You have to read following key parameters in TGA: The atmosphere in which your reaction is taking place, i.e, air, nitrogen, oxygen etc.,

IDT (or onset): Initial decomposition temperature is the point where your material starts disintegrating and is the measure of thermal stability of that material.

MRDT: maximum rate of decomposition temperature- shows the regime when the maximum component in your material is decomposing. 

D1/2 (or d half): is the temperature when 50 wt.% of your material has decomposed.

FR (final residue): the amount left after the end of the heating, as it gives the final composition of the material.

The area under the derivative curve qualitatively determines the amount of that component decomposed.

From your curves, in both cases, area under the main decomposition stage is very close (or similar), it means that similar amount of that component  is decomposing as a function of temperature. However, the rate or mode of decomposition has changed after irradiation. The decomposition of first component is less, probably because that particular component has evaporated between your steps. More importantly, the IDT has significantly decreased from 275 to 247 C while residue remains same (very close). It may be alarming depending on your application. For example, high-performance application needs increased IDT while lithography or drug delivery needs decrease in IDT.

I would recommend you reading my attached papers for better understanding of this technique.

Good luck!

Dear Fatima Ahmed;

I think it will be better to characterize the change on the polymer matrix after irradiation first. Generally the irradiation effect is a surface phenomenon, which means the bulk of the polymer matrix will not be altered, ofcource this is a function dose, duration, and the matrix diffusability. This for sure will help understanding the different portion evolved at each stage of your thermogramm. It looks a very usual behavior. Regards

You have to read following key parameters in TGA: The atmosphere in which your reaction is taking place, i.e, air, nitrogen, oxygen etc.,

IDT (or onset): Initial decomposition temperature is the point where your material starts disintegrating and is the measure of thermal stability of that material.

MRDT: maximum rate of decomposition temperature- shows the regime when the maximum component in your material is decomposing. 

D1/2 (or d half): is the temperature when 50 wt.% of your material has decomposed.

FR (final residue): the amount left after the end of the heating, as it gives the final composition of the material.

The area under the derivative curve qualitatively determines the amount of that component decomposed.

From your curves, in both cases, area under the main decomposition stage is very close (or similar), it means that similar amount of that component  is decomposing as a function of temperature. However, the rate or mode of decomposition has changed after irradiation. The decomposition of first component is less, probably because that particular component has evaporated between your steps. More importantly, the IDT has significantly decreased from 275 to 247 C while residue remains same (very close). It may be alarming depending on your application. For example, high-performance application needs increased IDT while lithography or drug delivery needs decrease in IDT.

I would recommend you reading my attached papers for better understanding of this technique.

Good luck!

I have seen many researchers using TGA to determine the thermal stability of polymers, and I am still wondering how a test that is based purely on the weight loss can give you information on thermal stability!!! Thermal stability and decomposition analysis (that we do by TGA) are not the same!!!

In TGA test, you observe the weight loss only when the degradation proceeds to a step that volatile low molecular weight substrates are produced which is far from the beginning of the degradation. For example, commercial poly(lactic acid) grades do not show a weight loss until a temperature around 350*C, but anyone who worked with PLA knows that the degradation begins at much lower temperatures!

I suggest you to use GPC to evaluate the degradation as the molecular weight and molecular weight distribution are the most sensitive parameters to the degradation. 

If you do not have access to GPC, you can use rheometry tests (SAOS tests) at low frequencies (if your materials shows the Newtonian plateau) and see the effect of time sweep on the plateau region at the desired temperature(s).

Hi,

Ebrahim is right: TGA only gives a very partial information. Consider for example a virgin PMMA with a very high molar mass and a the same after irradiation. molecular weight will be different but TGA will remain the same (degradation onset = depolymerization temperature almost constant for all PMMA).

GPC, DSC for Tg measurements, sol gel analysis or even FTIR can give more suitable informations on the irradiation induced changes at molecular or macromolecular level.

regards

I guess she uploaded two curves and asked for the help based on it. Again, be aware that she has asked for the interpretation of TGA plots. I don't see if she has asked for others methods to determine thermal stability. Help and answer on the topic if you can:) Material science deals with n number of testing and characterization techniques and not everyone has access to everything. He/she has to find solution from what is available to them. Moreover, if you doubt on the already established techniques, trying improving your knowledge rather finding faults in technology. Good luck:)

Thanks for the feedback everyone. Unfortunately at this time I only have access to TGA so I am trying to make the most of it...

Special thanks to Dr. Tiwari for his elaborate answer. If time permits, could you please suggest any techniques using which I can determine exactly what is decomposing at the three different peaks? From my brief experience with TGA, I have usually seen 1 peak degradation this is the first time I am seeing a 3 peak degradation, could you briefly mention what kind of functionalities can cause this difference in number of peaks?

In TGA degradation You have to watch the number of sudden drops of the curve along with themperature where it starts falling. You can try drawing tangemts and get the point of drop and temperature. Before it starts major drop, usually, solvent, moisture around 100degreeC occurs. In organic compound the degradation depends the bond: some bonds are weak which break first and so on.Under radiation there may be generation of various types organic groups. They may react among themselves. Some cases anhydride may form which degrade at final stages. At last it is oxidation of carbon. You may see DTG plot.

DSC/DTA can also be used to analyse thermal stability of polymer matrix. 

I performed the DSC as suggested by many people, attached is the graph...

Tg at 150°C and degradation towards 400°C (which would agree with the onset of your TGA) ?

what's about comaring the virgin and the irradiated one?

regards

Thanks for the feedback Dr. Richaud, correct me if I am wrong but in the TGA graph the degradation from the sample starts at around 247C, whereas in the DSC its around 400C so the difference is huge....

Also, from this DSC graph what/how can we tell about the crystallization of the sample?

the deviation of baseline starts at ca 220°C... you should find in literature what the mechanism of thermal degradation of cellulose is and see if the first step of mechanism is endo or exo thermal

for morphology, no melting so amorphous polymer ?

regards

Dear Ahmad you must read basic terms such as TG, DTG, DTA, DSC, Thermal dgradation, thermal decomposition, half decomposition temperature, final decomposition temperature, peak temperature, and some thermokinetics evaluations method to find out the thermodynamic parametrs such as kinetic triplets. If degradation is found in range between 25-140 0C which might be due the lattice water and 140-240 0C due coordinated water and further might be due the organic moieties.....these things apply for complexes or chelate complexes or other organometallic compounds.

I recomend you to try the webinars by Netzch for the basics.

http://www.netzsch-thermal-analysis.com/en/events-seminars/details/webinar-simultaneous-thermal-analysis-sta-basics-and-application-possibilities-1.html

For the interpretation of TGA thermograms, find the percenatge weigt loss of compound and predict the major difference in percentage weigt loss. In TGA termograms different steps responsible for the removal of specific groups from compounds. Eg. water molecules removed at first step near abuot 100 C.

Dear, firstly you read out some basic term such as TG, DTA, DTG, DSC and some initial , final , half decomposition temperature, peak temperature. Then after, you must read out thermal decomposition, thermal degradation, mass loss, weight loss, thermodynamic triplet etc