To make the discussion a little more confusing, but hopefully more insightful, the problem with measuring degree of crystallinity is that it is more of a concept than a physical reality with polymers. When a simple metal crystallizes, we are talking about individual atoms fitting into a discrete lattice with regular spacing and structure, and everything can be reduced to first principle calculations (in the most ideal case). When a polymer crystallizes, it is really just separating into regions with some degree of order that are separated by disordered (amorphous) domains. The amorphous domains may even penetrate the semi-crystalline domains, so the actual structure may vary significantly between different polymers and depends on treatment methods, presence of fillers or contaminants, etc. Some of the old literature on the crystal structure of a polymer as simple as PP will make your head spin...

When you measure the "crystallinity", you are really measuring an indirect property that has been conceptually related to an increase in local order. For example, a crystal will typically be more dense than an amorphous material of the same composition (ice being a nice exception), so you can use density to estimate the "relative" fractions of crystalline and amorphous regions using a rule-of-mixtures calculation. DSC is probably the best tool from a fundamental perspective because it directly connects thermodynamic variables associated with free volume. The trick is having an appropriate reference enthalpy to compare to. In many cases, people were able to synthesize single crystals with high perfection, so that delta H reference may be regarded as reliable. In other cases, single crystals have not been successfully prepared and the reference enthalpy is an extrapolation, such as for the PEEK family of materials. In that case, you need to connect other measurements, such as XRD, and microstructural observations, to try to complete the story.

In the end, as scientists we want the most meaningful number, but as engineers, we really just want a reference value to compare between materials and make correlations to understand other properties. From the engineering perspective, as long as you compare values obtained using the same technique, you're in good shape. The problem comes with the reliability of comparing measurements from different machines, taken at different times of the year, with different operators and calibrations, different computational approaches, how to define the "onset" of a transition - linear or secant approximation?, etc. In this case, I think DSC is probably among the safest, if there is a good reference to compare to. From a scientific perspective, it is probably best to get measurements using a few techniques to confirm the appropriate range of crystallinity for your samples, and in certain cases, to see why measurements might disagree. For example, small-angle and wide-angle X-ray diffraction are sensitive to crystal structure on different length scales, and comparing the degree of crystallinity between the two measurements has been used to understand the evolution of crystal structure for PP.

That got long-winded quick, but I hope it helped. If you're interested in any of the details of the features I pointed out above, I can probably scrounge up the reference without much of a problem.

Dr. Matar,

I believe the DSC is the most reliable method if executed properly. The melting transition is directly related to the content of polymer crystals, but would be somewhat affected by the heating rate, the contact of the material with the pan and the amount of the polymer in the pan.

Dear Dr. Matar,

I agree with Ivan. DSC usually gives accurate results, if the DSC equipment is well calibrated. That means that for each type of pan and heating rate a seperate calibration with at least 4 different elements has to be performed (to cover a wide temperature range). To use only indium for calibration is not suitable.

I agree with Ivan and Stefano, if DSC is calibrated and given the PVA reference you are using, either be real or calculated. Regarding cristallinity by FTIR, we must remember such technique is semi-quantitative, I mean, even with 5 or more references the reliability is lower than DSC. On the other hand, if you are dealing with a paper, It would be nice if you include all of the results.

To make the discussion a little more confusing, but hopefully more insightful, the problem with measuring degree of crystallinity is that it is more of a concept than a physical reality with polymers. When a simple metal crystallizes, we are talking about individual atoms fitting into a discrete lattice with regular spacing and structure, and everything can be reduced to first principle calculations (in the most ideal case). When a polymer crystallizes, it is really just separating into regions with some degree of order that are separated by disordered (amorphous) domains. The amorphous domains may even penetrate the semi-crystalline domains, so the actual structure may vary significantly between different polymers and depends on treatment methods, presence of fillers or contaminants, etc. Some of the old literature on the crystal structure of a polymer as simple as PP will make your head spin...

When you measure the "crystallinity", you are really measuring an indirect property that has been conceptually related to an increase in local order. For example, a crystal will typically be more dense than an amorphous material of the same composition (ice being a nice exception), so you can use density to estimate the "relative" fractions of crystalline and amorphous regions using a rule-of-mixtures calculation. DSC is probably the best tool from a fundamental perspective because it directly connects thermodynamic variables associated with free volume. The trick is having an appropriate reference enthalpy to compare to. In many cases, people were able to synthesize single crystals with high perfection, so that delta H reference may be regarded as reliable. In other cases, single crystals have not been successfully prepared and the reference enthalpy is an extrapolation, such as for the PEEK family of materials. In that case, you need to connect other measurements, such as XRD, and microstructural observations, to try to complete the story.

