Oil spills impose serious ecological threats to the environment and are of international concern. Novel approaches and materials are continuously being sought to improve the cleanup of oil spills. In widespread oil spills, the performance of many materials used as oil sorbents is limited by their low surface area. Here, we describe a novel nanofibrous oil sorbent composed of a fluorinated polyimide of intrinsic microporosity (PIM-PI) with a high Brunauer–Emmett–Teller (BET) surface area of 565 m2 g−1. The nanofibrous sorbent was produced by electrospinning of PIM-PI (6FDA–TrMPD), which was synthesized by a one-pot, high-temperature polycondensation reaction between 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,4,6-trimethyl-m-phenylenediamine (TrMPD). Electrospinning of 6FDA–TrMPD from a solution of DMF with a concentration of 10% (w/v) produced ultrafine nanofibers, whereas at lower concentrations, beaded-fibers were obtained. The adsorption performance of the nanofibrous sorbent using several oils (i.e. crude oil, silicone oil, gasoline, and diesel) and non-polar organic solvents (i.e. toluene and m-xylene) was explored. The developed sorbent showed high sorption capacities in the range of 25–56 g g−1, along with a rapid removal performance; the sorbent reached the equilibrium sorption capacity within a few minutes for oils and organic solvents. The feasibility of the designed hierarchically porous mat for oil spill cleanup was demonstrated by the treatment of real seawater and crude oil. The robustness and reusability of the sorbent were demonstrated through its regeneration by both mechanical recovery and toluene treatment.

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Hierarchically porous electrospun nanofibrous mats produced from intrinsically microporous fluorinated polyimide for the removal of oils and non-polar solvents

Crosslinked and quaternized poly(4-vinylpyridine) (QC-P4VP) nanofibers have been fabricated via electrospinning followed by reaction with 1-4-dibromobutane. Subsequent decoration of the nanofibers with Ag nanoparticles by in-situ reduction obtained a nanostructured composite humidity sensing material. The nanofibers and the composites were characterized by FT-IR and scanning electron microscopy. It was found that the morphology and humidity sensing properties of the nanofibers could be greatly modified by adding poly(vinyl butyral) into the electrospinning solution. Moreover, the decoration with Ag nanoparticles effectively reduced the impedance of the composite under dry atmosphere, and facilitated the measurement of low humidity. Under optimized conditions, the composite presented high response magnitude to humidity, fast response (t90% of 16 s an 26 s for response and recovery, respectively), small hysteresis (∼2.8%RH), good sensing repeatability and the capability of detecting very low humidity (∼3.6%RH), representing much improvement over QC-P4VP nanofibers alone. The complex impedance spectra of the composites under different humidity levels were measured, and the sensing mechanism was explored. It is proposed that the highly desirable humidity sensing properties of the composite result from its balanced hydrophilicity and the distinct nanostructure.

Humidity sensing properties of the composite of electrospun crosslinked polyelectrolyte nanofibers decorated with Ag nanoparticles

Sonication induced effective approach for coloration of compact polyacrylonitrile (PAN) nanofibers

The effects of solid solution treatment on microstructure and mechanical properties of SiCp/2024 Al matrix composite fabricated via powder thixoforming were investigated, as well as those of 2024 matrix alloy for comparison. The results indicate that the solution progress of the composite is more hysteretic than that of the alloy due to the obstacle role of SiCp to eutectic dissolution and grain coarsening. Interestingly, interface reactions of SiCp/2024Al, similar to those during fabrication, continuously occur during the solution treatment. Simultaneously, two constituents of the interface reaction layer, Al2Cu and MgAl2O4 phases, change from the original agglomerated distribution to uniform distribution and finally to segregated form again accompanied by coarsening and phase transformation of Al2Cu into Al2CuMg. Such changes of the reaction layer significantly affect the interface debonding of SiCp/matrix or SiCp cracking during tensile test, and thus, the fracture regime and mechanical properties of the composite. The achieved modified shear-lag strengthening model by considering the strengthening effect of eutectic compounds can well interpret the strengthening mechanisms of these two materials, especially the variations of each strengthening mechanism contribution with solution time and the corresponding differences between these two materials.

Effects of solid solution treatment on microstructure and mechanical properties of SiCp/2024 Al composite: A comparison with 2024 Al alloy

In this work, the effect of nanoclay addition to glass fiber-reinforced polyester composites is studied. The pristine glass fiber-reinforced polyester composites (i.e., staking sequence, kind of fabric used, etc.) and hybrid nanoclay in varying weight fraction (0, 1, 2, 3, 4 and 5 wt%) and glass fiber-reinforced polyester composite is prepared by vacuum-assisted resin infusion technique. Fracture toughness studies are done to analyze the critical stress intensity factor and critical strain energy release rate. The optimum mechanical properties are obtained for hybrid nanoclay glass fiber-reinforced polyester composites with clay content of 3 wt%. This paper also deals with the study of optimizing the cutting parameters (Cutting speed and feed rate) to obtain maximum mechanical properties in hybrid nanoclay glass fiber-reinforced polyester composites during drilling process. It has been found that the torque is unaffected with increase in cutting speed. On contrast with increase in feed and nanoclay weight fraction, the torque increases. The drilled samples are further subjected to mechanical testing. Tensile studies confirms that better mechanical properties are obtained for optimum machining parameter of (0.045 mm/rev, 210 rpm) for 3 wt% nanoclay and glass fiber-reinforced polyester nanocomposites. The hybrid clay and glass fiber-reinforced nanocomposites generally posses better mechanical properties compared with pristine glass fiber-reinforced polyester composites.

