Volume 39, Issue 3

Pharmaceutical residues coming from urban wastewater were recognized as a major source of pollution for the aquatic environment. Their occurrence in most municipal effluent seems to indicate that conventional wastewater treatments have only a limited ability to remove such substances from sewage. Therefore, the undesired effects caused by these emergent contaminants on the environment force the authorities to consider new measures to treat and recycle contaminated water. In this study, electrospun nanofibers made of chitosan and poly(ethylene oxide) (PEO) were used to remove the anti-inflammatory drug ibuprofen in solution. The electrospinning parameters such as the mixture solution concentration, applied voltage, distance needle-collector, and flow rate were optimized to get the best nanofiber morphology characterized by scanning electron microscopy (SEM). With the use of a high-performance liquid chromatography with ultraviolet diode array detection (HPLC-UV DAD) system, sorption tests were performed by modifying experimental conditions, e.g. pH, concentration of ibuprofen, and temperature of the tested solutions. Langmuir, Freundlich, and Dubinin-Radushkevich (DR) adsorption models were compared for the mathematical description of adsorption equilibria. Kinetic assays showed that the adsorption of chitosan nanofiber followed a pseudo-second-order model. After 20 min of exposure, 25 mg of nanofiber had removed 70% of the initial ibuprofen concentration.

The epoxidized ethylene propylene diene rubber (eEPDM) was successfully prepared by the epoxidation of ethylene propylene diene rubber (EPDM) using t -butyl hydroperoxide as the oxidant in association with molybdenum oxide as the catalyst and characterized by Fourier-transform infrared (FTIR) spectrometer and 1 H-nuclear magnetic resonance analyses. Then the poly(butylene terephthalate) (PBT)/eEPDM/polypropylene (PP) blends with different eEPDM contents were prepared using a twin-screw extruder, and the effect of eEPDM on nonisothermal crystallization kinetics of PBT/PP blend was investigated by differential scanning calorimetry. Meanwhile, morphological features of samples were observed using scanning electron microscopy. Also, the mechanical properties of samples were evaluated. Analyses of the crystallization data by various macro-kinetic models like Jeziorny modified Avrami and Liu-Mo model demonstrated that PP as diluents accelerated the crystallization of PBT in PBT/PP. Moreover, the addition of eEPDM into PBT/PP further facilitated the crystallization of PBT in PBT/eEPDM/PP. The eEPDM was an effective crystallization promoter for PBT/PP blend. And the presence of eEPDM promoted the uniform dispersion of PP in PBT matrix. When the content of eEPDM was 5 phr, the PBT/eEPDM/PP exhibited the highest notched impact strength and Young’s modulus among all the specimens.

Composites with thin layers of polyaniline (PANI) draped on the surface of a hybrid carbon (HC) array or assemblage were prepared by the oxidative polymerization route. The carbon array substrate is a consistent network architecture of carbon nanotubes and graphene, with the benefit of elevated conductivity and surface area of the carbon components. The exceptional improved electrochemical performances of PANI enfolded HC array electrodes are due to the synergistic effect of the pseudocapacitance of PANI and the electric double layer capacitance of the carbon array. The supercapacitive characteristics of composite materials were inspected by using cyclic voltammetry, the galvanostatic charge-discharge test and electrochemical impedance analysis. The 025PANI-HC composite sample revealed a maximum specific capacitance of 1397.82 F g −1 at a scan rate of 5 mV s −1 and 1430 F g −1 at 1 A g −1 from galvanostatic charge-discharge data, respectively, in 1 m H 2 SO 4. The composites exhibited a much larger specific capacitance value than pristine PANI. Also, the 025PANI-HC electrode had an unwavering operation and its specific capacitance retention was 89%, even after 5000 charge-discharge cycles at 1 A g −1 .

