This article is portion of a comprehensive study on the development of nanofiber-reinforced polymer composites for electrostatic discharge materials and structural composites. Vapor-grown carbon fibers with an average diameter of 100 nm were used as a precursor and model fiber system for carbon nanotubes. These nanofibers were purified and functionalized to provide for an open network of high-purity nanofibers. Banbury-type mixing was used to disperse the nanofibers in the polymer matrix. Rheological and microscopic analysis showed that the high shear processing of the polymer/nanofiber mixture led to a homogeneous dispersion of nanofibers with no agglomerates present and no shortening of the nanofibers. The shear thinning behavior of polymeric materials helps in the mixing of the nanofibers to form the composites. A percolation threshold for electrical conduction of 9 -18 wt % was observed for the highly dispersed nanofiber networks. The electrical behavior of these materials was not affected by changes in humidity. Microscopic analysis showed highly dispersed nanofibers with no indications of porosity. These conducting polymers are well suited for electrostatic discharge applications, and might well become multifunctional materials for strength/ electrical applications.
Vapor-grown carbon fibers (VGCFs) were exposed to a series of chemical treatments and to electrochemical deposition of copper to modify their surface conditions and alter their electrical properties. The fibers were then mixed with polypropylene using a Banbury-type mixer obtaining composites up to 5 wt % VGCFs. Rheological, electrical, and mechanical properties were evaluated and compared to unfilled polypropylene processed in a similar manner. The composites made with HNO 3 -treated VGCFs showed a lower electrical resistivity compared to the untreated samples. The composites containing VGCFs subjected to the copper electrodeposition process showed the lowest resistivity with no change in the mechanical properties. Changes in rheological properties demonstrated the effects of varying surface conditions of the VGCFs. Microscopic analysis of these composites showed a heterogeneous distribution of VGCFs forming an interconnected network with the presence of copper on the surface of the VGCFs and in the matrix. Both the interconnected network and the presence of copper led to a lower percolation threshold than those seen in a previous work where high dispersion was sought.
BackgroundChitosan and Alginate were used as biopolymers to prepare membranes for protein adsorption. The network requires a cross-linker able to form bridges between polymeric chains. Viscopearl-mini® (VM) was used as a support to synthesize them. Six different types of membranes were prepared using the main compounds of the matrix: VM, Chitosan of low and medium molecular weight, and Alginate.ResultsExperiments were carried out to analyze the interactions within the matrix and improvements were found against porous cellulose beads. SEM characterization showed dispersion in the compounds. According to TGA, thermal behaviour remains similar for all compounds. Mechanical tests demonstrate the modulus of the composites increases for all samples, with major impact on materials containing VM. The adsorption capacity results showed that with the removal of globular protein, as the adsorbed amount increased, the adsorption percentage of Myoglobin from Horse Heart (MHH) decreased. Molecular electrostatic potential studies of Chitosan–Alginate have been performed by density functional theory (DFT) and ONIOM calculations (Our own N-layered integrated molecular orbital and molecular mechanics) which model large molecules by defining two or three layers within the structure that are treated at different levels of accuracy, at B3LYP/6-31G(d) and PM6/6-31G(d) level of theory, using PCM (polarizable continuum model) solvation model.ConclusionsFinally, Viscopearl-mini® acts as a suitable support on the matrix for the synthesis of Chitosan–Alginate membranes instead of cross-linkers usage. Therefore, it suggests that it is a promise material for potential applications, such as: biomedical, wastewater treatment, among others.Graphical abstractChitosan, Alginate, and Cellulose beads-based membranes for protein adsorption. Special attention was given for preparation, charaterization, adsorption capacity, and molecular electrostatic potential studies calculation. Viscopearl-mini® gives support on the matrix of Chitosan–Alginate membranes instead of cross-linkers usage
Polymer solutions with different concentrations of SU-8 2002/poly(ethylene) glycol/tetrabutyl ammonium tetrafluoroborate (SU-8/PEO/TBATFB) were electrospun in a low-voltage near-field electrospinning platform (LVNFES) at different velocities. Their diameters were related to the concentration contents as well as to their Deborah (De) numbers, which describes the elasticity of the polymer solution under determined operating conditions. We found a direct correlation between the concentration of PEO/TBATFB, the De and the diameter of the fibers. Fibers with diameters as thin as 465 nm can be achieved for De ≈ 1.
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