Accurate Molar Mass Estimation of Polyolefin Blends Using High Temperature-size Exclusion Chromatography

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By Yogesha Subbaiah, Ahmad Salem AlAhmadi, Mark Debasagoiti, Balaji Nagarajan, Rawan Jassem Alhafs, Senthilkumar Shanmugm
R& D Laboratory, TASNEE Technology and Innovation Centre,Al-Jubail Industrial City, Saudi Arabiam

Abstract

In this study, a commercially available polypropylene homopolymer (H-PP) was blended with blow molding polyethylene (PE) grade via melt mixing using a compounding machine. The resulting blends were subjected to high-temperature size exclusion chromatography (SEC) analysis, coupled with infrared-5 (IR-5), viscometer (VISCO), and multi-angle laser light scattering (MALS) detectors. The molecular weight (MW) and MW distributions were investigated using SEC, and the exact blend compositions were evaluated using 13C nuclear magnetic resonance. The molecular-level mixing of the PP/PE blend composition was assessed by comparing the theoretical and measured weight-average MW (Mw) values obtained using different SEC detection modes. The measured average Mw values of different PP/PE blends obtained using VISCO and multi-angle light-scattering detection were found to be in close agreement with predicted blend ratios, compared to the conventional SEC technique (IR-5), with percentage errors ranging from -4.53 to -5.99 and 1.57 to 7.65, respectively. The linear relationship between the melt flow rate (MFR) and Mw was studied to assess the molecular-level mixing behavior of the prepared blends using different SEC detection modes. Furthermore, the SEC methodology was extended to other application grades of PE with varying MFRs to verify the blend mixing behavior with H-PP, and the obtained results are discussed.

Polyolefin, Polypropylene, Polyethylene, Size-Exclusion Chromatography, Gel Permeation Chromatography.