Being an important class of water-soluble synthetic polymers, polyacrylamide (PAM) and its derivatives have found a wide range of applications in the oil and gas industry. Due to the increasingly active exploration of deep and ultra-deep wells, PAM-based polymers are more and more frequently applied under hostile subterranean conditions, particularly high temperature. Therefore, it becomes an imminent research topic to elucidate the thermal degradation pathways of PAM-based polymers in order to upgrade these chemicals for more challenging scenarios. Neighboring groups attached to the same polyvinyl backbone have been suggested to exert an effect to the degradation of the PAM-based polymers. Herein we report a combined theoretical and experimental study on the energetics of such neighboring group effect. Taking advantage of a computational method based on density functional theory, we have identified two competing degradation pathways in neutral medium and have calculated their respective activation energies. These results enable us to predict the relative thermal stabilities of a series of PAM-based polymers, and we have also used temperature-variant rheology measurements to verify these predictions. This work will guide the design of better heat-resistant PAM-based products.

Blends of two biobased polymers, poly(lactic acid) and poly(trimethylene terephthalate) (PTT), were compatibilized with either maleic anhydride-grafted poly(ethylene-octene) (mPOE) or organically modified clay (Cloisite 30B). Dynamic rheological measurements revealed that the mPOE inclusion resulted in a four-fold increase in viscosity relative to the noncompatibilized blends. By loading 3 wt% Cloisite 30B, the storage moduli of the blends showed a distinct solid-like behavior and high complex viscosity in the low-frequency region, which can be interpreted by the reduced sizes of the PTT phase evidenced from the scanning electron microscopy (SEM) micrography. A temperature sweep of the viscosity of the blends starting from 180°C revealed that the existence of an unmelted PTT dispersed phase might impede the decline in viscosity with increasing temperature near the melting point of PTT. The introduced compatibilizers can restrict the temperature-dependent morphology evolution, and the use of the 3 wt% 30B clay can prohibit the morphology evolution during the temperature sweep.

Microporous polyvinylidene fluoride (PVDF) membranes were prepared by immersion precipitation of dimethylformamide/PVDF solutions, dissolved at 50°C, 60°C, 70°C, and 80°C in a nonsolvent bath. The formed membranes (M50, M60, M70, and M80) exhibited symmetric structures consisting of spherical particles whose size increased from ~1 μm for M50 to ~3 μm for M80. The desalination capabilities of the membranes were assessed via the direct contact membrane distillation process. For the case of desalting 3.5% NaCl (aq) , very high rejection ratios (>99.7%) were achieved for all tested membranes under the operation conditions: T hot stream =52°C, T cold stream =18°C, circulation rate=0.7 l/min, while the highest permeation flux obtainable was 16.3 l/m 2 h (LMH). When the feed temperature or circulation rate was raised, the permeation flux increased correspondingly. On the other hand, raising the salt concentration resulted in a strong decrease of the permeation flux. For the membrane M60 operated over the period of 48 h, the flux decreased slightly from 11.6 to 10.5 LMH, while the conductivity increased from 1.5 to 27 μs/cm indicating the occurrence of slight surface wetting during this extended operation period.

Ultra-high molecular weight polyethylene (UHMWPE) is a very attractive polymer employed as a high performance material, while filler-reinforced composites have demonstrated its feasibility in various applications. Melt-mixing in an extruder is a key process in the development of polymer nanocomposites. Due to its high melt viscosity, dispersion of fillers is considered as a challenge in UHMWPE nanocomposites preparation process. In this work, we have prepared graphite-filled UHMWPE nanocomposites using a novel octa-screw melt kneading extruder. The engineering properties as well as the morphology of kneaded nanocomposites were characterized using tensile tester, friction and wear tester, scanning electron microscopy, optical profilemeter, polarized optical microscope, thermogravimetric analysis, differential scanning calorimetry, etc. The experimental results suggested good dispersion of graphite in the UHMWPE nanocomposites, demonstrating the excellent capability of the octa-screw extruder in compounding the graphite-filled nanocomposites. The yield strengths of the nanocomposites increase by 10% (from 21.6 MPa to 23.8 MPa) with the addition of 2% graphite. When the filler percentage was increased to 20%, the yield strengths improved from 21.6 to 27.4 MPa (an increase of 26.8%) for the graphite-filled composites. Furthermore, the crystallinity of UHMWPE nanocomposites increased with the content of graphite fillers, while the pyrolysis temperature of the composites increased with the content of graphite fillers.

