Identification of Low Density Polyethylene, High Density Polyethylene, and Polypropylene in Asphalt Binder with a Handheld FTIR Spectrometer

Low density polyethylene (LDPE), high density polyethylene (HDPE), and polypropylene (PP) are some of the widely used plastic products around the world. As part of recycling, these plastics have been experimented to be utilized in the construction of pavements to offer an opportunity to mitigate environmental pollution. The objective of this study is to investigate if LDPE, HDPE, or PP modified asphalt binders can be identified using Fourier transform infrared (FTIR) spectroscopy. In this experiment, 3% and 9% of each of the three unused plastics flakes were added to asphalt binders using a high shear mixer. Additionally, two more grades of PP were used—industrial waste (IWPP) and solid waste (SWPP). The FTIR analysis was performed using the peak height method after performing a two-point method for index calculation. For LDPE and HDPE, the results indicate that these plastic-modified asphalt binders neither show any new peak nor show significant intensity difference in existing peaks in the spectra and hence cannot be identified. However, IWPP modified asphalt binder shows a new peak at 1,014 cm^–1 which is not present in any of the unmodified neat binders. Moreover, SWPP modified asphalt binder as well as pure PP modified asphalt binder show the presence of a new peak between 997 and 1,000 cm^–1. The height of the absorbance peak also increases with the change in PP percentage from 0% to 9% (R² = 0.891 for pure PP, R² = 0.950 for SWPP, and R² = 0.747 for IWPP). It is likely that the peak at 1,014 cm^–1 indicates the presence of siloxane, Si–O–Si stretching vibration, while the peak at 997 cm^–1indicates the isotactic polypropylene band functional group. The result of this study would help identify the presence of polypropylene in any asphalt binder with a handheld FTIR in a rapid, portable, and non-destructive technique.