Hello Everyone,
I did several DSC tests on the electrospun PA66 nanofibers to obtain the glass transition temperature. According to the material datasheet, the Tg point of PA66, as cast, is around 55 C, but I thought it might be different for the nanofibers compared to the bulk material. I got different results from the DSC tests. You can find some of the results attached.
- The first case: The sample was subjected to a heating-cooling-heating (HCH) cycle from 0 C to 180 C by a heating/cooling ramp of 10 C/min.
- The second case: The sample has experienced a HCH cycle from 0 to 300 C.
- The third case: It is similar to the second case, but I think the sample contained moisture.
What is the Tg of the nanofibers? Because in the first heating cycle, two break points, one before 50 C and one before 100 C, are visible and for the reheating cycle, there is no break point in this temperature range? What is the small drop observed around 150 C?
I would be grateful if you could help me with the interpretation of the results.
Thanks in advance!
As PA66 is semicrystalline material having very low percent of amorphous portion, it needs to heat the PA66 sample with a higher heating rate of about 30 C/min to find the glass transition. For detail, you may read the paper
Article 'Thermal analysis of ABS/PA6 polymer blend using differentia...
Dear Milad,
Firstly, I will agree with you that DSC analysis of initial semi-crystalline PA 66 (before, as granules) and processed i.e., as nanofibers, will show (more or less) some differences. We have not enough information about the experimental conditions used to produce these samples, thus some of my comments are for discussion. However, in some cases, and for polymers with high crystallinity, for determination of Tg could be better to use MDSC (modulated differential scanning calorimetry). Still, the first DSC heating scan will give the information about the initial thermal properties of PA 66 nanofibers. Let us go to consider your examples and to try to find some more explanations:
1. The first case: heating PA 66 up to 180°C (I suppose that are also nanofibers). From the first DSC heating a Tg at above 70-75°C can be for discussion, while the small peak at about 160°C can be a processing additive specific for PA (e.g. magnesium stearate). Based on my practical experience on PAs, this kind of thermal treatment (heating to 170°C/ANNEALING) can lead to the increase of PA crystallinity and eventually of molecular weights.
2. The second and third case: the most important differences are mainly revealed by the first DSC heating scans. Unfortunately, we have not more details about the peak seen at above 170°C (the temperature is higher, I will not exclude an experimental artefact !?) and about the melting enthalpies to do more comments.
3. Regarding the third case, if the moisture was present in sample, the water in PAs is claimed to lead to some plasticizing effects, thus usually a slight decrease of Tg is traditionally for discussion for conditioned samples. Here the peak at higher temperature is missing, thus it will be nice to repeat these analyses and to verify the correct calibration of DSC apparatus. Don’t hesitate to use the information from literature and other suggestions already received from other RG colleagues!
Good luck in 2021 and best regards,
Marius
PS: For eventual interest & support:
https://www.scielo.br/pdf/mr/v12n2/12.pdf
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