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Mirabella F.M.,Mirabella Practical Consulting Solutions Inc. | Boborodea A.,Certech ASBL
International Journal of Polymer Analysis and Characterization | Year: 2015

Analytical temperature rising elution fractionation (TREF) is a complementary technique of gel permeation chromatography (GPC) for the analysis of polyolefin structure. By connecting a high-temperature GPC with a gas chromatograph (GC) oven it is possible to build a fast analytical TREF, which permits a dramatic reduction in analysis time by directly injecting the polymer solution onto the cold column, as compared with the traditional TREF in which the slow cooling step usually takes more than 40 h. The method was successfully applied on six commercial random and homo polypropylenes for which similar thermograms were obtained for fast- and slow-cooling TREF. The obtained results show subtle differences in the behavior of polypropylene melting in solution as compared with previously analyzed polyethylene. The most important is the difference of 12.6°C between the melting temperatures in the presence of trichlorobenzene and xylene, which is much higher for polypropylene than the 3.7°C measured for polyethylene. © 2015, Copyright © Taylor & Francis Group, LLC. Source


Mirabella F.M.,Mirabella Practical Consulting Solutions Inc. | Boborodea A.,Certech ASBL
International Journal of Polymer Analysis and Characterization | Year: 2015

Recent developments on the temperature rising elution fractionation (TREF) technique, understanding the impact strength of polyethylene blends based on their chemical structure, as well as ongoing discussions on REACH legislation regarding the oligomer fraction of polymers, are all reasons for better comprehension of the separation mechanism in TREF. To achieve this goal, two carefully chosen blends of linear metallocene polyethylene were analyzed by TREF over a large domain of crystallization rates. The results allowed updating the “onion skin” model for the crystallization kinetics during the cooling step of TREF. The advantages and limitations of the TREF technique for different applications are discussed. © 2015, Copyright © Taylor & Francis Group, LLC. Source


Boborodea A.,Certech ASBL | Mirabella F.M.,Mirabella Practical Consulting Solutions Inc.
International Journal of Polymer Analysis and Characterization | Year: 2015

Analytical temperature rising elution fractionation (TREF) of linear polyethylene (PE) samples with different densities was done in 1-chloronaphthalene using a gel permeation chromatograph (GPC) coupled with a gas chromatograph. The corrected peak elution temperatures completed the previously obtained data in trichlorobenzene, xylene, and dibutoxymethane. A mathematical correlation was found for diluted linear PE samples between the α parameter of the Mark-Houwink-Sakurada equation governing the retention time in GPC, the bulk melting temperature measured by differential scanning calorimetry (DSC), and the TREF peak elution temperature. The extrapolation to the melting temperature measured by DSC gives α = 0.5, thus confirming the hypothesis that polymer conformations in the melt are similar to those in a theta solvent. © 2015, Copyright © Taylor & Francis Group, LLC. Source


Ramachandran R.,University of Cincinnati | Beaucage G.,University of Cincinnati | McFaddin D.,Equistar Chemicals | Merrick-Mack J.,Equistar Chemicals | And 2 more authors.
Polymer | Year: 2011

Commercial polyethylene is typically heterogeneous in molecular weight as well as in molecular topology due to variability in catalyst systems and catalyst activity. Further, processing of polyethylene after polymerization may also result in changes to the structure. While quantification of molecular weight is routine using gel permeation chromatography (GPC); quantification of the heterogeneity in molecular topology and microstructure is more difficult. In this paper, a novel method is used to examine the structure and branch content of a linear low-density polyethylene (LLDPE). The method uses a scaling model to analyze small-angle neutron scattering (SANS) data from dilute solutions of a series of LLDPE fractions. The scaling approach quantifies short-chain and long-chain branch content in polymers concurrently, thereby illustrating the distribution of these branches in the polyethylene fractions. Additionally, new quantities such as the average long-chain branch length and hyperbranch content are measured to provide further insight into the structure of these polymers. LLDPE used in this study is fractionated using temperature rising elution fractionation (TREF). Results from the analysis of these fractions show evidence of long-chain branching in commercial LLDPE which could be partly attributed to post-synthesis processing conditions. © 2011 Elsevier Ltd. All rights reserved. Source


Mirabella F.M.,Mirabella Practical Consulting Solutions Inc.
Journal of Liquid Chromatography and Related Technologies | Year: 2014

The effects of low molecular weight species in the analytical TREF (A-TREF) have been reported. Remarkably, no literature report, describes or even mentions, possible effects of high MW polymers on the TREF mechanism. The appearance of high temperature peaks in TREF elution has been experimentally linked to the presence of high molecular weight species in the case of high density (i.e., unbranched) polyethylene. Baseline resolved peaks or shoulders on the main peak (which main peak is presumably due to lower molecular weight fraction species) were observed with peak maxima as much as ∼10-25°C higher than baseline return of the high temperature side of the main peak. These high temperature peaks are apparently due to high molecular weight species, which undergo delayed dissolution, after melting in the presence of the diluent. These transiently "undissolved" species apparently cause irreproducible A-TREF elution curves, resulting in peaks moving along the temperature axis. These high temperature peaks were observed for a polymer having a highest molecular weight fraction of species with about 10 million molecular weight, but were not observed for another polymer having a highest molecular weight fraction of species with about 1 million molecular weight. Copyright © 2014 Taylor & Francis Group, LLC. Source

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