a Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, USA
b Facoltà di Ingegneria, Università di Bologna, Viale Risorgimento 2, 40136 Bologna, Italy
Traditional methods for polymer fiber production include melt spinning, dry spinning, wet spinning and gel-state spinning. These methods rely on mechanical forces to produce fibers by extruding a polymer melt or solution through a spinneret and subsequently drawing the resulting filaments as they solidify or coagulate. These methods allow the production of fiber diameters typically in the range of 5 to 500 microns. At variance, electrospinning technology allows the production of fibers of much smaller dimensions. The fibers are produced by using an electrostatic field [1].
Electrospinning is a fiber-spinning technology used to produce long, three-dimensional, ultra-fine fibers with diameters in the range of a few nanometers to a few microns (more typically 100 nm to 1 micron) and lengths up to kilometers (Fig. 16-1). When used in products, the unique properties of nano-fibers are utilized, such as extraordinarily high surface area per unit mass, very high porosity, tunable pore size, tunable surface properties, layer thinness, high permeability, low basic weight, ability to retain electrostatic charges and cost effectiveness, among others [2].
Sofia G.
The effects of surface elasticity and surface tension on the transverse overall behavior of unidirectional nano-scale fiber-reinforced composites are studied. The interfaces between the nano-fibers and the matrix are regarded as material surfaces described by the Gurtin and Murdoch model. The analysis is based on the equivalent inhomogeneity technique. In this technique, the effective elastic properties of the material are deduced from the analysis of a small cluster of fibers embedded into an infinite plane. All interactions between the inhomogeneities in the cluster are precisely accounted for. The results related to the effects of surface elasticity are compared with those provided by the modified generalized self-consistent method, which only indirectly accounts for the interactions between the inhomogeneities. New results related to the effects of surface tension are presented. Although the approach employed is applicable to all transversely isotropic composites, in this paper we consider only a hexagonal arrangement of circular cylindrical fibers.
Mao-hua
Pore structure and chloride permeability of concrete containing nano-particles (TiO2 and SiO2) for pavement are experimentally studied and compared with that of plain concrete, concrete containing polypropylene (PP) fibers and concrete containing both nano-TiO2 and PP fibers. The test results indicate that the addition of nano-particles refines the pore structure of concrete and enhances the resistance to chloride penetration of concrete. The refined extent of pore structure and the enhanced extent of the resistance to chloride penetration of concrete are increased with the decreasing content of nano-particles. The pore structure and the resistance to chloride penetration of concrete containing nano-TiO2 are superior to that of concrete containing the same amount of nano-SiO2. However, for the concrete containing PP fibers, the pore structure is coarsened and the resistance to chloride penetration is reduced. The larger the content of PP fibers, the coarser the pore structure of concrete, and the lower the resistance to chloride penetration. For the concrete containing both nano-TiO2 and PP fibers, the pore structure is coarser and the resistance to chloride penetration is lower than that of concrete containing the same amount of PP fibers only. A hyperbolic relationship between chloride permeability and compressive strength of concrete is exhibited. There is an obvious linear relationship between chloride permeability and pore structure of concrete.
Keywords: Nano-particles; Pore structure; Chloride permeability; Polypropylene (PP) fibers; Pavement concrete
Guoxin
We propose to measure the elastoplastic properties of micro- and nano-fibers by a normal indentation technique in which the vertically aligned fibers are embedded in an elastic matrix. Measurements are taken at two different indentation depths, which represent different levels of the matrix effects and lead to the establishment of two independent equations that correlate the fiber/matrix properties with the indentation responses. Effective reverse analysis algorithms are proposed, and by following which the desired fiber properties can be determined from a sharp indentation test. Comprehensive analysis is also carried out to verify the effectiveness and error sensitivity of the presented method. The extracted material properties agree well with those measured from the parallel experiments on human hair and glass fibers.
Yibing
The ultrafine composite fibers consisting of lauric acid (LA), polyethylene terephthalate (PET), and silica nanoparticles (nano-SiO2) were prepared through the materials processing technique of electrospinning as an innovative type of form-stable phase change materials (PCMs). The effects of nano-SiO2 on morphology, thermal energy storage, thermal stability, and combustion properties of electrospun LA/PET/SiO2 composite fibers were studied. SEM images revealed that the LA/PET/SiO2 composite fibers with nano-SiO2 possessed desired morphologies with reduced average fiber diameters as compared to the LA/PET fibers without nano-SiO2. DSC measurements indicated that the amount of nano-SiO2 in the fibers had an influence on the crystallization of LA, and played an important role on the heat enthalpies of the composite fibers; while it had no appreciable effect on the phase change temperatures. TGA results suggested that the incorporation of nano-SiO2 increased the onset thermal degradation temperature, maximum weight loss temperature, and charred residue at 700 °C of the composite fibers, indicating the improved thermal stability of the fibers. MCC tests showed that the heat resistance effect and/or barrier property generated by nano-SiO2 resulted in an increase of initial combustion temperature and a decrease of the heat release rate for the electrospun ultrafine composite fibers.
Keywords: Form-stable phase change materials; Electrospinning; LA/PET composite fibers; Nano-SiO2; Morphology; Thermal energy storage