I'm afraid the attached thermogram is so inaccurate to perform a reliable analysis. The test conditions have clearly been set incorrectly.

First, run a TGA experiment to check the thermal stability of your polymer and volatiles that might be present in your sample. Use the same purge gas and heating ramp for both TGA and DSC. Don't decompose the sample in the DSC cell, especially when using closed pans (burst danger)!

Re-run the DSC with recording the entire heat-cool-heat cycle, between room temperature (if you don't expect transitions at subambient temperatures) and the upper temperature, which is 50'C lower than the onset temperature of primary decomposition. In case a weight loss is observed by TGA within that temperature range, use an open/uncovered aluminum pan or a hermetic pan with a vent hole. A sample mass of 1 mg is definitely too small, use 5-10 mg instead to increase signal sensitivity.

Looking at the as-is thermogram, the endothermic peak centered at 125'C is highly unlikely to be associated with water evaporation. If it were so, a baseline drift would be expected after the transition due to a change in sample mass. Besides, the test was apparently carried out in a closed pan. The temperature range the main baseline spans over is surely selected incorrectly. The calculated enthalpy is enormously too high, about 370 J/g.

The sharp peak may be Tm, usually Tm peaks are kind of V shaped peaks. It would be better if you could provide the full cycle picture, it will be easy to answer.

I agree with Srikanth, a single heating scan is not very helpful, the heat flow may be complicated by moisture and processing history. It would be better to look at a heating/cooling cycle to a moderate temperature (eg. 300 deg.C)

The analysis of glass transition is completely messed up.

Beside the position and wrong curve shape you can check it when you have a look at the values you observe that the onset temperature is much higher as the inflection point or mid point. Possibly the wrong limits were set to analyse glass transition but to be honest i don't see a glass transition in the given picture.

The peaks are also strange. The first might be due to water evaporation as Srikanth and Peter suggested. And overall the broad peak might be melting of a very broad distribution of crystallites but i would suggest to repeat the measurement using the typical programme of heating/cooling/heating.

I'm not familiar with your equipment but possibly also a higher sample mass (5-10mg instead of the used 1mg) might be beneficial.

best regards

Matthias

I'm afraid the attached thermogram is so inaccurate to perform a reliable analysis. The test conditions have clearly been set incorrectly.

First, run a TGA experiment to check the thermal stability of your polymer and volatiles that might be present in your sample. Use the same purge gas and heating ramp for both TGA and DSC. Don't decompose the sample in the DSC cell, especially when using closed pans (burst danger)!

Re-run the DSC with recording the entire heat-cool-heat cycle, between room temperature (if you don't expect transitions at subambient temperatures) and the upper temperature, which is 50'C lower than the onset temperature of primary decomposition. In case a weight loss is observed by TGA within that temperature range, use an open/uncovered aluminum pan or a hermetic pan with a vent hole. A sample mass of 1 mg is definitely too small, use 5-10 mg instead to increase signal sensitivity.

Looking at the as-is thermogram, the endothermic peak centered at 125'C is highly unlikely to be associated with water evaporation. If it were so, a baseline drift would be expected after the transition due to a change in sample mass. Besides, the test was apparently carried out in a closed pan. The temperature range the main baseline spans over is surely selected incorrectly. The calculated enthalpy is enormously too high, about 370 J/g.

I totally agree with the other answers, especially a first TGA run could be useful to know the thermal stability range of the sample as Pawel suggested. Definitely you need to weight more than 1 mg, a too small sample is not representative in these analysis, and to put your sample in a dryer for 24 hours at least in order to do not consider the adsorbed/absorbed water contribute (if the water content is not the focus of your characterizations). Maybe for us it would be also helpful to know what kind of polymer we are discussing about.

I agree with Paweł P. Sobecki that the first endo-thermic peak has an onset point too high (~120 C) for elimination of adsorption water. This may be either melting of some crystalline substance with a relatively low molecular weight or thermally induced chemical decomposition like decarboxylation or elimination of water coordinated to some metal ions.

Some conclusions can be made from the enthalpy of this transition in J/g, which should be calculated separately for the first peak as well as for other peaks. Visually, the first peak has somewhere near 30 J/g, which is too high for polymer relaxation or irreversible processes in the first run of DSC experiment. The high value of this enthalpy shows that it relates rather to the main substance or some filler than to an impurity.

If this Netzsch device was calibrated using standard samples (Indium, etc.), so all peaks should be processed using this calibration, and their enthalpies should be given in J/g, not in mW/mg.

Proteus program of Nezsch surely gives a mathematical error in calculation of your glass transition obviously because of incorrect choice of its range on the back front of a narrow peak. To find such an error is a good achievement. You should report it to their support service.

I think that a stepwise drop of baseline above 250C is an indication of the polymer exothermal degradation process, similar to that observed in Oxidation Onset Tempearture (OOT) tests. That is the calculated area includes thermal effect of the degradation process. What is the polymer required for its DSC characterization heating up to 500C?

I would recommend also to obtain the basis line of the cell, just to see if there were some contamination.