Surface morphology

The surface morphology of electrospun fibres is affected by the polymer used, the voltage applied and the solvent, as well as the environmental conditions (e.g. humidity). The fibres may have either a smooth or a porous 5.6 SEM images of fibres electrospun from 2 PAN DMF solution (a) the solution does not contain any additives (b) the solution contains 0.1 (w v) dodecyltrimethylammonium bromide (DTAB). 5.6 SEM images of fibres electrospun from 2 PAN DMF solution (a) the solution does not...

Layered silicate clay minerals

Natural clays are most commonly formed either by the in situ alteration of volcanic ash or by the hydrothermal alteration of volcanic rocks. Bentonite is a rock that consists of commonly known smectite or montmorillonite group clays as its major component and auxiliary minerals such as kaolin, quartz, gypsum and iron ore. Sodium or calcium bentonite is not itself a mineral name more correctly, it is smectite clay composed primarily of the mineral montmorillonite having sodium or calcium ions as...

Vortex bath collector yarn

In this patent pending process developed at the National University of Singapore,41 a basin with a hole at the bottom is used to allow water to flow out in such a manner that a vortex is created on the water surface. Electrospinning is carried out over the top of the basin so that electrospun fibers are continuously deposited on the surface of the water. Owing to the presence of the vortex, the deposited fibers are drawn into a bundle as they flow through the water vortex. Generally, a higher...

Frequency selective surfaces for aerospace applications64 128137

Frequency selective surfaces (FSS) are an important application in many engineering sectors. In particular, it is useful for radomes, filters and radar communications. Traditional FSSs are constituted by two possible configurations periodically perforated metallic screens, or arrays of metallic patches printed on dielectric substrates. Aeronautic, military and naval applications are the typical technological fields involved in the FSS developments. The requirements of an FSS are to hide the...

Strategies for further development

A patented strategy for increasing charge density above the corona-induced breakdown point is to pulse the voltage of the charge injection device from a base value below the breakdown limit to a value above the breakdown limit, for a time shorter than that required for breakdown.50g It has been shown that under typical spraying condition, pulses of a few milliseconds duration should allow voltage to exceed the threshold level without a corona discharge effect occurring. Another approach is to...

Viscosity of nylon 66 solutions

It is well known that many parameters, such as viscosity, elasticity, conductivity, surface tension and distance between tip and collection screen, can influence the transformation of polymer solutions into nanofibers through electrospinning. Solution viscosity is one of the most important factors. Since both polymers have significantly different molecular weights, four different solutions of N6,6 with various concentrations were prepared. We used a mixed solvent consisting of formic acid and...

Properties of layered silicate polypropylene nanocomposites

Nanoparticles are able to provide PP with stiffening, reinforcing and toughening effects at rather low filler concentration. The influence of processing conditions on the nanocomposite structure, i.e. intercalated or exfoliated, and on the enhancement of mechanical properties of PP nanocomposites was studied by different researchers.44 Most polymer clay nanocomposites studies report tensile properties as a function of MMT content.19 The enhancements are strictly related to the processing...

Wideangle Xray diffraction

A Bruker AXS wide-angle X-ray diffractometer with a Cu Ka average source (A 1.5418A) was utilized to look at the crystalline structure of the overall composite sample and to calculate the Herman orientation factor. The samples were run in transmission and reflection modes. In the reflection mode, the 8.4 SEM images of 3 wt MWNT in PP (a) unoriented, (b) oriented, 12 1 draw ratio. 8.4 SEM images of 3 wt MWNT in PP (a) unoriented, (b) oriented, 12 1 draw ratio. fibers were mounted on a 1 cm x 1...

Spinbath collector yarn

In this recently published method, developed by our group at Stellenbosch University,38 continuous uniaxial fiber bundle yarns are obtained by electrospinning onto the surface of a liquid reservoir counter-electrode. The web of electrospun fibers, which forms on the surface of the spin-bath, is drawn at low linear velocity (ca. 0.05 m s) over the liquid surface and onto a take-up roller. A diagrammatic representation of the electrospinning set-up is given in Fig. 3.9. All the yarns obtained...

Ultrahigh molecular weight polyethyleneclay nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE) has extremely high abrasion resistance when compared with other thermoplastics. It also has exceptional impact resistance, even at cryogenic temperatures, and is superior to stainless steel. Other advantages of UHMWPE include low moisture absorption, good electrical and thermal insulation, self-lubrication and chemical inertness (except in some acids). Some formulations in which UHMWPE can be used are sheet, rod and tube. Some of its excellent...

Wear

During the wear test experiments it was found that not all samples could be run under the same conditions as originally planned since the maximum speed limit of most of the composites was very low. Wear measurements were thus made on each disc at the highest sliding speed achievable for a total sliding distance of at least 1 km and normalised to 10 km (assuming wear depth is linearly proportional to sliding distance) to compare with the best samples. Some of the samples show very good wear...

