A temperature dependent framework to predict and control physical pellet quality in biomass extrusion

Pellet manufacturing converts particulate biomass from food, feed, and bioenergy sources into dense, durable products with improved handling, nutritional, or calorific properties. However, the physical mechanisms that determine when loose particles bind to form dense, strong pellets remain insufficiently understood. This study establishes a mechanistic framework that links key process parameters to pellet quality in biomass extrusion. Systematic experiments were conducted to determine how steam conditioning, production rate, and die geometry affect temperature, residence time, and energy consumption during pelleting. The results show that these parameters interact to control the pellet temperature, which governs the formation of inter-particle bonds. A critical stickiness temperature ( T ∗ ) is introduced to describe the onset of adhesive interactions necessary for durable pellet formation. Once T ∗ is reached, strong pellets are produced, largely independent of the ingredient composition. The framework was validated using production data from various biomass ingredients and supplemented with literature data, demonstrating its broad applicability. The results confirm that pellet durability can be predicted from process conditions and the ingredient-specific T ∗ , providing a practical tool for process optimization. This approach reduces the need for empirical calibration and enables more energy-efficient and circular biomass utilization across diverse feedstocks. • Study of process parameters on pellet quality in biomass extrusion. • Linking steam, die, rate, time, and friction effects to pellet durability. • Combining process parameters into a single temperature-based relationship. • We identify an ingredient dependent stickiness temperature as limit for bond formation.