Ahmad Nawaz Khan

Polyamide-6-based composites reinforced with pristine or functionalized multi-walled carbon nanotubes produced using melt extrusion technique

Polyamide-6-based composites with pristine or functionalized multi-walled carbon nanotubes were produced using melt extrusion technique. After chemical functionalization, defect formation and attachment of carboxylic (−COOH) or amine (−NH2) groups on carbon nanotubes was confirmed from high-resolution transmission electron microscope and Fourier transform infra-red spectroscope studies. Carbon nanotubes incorporation promoted growth of α-form crystals with enhanced thermal stability through increase in crystallization temperature from 162 to 192℃. Dynamic mechanical thermal analysis (DMTA) indirectly pointed out to a homogeneous, uniform dispersion of nanotubes with reduction in free volume of the polymer, exhibiting a slight increase in glass transition temperature and a significant drop in coefficient of thermal expansion value. Composites containing 0.5 wt% NH2-carbon nanotubes show increases in elastic modulus and tensile strength by ∼60 and 76%, respectively. Uniform dispersion and high interfacial strength was manifested by drop in strain to failure and lack of evidence of carbon nanotubes debonding from the matrix.

Enhanced mechanical, thermal and antimicrobial properties of poly(vinyl alcohol)/graphene oxide/starch/silver nanocomposites films

In the present work, synthesis of poly(vinyl alcohol)/graphene oxide/starch/silver (PVA/GO/Starch/Ag) nanocomposites films is reported. Such films have been characterized and investigated for their mechanical, thermal and antimicrobial properties. The exfoliation of GO in the PVA matrix occurs owing to the non-covalent interactions of the polymer chains of PVA and hydrophilic surface of the GO layers. Presence of GO in PVA and PVA/starch blends were found to enhance the tensile strength of the nanocomposites system. It was found that the thermal stability of PVA as well as PVA/starch blend systems increased by the incorporation of GO where strong physical bonding between GO layers and PVA/starch blends is assumed to cause thermal barrier effects. Antimicrobial properties of the prepared films were investigated against Escherichia coli and Staphylococcus aureus. Our results show enhanced antimicrobial properties of the prepared films where PVA-GO, PVA-Ag, PVA-GO-Ag and PVA-GO-Ag-Starch showed antimicrobial activity in ascending order.

Enhancing Dielectric and Mechanical Behaviors of Hybrid Polymer Nanocomposites Based on Polystyrene, Polyaniline and Carbon Nanotubes Coated with Polyaniline

The dielectric and mechanical properties of hybrid polymer nanocomposites of polystyrene/polyaniline/carbon nanotubes coated with polyaniline (PCNTs) have been investigated using impedance analyzer and extensometer. The blends of PS/PANI formed the heterogeneous phase separated morphology in which PCNTs are dispersed uniformly. The incorporation of a small amount of PCNTs into the blend of PS/PANI has remarkably increased the dielectric properties. Similarly, the AC conductivity of PS/PANI is also increased five orders of magnitude from 1.6 × 10−10 to 2.0 × 10−5 S∙cm−1 in the hybrid nanocomposites. Such behavior of hybrid nanocomposites is owing to the interfacial polarization occurring due to the presence of multicomponent domains with varying conductivity character of the phases from insulative PS to poor conductor PANI to highly conductive CNTs. Meanwhile, the tensile modulus and tensile strength are also enhanced significantly up to 55% and 160%, respectively, without much loss of ductility for three phase hybrid nanocomposites as compared to the neat PS. Thereby, the hybrid nanocomposites of PS/PANI/PCNTs become stiffer, stronger and tougher as compared to the neat systems.

Relaxation behavior of poly(trimethylene 2,6-naphthalate) in nanoclay confinement

The relaxation behavior of poly(trimethylene 2,6-naphthalate)/nanoclay composites is investigated using differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA). The incorporation of two different types of nanoclays in the PTN matrix intercalated the PTN chains in the narrow space of clay intergalleries and constrained the polymer chains in the vicinity of nanoclay layers. Despite the presence of constrained region, the glass transition temperature of the PTN/nanoclay composite is decreased as compared to neat PTN. Moreover, the activation energy of the PTN is reduced and the relaxation rate of PTN becomes faster in the presence of nanoclays. The enhanced relaxation dynamics of PTN chains at Tg depends on the evolution of local free volume owing to the confining effect of chain intercalation.

