2.4. Preparation of (composite) spheres as masterbatch for extrusion/ melt-spinning
In this work, thermally induced phase separation (TIPS) [32] was used to produce composite spheres, as detailed in our previous work [28]. The method enables the homogeneous dispersion of large quantities of dry BC, modified-BC, as well as CNCs in a polymer melt using conventional extrusion processes at later stages.
Five types of composite feedstock were made: PLLA + 2 wt.% BC; PLLA + 2 wt.% C6-BC; PLLA + 2 wt.% C12-BC; PLLA + 7 wt.% CNC; PDLLA containing 7 wt.% CNC. For the production of CNC containing composite spheres, the concentration of CNCs was adjusted to the correct amount relative to PLA in 1,4-dioxane and thesolution homogenised at 20,000 rpm to disperse them in solvent prior to subsequent freezing in liquid nitrogen and freeze-drying [28]. Neat PLLA and PDLLA spheres were also produced as feedstock
[28]. Briefly, the resulting mixtures were poured separately into individual 50 ml syringes and added drop wise into a bath of liquid nitrogen to rapidly induce phase separation. The precipitates were collected in a 500 ml round bottom flask and subsequently freeze-dried to yield porous neat polymer and composite spheres, measuring circa 2–4 mm in diameter, suitably small to enter the extruder feed port.