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CRYSTAF-TREF Frequently Asked Questions

We are aware that acquiring a lab instrument is an important decision, furthermore if Polyolefins’ research is related with your core business.

Although you can ask directly to our consultants whenever you want, you may prefer to know first the answers to the most typical questions about our instruments. Here are packed the most relevant questions about TREF.


Questions


Answers

What kind of results can be obtained from the CRYSTAF-TREF instrument?
CRYSTAF (Crystallization Analysis Fractionation) and TREF (Temperature Rising Elution Fractionation) techniques were developed to obtain the Chemical Composition Distribution curves; CRYSTAF during the crystallization and TREF during the elution cycle. Therefore, at the end of a CRYSTAF or TREF run, a distribution in concentration versus temperature of crystallization or elution is obtained.

Which are the differences between CRYSTAF and TREF techniques?
CRYSTAF obtains the CCD curve during the crystallization step, and TREF does need an additional temperature cycle called elution to obtain the same results.

TREF obtains the CCD curve directly and in a continuous way, meanwhile the CRYSTAF technique does so in a discontinuous way: A series of data points from the cumulative composition distribution curve are actually measured and used to obtain the differential distribution by means of a smoothing splines fitting algorithm.

CRYSTAF obtains the CCD curve during the crystallization process, and TREF does need an extra temperature cycle called elution to obtain the same results. The results obtained with both techniques are very similar but when expressed in temperature scale there exists a shift to lower temperatures in CRYSTAF due to undercooling effects.

Why are both techniques CRYSTAF and TREF convenient when analyzing the CCD in polyolefins?
For most of the polyolefins, results obtained from CRYSTAF or by TREF will be equivalent, and therefore only one of the techniques is enough in most cases. However, for some specific kind of polyolefin, separation might be better achieved by CRYSTAF or by TREF due to the different behavior of the components in the crystallization or elution process. In this sense, if having both techniques available, the best possible separation will be achieved for every sample.

What is the advantage of having a combined CRYSTAF-TREF instrument?
CRYSTAF and TREF instruments hardware is very similar, and therefore both techniques can be run in the same physical equipment by changing the instrument internal mode. This is an excellent advantage considering the fact that for some specific types of polyolefins, a better separation might be obtained in one technique versus the other one. Thus, by having the possibility of running both CRYSTAF and TREF techniques, a more complete Chemical Composition Distribution characterization can be achieved for a given sample.

Does the CRYSTAF-TREF instrument provide the physical fractions in temperature?
CRYSTAF-TREF is an analytical instrument intended to obtain the chemical composition distribution curve by TREF or by CRYSTAF, but it doesn’t provide any physical fraction. In TREF mode, it might be possible to collect the fractions as they elute from the column, however the instrument is not optimized for this and the process is not automated. Please refer to the PREP mc2 for an automated fractionation instrument.

How many samples can be run at a time and how long will it take?
In CRYSTAF mode up to 5 samples can be run in about 8 hours with no supervision required, and in TREF mode up to 5 samples can be run in about 5 hours per sample and no supervision is required.

After a CRYSTAF or a TREF run, an automated cleaning is performed by the instrument and therefore it will be ready to start another run immediately.

How many grams of sample do I need?
The standard amount used in CRYSTAF analysis is around 40mg per sample, and in TREF analysis is around 80mg.

Which solvents can be used?
1.2.4-Trichlorobenzene (TCB) and Orto-Dichlorobenzene (oDCB) are the most used solvents. Perchloroethylene could be used too. To use other solvents please consult Polymer Char first.

What kind of sample preparation is required by the user?
No samples preparation is required by the user but weighing the dry samples and putting them inside of the vessels. The rest of the steps are performed by the instrument automatically: filling, dissolution, column loading, crystallization, elution, final cleaning, etc. Therefore, when a run is finished, another one can be started immediately.

Do I need to handle solvents?
Solvents don’t need to be handled at any time; the whole process is fully automated and the instrument is in charge of all the needed steps: filling, dissolution, column loading, crystallization, elution, final cleaning, etc. So after a CRYSTAF or a TREF run, the instrument is ready to start again immediately.

How long will my TREF column last? Are temperature or flow changes affecting my TREF column?
TREF column is not a consumable part of the instrument and it is not affected by temperature or flow changes. It has been designed in Polymer Char especially for TREF instrument to achieve good resolution when analyzing 5 samples a day.

Which kind of samples can be analyzed?
LLDPE, LDPE, HDPE, PP, E-P copolymers, multicatalyst reactor resins, and any semicrystalline polymer soluble in TCB or oDCB, giving response to C-H absorption.

Which is the detector used for concentration in the CRYSTAF-TREF?
CRYSTAF-TREF incorporates an infrared detector to measure the concentration. This detector is Polymer Char’s IR4 in its OEM version and therefore a composition sensor can be incorporated as well to obtain methyls or carbonyls content information.

May I couple additional detectors to a CRYSTAF-TREF instrument?
A capillary viscometer detector can be connected to the instrument to be used in the TREF mode, to obtain information on composition-molar mass interdependence.

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