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Cheruthazhekatt S.,Stellenbosch University | Pijpers T.F.J.,SciTe | Pijpers T.F.J.,Catholic University of Leuven | Harding G.W.,Stellenbosch University | And 3 more authors.
Macromolecules | Year: 2012

For the first time, the complex composition of a two-reactor-produced impact polypropylene copolymer (IPC) has been fully revealed by advanced thermal analysis, using the combination of fast scanning DSC (HPer DSC, flash DSC, and solution DSC) with SEC fractionation subsequent to TREF fractionation. The dual TREF-SEC separation provided fractions of a few micro- or nanograms that were used to correlate the molecular structure of the polymer chains and their thermal properties (melting and crystallization behavior of the different macromolecules under a variety of different conditions). The SEC fractions were collected using the LC transform interface and subjected to FTIR and fast scanning DSC analysis. The SEC curves showed mono-, bi-, and multimodal molar mass distributions. The SEC fractions collected were analyzed by HPer DSC at 50 °C/min by which the thermal properties of the fractions could be established and salient details revealed. The findings were confirmed by structural information that was obtained using FTIR measurements. These results confirmed that even after TREF fractions were obtained they were complex regarding molar mass and chemical composition. By applying HPer DSC at scan rates of 5-200 °C/min and flash DSC at scan rates of 10-1000 °C/s, the metastability of one of the fractions was studied in detail. The high molar mass part of the material appeared to be constituted of both highly isotactic PP and low to medium propylene content ethylene copolymers (EPC). The medium molar mass part consisted of high to medium isotactic PP and of low propylene content EPC. The low molar mass part did not show ethylene crystallinity; only propylene crystallinity of medium to low isotacticity was found. DSC measurements of TREF-SEC cross-fractions at high scan rates in p-xylene successfully connected reversely to the slow scan rate in TREF elution, if corrected for recrystallization. All EPC's show only ethylene-type crystallization. The wealth of information obtainable from these method combinations promises to be extremely useful for a better understanding of the melting and crystallization processes of such complex materials. The ability to run DSC experiments at very high scan rates is an important prerequisite to understanding the melting and crystallization behavior under conditions that are very close to melt processing of these key commodity polymers. © 2012 American Chemical Society.


Cheruthazhekatt S.,Stellenbosch University | Pijpers T.F.J.,SciTe | Pijpers T.F.J.,Catholic University of Leuven | Harding G.W.,Stellenbosch University | And 3 more authors.
Macromolecules | Year: 2012

A new multidimensional fractionation technique, temperature rising elution fractionation (TREF) combined with high temperature size exclusion chromatography FTIR (HT-SEC-FTIR), HT-SEC-DSC and high temperature two-dimensional liquid chromatography (HT-2D-LC) is used for the comprehensive analysis of a commercial impact polypropylene copolymer. HT-SEC-FTIR provides information regarding the chemical composition and crystallinity as a function of molar mass. Thermal analysis of selected SEC fractions yields the melting and crystallization behavior of these fractions which is related to the chemical heterogeneity of this complex copolymer. The thermal analysis of the fractions is conducted using a novel DSC method - high speed or high performance differential scanning calorimetry (HPer DSC) - that allows measuring of minute amounts of material down to micrograms. The most interesting and complex "midelution temperature" TREF fraction (80 °C) of this copolymer is a complex mixture of ethylene-propylene copolymers (EPC's) with varying ethylene and propylene contents and sequence length distributions, as well as iPP. High temperature solvent gradient HPLC has been used to show that there is a significant amount of PE homopolymer and EPC's containing long ethylene sequences in this TREF fraction. High temperature 2D-LC analysis reveals the complete separation of this TREF fraction according to the chemical composition of each component along with their molar mass distributions. © 2012 American Chemical Society.


Cheruthazhekatt S.,Stellenbosch University | Pijpers T.F.J.,SciTe | Pijpers T.F.J.,Catholic University of Leuven | Mathot V.B.F.,SciTe | And 2 more authors.
Analytical and Bioanalytical Chemistry | Year: 2013

