Samuel C. Ugbolue

Electrospinning and Properties of Some Nanofibers

Electrospinning is a unique process that is capable of producing fibers with diameters ranging over several orders of magnitude, from the micrometer range typical of conventional fibers down to the nanometer range. Electrospun fibers possess unusually large surface-to-volume ratios and are expected to display morphologies and material properties different from their conventional counterparts. In this paper, details of recent designs and construction of equipment for controllable and reproducible electrospinning or electrostatic spinning are presented. An understanding of the electrospinning process is linked to processing conditions and polymer fluid characteristics, as well as the structure and properties of the final electrospun nanofibers.

The formation and performance of auxetic textiles. Part I: theoretical and technical considerations

Auxetic textiles belong to a class of extraordinary materials that become fatter when stretched. Sustained efforts to fabricate auxetic fabric structures are limited. Indeed, several geometrical configurations have been previously proposed but none has been engineered into functional auxetic textile fabrics. The use of auxetic materials has been limited because of problems with deploying them in their fabricated forms. Our thrust in this research is to combine our knowledge of geometry and fabric structural characteristics to engineer auxetic textiles and to determine the properties of such auxetic textile fabrics. In this paper, we have presented the technique we developed for producing several knit structures in which filling yarn inlays are used to effect compound repeating units. In these productions, the chain is used as a base structure and a minimum of two guide bars and maximum of six guide bars are deployed to produce such warp knit auxetic fabrics.

Nanoclay and Modified Nanoclay as Sorbents for Anionic, Cationic and Nonionic Dyes

The nanoclay, montmorillonite, and some modified nanoclays were used as sorbents for nonionic, anionic and cationic dyes. From the sorption differences among the different dye and clay structures, both chemical and morphological, the sorption forces that played important roles were identified. The nanoclay could easily have a sorption capacity of more than 600 mg sorbate per gram of sorbent at a liquor-to-sorbent ratio of 100 to 1. Furthermore, it could have a sorption of 90% at an initial dye concentration of 6 g/L, or 60% based on the weight of the sorbent, indicating an extremely high dye affinity. This study showed that with certain modifications the nanoclay, montmorillonite, could easily become an excellent sorbent for anionic, cationic and nonionic dyes.

The formation and performance of auxetic textiles. Part II: geometry and structural properties

Some exceptional materials become fatter when stretched and are described as auxetics or having negative Poisson’s ratio. Auxetic textiles belong to this class of extraordinary materials that are increasingly attaining some prominence in many applications of technical textiles. We have sustained the efforts to fabricate auxetic fabric structures based on non‐auxetic yarns. The focus is to combine our knowledge of geometry and fabric structural characteristics to engineer auxetic textiles and to determine the properties of such auxetic textile fabrics. To realize our objective, we designed and investigated hexagonal knit structures as auxetic textiles offering optimum performance. The factors that influence Poisson’s ratio are identified as yarn type, number of chain courses and strain level. Also, a method has been developed for quantifying the geometrical structural unit cell of the auxetic structure based on measured parameters, namely a 1, a 2, b 1, b 2, h and c, as detailed in this paper.

Size Reduction of Clay Particles in Nanometer Dimensions

Abstract : This research work focuses on combining ball milling and ultrasonication to produce nano-size clay particles. Our work also emphasizes on increasing the specific surface area of montmorillonite clay particles by reducing the particle size to nanometer dimensions. We have characterized the as-received clay particles by using particle size analysis based on laser diffraction and found that the size of the clay particles is not consistent and the particle size distribution is very broad. However, after the unique treatment and processing, the clay particles were obtained in nanometer dimensions with narrowed particle size distribution.

The Melt Electrospinning of Polycaprolactone (PCL) Ultrafine Fibers

Electrospinning is a technique of producing nanofibers from polymer solution/melt solely under the influence of electrostatic forces. In this research, we investigated the formation of nanofibers by melt electrospinning polycaprolactone (PCL). The effect of process parameters such as molecular weight, applied voltage, and electrode separation on the fiber diameter was investigated. Controlling the process parameters could help increase the proportion of ultrafine fibers in the melt electrospun nonwoven mat. The velocity of the straight jets was in the range of 0.2-1 m/s. The melt electrospun fibers were characterized with respect to fiber diameter, distribution, mechanical properties and birefringence. Melt electrospun polycaprolactone fibers had a diameter distribution of the order of 5 -20 μm. The birefringence of the melt electrospun fibers increased with decrease in fiber diameter.

Geometrical Analysis of Warp Knit Auxetic Fabrics

Despite considerable interests that have been shown on the formation, properties and characteristics of auxetic knit structures there remains a dearth of information about the fundamental geometrical analytics of warp knit auxetic fabrics. This paper examines the geometrical model of auxetic warp knit structure and validates its characteristics with data obtained from experimental analysis of nine recently produced warp knit auxetic fabrics.

10 – Testing, product evaluation and quality control of polyolefins

This chapter focuses on the testing, product evaluation and quality control of polyolefins, polyolefin nanocomposites, and auxetic fabric structures. Important physical and chemical tests that impact the raw materials and facilitate the evaluation of the products for various end uses and quality control regimes are presented. In recent years, the trends and developments in metrology have had their underpinnings on automation, speed, and advanced instrumentation. However, differences between test results may still arise because of variations in test specimens and test conditions.

Improved crosslinking systems for high-quality fiber/fabric performance

Crosslinking is a possible route for modifying fiber, fabric and polymer properties. Most of the crosslinking agents contain formaldehyde whose emissions into the air from textile materials have been limited to 0.1 mg/m3. Formaldehyde has irritant effect on the respiratory tract and mucosa in concentrations above 0.5 mg/m3 air and gives allergenic and sensitizing effect. Thus, several countries limit the formaldehyde content of textiles by law. The most widely used reactant resin in the textile industry is the DMDHEU (dimethyloldihroxyethyleneurea) which is based on reaction of glyoxal, urea and formaldehyde with cellulose by forming ether linkages under the influence of acid catalyst. Our research highlights an improved crosslinking system involving the use of considerably reduced formaldehyde, resulting in environmentally friendly processing flexibility, improved tenacity and toughness. This system is expected to provide crosslinks that can slide along the polymer backbone and cause the fiber to elongate under an applied load. The combination of enhanced tenacity and extensibility contributed to improved toughness, or work-to-failure properties.