Glass transition behavior of poly(trimethylene 2,6-naphthalate) in nanoclay confinement

The glass transition behavior of poly(trimethylene 2,6-naphthalate) (PTN)/nanoclay composites was investigated using differential scanning calorimetry and dynamic mechanical analysis. The incorporation of two different types of nanoclays in the PTN matrix resulted in intercalation of the PTN chains in the narrow space of the clay intergalleries (d 001(clay)) and constrained the polymer chains in the vicinity of the nanoclay layers. Despite being in constrained regions, the glass transition temperature of the PTN/nanoclay composite was decreased as compared to neat PTN. Moreover, the characteristic length of the polymer chains (ξa) at T g was evaluated by employing the cooperatively rearranging region theory. The glass transition of the PTN chains depended on the correlation between ξa and the interlayer gallery distance (d 001(clay)). The decrease in T g of PTN/nanoclay composites is ascribed to the development of local free volume owing to the confining effect of the chain intercalation.

Enhanced mechanical properties and biocompatibility of novel hydroxyapatite/TOPAS hybrid composite for bone tissue engineering applications

The bioactivity and mechanical properties of hybrid composites of hydroxyapatite (HA) in cyclic olefinic copolymer (COC) also known commercially as TOPAS are investigated, first time, for regeneration and repair of the bone tissues. HA is synthesized to obtain the spherically shaped nanoparticles in the size range of 60±20nm. Various concentrations of HA ranging from 1 to 30wt% are dispersed in TOPAS using sodium dodecyl sulfate (SDS) coupling agent for better dispersion and interaction of hydrophilic HA with hydrophobic TOPAS. Scanning electron microscope shows the uniform dispersion of HA≤10wt% in TOPAS and at higher concentrations >10wt%, agglomeration occurs in the hybrid composites. Tunable mechanical properties are achieved as the compressive modulus and strength are increased around 140% from 6.4 to 15.3MPa and 185% from 0.26 to 0.74MPa, respectively. Such increase in the mechanical properties of TOPAS is attributed to the anchoring of the polymer chains in the vicinity of HA nanoparticles owing to better dispersion and interfacial interactions. In comparison to neat TOPAS, hybrid composites of TOPAS/HA promoted the cell adhesion and proliferation significantly. The cell density and proliferation of TOPAS/HA hybrid composites is enhanced 9 and 3 folds, respectively, after 1day culturing in preosteoblasts cells. Moreover, the morphology of cells changed from spherical to flattened spread morphology demonstrating clearly the migration of the cells for the formation of interconnected cellular network. Additionally, very few dead cells are found in hybrid composites showing their cytocompatibility. Overall, the hybrid composites of TOPAS/HA exhibited superior strength and stiffness along with enhanced cytocompatibility for bone tissue engineering applications.

Fabrication and characterization of cellulose acetate/hydroxyapatite composite membranes for the solute separations in Hemodialysis

Asymmetric composite membranes of cellulose acetate (CA)/hydroxyapatite (HA) are prepared using phase inversion method for the separation of water, urea, glucose, and protein. Various concentrations of HA up to 15 wt% are dispersed uniformly in the CA matrix. The pore size of the CA matrix is tunable by varying the concentration of HA. The flux of water, urea and glucose is ~7 times higher while for BSA ~12 times higher in CA/HA composite membranes than pure CA. Similarly, water absorption capacity of CA/HA composite membranes are increased owing to the incorporation of hydrophilic HA in CA matrix. Moreover, the retention rates are also reasonable in CA/HA composite membranes depending on the difference in porosity of the membranes. The permeation of urea is much higher in the CA/HA composite membranes as compared to pure CA, which is more suitable for hemodialysis. Thereby, such CA/HA composite membrane offers the potential to be used in hemodialysis applications.

Evaluating Mechanical Properties of Few Layers MoS2 Nanosheets-Polymer Composites

The reinforcement effects of liquid exfoliated molybdenum disulphide (MoS2) nanosheets, dispersed in polystyrene (PS) matrix, are evaluated here. The range of composites (0~0.002 volume fraction () MoS2-PS) is prepared via solution casting. Size selected MoS2 nanosheets (3~4 layers), with a lateral dimension 0.5~1 µm, have improved Young’s modulus up to 0.8 GPa for 0.0002 MoS2-PS as compared to 0.2 GPa observed for PS only. The ultimate tensile strength (UTS) is improved considerably (~×3) with a minute addition of MoS2 nanosheets (0.00002 ). The MoS2 nanosheets lateral dimension and number of layers are approximated using atomic force microscopy (AFM). The composites formation is confirmed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Theoretical predicted results (Halpin-Tsai model) are well below the experimental findings, especially at lower concentrations. Only at maximum concentrations, the experimental and theoretical results coincide. The high aspect ratio of MoS2 nanosheets, homogeneous dispersion inside polymer, and their probable planar orientation are the possible reasons for the effective stress transfer, resulting in enhanced mechanical characteristics. Moreover, the micro-Vickers hardness () of the MoS2-PS is also improved from 19 (PS) to 23 (0.002 MoS2-PS) as MoS2 nanosheets inclusion may hinder the deformation more effectively.