DSC - Science topic

Hi,

it looks like a measuring artifact. Something similar can happen when the sample loses contact with the pan/platform and decouples the heat transfer to the sensor. It might also be a calibration issue. What are the absolute readings in the drop? Does that appear in repeated runs in exactly the same position? Does that appear in different samples or on a different device?

Kaushik Shandilya Thanks

"eV" is get written by mistake; temperature is in centigrade.

Please share the references as well.

We have obtained the similar curve for DSC of rigid PU foams

You have melting peaks of PU components

I would be much grateful if you could kindly share the reference paper as an attachment.

tes

Sharp endothermic peak is usually correlated to the melt of crystals whilst exothermic to re-crystallization of amorphous materials, provided the materials were not degraded.

According to DSC/TGA of your sample, it can be concluded that the material was melted (1st sharp peak) during degradation (2nd broad peak) and the last (can be anything like recrystallization of different materials, or artefacts due to degradation etc. )

Hi, This can ba a potential topic: Investigation of the Physicochemical Properties and Stability of Food-Grade NLCs

In my suggestion the title may be " Characterization of Food materials for their quality"

Dear Samir Zergat ,

Since the dissolution of a crystal involves changes in the heat flow of the system, it should me possible to measure this using DSC. I will leave you here some links that might be useful:

Best of luck!

Dear Rob Keller,

Thank you so much for your reply, I converted the X-axis to the reference temperature, and the loop is missing!

Best regards!

Marius Murariu Thank you very much for your good answer and suggestions. I will look further for this analysis🙏

Dear Vs

1. The increase and decrease of cp with increasing temperature is due to the change in the heat capacity of the sample. As the temperature increases, the heat capacity of the sample increases until it reaches a maximum value, then decreases as the temperature continues to increase. This is due to the fact that the molecules in the sample are vibrating more and more as the temperature increases, and the heat capacity of the sample is a measure of the amount of energy required to increase the temperature of the sample. 2. To determine if the domains of a protein interact with each other, we can look at the thermogram of the protein. If the thermogram shows a single peak, then the domains are likely not interacting with each other. However, if the thermogram shows multiple peaks, then this indicates that the domains are interacting with each other. This is because the multiple peaks indicate that the domains are undergoing different transitions at different temperatures, which suggests that they are interacting with each other.

MDSC - modulated DSC.

Dear Aisha Abdo ,

what is the issue?

melting point versus crystallinity?

Do you expect any relation?

By the way; your XRD measurement is related Ketoprofen as nanosuspension; thus I expect, that you mainly see the dispersing agent in the XRD pattern, but not the KP.

Liquids have XRD pattern like that you presented.

So, to my opinion, any conclusions do not work here...

Best regards

G.M.

Hi Vlado,

I would recommend to address your question directly to the TA Instruments' people:

Dear Maheep Kumar,

We can get the specific heat capacity from DSC data using the following equation:

dQ/dT = Cp*beta*W

dQ/dt = heat flow; beta = heating rate; W=sample specimen mass

Step1: convert DSC values (mW/mg) into mW by dividing the mass of the sample to get heat flow

Step2: heat rate is step size to raise the temperature during the run

step3: specific heat capacity is obtained by rearranging the equation (1)

Reference: https://www.tainstruments.com/pdf/literature/TA279.pdf

I hope this may help

With regards,

R. Rajesh

Dear Abeer Osama . Don't know about IR, but with DSC you can see if there is an amorphous phase in your system. Attached is an paper that describes the main points of this analysis (Paper 1). In addition, I propose to consider the option of using a microscope with polarized light. The amorphous form of a component under a polarized microscope will not appear in color, just clear so that the color matches the observation base in the microscope. This experiment does not require special equipment, only a microscope with an appropriate device. I am also attaching an paper where a similar experiment was carried out (Paper 2).

Thank you for your answer, I will consider this

Hello Graça Brotas ,

There is one caveat which I forgot mention. In the statement of your question, you mentioned using a DSC apparatus. This type of instrumentation is usually used to detect phase transitions in materials over some temperature range, i.e., an inert reference material and a sample material have their temperature swept over a fixed temperature range, and any heat evolved or absorbed by the sample, due to phase transition, is measured with reference to the inert reference material; the inert reference material is chosen not to exhibit any phase transitions in the swept temperature range. If you employ a steady state apparatus (thermal conductivity comparator or an absolute thermal conductivity setup) to measure the thermal conductivity, make sure that the material(s) subjected to the spatial temperature gradient do not undergo a phase transition anywhere in the temperature range of the gradient, as this will usually cause the thermal parameters of the material to change, at that point in the material(s), and invalidate the measurement.

