2.1. Materials and Nanoreinforcements

Poly(lactic acid) (PLA), 2003D (specific gravity ¼ 1.24; MFR g/10 min (210 °C, 2.16 kg)) was purchased from Natureworks^® Co. (Minnetonka, MN, USA). Gohsenol type AH-17 polyvinyl alcohol (PV) (saponification degree 97%–98.5% and viscosity 25–30 mPa s) was obtained from the Nippon Synthetic Chemical Co. (Osaka, Japan). Starch (ST), cellulose fibers (CF) (powder 80–145 µm), and polyethylene glycol (PEG) were supplied by Sigma Aldrich (Santiago, Chile). Chloroform and sulfuric acid 95%–97% were supplied by Merck (Santiago, Chile). Low-flow PES (polyethersulfone) 170 dialysis membranes (35 µm thickness, 20.000 Da pore size) were purchased from the Nipro Medical Corporation (Santiago, Chile).

Ten grams of cellulose fibers (CF) was mixed with 50 mL of deionized water and put in an ice bath and stirred while 50 mL of concentrated sulfuric acid were added dropwise until the solution achieved 9 M concentration. The suspension was then heated at 45 °C and stirred for 120 min, followed by the addition of water to stop the hydrolysis. The resulting mixture was centrifuged at 4000 rpm for 20 min, and the clear supernatant containing acid residues and amorphous regions of the cellulose fiber was removed. Subsequently, successive washings were performed adding 50 mL of distilled water and the tubes were shaken again and centrifuged at 4000 rpm for 12 min. This operation was repeated until the supernatant was a turbid suspension containing the CNC [29,30]. The suspension obtained was dialyzed until the washing water maintained at constant pH. A known volume of the previous CNC suspension was freeze-dried to calculate the concentration of CNC and to obtain dry CNC to cast CNC nanocomposites used as control nanocomposites.

CNC solution (CNC-A) obtained from dialysis was concentrated through evaporation until a final concentration of 2% (w/v) (CNC-B) with the purpose to achieve a high incorporation degree of CNC into the electrospun fibers and lowest influence of PV/starch polymers in the blends with PLA. Furthermore, 1.6 g PV and 0.6 g starch were added to 20 mL of CNC-B solution and stirred at 90 °C until polymers were dissolved. In order to study the incorporation of CNC into the fiber, PV/starch solution at the same concentration without CNC was also prepared to be electrospun. Solutions were transferred to 5 mL plastic syringes and connected through a PTFE (polytetrafluoroethylene) tube to an 18-gauge blunt stainless steel needle charged by a high voltage power supply with a range of 0–30 kV. The collector plate was fixed at a working distance of 8.5 cm below the needle tip and connected to the grounded counter electrode of the power supply. A voltage of approximately 15 kV and a flow rate of 1.5 mL/h were used. CNC containing PV/starch fibers were named “(PVST/CNC)_f“ and PV/starch nanofibers “(PVST)_f”.