What primary material property dictates the optimal nozzle temperature in FDM when switching from PLA to ABS?

The primary material property that dictates the optimal nozzle temperature when switching from PLA (Polylactic Acid) to ABS (Acrylonitrile Butadiene Styrene) in FDM (Fused Deposition Modeling) is the material's glass transition temperature (Tg). The glass transition temperature is the temperature range at which an amorphous solid, like these filaments, transitions from a hard, glassy state to a more rubbery, viscous state. To effectively extrude the filament, the nozzle must heat the material to at least its Tg. ABS has a significantly higher Tg than PLA, typically around 105°C compared to PLA's Tg of around 60°C. Therefore, the nozzle temperature must be increased to adequately melt and extrude ABS. A nozzle temperature that is too low will result in poor extrusion, layer adhesion, and potential nozzle clogging, while a temperature that is too high can lead to material degradation, stringing, and warping. For example, while PLA is commonly printed around 200-220°C, ABS usually requires a nozzle temperature of 230-260°C to achieve optimal results. Therefore, the difference in glass transition temperatures dictates the need for a significant adjustment in nozzle temperature when switching between these materials.