Regards,

Thomas Cuff

@Vadim S. Gorshkov. The expected result from DSC is that the stable sample should show melting point greater than the unstable one. But I am not getting as such.

Yes exactly, and it is well explained in one of the attached files. It adds also that the induction of crystals formation for sure will not be the same as in the reference enthalpy you refered to, because of many factors. This may include the environmental conditions, the instrument used and its accuracy (expected high compared to old instruments), the specimen holder (nature and geometrical form), and possibly others, all contribute to the obtained values. However as a general view, the values are not so far from each other. Good Luck in your work

dimethoxyethane as an ether all ethers are prone for form peroxides which can be explosive when the solvent drys. There is a free radical inhibitor (typically butylated hydroxytoluene) that is added at ppt levels to most ethers that inhibits peroxide formation. This increases the shelf-life of the ether.

Appreciate your comment sir.

Mr. piotr

I think its because of chemical structure of PEG , the PEG chemical structure contains carbon and hydrogen bonds which may disturb the chemical structure of PLA.

Suggest the following paper:

Gerhard Martens

As per the material data sheet from a supplier, the degradation temp is >200 degrees and It is a thermoset material so I don't think it had structural change property after first heating.

If structural change is the real reason, In a few works of literature there is Tg in the second heating ramp for thermoset materials(Epoxy resin). This information made me raise a question.

Q) Is the DSC test reliable to find Tg values for composites or It only reliable for pure resin systems?

Q) Does it really thermoset composite matrial show Tg values in second heating?

Thanks in advance.

Best regards

Bharath. G

Dear Gyanendra Prasad Panda, please have a look at the following books. My Regards

- Thermal analysis of polymers: fundamentals and applications Joseph D. Menczel, R. Bruce Prime (2009)

- Principles and Applications of Thermal Analysis, Paul Gabbott (2008)

Dear Hariharan Sekar, repeated scans of the same sample may give results, but becareful may be the Tg is located out of the scan range of temperature. My Regards

Dear Xiao Yuhan, you can assist and enhance drying by applying vacuum. Also may be changing THF by other highly volatile solvent will solve the problem of residual solvent. Melt casting between PTFE sheets also is an option to avoid completely the use of solvents. My Regards

Direct conversion of heat flow curve into heat capacity as suggested by Jarosław Ferenc would not provide heat capacity; the whole answer is rather misleading.

(1) There are two "standard" methods for determination of cp using DSC - a three step method (sample, reference, baseline) or two step mehod (sample, baseline). They BOTH require measuring isotherms before and after a heating segment in order to "anchor" the heat flow curve with respect to zero.

(2) As "pure cp" is rather weak thermal effect (compared to phase transitions), usually higher heating rates and higher samples masses are employed. The choice certainly depends on the material properties (expected cp, heat conductivity, geometry); however, 10 mg and 10 °C/min is usually a good choice.

Essentially all books about DSC contain a chapter devoted to cp measurement. I would recommend

Vadym Chibrikov Thank you for your curiosity!

Tzero Lid was pressed using the DSC Tzero Press. What do you mean by "pressing should be done in triplicate" ? Maybe it helps to know, that many of my Tzero lids were displaced and pressed out. It was not a singular event. Additional info, I use the black pressing die with the concave top.

The material is powdery formulation of zein and glycerol (around 20% glycerol w/w). heating rate 15°C/min. Preliminary measurements (which didn't show lid displacement allowed me to tell that there is some amount of water contained in my material, which results in an endothermic deformation during the first heating cycle. second and third heating cycles usually coincide, suggesting that all water evaporated during the first cycle and that the curve form the second (or the third) cycle is "analysable". Note: the material becomes sticky when in the viscous state, so the lid isn't fully pressed out, it just stays half open, oblique, with some material peaking through.

https://folk.ntnu.no/deng/fra_nt/other%20stuff/DSC_manuals/QDSC/Preparing_DSC_Samples.htm this manual suggest using samples 10 - 20 mg for Glass Transition measurement, which is what I'm aiming to analyse here.

