My polymer is PLA and I follow the following steps (DSC 25):
first heating " rate 10 C/min- fixed at 200 C for 5 min"--> remove the thermal history
cooling " rate 5 C/min - fixed for 2 min at 0 C"
second heating " rate 5 C/min - until 200 C"
Additional Question: what will be the steps if i want to study the annealing affect?
If your material had irreversibly crystallized through the first heating cycle, you obviously cannot see any peaks of Tg and crystallization through the further heating cycles. I think, the absence of these peaks is an evidence for irreversibility of the processes occurred at the first heating.
Dear Mohamed,
Based on my practical experience regarding the characterizations by DSC of diverse grades of PLA, the different rates of cooling or heating could influence the thermal behavior of your polymer.
In your case, using a relatively slow cooling from the molten state, i.e. 5°C/min, the polymer could crystallize even that you didn’t see an evident crystallization exotherm on your DSC cooling curves. Thus, because your PLA is more or less crystallized, in the second heating it will be difficult to determine the glass transition temperature with a traditional DSC instrument, while it is possible to not have an additional cold crystallization process.
Regarding the second question, i.e., the annealing effect, for instance I will recommend two techniques: a) rapid cooling from the molten state to the temperature of interest and keeping in isothermal conditions the required time; b) Prepare firstly an amorphous PLA (e.g. by rapid quenching of melted polymer using nitrogen liquid or other cooling agent) and then heat the samples at the temperature of interest and keep them in isothermal conditions.
Finally, I will say that my comments are quite general. The nature of your PLA (molecular weights, isomer purity, presence or not of some additives, eventually a previous processing and degradation, etc.) could affect the thermal behavior of this polymer.
I will comeback with some selected references !
Good luck in your R&D study and best regards,
Marius
Marius Murariu
Dear Dr. Marius
Thank you for your great answer, and I'm looking forward to the references
Regards,
Mohamed
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering
- Annealing