Full-Factorial Rheological Investigation of Carbopol ETD2020 for Embedded Printing: Effects of pH and Carbomer...

Embedded printing of soft materials relies on yield-stress support matrices to prevent sagging and enable freeform fabrication. The rheological parameters of the matrix material directly influence critical printing outcomes such as strand positioning, cavity formation, structural stability, and defect suppression in embedded printing. Despite widespread use of Carbopol^® formulations, a systematic rheological characterization of ETD2020 across relevant polymer concentrations and pH levels for embedded printing is lacking. Here, we implement a full-factorial design with polymer concentrations from 0.1wt% to 0.9wt% and triethanolamine dosages of 30-50µL per 100g. Steady-shear (0.001-200s-1) and oscillatory (1Hz) rheometry yielded Herschel-Bulkley parameters τy, k, n as well as storage and loss modulus G'/G''. All formulations exhibited pronounced shear-thinning, with τy increasing nonlinearly from <1Pa to 41.1Pa and G' reaching ≈400Pa at 0.9wt%. A five-hour window of invariant rheology was identified, followed by a Δτy≈10Pa increase after five days, indicating delayed polymerization. The comprehensive material characterization defines a rheological window for ETD2020 and facilitates simulation-based modeling and the targeted tuning of matrix properties. Heatmaps provide an interpolated depiction of combined carbomer and triethanolamine concentrations, enabling tunable support matrices for embedded printing.