A quantitative analysis of low density polyethylene and linear low density polyethylene blends by differential scanning calorimetery and fourier transform infrared spectroscopy methods

Abstract

Abstract Blends of low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) are widely used for blown film applications. An accurate and rapid test scheme to identify the type and composition of α‐olefin in LDPE/LLDPE blends has been developed that utilizes differential scanning calorimetery (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. The melting point of LDPE varies with density and usually is in the range of 106°C to 112°C for film grade resins. The DSC thermogram of LLDPE is characterized by a broad range of melting peaks with a lower melting peak around 106°C to 110°C and a higher one in the range of 120°C to 124°C. In a blend with LDPE, the ratio of the two endothermic peak heights changes. At a given weight percent of LDPE, this ratio depends on the type of LLDPE (i.e., the comonomer used). Separate calibrations for butene‐1, hexene‐1, and octene‐1 LLDPEs have been developed to quantify the blend composition from DSC thermograms where the α‐olefin type is successfully identified by FTIR over the entire blend composition range. The calibration curves are applicable to narrow melt index (MI) and density range conventional film grade LDPE and LLDPE resins and are not intended to be used for the metallocene type LLDPEs.