Quantitative analysis of polyethylene blends by Fourier transform infrared spectroscopy

The quantitative analysis of binary polyethylene (PE) blends by Fourier transform infrared (FT-IR) spectroscopy has been achieved based on the ratio of two absorbance peaks in an FT-IR spectrum. The frequencies for the absorbance ratio are selected based on structural entities of the PE components in the blend. A linear relationship between the absorbance ratio and the blend composition was found to exist if one of the absorbance peaks is distinct to one of the components and the other peak is common to both components. It was also found that any peak resulting from short-chain branching in copolymers (such as linear low-density polyethylene (LLDPE) or metallocene-catalyzed LLDPE (mLLDPE)), is suitable for use as the peak that is designated as being distinct to that component. In order to optimize the linearity of the equation, however, the selection of the second common peak is the most important and depends on the blend system studied. Indeed, under certain circumstances peaks that are not spectrally distinct can be used successfully to apply the method. The method exhibits potential for the routine analysis of PE blends that have been calibrated prior to its application.