improve the material properties.
Strategy
To solve the problem, a chemical and thermal characterization of the plastic was carried out to determine the transformation temperatures and enthalpies and thus optimize the crystallinity and toughness of the material.
Step 1: Material determination using FTIR spectroscopy
The plastic was analyzed using FTIR spectroscopy (Fourier transform infrared spectroscopy) to determine its chemical composition and possible additives.
- Result: The plastic is amorphous PET (PET-A).
- additives: There were no fillers or additives detected.
Step 2: Characterization of the processed plastic using differential scanning calorimetry (DSC)
The DSC method was used to investigate the crystallinity and thermal behavior of the plastic under different temperature conditions.
- Result: The plastic has a high degree of crystallinity of 48% .
- Thermal behavior: PET crystallizes above the glass transition temperature (Tg), which leads to a change in the material properties.
Intermediate result
The cooling rate during production is too low, which does not sufficiently prevent complete crystallization of the PET. This insufficient cooling leads to higher crystallinity, which promotes the brittleness of the material.
Step 3: Identification of the optimal cooling rates on the starting material
To avoid unwanted crystallization, a temperature-time kinetics developed to determine the optimal cooling rates.
- Objective: Adjust the cooling rate to achieve lower crystallinity and improve the toughness of the material.
final report
The investigation revealed that a cooling rate of at least 30 K/min is required to reduce the degree of crystallization while increasing the toughness of the material.
Suggestions
For the intended use of the material, a faster cooling during production to reduce brittleness. Alternatively, glycol-modified PET (PET-G) because this material has lower crystallinity and improved toughness.