Dear Eanest Jebasingh,

The melting peak can be seen if the sample has crystalline phase. First of all it is necessary to be sur about it. Then, the range of temperature is important for appearing melting peak.The temperature range should be wide enough to observe the melting phenomenon.

Your DSC endotherm is more or less at the right temperature but it is very broad and the enthalpy is improbably high. What you observe is most likely the evaporation of water (ca 2200 J/g). This points to DSC pans that are not properly sealed. Your DSC profile suggests that your upper temperature was largely in excess of 120 Celsius, which may have caused pan leakage. Follow the instructions of the supplier for the maximum T to be allowed if water is present. For this type of experiments starch concentration has to be below 40 % and a starch weight of a few milligrams is recommended. Look into the literature for details.

Dear all, Please have a look at the following links and the attached file. My Regards

You are most welcome dear Hasfi F. Nurly . Wish you the best always

"... My DSC curve (Figure1) do not show a horizontal shape. It may be related to the calibration, even though we recently calibrated the instrument.

Is this (Fig. 1) the blank line???

You can take your measurements without using the settings tab: DSC/DTA Horizontal in off !! And then subtract the blank line from the curve.

Hi Jisou Lyu ,

1) PLA can be amorphous or semi-crystalline depending on your processing method. For example, a semi-crystalline PLA pellets can be transformed to amorphous PLA compounds or products if the cooling rate is too fast and the polymer chains don't have enough time to arrange themself into ordered state.

2) PBAT is a co-polyester with a very low glass transition temperature (Tg), which is below 0 degree. This means that the polymer itself is very ductile in room temperature as polymer chains are quite flexible.

PLA, on the other hand, has a high Tg, being around 55-60 C degree. It means that the polymer is rigid at room temperature.

Best regards,

Cuong

It's perfectly normal that the heat flow of cooling and heating cycle is defferent. The cooling cycle is carried out to omit the heat history of samples. The heat flow of the second heating cycle mut be considered as the DSC result.

Waseem,

I am awfully sorry for my mistake with your name :-(

Dear Mck Swamy, better to follow a standard testing protocole such as ASTM (see attached). There is also a free access document on RG. My Regards

Hello, were you able to solve this? I am in the same situation, thanks

Dear Andres Rivera, table 1 in the attached file gives the correlation between Tg and % plasticizer. My Regards

In my opinion DSC is the best method. Try to use not too much material for your experiments

The question is about the baseline as he has shown attached with @Ong Hui Ling question. My answer is not to use such base and I have given a suggestion above.

Dear all, please have a look at the following documents. For the integration, normally the DSC instrument is equiped with software for data processing, if not, origin program may do such a task. My Regards

Jaime Orellana thank you for your thoughtful answer. Kind regards, MJY

Thank you all for your answers. I am running an isothermal experiment to confirm if the peak is indeed coming due to the moisture loss.

Andrew Strzelecki I did not mention this, but the data I have is the mass loss (in %). So probably the main question is whether this is percentage related to the entered mass (270.023), or should it somehow be connected to 20.681 as well. Otherwise, how are those compared to the reference crucible mass?

Dear all, please check the following RG thread and the attached files. My Regards

Dear all, please have a look at the following RG thread. My Regards

Hello,

You should use the onset point which is determined in the same way as the melting point is determined - as the intersection point of the base line and tangent drawn from the inflection point of the front of DSC melting peak.

Dear all, please have a look at the following document, hope it will be usefull. My Regards

Dear all, ORIGIN is the most suited for scientific data processing. It is not a free software. My Regards

-> "How to identify that temperature at which the nitrogen atmosphere is changed to Oxygen atmosphere? " -

This information is determined by you when programming the DSC device. Is this really your question?

Or, are you wanting to study the oxidation process of Cu?

In this case, see the paper below, for example:

Thermal oxidation of copper over a wide temperature range: for the formation of cupric oxide (CuO)

Víctor-Hugo Castrejón-Sánchez et al 2019 Mater. Res. Express 6 075909

Dear all, though it concerns Tg of thin film, the following old RG thread is full of opinions, they may be of importance to take profit. My Regards

There are two types of DSC instruments: heat flex type and power compensation type. In the original data, heat flex type DSC (and DTA) usually suggests exothermic change in the positive direction. In the power compensation type DSC, the endothermic change (positive enthalpy change) is in positive direction. Therefore, the direction of exothermic and endothermic changes should always be suggested in the DSC figures.

Yes, absolutely.

