Dear Catherin,

There are so many “if-s” to answer your question… Let me try

1-st: if you work with well detectable rates of conversion (means above 2-3 wt%) you should normalize your results. You should find some bands with constant intensity (referring points, Ir. In your case these could be the bands of medium intensity around 1430 or 800 cm-1) and the active bands (IA) intensity of which is sensitive to the reaction rate. In your case: ~ 650, 1250, and high intensity group around 1000 – 1200.

Then you should calibrate your results finding IA/ Ir ratios for the several samples with known reaction rates. Thus, IA/ Irfor the unknown sample would be the function of the conversion rate.

However, you can do it only (2-nd) if you are sure about conversions. And this is of imperative importance! That means that you should learn first about the kinetics of your reaction to assure that you reach the certain conversion rate at the certain time, temperature, etc.

With the contents of functional groups below 1% accuracy of the measurements becomes critical. You must insure reproducibility of your results. Even construction of the IR cell, the way it located in the compartment can make an effect.

It looks like you work with free standing films /or films on a substrate/. In this case, you must exclude absolutely any deviation in possible reflection of the IR beam on the surface of the samples.

Finally, you work in transmission mode. That means you should use logarithmic IA/ Ir ratios. Direct ratios could be used if you switch to the optic density mode.

And any way, it is hard to me to give confidence to the results of FTIR obtained below 1 wt%. Good luck to you

Dmitri

Hello dear, with degree grafting lower than 1 % the signals of the grafting agent are distinguished from those of the noise. Furthermore, the minimum grafting percentage for being detected by ATR will depend on the sensibility of the equipment employed. In your spectrum the intensity of the signal between 2000 and 2250 1/cm has almost the same intensity.

Catherine Esnaashari,

polymer functionalized with less than 1wt%. what does it mean ?

Dear Anil Kumar,

It means the weight percent of the functionalizing reactant grafted to the polymer backbone is less than 1 wt%.

It's hardly possible. At least some very special equipment, methods and technique will be required. Tasks of this kind should be considered as a subject of special studying by itself   

@ Dr. Likhatachev, Thank you so much for your answer. Yes it seems that IR cannot accurately detect substances at less than about 1 wt%.

The red line in the above graph shows the spectrum of PLA after processing. What information can be obtained from the peak intensity differences between processed and unprocessed PLA in the range 1000-1400 1/cm?

Dear Catherin,

There are so many “if-s” to answer your question… Let me try

1-st: if you work with well detectable rates of conversion (means above 2-3 wt%) you should normalize your results. You should find some bands with constant intensity (referring points, Ir. In your case these could be the bands of medium intensity around 1430 or 800 cm-1) and the active bands (IA) intensity of which is sensitive to the reaction rate. In your case: ~ 650, 1250, and high intensity group around 1000 – 1200.

Then you should calibrate your results finding IA/ Ir ratios for the several samples with known reaction rates. Thus, IA/ Irfor the unknown sample would be the function of the conversion rate.

However, you can do it only (2-nd) if you are sure about conversions. And this is of imperative importance! That means that you should learn first about the kinetics of your reaction to assure that you reach the certain conversion rate at the certain time, temperature, etc.

With the contents of functional groups below 1% accuracy of the measurements becomes critical. You must insure reproducibility of your results. Even construction of the IR cell, the way it located in the compartment can make an effect.

It looks like you work with free standing films /or films on a substrate/. In this case, you must exclude absolutely any deviation in possible reflection of the IR beam on the surface of the samples.

Finally, you work in transmission mode. That means you should use logarithmic IA/ Ir ratios. Direct ratios could be used if you switch to the optic density mode.

And any way, it is hard to me to give confidence to the results of FTIR obtained below 1 wt%. Good luck to you

Dmitri

Dear Dr. Likhatchev,

Thank you very much for your timely, informative answer. I really appreciate it.

Dear Catherine Esnaashari,

I think the process of grafting should be very precise. than It may be possible. I don't know how you graft it.

Secondly, you can tune the wt% near to 1 weatherabove 1wt% and below it.

Good Luck

Catherine

In fact this PLA was sold to us as Natureworks 2003D, but its Mw increases significantly during processing. I am getting very favorable results with this PLA so I want to know whether it has been functionalized or it contains chain extenders. 

What other characterization methods do you recommend (except EDX and elemental analysis)?

Dear Catherine, to know the functional group FTIR is best technique but if you are not satisfy with FTIR than you may go for TEM and Raman also.

Anil 

Both IR spectra are similar. Therefore, I think that the grafting process was not good, since by  FTIR analysis have been determined grafting degrees lower than 1 %. It can be seen in so many papers.

Based on my experience in hybrid polimer and nanocomposite, I can say that the detection of functional groups of polimer modifiers in amounts of less than 1-2% is often not possible using the FTIR-ATR technique.

peaks in the ranges of 1600 - 1750 that are characteristic of

carboxyl (-COOH)  functional groups

The sensitivity of both the methods: FTIR and FTIR-ATR is simlar and only in the case of very narrow and sharp peaks (not crowded by another bands) you possibly can detect 1% of grafting.

BUT there is an exclusion of the above-mentioned rule. Namely, very often in case of BLENDS of 2 polymers (say, A and B) - there appears a gradient of concentratons. For example on the "AIR"side in case of FTIR-ATR concentration of polymer may become substantially higher then on the "substrate"-side. (this phenomenon mainly depends on strength of interaction of polymer B with substrate. And in limiting case almost ALL the IR bands  near substrate side will belong to polymer B.

Your spectra are of very high quality !  But unfortunately - the effect of grafting can not be detected, thus the amount of grafting s really lower than 1-2%.

Good Luck,                                                        Leonid

if the band of the functional group is not superimposed with bands of the polymer matrix and its epsilon is high you can reveal less than 1%. On the surface modification you can have only qualitative results. However a calibration method using band ratio could be good for having a better determination