*2.2. Chemical Post-Processing*

#### 2.2.1. Vapor Smoothing

The first treatment was intended to improve the surface quality of Ultem parts through the partial dissolution of their outer layer due to prolonged contact with a chemical vapor (a process known as vapor smoothing). Due to the low compatibility between Ultem and chlorinated solvents [41], and its low boiling point (around 61 ◦C), chloroform (purity of 99.9%) was chosen for the smoothing process.

Vapor smoothing was performed by placing the substrates on an elevated sample bed (whose function was to avoid direct contact between the liquid solvent and the parts) within a 200 × 130 × 60 mm glass container. Next, 50 mL of chloroform were added to the bottom of the container, which was then sealed for 120 min. After the 120-min cycle, samples were removed and allowed to dry in ambient laboratory conditions for at least 24 h before further processing. Finally, two more sets of samples were treated for 180 and 270 min, respectively.

#### 2.2.2. Support Removal Solvent

The second chemical treatment was aimed at analyzing the surface integrity of Ultem parts after being treated with a solvent mixture capable of dissolving polysulfone, a thermoplastic commonly used as support material for Ultem in FFF. The effect of this treatment on the mechanical performance of Ultem and the optimal treatment time has been previously demonstrated [42].

Samples were submerged in a mixture of equal volumetric parts of 1,4-dioxane and toluene for a period of 4 hours. A similar setup as the one used for the vapor smoothing was used. This time, though, samples were fully immersed in the solvent (the volume used was 400 mL), and the liquid mixture was constantly agitated using a magnetic stirrer. After the treatment cycle, samples were removed and allowed to dry in a vacuum chamber for at least 12 h before further processing.

#### *2.3. Thermal Annealing*

A differential scanning calorimetry (DSC) of Ultem enabled identifying its glass transition temperature at 181 ◦C. This analysis was performed using a DSC821 measuring device from Mettler Toledo and a heating rate of 10 K·min−1. The lack of other phase transitions such as crystallization or melting, indicated the amorphous nature of the studied polymer. A sudden release of energy at 370 ◦C revealed a loss of integrity and irreversible degradation of the material. Another point to consider is that, during manufacturing, the material is exposed to a temperature of 195 ◦C for long periods inside the printing chamber. For these reasons, temperatures of 210 ◦C, 225 ◦C, and 240 ◦C were chosen as annealing temperatures. Thermal annealing of Ultem samples was performed at the set temperature for 30 min in an electric furnace from Hobersal, preheated before introducing the samples. Once the treatment was completed, cooling was performed at a constant rate of 1.5 ◦C·min−<sup>1</sup> until it reached a temperature of 150 ◦C to minimize thermal stresses. Then, the cooling rate was increased to 8 ◦C·min−<sup>1</sup> until room temperature.