Electrophoresis

Each method is characteristic of a different synthesis process. Carbon nanotubes in aerospace engineering 153 6.5.1 Sonication Sonication is employed in the sample preparation procedures for microscopy characterization (SEM, TEX, EDX, etc.). It is useful to separate nanostructures from residuals using the following procedures mechanical removal of the nano-powders from the synthesis deposit (e.g. in the case of the arc discharge from the cathode electrode surface) dispersion of the removed...

Nanotube dispersion

A high-quality nanotube dispersion in any polymer matrix is a crucial prerequisite for good mechanical composite performance, and is often difficult to achieve. Each nanotube should be loaded separately and equally if the filler is agglomerated, some nanotubes will be shielded from the mechanical load. In addition, the agglomerates will act as defects, leading to stress concentration and premature failure. Good dispersion becomes harder to achieve as the particle size shrinks into the nanoscale...

The development and structure of carbon nanotubes164

The first carbon filament possessing a very small diameter (less than 10 nm) was produced in the 1970s by the decomposition of hydrocarbon at high temperature using transition metal catalysts. The 1985 discovery of the third allotropy form of ordered carbon (after the graphite and diamond forms, respectively hybridized sp2 and sp3), commonly known as fullerene, spurred the subsequent discovery of a number of related forms of carbon. Among these the most famous are nanotubes (Fig. 6.1), observed...

Exfoliation by extensional flow deformation

Fornes et al. (2001) proposed that the layered-silicate exfoliation during an extrusion process was initiated by the break-up of taller silicate stacks into smaller stacks, following a layer-by-layer peeling mechanism of the top and bottom silicate stack platelets by the extrusion shear stress. They also reported that this mechanism was proportional to the polymer Mw (viscosity), in which higher effective shear stress associated with higher Mw would lead to a more exfoliated morphology....

References

Jagur-Grodzinski, J., Heterogeneous Modification of Polymers Matrix and surface reactions, John Wiley amp Sons, Chichester, 1997. 2. Uyama, Y., Kato, K., Ikada, Y., Adv. in Polym. Sci. 1998, 137, p. 1. 3. Alexander, S., J. Phys. Paris 1977, 38, 983. 4. de Gennes, P.-J., Macromolecules 1980, 13, 1069. 5. Zhao, B., Brittain W. J., Prog. Polym. Sci. 2000, 25, 677. 6. Laub, C. F., Koberstein, J. T., Macromolecules 1994, 27, 5016. 7. Luzinov, I., Iyer, K. L. S., Klep, V., and Zdyrko, B., US...

Sidebyside nanofibres and sharpedged crosssectional nanofibres

Early attempts to prepare the 'side-by-side' bicomponent nanofibres were also based on a co-electrospinning process Gupta and Wilkes, 2003 . In the experiment, two charged polymer solutions were delivered via different syringes to the tip of a single nozzle and then electrospun into nanofibres. Although energy dispersive X-ray spectrometry EDS analysis confirmed that the as-spun nanofibre mat had both polymer components, there is no clear proof to indicate whether the fibre has a 'side-by-side'...

Improving the tribological properties of polymer nanocomposites

There are a number of ways in which the addition of a particle to a polymer can improve its friction and wear properties and all of these have been exploited in the production of nanocomposites. One approach is to reduce the adhesion of the composite to its sliding counterface by adding friction-modifying reinforcements which may also reduce the heat generated in a sliding contact. These friction modifiers may be in the form of low-friction particles which form low-friction transfer layers at...

Polymerclay nanocomposites

Intercalated Nanocomposite Diagram

PC nanocomposites are an emerging class of organic-inorganic hybrids that contain a relatively low wt of nanometer-sized clay. These were first developed in the late 1980s. The dispersion of the nanometer-sized clay in the polymer matrix significantly improves the mechanical, thermal, barrier properties and flame retardancy of the base polymer. Three main types of nanocomposites can be obtained when clay is dispersed in a polymer matrix. This depends on the nature of the components used,...

Friction coefficient measurements

For all materials the friction coefficient was approximately constant as a function of sliding speed until close to seizure when friction increases rapidly. Typical plots are shown in Fig. 9.2 and 9.3. Two important parameters can thus be extracted from the test data the average friction coefficient at all sliding speeds the speed at which seizure occurs under the contact conditions in the test. The average friction coefficient data for all the samples are collected in Fig. 9.4. It can clearly...

Principles of electrostatic selfassembly for creating nanolayer films

The Langmuir-Blodget LB technique allows monolayers to be created by using a non-solvent as a substrate. Once the monolayers have formed over the surface of a non-solvent system, they can be transferred onto a solid support. This technique, pioneered in the 1960s, is believed to be the first synthetic nano-scale heterostructure. These LB experiments were the first true nanomanipulations and they offered unprecedented control of the deposition of individual molecular layers. The creation of LB...

