The Influence of Rheological Properties on the Adhesiveness of Food Waste and Its Implications for Mechanical Separation

Abstract

The viscoelastic and adhesive properties of food waste materials are critical factors influencing the efficiency of mechanical separation processes in waste management. This study investigated the moisture-dependent rheological behavior─specifically storage modulus in both shear (G′) and compression (E′) modes, alongside the loss factor (tan δ)─of various food waste types, categorized as solid-like (steamed rice, banana pulp, raw meat) and paste-like (mashed banana, ketchup, mashed steamed rice, yogurt). These properties were correlated with adhesion strength on aluminum and high-density polyethylene (HDPE) surfaces using 90° peel tests. Results identified specific moisture-induced viscoelastic transitions for different materials. Steamed rice demonstrated a sharp increase in tan δ at a critical moisture range, indicative of starch gelatinization. Material-specific correlations revealed that higher tan δ (more viscous behavior) closely corresponds to structural softening and enhanced interfacial adhesion within individual paste-like materials, with consistently stronger adhesion observed on aluminum foil compared to HDPE sheets. However, carbohydrate-rich pastes showed increased adhesion at very low moisture levels. These findings highlight the significant impact of moisture-dependent rheological properties, where tan δ serves as a critical within-material transition indicator for identifying localized risk of clogging, screen blinding, and material agglomeration in processing equipment. The study underscores the importance of considering material-specific viscoelastic behavior and surface interactions in optimizing waste processing technologies and suggests potential benefits of moisture control and material selection in equipment design, as well as the strategic implementation of source separation for problematic waste fractions, particularly those exhibiting high tan δ and high viscoelasticity.