In the end, as scientists we want the most meaningful number, but as engineers, we really just want a reference value to compare between materials and make correlations to understand other properties. From the engineering perspective, as long as you compare values obtained using the same technique, you're in good shape. The problem comes with the reliability of comparing measurements from different machines, taken at different times of the year, with different operators and calibrations, different computational approaches, how to define the "onset" of a transition - linear or secant approximation?, etc. In this case, I think DSC is probably among the safest, if there is a good reference to compare to. From a scientific perspective, it is probably best to get measurements using a few techniques to confirm the appropriate range of crystallinity for your samples, and in certain cases, to see why measurements might disagree. For example, small-angle and wide-angle X-ray diffraction are sensitive to crystal structure on different length scales, and comparing the degree of crystallinity between the two measurements has been used to understand the evolution of crystal structure for PP.

That got long-winded quick, but I hope it helped. If you're interested in any of the details of the features I pointed out above, I can probably scrounge up the reference without much of a problem.

DSC and XRay are the more accuracy methods to collect more reliable data in crystalline degree of a polymer sample

Dr. White has covered some of the most important theoretical aspects in crystallization of polymeric materials with much insight. I would like to add more insight in the specific case of PVA.

When dealing with semi-crystalline polymers, PVA stands aside because it is not crystalline in the accepted sense. It does not form crystallites, it does not exclude ammorphous regions, it does not have a crystalline melt temperature. Spatial order in this polymer manifests itself as low or high extension of hydrogen bonds between dangling hydroxyl groups, which are small enough to make that intermolecular force count. "Crystallinity" here is a function of molar mass and, mainly, of degree of hydrolysis. I have studied cross-linked PVA hybrid systems during my master's, and found that, for a given sample, the crystallinity degree (bear with me, if you may...) decreased with the increase in the concentration of the cross-linking agent that I had used, a dialdehyde. So, that characteristic was linked directly to the number of available hydroxyl groups.

What I am trying to convey here is that DSC, XRD, FTIR (by means of observation of a absorption mode of C-O that is sensitive to spatial confinement) and NMR Relaxometry (through the mathematical analysis of both longitudinal and transversal relaxation time constants) can provide information about the relative crystallinity degree of a series of annealed PVA samples.

Regards.

Basically the contribution by Kevin L. White exhausts the question. There is no absolute answer to the question about crystallinity degree in the case a polymer. Different methods are sensitive to different things and that's why you have three different nubmers (pretty consistent though). Packing density of chains in crystals is higher than those present in the chaotic amorphous regions. So, in other words, the density measurements show you how much of the 'packed stuff' you have in your specimen, regardless of the internal structural arrangement. It gives therefore little chance to distinguish between different polymorphs and brings little insight when it comes to e.g. liquid-crystalline/crystalline systems. In DSC you typically melt crystals in the sample when measuring the crystallinity degree. Hence you measure how much of heat (~ the enthalpy) you need to destroy local intermolecular couplings forming, at the larger scale, ordered domains. Please take it easy - this was just a weird way to say 'melting' ;-). There is a certain heat released on a unit act of coupling of molecules/moieties into, first, small aggregates and then crystals. First-order phase transitions (like the crystallization) are reversible and require roughly the same amount of heat when going in the opposite direction i.e. when turning crystals into a mess of conformational states. Er... sorry, I wanted to say melt the crystal to form highly-mobile amorphous state.... Er... never mind. Something soft and not really ordered, that's the best. So DSC shows the number (and therefore the mass) of acts of a certain kind that occur in the sample. Unlike X-ray diffraction methods, you didn't mention, DSC disregards the sizes or shapes of domains where these acts happen. In terms of philosophy, FTIR shows something similar but the infrared light sees 'states of oscillations'. In other words FTIR distinguishes molecules/moieties that are able to oscillate in a certain way from those geometrically trapped and frozen in a densely packed crystalline domains. Other techniques, like X-ray diffraction are sensitive not only to the total amount of ordered things but also to their quality. Wide-angle X-ray diffraction (WAXD) is a good tool to measure the mass crystallinity index of polymers but is insensitive to very small or very imperfect aggregates/crystals since they do not scatter X-ray radiation in a coherent way. Small angle X-ray diffraction may provide an information about the volume crystallinity. But this is a separate story. Finally, please be careful with numbers and units. Some people, having less experience, may confused if these are weight or volume percentages. If you find the discussion about polymer crystallinity interesting, you might be also interested in this paper: http://onlinelibrary.wiley.com/doi/10.1002/anie.201205075/abstract

Dear Dr. Nizar Matar;

the problem of measuring the degree of crystallinity in polymers is an identical situation to that of measuring the molecular weight, what I mean is that whatever the experimental techniques, it is an average value you get, since obviously crystallites or spherolites should not have the same or uniform dimensions, and from here comes the difference between these techniques, for example small cryatalline zones will melt easily and rapidly with lets say small exothermic that is below the resolution or the sensitivity of the DSC instrument, and so forth. So, as a conclusion all values obtained with the different techniques used are in fact reflecting the most parts of the crystalline zones that contribute or reflect the sensitivity of the technique in question.

For a polymeric sample DSC is one of the best method for the calculation of crystallinity

Thanks to all of you distinguished scholars for answering the question. All of you agreed that DSC is the best.I took advantage from your answers besides my "humble" experience in the subject to recommend DSC for (Muruganathan Ramanathan) who wanted advice in (RG) to determine Tg for a polymer thin film. A teacher & HIS pupil (who I know very well) downvoted my answer ,which made me delete my answer following that with brief comment. Take care, downvoting is not necessarily for scientific reasons.

