The processing conditions of graphene oxide and graphene fibers are important for final fiber properties. The effect of different processing conditions such as feed rate, nozzle size (length and diameter), and reduction time by vitamin C on fiber properties such as morphology, mechanical properties and electrical conductivity has been analyzed. It has been observed that at the constant feed rates, increase in nozzle length results in higher mechanical properties. For the samples produced with long nozzle, thinner nozzle results to higher mechanical properties than thicker one. Decrease in nozzle length and increase in feed rate and reduction time by vitamin C resulted in an increased crimpy structure of fiber surface. Higher fiber strength was observed when the reduction time was decreased. The increase in the feed rate resulted in an increase of fiber linear densities (tex). All fibers experimented were in the semiconductor range. In this study, it has been seen that short, thin nozzles with 10 ml/h feed rate and reduction with 2.5 h provided better mechanical properties along with electrical conductivity.
Graphene, a carbon allotrope, became a significant area of research with its superior electrical, mechanical, optical properties, etc. There are several methods to obtain graphene oxide from graphite, one of which is the Hummers method. In this study, several modifications and pre-treatments preceding the Hummers method have been employed. Three different graphene oxide fibers have been produced by three different procedures, i.e. fibers obtained by Hummers method with pre-oxidation step, modified Hummers method and modified Hummers method with pre-oxidation step. It has been observed that pre-oxidation has a significant effect on graphene oxide fiber properties produced by wet spinning process (coagulation). Modified Hummers method without pre-oxidation leads to the highest breaking strength and breaking elongation. Reduced fiber linear density, breaking strength and breaking elongation together with increased crimp were observed in graphene fiber due to the addition of pre-oxidation step.
The aim of this study is to determine the effect of sub-micron fibre web layers on sound absorption properties when they are placed on rigid substrate and flexible substrate. Elastomeric thermoplastic polyurethane (TPU) and composite TPU/PS (polystyrene) submicron fibre webs with both rigid glass fibre fabric reinforced epoxy composites (GFEC) and flexible polypropylene (PP) spunbond nonwovens have been examined. Elastomeric TPU sub-micron fibres and TPU/PS fibre web before and after soxhlet extraction were studied. Even though a thin layer of (less than 1 mm) electrospun sub-micron fibres were used with GFEC, sound absorption coefficient (SAC) improved from 0.1 to 0.4. Maximum SAC is drawn back to lower frequency (from 1250 to 500-630 Hz), when sub-micron fibre web is used on nonwoven. In conclusion, the mechanism of elastomeric thin sub-micron fibre webs on sound absorption for rigid GFEC and for flexible nonwoven is totally different than each other.
In this study, composite thermoplastic polyurethane (TPU)/polystyrene (PS) nanofiber web and TPU nanofiber web and PS-extracted TPU/PS microfiber web have been experimentally investigated with regard to sound absorption and thermal conductivity coefficients to observe a potential use in sound and thermal insulation areas. Moreover, other properties such as surface area, morphology, tensile strength/elongation, air permeability, and thermal degradation have been analyzed. It has been observed that nanofiber web properties such as fiber diameter, extensibility, pore volume, and porosity have been clearly changed by Soxhlet extraction of PS from the composite TPU/PS nanofibers. PS-extracted TPU/PS fibers can be preferred for the low frequency (600–800 Hz) due to higher SAC (0.7). On the other hand, TPU nanofibers were more effective at medium frequencies (around 3000 Hz, SAC 0.6). Both TPU and PS-extracted TPU/PS composite fibers had similar thermal conductivities, whereas TPU/PS composite nanofibers had lowest thermal conductivity (0.05 W/mK) with moderate maximum SAC value (around 1000 Hz, SAC 0.5–0.6).
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