Characterization of fractionated LLDPE by DSC, FTIR, and SEC

Abstract

SYNOPSISSamples of ethylene/ 1-butene copolymer were fractionated according to chemical composition by preparative temperature rising elution fractionation ( T R E F ) in the range of 27-117OC. The resulting fractions were submitted to DSC, SEC, and FTIR analyses. For each fraction, the methyl group content, melting temperature, crystallinity, average molecular weight, and molecular weight distribution were determined. From the results, it was found that the melting temperature increased linearly with the extraction temperature in the range of low temperatures and remained constant at high temperatures. Similar behavior was observed for crystallinity. It was also verified that the first two fractions showed a higher degree of supercooling than the fractions extracted at higher temperatures. These results were explained by the existence of a heterogeneous intermolecular distribution of comonomer molecules. In a general way, the comonomer units, present at higher concentrations in the low temperature fractions, tended to destroy the crystalline order of the polymer.

High-temperature gradient HPLC for the separation of polyethylene–polypropylene blends

“…With this technique the separation of polymer blends as well as the determination of chemical composition distributions of various polyolefins, including linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and polypropylene (PP) were accomplished [13][14][15][16][17]. Other techniques to separate polymer blends are selective extraction with appropriate solvents, solution-precipitation, or size exclusion chromatography (SEC) [18][19][20][21][22].…”

Influence of comonomer distribution on crystallization kinetics and performance of polyethylene of raised temperature resistance

“…The peak at 2019 cm −1 is the internal standard peak, which is the combined frequency vibration peak of the 1303 cm −1 peak (absorption of non‐crystalline structure) and the 719 cm −1 peak (methylene in‐plane rocking vibration, affected by crystallization). Therefore, the ratio R of the altitude of the 1378 cm −1 peak to the area of the 2019 cm −1 peak can characterize the relative comonomer content of the copolymers with the same comonomer …”

“…Therefore, the ratio R of the altitude of the 1378 cm −1 peak to the area of the 2019 cm −1 peak can characterize the relative comonomer content of the copolymers with the same comonomer. [11][12][13][14][15][16] Standard samples were obtained by mixing the NMR standard substance (known as comonomer type and content) with linear polyethylene in a series of mass ratios. Then, the mixtures were dissolved in hot xylene and the solvent was removed to obtain uniform mixtures.…”

Analysis of polyolefin blends by crystallization analysis fractionation

“…A separation by molar mass is possible using size exclusion chromatography (SEC). As SEC separates according to the hydrodynamic volume of the macromolecules, this method is limited to blends containing components of sufficiently different molar mass 4,5) . Another approach to compositional analysis is the investigation of the melting and crystallization behavior by differential scanning calorimetry (DSC) or temperature rising elution fractionation (TREF).…”