Polystyrene fiber diameters

The effect of fiber diameter on the tensile strength of a glass-fiber-reinforced polystyrene composite is shown in Figure 5.100. Some reinforcements also have a distribution of fiber diameters that can affect properties. Recall from the previous section that the fiber aspect ratio (length/diameter) is an important parameter in some mechanical property correlations. 

Figure 5.100 Effect of glass fiber diameter on strength of reinforced polystyrene. Reprinted, by permission, from G. Lubin, Handbook of Fiberglass and Advanced Plastics Composites, p. 130. Copyright 1969 by Van Nostrand Reinhold.

Figure 3.71 shows the change of average polystyrene phase diameter versus distance along the radial direction. The gradient phase structure was intensely related to the polystyrene content. With increasing amount of polystyrene, the size of the dispersed phase in the fiber center decreased continuously to nanosized fibrillar structure [257]. 

Figure 1. (a) Basic apparatus for electrospinning (2). (b) A typical SEM image of electrospun polystyrene fibers with an average diameter of 43 nm (4). Scale... 

Poly(dimethylsiloxane) (PDMS) is a well-known hydrophobic polymer with higher repellency for water than PS crosslinked siUcone elastomers (WCA = 112° for a smooth film) are commonly used for fabricating microfluidic devices. But forming solid fibers comprised solely of linear PDMS is not possible, due to its low glass transition temperature. Instead of using linear homopolymer PDMS, Ma et al. [21] electrospun fibers of poly(styrene-b-dimethylsiloxane) block copolymers blended with 23.4 wt% homopolymer polystyrene (PS-PDMS/PS) from a solution in a mixed solvent of THF and DMF. The resultant fiber mat, with fiber diameters in the range of 150-400 nm, exhibited a WCA of 163° and a hysteresis of 15°. An illustration of water droplets beaded up on such a mat is provided in Fig. 3. A PS mat of similar fiber diameter and porosity exhibited a WCA of only 138°. The difference was attributed to the lower surface tension of the PDMS component, combined with its spontaneous segregation to the fiber surface. X-ray photoelec-... 

The imiformity and stability of nanotube dispersion in polymer matrix are probably the most fundamental issue for the performance of composite materials. A good dispersion and distribution of CNTs in the polymer matrix minimizes the stress concentration centers and improves the uniformity of stress distribution in composites [80]. On the other hand, if the nanotubes are poorly dispersed within the pol mier matrix, the composite will fail because of the separation of the nanotube bundle rather than the failure of the nanotube itself, resulting in significantly reduced strength [117], Mazinani et al. studied the CNT dispersion for electrospun composite fiber, as well as its effect on the morphologies and properties of electrospun CNT-polystyrene nanocomposite [42]. They demonstrated that the CNT dispersion is an important controlling parameter for final fibers diameter and morphology. 

Smith and coworkers reported the preparation of both particles and fibers via RESS from a variety of polymers (57,68-72,80). For example, a solution of polystyrene (molecular weight about 300,000 and melting point about 170°C) in supercritical pentane was rapidly expanded at 350°C and 170 bar using a 25-p,m nozzle the result was spherical particles with an average diameter of 20 p,m (68). Other polymers, including polypropylene, poly(carbosilane) (an important precursor for silicon carbide), poly(phenylsulfone), poly(methyl methacrylate), and cellulose acetate, were processed into micrometer-sized particles via RESS in a similar fashion (68). However, when the preexpansion temperature of the supercritical pentane solution was lowered from 350°C to 200" C, polystyrene fibers (100-1000 txm in length and 1 ixm in diameter) were obtained. 

In 2006, Gopal and co-workers first explored the viability of using ENM for liquid filtration and demonstrated the separation performance on particulate removal [81]. A complete self-supporting membrane was electrospun with PVDF in DMF/acetone solution, with heating as a posttreatment. The membrane had a thickness of 300 p,m and a fiber diameter range of 380 106 nm, with an effective pore size range of 4.0-10.6 p,m, which were close to the properties of conventional microfiltration membranes. The filtration performance was examined by separation of 1-, 5-, and 10-p,m polystyrene particles. More than 90 % of the microparticles were successfully rejected, as shown in Fig. 13.7. However, the fouling on the top layer of the membrane surface due to particle deposition compromised the... 

In the first approach, a maleimide-functionalized polystyrene of 40 repeat units (P DI = 1.04) was covalently coupled to the sulfur atom of a reduced disulfide bridge on the surface of the lipase B from Candida antarctica (CALB) (Figure 6.11a) [33]. TEM studies of the reaction mixture in water/THF revealed well-defined enzyme fibers with a length of several micrometers. The fibers consisted of bundles of rods, of which the smallest had diameters between 25 and 30 nm. These diameters were in... 

FIGURE 7.44. Transmission electron micrographs of the micellar assemblies formed by the aggregation of a lipase-polystyrene giant amphiphile in water. Expansion reveals a single micellar fiber with a diameter of 20-30 nm. Schematic representation of the micellar rod which possesses a polystyrene core. 

Figures 7.18(b) and 7.18(c) show the breakup into droplets of an extended filament of high density polyethylene in a polystyrene matrix. In Fig. 7.18(b) the distance between the extruder die and the quenching bath is short and the fiber freezes before breaking up, whereas in Fig. 7.18(c) the distance was increased, giving the filaments sufficient time for breakup. As the filament extends, its diameter is reduced until shear forces no longer dominate the surface tension cohesive forces and the filaments breaks into droplets, just like a stream of water from a faucet breaks up into droplets.

The polystyrene simulation followed the experiments of Bell and Edie (12) with good agreement. Figure 14.8 shows the simulation results for fiber spinning nylon-6.6 with a draw ratio of 40. The figure demonstrates the wealth of information provided by the model. It shows the velocity, temperature, axial normal stress, and crystallinity fields along the threadline. We see the characteristic exponential-like drop in diameter with locally (radially) constant but accelerating velocity. However, results map out the temperature, stress, and crystallinity fields, which show marked variation radially and axially. 

Tubular and columnar apparatus (apparatus length-to-diameter ratio L/d > 100) including screw equipment relate to plug-flow reactors type [7,8]. Plug-flow reactors are applied for many of gas-phase reactions realized in production quantities, in particular for ethylene polymerization under high pressure conditions [9], and for some liquid-phase reactions, for example polystyrene synthesis in columns and other rubbers and plastics productions. Near 10% of polymer and 30% of fibers manufacture are produced in apparatus of such types [10]. 

The diameter of as-spun fiber decreased from around 20-30 p,m to about 15 pm after drawing, while the size of the polystyrene morphology reduced about 10%. This indicates the drawing process did not effectively deform the solid dispersed phase, because it is difficult for the draw stress to transfer from the matrix to the dispersed phase through the solid interface, and the free space for the polystyrene phase deformation is limited. 

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