So, I have this epoxy/curing agent mixture. I run the non-isothermal DSC, and got the curing peak (see attachment). Based on the DSC data, how can I determine the curing time and temperature? I need to produce an epoxy composite to test on DMA, so I really need to know the curing time/temp before proceeding to the DMA step. Thanks in advance!!
hi
you can read the journal "thermochimica acta". basically, the first curing temperature is the onset in your thermogram. then, after sufficient cure, the network displays a Tg1 value which can correspond to a "vitrified" network, and might be below the value corresponding to 100% cure.
you have thus to perform an isothermal post cure above the Tg1 value.
complementary papers to eb read: Simon and Gillham in Journal of Applied Polymer Science
regards
Yes, the suggestions from Dr. Richaud are correct in view to have a look of the physics and chemistry involved during crosslinking. In general the reaction kinetics (and thus the time of curing) can be obtained both from isothermal and non isothermal DSC test.
(Please, have a look to my contribution to the Encyclopedia of Polymer Science -Wiley- on my Reserch Gate page)
However, if you want a rapid solution to your problem, please, do what follows.
1 - FIXING THE CURING TEMPERATURE
Using the same pan (and the fully reacted material therein) you used during the temperature ramp do a second temperature ramp from ambient temperature and check the Tg (glass transition temperature) of your system. The curing temperature of your laminate is just a Temperature above the Tg you have found, say Tcure = Tg+20°C.
2- FIXING THE CURING TIME
Concerning the time of curing it can be rapidly achieved by DSC subjecting a fresh sample to a rapid heating up to the curing temperature (fixed as described above) and holding the temperature constant for , say 30 min.. After that, cool down the sample and do a ramp test similar to that you have used in your first experiment (where you have obtained the total heat of reaction by integrating the reaction peak). If some peaks appear this means that a residual reaction has occurred and the cure time is not enough for a fully cured sample.
Incidentally the ratio of this peak area and the total heat of reaction obtained during your first experiment is a measure of the extent of unreacted resin. At this point you can , for example, double the time of curing (again on a fresh sample) and use the same procedure to ascertain that no residual reaction are in play. If so you have finally , found (in a few hours!) the curing time of your specific system.
P.S. Sometimes post-cure processes (isothermal holding at T=Tcure+50°C) are added to the first isothermal curing in order to relax the residual stresses that develop inside the laminate due to the crosslinking reactions.
Drs. Richaud and D'Amore, thank you so much for your answers! I guess I understand what to do now. Appreciated!
I would perform a model free kinetic measurement on the DSC to select curing temperature and time
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