Determination of the Percentage of Homopolymer Component in Ziegler/Natta Catalyst Linear Low-Density Polyethylene Resins Using High-Temperature Cell Fourier Transform Infrared and Partial Least Squares Quantitative Analysis Technique

Abstract

A new method for the determination of the percentage of homopolymer component, using high-temperature cell Fourier transform infrared (FT-IR) by partial least squares (PLS) quantitative analysis technique, was developed and applied to Ziegler Natta linear low-density polyethylene (LLDPE). The method is based on the IR spectrum changes between the 730 cm⁻¹ band and 720 cm⁻¹ band at the temperature of 110 °C, which is near the melting point of the polyethylene. The HD% (the percentage of high-density component, i.e., the percentage of homopolymer component) results obtained by CTREF (CRYSTAF in TREF mode) technique are used as the input data together with the respective FT-IR spectra for PLS analyses to establish a calibration curve. The PLS quality is characterized by a correlation coefficient of 0.997 (cross-validation) using four factors and a root mean square error of calibration (RMSEC) of 0.772. The HD% of the unknown can then be predicted by the PLS software from the unknown FT-IR spectrum. A control resin was tested seven times by CTREF and FT-IR. The HD% of the control resin was 28.59 ± 0.88% by CTREF and 29.05 ± 2.37% by FT-IR. It was found that the method was applicable for the same comonomer type of LLDPE within a melt index range and density.