Add your TGA and DTA graph and detail.

My graph is an unpublished one..So adding is public is difficult.Can you give me suggestion or general rules in interpreting DTA data

In general, the number of peaks observed in the DTA graph correspond to the number of degradation stages. And the temperature of the peak in the DTA corresponds to the temperature at which max degradation occurs. Hope this helps.

For TGA we can plot weight % vs temperature . DTG : Derivative weight loss vs Temperature. Derivative weight loss can we found from the TGA data itself. http://www.sciencedirect.com/science/article/pii/S0306261912009415 . In this article you can find the plots. 

Thanks Vinoth..The paper was too informative... :)

My opinion is to read papers.

The more papers your read, the more physical meaning you understand.

I also attach 2 websites for your references.

https://www.researchgate.net/profile/Wei-Hsin_Chen/publications?sorting=newest&page=4

https://www.researchgate.net/profile/Wei-Hsin_Chen/publications?sorting=newest&page=2

Please read review article on Thermal analyses. 

Differential Thermal Analysis

M. J. Vold

Anal. Chem., 1949, 21 (6), pp 683–688

DOI: 10.1021/ac60030a011

Interpretations of TGA data depend on your initial experimental setup. From the basic percentage weight loss versus temperature (or time), you can derive the rate of degradation with the respective independent variable.  The onset of temperature or time of the initial weight loss  could mean loss of volatiles or lower molecular weight constituents.  The onset of irreversible weight loss could suggest thermal degradations.  The rates are also derivable.  I suggest you do more literature search.

Thanks Gabriel..

Hi Noble

Have a look at these papers:

Properties and Functions of Melanin Pigment from Klebsiella sp. GSK

http://www.academia.edu/8037814/Properties_and_Functions_of_Melanin_Pigment_from_Klebsiella_sp._GSK

Filip Z., Semotan J., Kutilek M. Thermal and spectrophotometric analysis of some fungal melanins and soil humic compounds  (1976) Geoderma, 15 (2) , pp. 131-142.

E.A. Shurygina, N.K. Larina, M.K. Chubarova, M.M. Kononova Differential thermal analysis (DTA) and thermogravimetry (TG) of soil humus substances Geoderma, 6 (1971), pp. 169–177

Do you have some reference about melain? Usually, I think it is important you know the regions that happen the transitions of this. See some  reference.

Hi Noble

Please see this article. I hope it will help you.

http://www.sciencedirect.com/science/article/pii/S0022309310002930

But do take care of atmospheric condition of TGA analysis.Because thermal degradation in presence of  air and inert gas show completely different degradation steps.

For DTA data interpretation please see this article. I hope it will help you lots.