Crystallization Analysis Fractionation.
Innovative and fast approach to the Chemical Composition Distribution analysis in Polyolefins needing a single temperature.
Crystallization Analysis Fractionation (CRYSTAF) is a technique used to measure the Chemical Composition Distribution (CCD) in polyolefins based on the segregation of crystals of different morphology or comonomer content by crystallizability.
With this technique, separation and analysis are performed in a single step; the crystallization cycle, where the polymer solution is sampled and its concentration are analyzed at the same time that the temperature is decreasing for the crystallization by using an Infrared (IR) detector (IR4). Concentration data obtained at each temperature sampled correspond to the cumulative curve of the CCD.
CRYSTAF is a fully-automated instrument intended for the fast measurement of the Chemical Composition Distribution in Polyolefins. The instrument performs the Crystallization Analysis Fractionation technique to separate the polymer by its comonomer content. The process is done in a single temperature ramp (crystallization step), while the polymer solution concentration is monitored by using the Infrared Detector IR4 of Polymer Char.
The virtual instrumentation software controls the full process, therefore, no manpower is required. Dry samples are put into the crystallization vessels and the instrument fills them with solvent and performs the dissolution, crystallization, sampling, and cleaning.
Up to five different samples can be analyzed at a time in an 8-hour period under standard conditions. At the end of the process, vessels and lines are automatically cleaned and the CRYSTAF is ready to analyze more samples. Results of the Chemical Composition Distribution are obtained directly from the software.
CRYSTAF can be converted into a CRYSTAF-TREF combined system capable of running both techniques by using the same hardware. Each technique can provide complementary information on the CCD in some complex resins.
CRYSTAF is a technique developed and patented by The Dow Chemical Company and licensed to Polymer Char.
· Analysis of up to 5 samples simultaneously.
· Analysis time of 8 hours for 5 samples under standard conditions.
· Fully-automated process including a final cleaning of the lines and vessels. No manpower and no solvents handling along the whole process.
· One single temperature cycle needed.
· Possibility of calibrating the instrument to obtain the CCD curve in comonomer content units.
· Analysis of one sample in 2 hours for Quality Control needs through isothermal steps conditions.
· Infrared Detector IR4 incorporated.
· Low solvent consumption.
· Possibility of subambient capability (down to -20ºC) for low crystallinity samples.
· Virtual Instrumentation software with whole control of the instrument hardware and process.
· Possibility of converting it into a CRYSTAF-TREF instrument.
· Possibility of remote control connection to allow fast diagnosis from Polymer Char Service Center.
The following are the detectors available for CRYSTAF:
The IR4 is the standard Detector integrated by default in all the Polymer Char analytical instruments. IR4 is a dual-wavelength infrared detector, which uses the principle of infrared absorption spectroscopy to measure the concentration and composition in polyolefins.
The CRYSTAF Software is specifically developed for controlling and monitoring the automated CRYSTAF technique. It offers two operation modes: automated analysis and manual action. In the automated mode, an easy and complete interface defines all the conditions for the CRYSTAF analysis, such as the crystallization ramps, temperatures, times or volumes; to be adapted to all kind of Polyolefins and research studies by CRYSTAF technique.
Furthermore, a set of standard methods are previously saved in the instrument to be used by the analyst for the routine sample analysis, based on Polymer Char’s standard conditions. The user’s methods can also be saved and recovered for successive analyses.
On the other hand, the manual action operation offers the full control of the instrument, thought to be used as a fast and powerful diagnosis tool directly by the user and also by Polymer Char service engineers.
The Calculations screen is linked to the instrument database to facilitate the samples results organization.
CRYSTAF technique (Crystallization Analysis Fractionation) was developed to obtain the Chemical Composition Distribution curve during the crystallization step. Therefore, at the end of a CRYSTAF run, a distribution in concentration versus temperature of crystallization is obtained.
CRYSTAF is an analytical instrument which was designed to obtain the chemical composition distribution curve, but it doesn’t provide any physical fraction. For this purpose, please read about PREP mc2.
Up to 5 samples can be run in about 8 hours with no supervision required. After the run, an automated cleaning is performed by the instrument and therefore it is ready to start another run immediately.
The standard amount used in CRYSTAF analysis is around 40mg per sample, therefore the instrument can be used both for research and also for quality control.
1,2,4-Trichlorobenzene (TCB) and Orto-Dichlorobenzene (oDCB) are the most used solvents. To use other solvents please consult Polymer Char first.
No samples preparation is required by the user but weighing the dry samples and putting them inside of the crystallization vessels. The rest of the steps are performed by the instrument automatically: filling, dissolution, crystallization, final cleaning, etc. Therefore, when a run is finished, another one can be started immediately.
Solvents don’t need to be handled at any time; the whole process is fully automated and the instrument performs the rest of all the needed steps: solvent filling, dissolution, crystallization, final cleaning, etc. So after a run, the instrument is ready to start again immediately.
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.
CRYSTAF incorporates an infrared detector to measure the concentration of the solution while the temperature is decreasing in the crystallization cycle. 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.
The CRYSTAF Software incorporates a database to easily access all the analyzed samples, which is connected to the calculations and results screens. Any result can be accessed and reviewed at any time, even when the instrument is running other samples. Comparative results among different samples are also possible.
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.
Results obtained by CRYSTAF or by TREF will be equivalent in most of the polyolefins; therefore only one of the techniques is enough in most cases. However, for some specific kind of polyolefin blends, separation might be better achieved by CRYSTAF or by TREF due to the different behavior of the components in composition. In this sense, having both techniques available, the best possible separation will be achieved for every sample.
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