RAPID SERVICES TA - Thermal Analysis - Details
Example for a thermal analysis
What results do you get with the thermal analysis?
The thermal analysis can be used for a variety of purposes in the field of polymer technology as the following examples show for a Differential Scanning Calorimetry device (DSC).
The DSC is useful for the identification of materials. Out of the results of this chart the material was identified as Polyethylenterephthalat (PET).
The test specimen has been measured under nitrogen conditions and the first temperature increase has been evaluated. The first endothermal effect at a temperature of +81 °C shows the glass transition of the polymer. After a further increase of the temperature occurs an exothermic effect with a maximum of +141 °C. At this point a post-crystallization of the polymer takes place. It is recognizable that the material is in the amorphous phase.
After the post-crystallization at a temperature of +250 °C another endothermal effect occurs which characterises the melting process of the polymer. Because of the determination of the post-crystallization enthalpy or melt enthalpy (area under the graph) and the included value of a 100 % crystalline material (out of technical literature) it is possible to work out the crystallinity of the material.
At the given case of application the mold temperature has been kept very low during the processing to let the polymer hardly crystallise and get a transparent appearance.
Characterisation of PC/ABS
The figure shows three different DSC-measuring graphs of a Polycarbonat/Acrylnitril-Butadien-Styrol (PC/ABS)-blend. To draw reproducible conclusions for the processing the corresponding granulate of the respective test specimen has been measured.
The green graph shows the thermal constants of the granulate. Out of the component part, which is made of this granulate, DSC-test specimens have been taken. The red graph shows the test specimen which has been taken near the gate and the black graph shows the test specimen which has been taken away from the gate. To get the effects of processing out of the DSC-graphs the first temperature increases have been compared. Synthetic air has been used as flushing medium. The glass transition at a temperature of +110 °C characterises the SAN-component of the ABS-share. At a temperature of about +140 °C begins the glass transition of the PC-share.
Endothermal and exothermic effects at the PC-glass transition are recognizable at the measuring graphs of the test specimens of the component parts, which have been put down to entropy-elastic relaxations. These entropy-elastic relaxations characterise frozen-in macromolecule chain conditions which come into being during the processing. At the glass transition zone these macromolecules have the possibility to relax as a result of the temperature increase.
It is also recognizable that after the softening of the ABS-component (glass transition) because of the immobility of the PC-share no frozen-in tensions are able to relax. The glass transition stage (characterized by the CP-value) is as higher marked on the granulate graph as on the graphs of the component part test specimens. This shows that as more energy is required to transfer the macromolecules of the granulate into the softening phase as for the component part specimens. This effect can be put down to the high temperature difference between the mold temperature and the melt temperature whereby the macromolecules do not fall into the lowest-energy condition but already freeze at an earlier moment. Because of this fact the macromolecules can already relax at a low amount of energy required.
The granulate measuring-graph follows the baseline approximately again after the PC-glass transition and begins to fall off at a temperature of about +220 °C. This process characterises the beginning of the thermo-oxidative degradation. The component part specimens already begin to degrade thermo-oxidative immediately after the PC-glass transition. The onset temperatures for this degradation are about 25 °C lower than the temperature which has been determined at the granulate. The thermal influence by the injection molding process is recognizable, which was relative high at the given case of application. For the elucidation of the effects the measuring-graphs had been pushed together at a temperature of about +125 °C.
Contact: DI Jürgen Hohenbichler