Managing Stickiness and Wall Deposition in Spray Drying of Low-Tg Materials
Summary
Spray drying low glass transition temperature (Tg) materials presents significant operational challenges due to particle stickiness and wall deposition. When particle surface temperature exceeds Tg at a given moisture level, powders become rubbery and adhere to equipment surfaces, reducing yield and process stability. Effective mitigation requires integrated control of feed solids, atomization parameters, outlet temperature relative to product Tg, and optimized airflow design. By aligning product properties with equipment configuration, manufacturers can minimize fouling, improve powder flowability, and achieve consistent, high-quality production across scales.
Spray drying materials with low glass transition temperature (Tg) presents a persistent engineering challenge. Sugars, polyols, protein hydrolysates, botanical extracts, and many encapsulated actives can become rubbery or tacky during drying, leading to wall deposition, cyclone fouling, reduced yield, and unstable operation.
Stickiness occurs when particle surface temperature exceeds the material’s Tg at the prevailing moisture content. Under these conditions, particles lose structural rigidity and adhere to hot surfaces or to each other. Simply lowering inlet temperature is often ineffective, as insufficient drying may produce wet particles that remain sticky downstream.
Effective mitigation requires coordinated control of thermal, physical, and aerodynamic parameters. Key strategies include optimizing feed solids to shorten the constant-rate drying phase, selecting atomization conditions that produce appropriate droplet sizes, and controlling outlet temperature relative to product Tg rather than absolute temperature limits.
Airflow pattern and chamber geometry also influence deposition behavior. Designs that minimize particle–wall contact, reduce recirculation zones, and promote rapid transport to separation systems significantly improve operational stability. In some cases, staged drying or controlled humidity can maintain particle surface below the sticky region while still achieving target moisture.
Surface engineering through formulation adjustments or carrier selection may further increase Tg and improve powder flowability. However, such changes must be balanced against product functionality and regulatory constraints.
Successful processing of low-Tg materials therefore depends on integrating product properties with equipment design rather than relying on generic operating windows. Customized system configuration enables consistent yield, reduced fouling, and reproducible powder quality for demanding applications across scales