RESUMO
Non-woven nanoporous membranes of poly(caprolactone), PCL, incorporated with multi-walled carbon nanotubes, CNTs, could be fabricated via an industrially-scalable hybrid twin screw extrusion and electrospinning process. The utilization of a spinneret with multiple nozzles allowed the increase of the flow rate beyond what is possible with conventional electrospinning using a single nozzle, albeit at the expense of difficulties in the control of the thickness distributions of the nanofibrous membranes. The thickness and orientation distributions and the resulting mechanical properties of the membranes could be modified via changes in voltage, angular velocity of the collector mandrel and separation distance of the collector from the spinneret. The increases in crystallinity due to the presence of the CNTs and the preferential alignment of the nanofibers via rotation of the collecting mandrel led to increases in the tensile properties of the nanoporous membranes. The use of poly(ethylene oxide), PEO, together with PCL, followed by the dissolution of the PEO, rendered the nanofibers themselves nanoporous with typical surface porosity values of around 50% and pore sizes of about 220 nm. The demonstrated versatility of the hybrid twin screw extrusion and electrospinning process and the manipulation of mesh dimensions and properties are indicative of the applicability of the hybrid process for fabrication of nanoporous membranes for myriad diverse industrial applications ranging from water treatment to tissue engineering applications.
RESUMO
A new type of material, a "nanobursa" mesh (from "bursa" meaning "sac or pouch"), is introduced. This material consists of sequential layers of porous polymeric nanofibers encapsulating carbon nanotubes, which are functionalized with different metal nanoparticles in each layer. The nanobursa mesh is fabricated via a novel combination of twin-screw extrusion and electrospinning. Use of this hybrid process at industrially-relevant rates is demonstrated by producing a nanobursa mesh with graded layers of Pd, Co, Ag, and Pt nanoparticles. The potential use of the fabricated nanobursa mesh is illustrated by modeling of catalytic hydrocarbon oxidation.
RESUMO
Twin screw extrusion based pretreatment of biomass is an attractive option due to its flexibility to carry out chemical reactions under relatively high stresses, temperatures and pressures. However, extrusion processes are rarely utilized in biomass pretreatment because such processing is constrained by rheological behavior of typical biomass suspensions. Without the manipulation of their rheological behavior, biomass suspensions become unprocessable within the extruder at modest biomass concentrations. Here it is demonstrated that gelation agents can render biomass suspensions processable. Specifically, carboxy methyl cellulose, CMC, could be used in conjunction with alkaline pretreatment of hardwood-type biomass and enabled separation of lignin from cellulose fibers. Furthermore, recycled black liquor, obtained upon pretreatment, was determined to be as effective as CMC for rendering biomass suspensions flowable by again facilitating the concomitant application of high shearing stresses and chemical treatment for the pretreatment of the biomass in the twin screw extruder.
