Study on recycled LLDPE modified asphalt using fluorescence microscopy and entropy-weight evaluation for process selection

Road engineering is critical for large-scale waste plastic recycling. Agricultural mulch films have huge annual consumption but extremely low recycling rates. Unrecycled ones degrade slowly (over 400 years) and release microplastics, harming ecosystems. This study used LLDPE from these films as an asphalt modifier to boost recycling and improve properties of virgin asphalt. The study prepared LLDPE modified asphalt with 4 % LLDPE content adjusting shear temperatures (160 ℃, 180 ℃, 200 ℃), shear rates (2000 rpm, 3000 rpm, 4000 rpm), and feeding methods (direct blending, pre-melting blending). The mechanical tests were used to assess LLDPE’s effects on asphalt’s road performance and storage stability. Based on combined fluorescence microscopy with image processing, the indicators such as average particle size (Aps), roundness (Rs), nearest neighbor distance (NND) and coefficient of variation (CV) for quantitative evaluation of LLDPE’s melting and dispersion in asphalt were proposed. Finally, a 100-point evaluation system for modification effects via the entropy weight method was established. LLDPE improved asphalt’s high temperature deformation resistance but reduced low temperature ductility. The optimal process was 180℃, 3000 rpm and direct blending, which achieved the only full score. • Recycled mulch-film LLDPE is used as a sustainable asphalt modifier. • LLDPE improves high-temperature deformation resistance but reduces low-temperature ductility. • Fluorescence microscopy quantifies LLDPE dispersion using Aps, Rs, NND and CV. • Entropy weight scoring selects 180 °C/3000 rpm/direct blending as best process.