Experimental investigation of mechanical and machining parameters of hybrid nanoclay glass fiber-reinforced polyester composites

In the present work, the effect of aging temperature and particle size ratio of SiC particles on the mechanical and tribological properties of A357 composites reinforced with dual particle size SiC were investigated. The composites were prepared by melt-stirring assisted permanent mold casting technique with different weight fractions (3% coarse +3% fine, 4% coarse +2% fine, and 2% coarse +4% fine) of large and small size SiC particles. These three prepared composites are referred as DPS1, DPS2 and DPS3 composites. The solutionizing temperature was maintained constant at 540 °C for 9 h while the aging was done at 160 °C, 180 °C and 200 °C (T6 treatment) for 6 h. Optical and scanning electron microscopy studies showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. High-resolution transmission electron microscopy images showed formation of uniformly dispersed needle-like β″ phase and spherical shaped β-Mg2Si precipitates under peak aging conditions. Compared to T6 treated A357 alloy, the T6 treated DPS A357 composites showed improved yield strength, tensile strength, hardness and wear resistance. Among the three composites, hardness and wear resistance of T6 treated DPS2 composite was found to be significantly higher when compared to the other two composites (DPS1 and DPS3). Ratio of large particles to small particles also seems to effect the mechanical and tribological properties. Presence of more small particles was found to be good for strength and ductility whereas more large particles were found to be good for hardness and wear resistance.

The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites

Electrospinning is an effective process for synthesis of polymer fibers with diameters ranging between nanometers and micrometers by employing electrostatic force developed due to application of high voltage. The present work aims to develop an electrospinning system and optimize the process parameters for synthesis of Polyvinyl Acetate thin films used for gas and humidity sensors. Taguchi’s Design of Experiment was adopted considering three main factors at three different levels for optimization of process parameters. The factors considered were flow rate (0.5, 0.6 and 0.7 ml/h), voltage (18, 19 and 20 kV) and spinneret to collector distance (8, 9, 10 cm) with fiber diameter as the response factor. The main effect plots and interaction plots of the parameters were studied to determine the most influencing parameter. Flow rate was the most significant factor followed by spinneret to collector distance. Least fiber diameter of 24.83 nm was observed at 19 kV, 0.5 ml/h flow rate and 8 cm spinneret to collector distance. SEM images revealed uniform fiber diameter at lower flow rate while bead formation increased monotonically with rise in flow rate.

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Development of polyvinyl acetate thin films by electrospinning for sensor applications

Abstract This paper deals with the study of screw configuration for dispersing nanofillers in thermoset polymers using an intermesh co-rotating twin screw extruder. The influence of kneading elements on the dispersion of nanoclay in epoxy was examined using 10 different screw configurations. Nanoclay was dispersed in epoxy at a barrel temperature of 5°C and a screw speed of 100 rpm. The combination of right hand kneading block and three/four lobed kneading blocks resulted in uniform dispersion of nanofiller. Positive staggered angle with right hand kneading elements yielded uniform dispersion of the nanofiller. Mechanical properties of epoxy nanocomposites processed with these configurations were better than those of neat epoxy. Excessive shear was associated with four lobed kneading block (4KB)/4KB configuration and hence degradation of polymers leading to shorter chains, whereas inadequate shearing in neutral kneading block (NKB)/NKB configuration led to agglomerations. These observations were evidenced by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Effect of screw configuration on the dispersion of nanofillers in thermoset polymers

The objective of the present investigation was to investigate the effect of conventional annealing and microwave irradiation on the structural, optical and dielectric properties of SiO2–TiO2 thin film developed by sol gel technique. SiO2–TiO2 thin film prepared using spin coater with optimized conditions, then heat treated by conventional annealing and microwave irradiation. The phase, morphology, topography, film thickness and optical properties were measured by X-ray diffraction, scanning electron microscopy, atomic force microscopy, profile-meters and UV-VS-NIR spectrophotometer respectively. The results show the dielectric constants of the microwave exposed films were superior to those of conventional annealed films. Microwave exposed films exhibited low leakage current densities and high resistivity. The microwave irradiation improves SiO2–TiO2 thin film with higher dielectric constant and lower leakage current density.

Krishna Munishamaiah

Papers

The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites

Development of polyvinyl acetate thin films by electrospinning for sensor applications

Effect of screw configuration on the dispersion of nanofillers in thermoset polymers

Improved dielectric properties of microwave irradiated sol-gel derived SiO2–TiO2 thin film