DSC can give good average estimation.However, crystallinity based analytical techniques give a good insight into distribution of crystallinity of the polymers. These include TREF, CRYSTAF and the newest modification in the techniques called CEF. For more information please consult our article

http://link.springer.com/chapter/10.1007%2F12_2012_167

I hope it will help

Thanks Dr.Muhammad Imran Malik for your answer. I understand from the abstract of your article that the new technique (CEF) gives insight into crystallization, so does this mean the percentage of the crystalline domain plus the temperature at which cystallites form (i.e. the Tm) and ,in addition to this, does the technique enable us to determine the Tg of the amorphous regions plus their percentage in a certain polymeric sample ?

These techniques are actually used for chemical composition distribution of polyolefins based on their crystallinty as a function of temperature. However, these techniques can not address the amorphous part

This is addressed to Prof. Adam Kiersnowski: You mentioned that X-Ray scattering can be insensitive to small or imperfect crystallites: please could you direct me to a relevant publication which I could cite? Thank you- Andy 

http://en.wikipedia.org/wiki/Crystallization_of_polymers  

The above reference is from Wikipedia available on line.  It is a good survey of the subject matter, including examples of reporting results together with technique used.

From my experience, the DSC technique provides the simplest and most representative method, giving both TG (amorphous) and Tm (crystalline) information.  The areas under the peaks of the loss modulus are believed to correspond to the relative degree of crystallinity for a given sample.  As I recall, the instrument is calibrated by using Gallium samples from good reference sources. 

Because any polymeric sample will necessarily be a mixture of both crystalline and amorphous components, DSC measures a useful average for all crystalline components, including varying sizes and distributions.  The breadth of the loss peak is proportional to the distribution of crystallite sizes, while the temperature of the maximum is representative of the crystalline region alone. 

Degree of crystallinity has a maximum of around 80%, with the remaining material representing the fraction of the material involved in connecting the various crystalline regions.  Separate studies of particle filled systems suggest that the maximum will range from ~60% to 80%, depending on the range of distributions used (allowed) for the filler system.  The ~80% maximum is a common number encountered in virtually all forms of "filled" systems, whether particulate of crystallite in nature. 

The fact that DSC produces results that agree well with physical models of filled systems is what leads most workers in the field to prefer that technique for characterization. 

Thank you professor Floyd for your contribution. I have really worked with the 3  methods, mentioned in the question, plus XRD but the work was on acrylic polymers. DSC gave good results and that was nearly 3 decades ago. When I gave an answer to a question in another thread, someone downvoted it so my trust in DSC was hit. But the downvoter did not give, then, an alternative convincing explanation afterwards, at all. So I realized that there was abuse of downvoting. Any technique can work but they may differ in reliability but the differences are not large.

what is difference between degree of crystallinity and index of crystallinity?

The degree of crystallinity, in a polymer, is the fractional amount of crystallinity in the polymer sample and this degree may be expressed as mass fraction "frctn" or as volume fraction. Given that the degree of crystallinity is 70%, you will deduce that there are 30% amorphous domains but you have to specify the method used to get this figure and whether it is mass frctn or volume frctn.

Crystallinity index is an empirical measure of relative crystallinity by X-ray expressed by percent crystalline material in the total as well and is usually meant to be "X-ray crystallinity index".

Dear N. Matar,

If a second-heating cycle (heating-cooling-heating) is applied in the DSC experiments of polymer samples, it provides more reliable data to crystallinity calculation. Other methods, like XRD, are very sensitive to the polymer history and non-relaxed thermodynamic situations of the polymer chains.

Polarizing Optical Microscope (POM) is a standard tool in the identification of which the optical axis is defined by the director and considering light containing both x-polarized and y-polarized electric field .or Differential Scanning Calorimetry (DSC)

DSC is a technique to determine the thermal behavior. Since many physical or chemical transformations are associated with endothermic (heat absorption) or exothermic (heat evolution) can easily detected by heat flow between a sample and an inert reference material. Also, by increasing temperature, involve a change in enthalpy or heat capacity. Therefore, DSC is a widely used possible to observe the small energy changes that occur as matter transitions. these two methodes provides more reliable data to crystalline .

Only X-ray is the best method and most reliable

I cannot deny that XRD is a superb tool but upon studying polymers, long time ago, I found out that a combination of XRD & DSC will give more precise results. My experience in IR is far better than the 2 methods but it requires more hard work!

From my experience as material engineer for the last 34 years I worked a lot on characterization of polymers and X ray gave the best results. DSC is OK but is dependent on the concentration or film width and other parameters. Good luck

Dear Alisa, there are 3-4 methods to determine crystallinity i.e. Segal's, Ruland, Ruland-Vonk etc. Which one is best among these to calculate crystallinity?

DSC almost give high crystalline % value due to the DSC technique is used heating that give chance of chine to alignment and the crystalline value will be increased.

i see XRD more reliable