2.1. Preparation of PCL/Graphene-Based Nanomaterial Hollow Fibers

In the present study, instead of laboratory-made graphene oxide or reduced graphene oxide, which are widely studied in the literature, we decided to explore the feasibility of using commercial graphene/graphite (G) nanoplatelets (Av-PLAT-7, Avanzare) produced at a large industrial scale by mechanical exfoliation. The PCL/G polymer dope solution was prepared as follows: 0.1 wt% of G were homogeneously dispersed by sonication during 20 min in N-methyl pyrrolidone (NMP, 99%, extrapure, Acros Organics, Madrid, Spain). Afterwards, 15 wt% of PCL pellets (MW, 80 kDa, Sigma Aldrich, Madrid, Spain) and 5 wt% of absolute ethanol (EtOH, Sigma Aldrich, Madrid, Spain) were dissolved by rolling (Roller Shaker 6 Basic, IKA, Staufen, Germany). The polymer solution was left to degasify overnight at room temperature. As a control, a PCL dope solution was prepared similarly without graphene.

The PCL and PCL/G HFs were fabricated by non-solvent induced phase separation produced by immersion precipitation using a small dimension spinning set-up to process the polymer solution [27,28]. Polymer solution and bore fluid were simultaneously pumped through a tube-in-orifice spinneret. The formation conditions for the fibers are summarized in Table 1. From each polymer solution, several meters of HF membranes were prepared, and only homogeneous and reproducible sections were selected for experimental purposes.

Spinning conditions and process parameters for poly(ε-caprolactone) (PCL) and PCL/G hollow fiber (HF) synthesis.