Deformulation of commercial linear low‐density polyethylene resins by advanced fractionation and analysis

Abstract

Linear low density polyethylene (LLDPE) exhibits a complex molecular structure that is characterized by molar mass and chemical composition distributions. Both molecular parameters complementarily influence the final application properties. Typically, the molecular structure of commercial polyolefins is characterized by a set of technical parameters including the melt flow index, the crystallization and melting temperatures and the comonomer content as obtained using Fourier transform infrared or NMR spectroscopy. LLDPEs with high comonomer contents are typically regarded as plastomers or elastomers. Due to their low crystallinities, characterization of these materials using crystallization‐based analytical techniques is of limited use since the majority of the material is rather amorphous. Such materials need specific alternative analytical methods that may be based on molar mass and/or chemical composition fractionation. Here it is shown that for a comprehensive analysis of LLDPEs with similar bulk properties, preparative molar mass fractionation (pMMF) and advanced analysis of the fractions are required. The pMMF fractions are comprehensively analyzed using size exclusion chromatography, differential scanning calorimetry and high‐temperature high‐performance liquid chromatography to provide detailed information on molar mass and copolymer composition. Correlated information of these molecular parameters is obtained by comprehensive two‐dimensional liquid chromatography. © 2019 Society of Chemical Industry

Recent Advances in Separation-Based Techniques for Synthetic Polymer Characterization

“…The fractions were also characterized by a number of off-line techniques such as SEC-MALLS, SEC-IR, DSC, and successive self-nucleation and annealing to provide insight on the bivariate distributions of molar mass and branching, and how these features impact crystallinity in LDPE. A similar approach for characterization of LLDPE was also reported . Preparative cross fractionation followed by off-line characterization via a combination of techniques, including comprehensive 2DLC, provided clear structural differentiation of two LLDPE materials having similar bulk molar mass and chemical composition.…”

“…HT-GPC was recently used to assist in the understanding of the polymerization mechanism, such as chain walking polymerization, to support synthesis and characterization of model linear low density polyethylene (LLDPE) polymers, , for understanding changes in MWD as a result of hydrogen–deuterium exchange reactions, comprehensive analysis of novel grafted polyethylenes using multidimensional fractionation methods, deformulation of commercial LLDPE materials, and structure performance correlations involving adhesion of waxes . With the great enhanced awareness of environmental sustainability, HT-GPC was recently used to characterize plastic waste in the ocean and plastic residues digested by marine animals. , …”

“…It was also shown that HTLC separations depended on both the number of chlorine atoms on the desorption promoting solvent and to a larger extent on the polarity of the adsorption promoting solvent . Additionally, HTLC was one of the many analytical techniques used to analyze fractionated components from different LDPEs, − HDPE-g-LDPE, and LLDPE. , Finally, an advanced LC method was demonstrated by using the principles of both solvent gradient and temperature gradient in the same experiment, and this approach could provide a unique path for future HTLC-based separations of polyolefins.…”

“…99 Additionally, HTLC was one of the many analytical techniques used to analyze fractionated components from different LDPEs, 100−103 HDPE-g-LDPE, 33 and LLDPE. 30,107 Finally, an advanced LC method was demonstrated by using the principles of both solvent gradient and temperature gradient in the same experiment, 121 and this approach could provide a unique path for future HTLC-based separations of polyolefins. The stationary phase of choice for most research work has been porous graphitic and its use for polyolefin separations was reviewed recently.…”

Multidimensional analytical protocols for the fractionation and analysis of complex polyolefins

“…More examples of HT-2D-HPLC are given in Refs. [104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120].…”