DSC measurement for crystallinity of HDPE

Introduction

The crystallinity of high-density polyethylene (HDPE) can be evaluated by measuring the melting enthalpy using differential scanning calorimetry (DSC). In this study, the crystallinity of two HDPE samples, an original sample and those subjected to heat treatments by rapid quenching and slow cooling after melting, was compared based on the melting enthalpy.

Measurement and analysis examples

Figure 1 shows a comparison of the DSC results for HDPE. Endothermic peaks associated with melting are observed in the range of 90°C to 130°C for all samples. Rapid quenching was performed by immediately removing the sample from the device after melting, while slow cooling was carried out by leaving the sample in the device until the temperature decreased gradually to approximately 30°C.

Figure 1:  Comparison of DSC results for HDPE

A comparison of the melting enthalpy (endothermic peak energy) of each sample is summarized in the table below. The melting enthalpy of fully crystallized HDPE has been reported to range from 286 J/g to 293 J/g. In this study, a value of 290 J/g was used to calculate the degree of crystallinity of each sample.

In all samples, the degree of crystallinity was lower after rapid quenching and higher after slow cooling, relative to the original state. This demonstrates that the crystallinity of HDPE is influenced by the cooling rate.

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