Ahmed Jalal Uddin

Toward "strong" green nanocomposites: polyvinyl alcohol reinforced with extremely oriented cellulose whiskers.

To exploit the maximum potential of cellulose whiskers (CWs), we report here for the first time the successful fabrication of nanocomposites reinforced with highly oriented CWs in a polymer matrix. The nanocomposites were prepared using polyvinyl alcohol (PVA) and a colloidal suspension of cotton-derived CWs. The macroscopically homogeneous PVA-CW suspensions were extruded into cold methanol to form gel fibers followed by a hot drawing. Compared to the neat PVA fiber, the as-spun fiber containing a small amount of CWs (5 wt % of solid PVA) showed higher drawability, leading to an extremely high orientation of CWs with the matrix PVA. The stress-transfer mechanism, a prime determining factor for high mechanical properties of nanocomposites, was studied by X-ray diffraction. The stress on the incorporated CWs was monitored by applying an in situ nondestructive load to the composite fibers. The applied stress to the whole sample was found to be effectively transferred to the CWs inside the composites, suggesting strong interfacial bonding between the filler and the matrix. Effective stress transfer to the oriented whiskers resulted in outstanding enhancement in mechanical properties of the nanocomposites.

Fabrication of carbon fibers from electrospun poly(vinyl alcohol) nanofibers

Carbon fibers were fabricated from electrospun poly(vinyl alcohol) (PVA) nanofibers. Electrospun PVA nanofibers were treated with iodine vapor for different periods, subsequently carbonized at different temperatures, and the structural changes of the PVA nanofibers were analyzed. The nanofibers iodinated at 80 °C for 24 h led to a good carbon yield of 21% when carbonized at 1200 °C. The influence of metal nanoparticle on the fabrication of carbon fiber and its properties was also investigated by the addition of a metal salt, nickel(II) acetate tetrahydrate [(CH3COO)2 Ni·4H2O], to the PVA spinning solution. Noticeably, after incorporation of nickel (Ni) nanoparticle continuous electrospinning was realized at lower polymer concentration than that of neat PVA. Moreover, smaller fiber diameter and a higher carbon yield (~34%) were obtained after carbonization. Transmission electron microscopy observation of the carbon fibers revealed that the addition of Ni-nanoparticles accelerated the formation of a graphitic structure at a lower carbonization temperature of 1200 °C.

Preparation and Physical Properties of Regenerated Cellulose Fibres from Sugarcane Bagasse

To produce cellulose regenerated fibres with high mechanical properties at low cost, sugarcane bagasse was chosen as a cheap raw material. In this study, bagasse was dissolved in N-methylmorpholine-N-oxide (NMMO) 0.9 hydrate, and fibres were prepared by the dry jet-wet spinning method by using dilute water/NMMO mixture as a coagulant, as is done in the production of commercial lyocell fibre. The effects of other coagulants, including water, methanol, isopropanol and ethanol, on the physical properties of the fibres were also investigated. Among these coagulants, fibres produced in ethanol and water/NMMO mixture exhibited the superior tensile strength and initial modulus although had some NMMO trapped in fibre matrix. After removal of NMMO by a simple heat treatment, much improvement in the fibre structure and mechanical properties was observed. The cross-sectional morphology and surface of these two fibres reveal the occurrence of fibrillation due to their high degree of crystallinity and overall high molecular orientation. The bagasse regenerated fibres produced in this study had a tensile strength of approximately 530 MPa and Young’s modulus of approximately 33 GPa, which are comparable to those of commercial lyocell fibre.

Green tea-aided dispersion of single-walled carbon nanotubes in non-water media: Application for extraordinary reinforcement of nanocomposite fibers

Green tea has recently been reported to be a good dispersant of single-walled carbon nanotubes (SWCNTs) in aqueous media. In the current work, green tea extract powder was examined for dispersion of SWCNTs in organic solvents. Dimethyl sulfoxide (DMSO) was found to be a good solvent of green tea extract for dispersing SWCNTs. A combination of green tea (dispersant)/DMSO (solvent)/polyvinyl alcohol (PVA) (nanotube wrap) was obtained that resulted in the dispersion of SWCNTs almost to individual nanotubes or to very thin nanotube bundles. The reinforcing ability of highly dispersed SWCNTs was explored in a PVA matrix producing PVA-SWCNT gel-spun fibers. Extraordinary reinforcing effects on the tensile and dynamic mechanical properties of the composites were observed by incorporating a minute amount of SWCNTs (∼1 wt% to PVA). The analysis revealed effective stress transfer through the PVA crystalline interfaces surrounding the nanotubes.

A novel approach to reduce fibrillation of PVA fibres using cellulose whiskers

The present study explored, for the first time, the potential for using cellulose whiskers (CWs) for reducing the fibrillation properties of highly oriented and crystalline fibres such as poly(vinyl alcohol) (PVA). The CWs were prepared from native cotton, and their aqueous suspension was homogeneously mixed with the PVA solution. The PVA-CW suspensions were gel-spun and hot-drawn up to their maximum possible draw ratio. The PVA-CW fibres, even when containing a small amount of CWs (5 wt% of PVA), showed a drastic reduction in fibrillation under a severe beating action. Upon incorporating CWs, a dramatic reduction in inter-fibrillar voids, which are responsible for the fibrillation, in highly drawn PVA fibres was observed. The oriented CWs were assumed to be embedded in the inter-fibrillar regions and formed lateral interlinks between fibrils by hydrogen bonding that resist the PVA fibrils from being pushed apart.