Polycaprolactone

Commercially available nano-sized hydroxyapatite (Sigma-Aldrich, St. Louis, MO, USA) and polycaprolactone (Polysciences, Warrington, PA, USA) were used as 3D-printable materials. Our previous study describes the preparation of composite materials for 3D-printing systems in detail [27 (link)]. In brief, PCL pellets were dissolved in 5 w/v% dichloromethane (Daejung Chemicals and Materials, Siheung, Korea), followed by the addition of 10 wt% nHA powder to the 5 w/v% PCL solution. The solution was sonicated with a sonicator (Korotec, Seoul, Korea) at 450 W for 45 min to uniformly disperse the nHA particles in the PCL matrix. The dispersed solution was dried in a vacuum oven at 80 °C to remove the residual dichloromethane. The prepared composite material was melted in a stainless-steel barrel with a ceramic nozzle with an inner diameter of 100 μm at 100 °C for 1 h. The melted material was extruded by a single screw at 45 rpm, and the 3D scaffold with a dual-pore kagome structure was fabricated by a pathway created from the STL file simultaneously (Figure 1). The control scaffolds were fabricated using a nozzle with an inner diameter of 500 μm using the abovementioned method.

The following materials were selected as components for molding sands that were subjected to mechanical regeneration:

Furfuryl resin, without the presence of nitrogen; free formaldehyde in the range of 0.05–0.15%; the amount of furfuryl alcohol 78%;

Hardener—an aqueous solution of paratoluenesulfonic acid;

Polycaprolactone (PCL)—a biodegradable additive and plasticizer with the formula –(O(CH2)5CO)-_n; molecular weight 50,000 Da and melting point 58–60 °C; a biodegradable polymer in solid form with an end of hydroxyl group from Polysciences Inc., Warrington, PA, USA.

The dust samples after the process of mechanical regeneration of molding sands: standard molding sand with organic binders (MS no. 1) and molding sand with organic binder and the addition of Polycaprolactone PCL (MS no. 2) were the subjects of our examination. The composition of the molding sands and dust-sample types are presented in Table 1.
The material has been processed the biodegradation process. Three g samples of dust were placed in polypropylene containers and filled 100 mL of water from the Vistula River, with a confirmed composition and specific physicochemical properties (Table 2). The samples were stored in closed containers at room temperature for 3 months.