Applications

Triple Detection SEC/GPC of Polyethylenes

Introduction

Polyethylene, Figure 1, is the most widely used plastic material in the world. It is the most famous member of the polyolefin polymers.

Polyethylene resins can be produced in a variety of forms based on branching of the polymer backbone. The most common forms are low-density polyethylene (LDPE) and high-density polyethylene (HDPE).

Polyethylene has been used primarily in food packaging such as plastic films and food containers.

Black Vector Depicting Chemical Structure of Polyethylene

Figure 1. Chemical Structure of polyethylene.

Results

Comparison of the HDPE and LDPE samples is shown in Figure 2 with the GPC elution curves obtained from the RI detector response.

Molecular weights and physical parameters of these two PE samples have been calculated by Conventional Calibration Relative to PS standards as well as Triple Detection GPC technique (Table 1).

Table Showing Molecular Weights of Two Polyethylene Samples Calculated By Conventional Calibration

Overlay Chromatogram Obtained From The RI Detector of HDPE Sample (Black) and LDPE Sample (Green)

Figure 2. Overlay chromatogram obtained from the RI detector of HDPE sample (black) and LDPE sample (green).

Overlay of the Mark-Houwink Plots of Log Intrinsic Viscosity

Figure 3. Overlay of the Mark-Houwink Plots of Log Intrinsic Viscosity as function of Log Molecular Weight of the HDPE sample (black) and LDPE sample (green).

Conclusion

Molecular weights calculated relative to PS standards are significantly different from the absolute molecular weights calculated by Triple Detection SEC/GPC.

Addition of the viscometer enabled advanced structural analysis including branching analysis to compare between HDPE and LDPE.

Batch-to-batch variations and structural comparison between grades can be easily studied using advanced detection SEC/GPC.

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