The aim of the current study was to develop a dual-loaded core shell nanoparticles encapsulating paclitaxel (PTX) and ellagic acid (EA) by membrane dialysis method. Based on particle size, polydispersity index (PDI), and entrapment efficiency, the dual drug-loaded nanoparticles (F2) was optimized. The optimized nanoparticles (F2) showed a particle size of 140±2 nm and a PDI of 0.23±3. The size and the morphology were confirmed by transmission electron microscopy (TEM) and found agreement with the results of dynamic light scattering. The entrapment efficiencies of total drug (PTX and EA), PTX, and EA in the nanoparticles (F2) were measured as 80%, 62.3%, and 37.7%, respectively. The in vitro release profile showed a controlled release pattern for 48 h. A higher cytotoxicity was observed with nanoparticles (F2) in comparison to free PTX. The results revealed that co-delivery of PTX and EA could be used for its oral delivery for the effective treatment of breast cancer.

Poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA) blends were prepared by hand mixing, followed by injection molding at 210°C to produce tensile specimens. Thermal properties, crystalline structure, and mechanical properties were measured by differential scanning calorimetry (DSC), thermogravimetric analysis, wide-angle X-ray diffraction (XRD), and tensile testing. From the DSC tests of blends ranging from 10% to 30% PDLA in PLLA, the PDLA melting peak was absent and was replaced by a stereocomplex melting peak at 210°C, which was ~50°C higher than that for neat PLLA or PDLA. The reverse blending of PLLA into PDLA showed a similar behavior. Surprisingly, three melting peaks (for PLLA, PDLA, and the complex crystal) appeared in the 1:1 PLLA:PDLA pellet blends. However, the PLLA and PDLA powders (ground to less than 200 μm) and hand mixed, prior to injection molding, showed only small amounts of homocrystals and much higher fractions of stereocomplex crystals (18–44%). Compared to the hand mixed un-ground pellets, molded specimens from the PLLA and PDLA powders also exhibited higher tensile strengths (33–48 MPa) and moduli (1100–1250 MPa). Moreover, the stereocomplex formation was found to enhance the thermal stability compared with those of the pure PLLA and PDLA.

The single-screw extruder with a perturbation baffle is a novel piece of equipment for polymer processing, in which the polymer melts undergo complex chaotic mixing. In this paper, from a new Lagrangian perspective, the fluid transporting mechanism in chaotic flow of the unwound screw channel was analyzed based on the finite element method. Firstly, two-dimensional velocity distributions in the unwound screw channel were calculated based on the mesh superposition technique. Fluid particle evolution processes in the extruder were tracked based on the fourth-order Runge-Kutta scheme. The numerical method used in this paper was validated by grid independence and experiments obtained from literature. Moreover, the finite-time Lyapunov exponent (FTLE) and Poincaré sections were adopted to discuss the chaotic mixing in the novel single-screw extruder. The effects of baffle width and height on the manifold structures in the flow dynamic system were analyzed. The results show that the homoclinic point of the manifold structure can give rise to chaotic mixing in the single-screw extruder. The height of the baffle is an important parameter to control the chaotic strength. In a way, increasing the height of the baffle can enlarge the kink scale and increase the stretching and folding actions, which results in the decrease of regular regions and an increase of the mixing efficiency in the single-screw extruder.

The influence of talc and rubber contents included in polypropylene (PP) on surface replication properties for microstructure was analyzed. By increasing the talc and rubber contents, surface replication on the injection-molded parts has been reduced. From the surface observation, an uneven microstructure surface was formed for a material containing talc during the shrinkage process. It was confirmed that if the PP resin contains talc, then the correlation between glossiness of the mold and glossiness of the molded product was lost and glossiness was decreased. On the contrary, as the rubber content increased, the replication properties improved. At the same time, generation of the streak pattern in the transferred area, which was generated in the base PP, decreased and glossiness increased. Moreover, the fine uneven structure of the nontransferred area, as observed in the talc-containing material, was not observed in the rubber-containing material.