And actually for two reasons:

1) The PCM can behave different

The PCM can supercool, it can have hindered crystallization (e.g. hysteresis in PE), it can go to a different crystal phase or an amorphous one, it can show phase separation ... and it could even happen that a material does not solidify at all (e.g. because of decomposition)

2) The hysteresis could also be from measurement (at least partly)

Due to temperature gradients in your calorimeter you could have artificial hysteresis in your results; if you just measure on heating once you might not become aware of it. Therefore you should do a heating rate test, including also cooling measurements.

For the last you can check for example my There is also a whole project with literature https://www.researchgate.net/project/Caloric-measurements-on-PCM-collection-of-key-publications-and-discussion

See the question at RG

Question

Asked 16th Nov, 2015

📷

Muzammil Iqbal

How to calculate glass transition temperature from DSC curves?

How to calculate glass transition temperature from DSC curves polymer?  experimental results seems different from theory.

If suitable computer software is available for automatic calculation of the glass

transition temperature

Dear Eren Dikmen, please have a look at the following RG thread and the other documents. My Regards

Dear all, what is the metallic microparticles ? Does it have any possibility on: 1- degradation of PP, and 2- nucleation of crystallization from melting. Neat PP in some cases is known by this double melting. Please have a look at the following link and attached file. My Regards

Purity determination by DSC is only possible in case (1) when solid-liquid equilibrium is observed at quasi-static conditions (slow heating). DHA purity must be determined by some other method (e.g. HPLC).

What about the sample description? Is that powder or granules? Not enough sample could be the reason why your peak is small, or maybe you can check calibration or must do baseline check for your DSC. Is there any reference standard for your sample? If possible you can compare thermal profile with your sample

Dear Sophia,

The degree of crystallinity (Xc) can be calculated based on following equation

where DHm, DHcc, and W are the enthalpy of melting, enthalpy of cold crystallization, and the weight fraction of polymer in sample (maybe it is 100% or less than 100% if blend of polymers has been used in samples) respectively. DH0f is the enthalpy of fusion of complete crystalline polymer that can be find in handbook.

Xc(%)= (DHm-DHcc)*100 /(W* DH0)

Rahmathulla Mohamed Nikzaad Since you mentioned that you prepared filaments containing 2 components then the two melting endotherms can be for the individual components.

Additionally you can also calculate crystallinity from the melting peaks by taking the area under the curve (delta Hm) and substituting it in the formula:

Xc (%) = delta Hm / [(1-w) * Hm]

Hm = value from literature for specific material (at 100% crystallinity)

w = weight fraction of the component

Hope this helps. Thank you!

Raman mapping is the best to determine low content of crystal in amorphous.

Dear Mohamed sayed Ahmed Mostafa ,

I found the following two papers that might be of interest to you:

Coscia, K., Neti, S., Oztekin, A., Nelle, S., Mohapatra, S., & Elliott, T. (2011, January). The thermophysical properties of the NaNO3-KNO3, LiNO3-NaNO3, and LiNO3-KNO3 systems. In ASME International Mechanical Engineering Congress and Exposition (Vol. 54907, pp. 889-894). (see enclosed file).

Zhang, X., Xu, K., & Gao, Y. (2002). The phase diagram of LiNO3–KNO3. Thermochimica acta, 385(1-2), 81-84. (see enclosed file).

Best regards.

You are right in some view. Indeed, At a high concentration of urea or guanidine hydrochloride in an aqueous solution, complete denaturation occurs, which in some cases is reversible after removal of the denaturing substance by dialysis. For a number of amino acids with functional groups in side radicals, surprises were observed, for example, poly (l-benzyl-β-histidine) in solutions containing small amounts of simple mineral acids takes on a disordered conformation, while in the presence of a stoichiometric amount of perchloric acid it exists in the form a -spirals. The answer to your question depends on which goal you are searching for.

Dear Xingfa Ma, detalled analysis procedure is presented in the following document. My Regards

I agree with Masoud Tayefi, you have to delete the thermal history of the polymer before making hypotheses.

Record DSC for at last two heating/cooling cycles, possibly by quench cooling, and by comparison between the first and second cycle you will get information about your sample crystallinity. Melt spinning implies a cooling stage that can impart a different degree of crystallinity to the final product: this piece of information is embedded in your first cycle DSC.

However, I suggest performing a parallel TGA experiment to exclude that the second exothermic peak is due to a decomposition reaction.