Novel processing methods based on the twin screw extrusion platform: Flowability control and reactive extrusion, development of hybrid methods with electrospinning and fabrication of graded nanobursa* meshes.

摘要

The twin screw extrusion process is a flexible processing platform which enables feeding of solid powders or polymer pellets at controlled rates, melting of polymers, mixing and dispersion of additives, multi zonal temperature control, flexibility to carry out chemical reactions under relatively high stresses, temperatures and pressures, devolatilization and capabilities for both distributive and dispersive mixing. Here new twin screw extrusion, TSE, based technologies and new applications of twin screw extrusion process were developed. First TSE was utilized as a reactive extrusion process to pretreat biomass under high shearing stresses for the first time enabled by the manipulation of the rheological behavior of biomass suspensions. Upon rheology control TSE was demonstrated to be a very effective processing platform for the pretreatment of hardwood biomasses at high stresses, temperatures and pressures. The TSE process was also modified by first time combination with electrospinning and run at throughput rates not encountered with conventional electrospinning while also facilitating the dispersion of nanoinclusions and generating graded meshes (meshes with tailored distributions of porosity, fiber size and compositions). The dynamics of the generation of meshes for poly(caprolactone) (PCL) and PCL incorporated with multi-walled carbon nanotubes, MWNTs were studied by systematically varying the distance of separation of the nozzles from the conductive collecting mandrel/plate, applied voltage, and linear velocity of the collection platform. The dimensions, crystallinity and mechanical properties of the meshes were investigated. In a further novel development MWNTs were functionalized with different kinds of metallic nanoparticles, i.e., Co, Pd, Pt and Ag and embedded into PCL "nanobursa fibers" via the hybrid twin screw extrusion and electrospinning method to generate contiguous graded meshes possibly to be used in sensor, catalyst and filtering applications.;* Nanobursa (from Latin- bursa "pouch or sac") refers to a new nanofiber structure that is generated in this study, involving porous polymeric nanofibers carrying multi-walled carbon nanotubes which themselves carry different types of metallic nanoinclusions within their lumens and on their surfaces.