A novel, powerful analytical technique, preparative temperature rising elution fractionation (prep TREF)/high-temperature (HT)-HPLC/Fourier transform infrared spectroscopy (FTIR)/high-performance differential scanning calorimetry (HPer DSC)), has been introduced to study the correlation between the polymer chain microstructure and the thermal behaviour of various components in a complex impact polypropylene copolymer (IPC). For the comprehensive analysis of this complex material, in a first step, prep TREF is used to produce less complex but still heterogeneous fractions. These chemically heterogeneous fractions are completely separated by using a highly selective chromatographic separation method - high-temperature solvent gradient HPLC. The detailed structural and thermal analysis of the HPLC fractions was conducted by offline coupling of HT-HPLC with FTIR spectroscopy and a novel DSC method - HPer DSC. Three chemically different components were identified in the mid-elution temperature TREF fractions. For the first component, identified as isotactic polypropylene homopolymer by FTIR, the macromolecular chain length is found to be an important factor affecting the melting and crystallisation behaviour. The second component relates to ethylene-propylene copolymer molecules with varying ethylene monomer distributions and propylene tacticity distributions. For the polyethylene component (last eluting component in all semi-crystalline TREF fractions), it was found that branching produced defects in the long crystallisable ethylene sequences that affected the thermal properties. The different species exhibit distinctively different melting and crystallisation behaviour, as documented by HPer DSC. Using this novel approach of hyphenated techniques, the chain structure and melting and crystallisation behaviour of different components in a complex copolymer were investigated systematically. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.


Van Herwaarden S.,Xensor Integration | Iervolino E.,Xensor Integration | Iervolino E.,Technical University of Delft | Van Herwaarden F.,Xensor Integration | And 3 more authors.
Thermochimica Acta | Year: 2011

This paper presents a new twin-membrane calorimeter chip for fast differential scanning calorimetry (DSC) with the Flash DSC 1 of Mettler-Toledo. The thin silicon nitride membranes enable scan rates in excess of 10 kK/s in heating and up to 4 kK/s in cooling for sample masses between 100 ng and 10 μg in the temperature range of -100 °C to 450 °C. The time constant for cooling is about 12 ms, the power resolution is typically 0.1-0.5 μW, the temperature accuracy of non-calibrated chips is typically better than ±5 K. The paper also shows measurements for the scan-rate dependent thermal lag of the device, showing an empty sensor thermal lag of about 0.2 ms, and a mass dependent thermal lag of about 0.3 ms/μg for Indium for a good thermal contact between Indium and membrane. © 2011 Elsevier B.V. All rights reserved.


Mathot V.,SciTe | Pyda M.,SciTe | Pyda M.,Poznan University of Medical Sciences | Pyda M.,Rzeszow University of Technology | And 6 more authors.
Thermochimica Acta | Year: 2011

The performance of the Flash DSC 1, a recently introduced, commercial available chip fast scanning calorimeter (FSC) based on MEMS sensor technology, was studied. Topics included calibration; symmetry; repeatability; scan rate control windows of operation. Scan rates up to 20 000 °C/s for empty cell measurements in cooling and heating have been achieved. By combinations of scan rates up to 1000 °C/s various topics in between -95 to 450 °C were studied on polymers including self nucleation; annealing and thermal fractionation; 'hot' and 'cold' crystallization; amorphization; and cross-over of crystallization behavior with scan rate variation for two polymers. Sample masses around 1 μg and less gave good results with excellent repeatability and acceptable thermal lags. The Flash DSC 1 enables to mimic realistic conditions of practice and to measure (meta)stability and reorganization phenomena of substances and materials, including polymers, metals, pharmaceuticals etc. © 2011 Elsevier B.V. All rights reserved.


Poel G.V.,Royal DSM | Istrate D.,Royal DSM | Magon A.,Royal DSM | Magon A.,Rzeszow University of Technology | Mathot V.,SciTe
Journal of Thermal Analysis and Calorimetry | Year: 2012

For the new Flash DSC 1, the temperature windows-to-operate-the temperature ranges where the real, achieved scan rate is constant-have been determined for unloaded sensors under various conditions like purge gas and flow rate variations; cooling to -90 °C and heating to 450 °C; scan rates from 1 up to 20,000 °C s-1 in heating and 15,000 °C s-1 in cooling. Compared to nitrogen, helium purge gas offers better access to low-temperature transitions and enables faster cooling. Drawback is the decreased temperature window-to-operate in heating at the high-temperature side. The temperature calibration protocol according to the recent DIN SPEC 91127 for sample mass and scan rate was found to be useful. The correction factors are maximal -1.4 °C as measured for 1 μg at 1,000 °C s-1 heating. Using liquid crystalline substances it was proved that the Flash DSC 1 has symmetry, meaning that calibration data found in heating also can be applied in cooling. © Akadémiai Kiadó, Budapest, Hungary 2012.

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