Producing continuous yarns

A common misconception in recent electrospinning literature is that the first literature on electrospinning dates back to 1934 when Formhals patented a method for manufacturing yarns from electrospun fibers.25 Some of the first publications on electrospinning date back as far as 1902, when first Cooley26 and then Morton27 patented processes for dispersing fluids. In both patents, the authors describe processes for producing very fine artificial fibers by delivering a solution of a fiber-forming...

Scaffolds for tissue engineering

It is well known that biological tissues consist of well-organized hierarchical fibrous structures14 ranging from nanometer to micrometer scale as described in Fig. 2.2. The successful regeneration of biological tissue and organs calls for the development of fibrous structures with fiber architectures conducive to cell deposition and cell proliferation. Of particular interest in tissue engineering is the creation of reproducible and biocompatible 3D scaffold for cell ingrowth, resulting in...

Polymerpolymer hybrid layers

Mixed and block-copolymer brushes are polymer-polymer hybrid thin films tethered to solid substrates. The well-defined architecture of end-tethered chains in polymer brushes allows for a deep study of the mechanisms of the brushes' response to their environment. Nevertheless, for practical applications a very similar mechanism can be approached using polymer layers when a polymer can be grafted by end groups, and also by side functional groups. The polymer chains randomly grafted by side...

Macromolecular platform for nanofabrication

The chemical grafting of polymers can be accomplished by either 'grafting to' or 'grafting from' methods.5 According to the 'grafting to' technique, end-functionalized polymer molecules react with complementary functional groups located on the surface to form tethered chains. The 'grafting from' technique utilizes the polymerization initiated from the substrate surface by attached usually by covalent bonds initiating groups. It is necessary to highlight that most of the developed grafting 'to'...

Enhancing the functionality of polymer nanocomposites

The results presented here demonstrate the benefit of nanoscale reinforcement to improve wear resistance of the composite material but to improve the overall performance of the materials for a sliding seal application no single reinforcement material is suitable. However, a combination of reinforcements can be developed which impart multiple functionality to the composite. For instance, both silica and MoS2 nanoparticles added to a polyurethane resin matrix can generate improvements in both...

The development of functional polymer nanocomposites

Making good samples of polymer nanocomposites is a challenge and a range of processing techniques are being actively developed at present including melt mixing Chan et al., 2002 , in situ polymerisation Yang et al., 1998, Reynaud et al., 2001 and other approaches. A full discussion of the technologies available is beyond this chapter but the interested reader is referred to the review of Jordan et al. 2005 . A single processing approach is unlikely to deliver viable composites in every system...

Nanosilica filled polypropylene nanocomposites

The incorporation of inorganic fillers in polymers contributes effectively to the improvement of the mechanical properties and in particular the toughness however, the procedure is often limited owing to the high filler contents that are needed for desired composite properties. For this reason nanocomposites with unique nano-scale microstructure, obtained by low particle loading represent a particular advantage. However, it is very difficult to disperse nanoparticles in a polymeric matrix...

Electrospinning of nanofibers and the charge injection method

SALEM, Charge Injection Technologies Inc., USA The use of electric charge to break up liquids into small particles has been well known and extensively studied for over a century, but commercial applications have been constrained by difficulties in surmounting flow rate limitations associated with the underlying physics of the process. This is true for both electrospraying, in which low-viscosity liquids can be atomized into droplets, and electrospinning, in which viscoelastic liquids can...

Compatibilization issues in polyolefinclay nanocomposites

Mere organophilization of the clay is often not sufficient to obtain intercalated or exfoliated PC nanocomposites. This is mostly true in the case of PO. This is mainly due to the low polarity of these polymers, which makes it difficult to get the exfoliation and homogeneous dispersion of the silicate layers at the nanometer level in the polymer. Silicate layers have polar hydroxyl groups, which are compatible only with polymers containing polar functional groups. This necessitates the use of a...

Mechanical properties of nylon 66 electrospun webs

Table 4.2 shows the mechanical properties of electrospun N6,6 nonwoven webs that were made under various experimental conditions. It is evident that the polymer concentration and the molecular weight of N6,6 influence the fiber morphology and, therefore, the elongation at break and initial modulus, as well as the strength of these materials. Figure 4.12 gives the dependence of these properties as a function of N6,6 concentration. The lowest elongation at break of 25.4 can be seen for the fibers...

Twisted nonwoven web yarn

This method, patented by Raisio Chemicals Korea Inc.,39 involves electrospinning nanofibers through multiple nozzles to obtain a nonwoven nanofiber web, either directly in a ribbon form or in a larger form, which is then cut into ribbons, and subsequently passing the nanofiber web ribbons through an air twister to obtain a twisted nanofiber yarn. A diagram depicting the process is given in Fig. 3.13. Table 3.1 shows process variables and yarn characteristics for three polymer yarns that have...