Plasticized poly(vinyl chloride) composites: Influence of different nanofillers as antimigration agents

In this study, plasticized poly(vinyl chloride) (PVC) composites with different nanofillers, including single‐walled carbon nanotubes (SWCNTs), organoclay, TiO₂, and ZnO nanoparticles, were prepared, and their effects on plasticizer migration were investigated. Scanning electron micrographs revealed the dispersion quality of the nanofillers in the polymer matrix. It had a significant influence on the performance of the nanofillers in the process of plasticizer migration. Migration and exudation tests showed that the nanofillers could efficiently hinder plasticizer migration. On the basis of these results, we concluded that carbon nanotubes were the best antimigration agent in the plasticized system. This was ascribed to the high aspect ratio of the SWCNTs and the good interactions between them and the plasticizer. Also, TiO₂ nanoparticles showed a better performance compared to the ZnO nanoparticles. This was due to the more homogeneous dispersion of the TiO₂ in the polymer matrix and the higher surface area of the particles. The differential scanning calorimetry thermograms were in good agreement with the migration tests. The lowest change in the glass‐transition temperature was observed for the composite filled with SWCNTs. This indicated that a lower amount of the plasticizer migrated from PVC. The thermogravimetric analysis curves showed that the incorporation of the nanofillers improved the thermal stability of the PVC. The results could be useful for determining the efficiency of plasticized PVC in applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42559.     

Al2O3 Colloidal Nanocrystals with Strong UV Emission

A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al₂O₃ sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X‐Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al₂O₃ powder. High‐resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before.     

Kinetic Model for Invertase‐Induced Sucrose Hydrolysis: Initial Time Lag

The kinetics of sucrose hydrolysis by invertase was studied in order to find a comprehensive model for the reaction pathway and mechanism. First, three common models of Michaelis‐Menten (MM), substrate inhibition (S²), and substrate clusters' inhibition (S³(I)) were investigated. The third model was found to better predict the initial sucrose concentration. Then, the S³(I) model was modified to cover the remaining pathway (S³(II)). Finally, a new comprehensive model (S³(III)) was evaluated, which in addition to what is considered in the two previously mentioned models (S³(I) and S³(II)) also involved the initial time lag. The model predictions showed an excellent agreement with the experimental data. The mean absolute error for the MM model is significantly reduced for the S³(III) model.     

Interrelationship of thermal and mechanical properties of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate)/graphene nanocomposites

In the present work, attempts were made to investigate the thermal and mechanical properties of melt‐processed poly(ethylene terephthalate) (PET)/poly(ethylene 2,6‐naphthalate) (PEN) blends and its nanocomposites containing graphene by using differential scanning calorimetry and tensile test experimenting. The results showed that crystallinity, which depends on a blend ratio, completely disappeared in a composition of 50/50. By introducing graphene to PET, even in low concentrations, the crystallinity of samples increased, while the nanocomposite of PEN indicated reverse behavior, and the crystallinity was reduced by adding graphene. In the case of PET‐rich (75/25) nanocomposite blends, by increasing the nano content in the blend, the crystallinity of the samples was enhanced. This behavior was attributed to the nucleating effect of graphene particles in the samples. From the results of mechanical experiments, it was found in PET‐rich blends that by increasing the PEN/PET ratio, the modulus of samples decreased, whereas in the case of PEN‐rich blends, a slight increment of modulus is seen as a result of the increment of the PEN/PET ratio. The two contradicting behaviors were attributed to the reduction of crystallinity of PET‐rich blends by enhancement of PEN/PET ratio and the rigid structure of PEN chains in PEN‐rich blends. Unlike the different modulus change of PET‐rich and PEN‐rich blends, the nanocomposites of these blends similarly indicated an increment of modulus and characteristics of rigid materials by increasing the nano content. Furthermore, the same behavior was detected in nanocomposites of each polymer (PET and PEN nanocomposites). The alteration from ductile to rigid conduction was related to the impedance in the role of graphene plates against the flexibility of polymer chains and high values of graphene modulus. J. VINYL ADDIT. TECHNOL., 23:210–218, 2017. © 2015 Society of Plastics Engineers     

Physical,morphological, and biological studies on PLA/nHA composite nanofibrous webs containing Equisetum arvense herbal extract for bone tissue engineering

A series of herbal extract incorporated into poly(lactic acid) (PLA) composite nanofibrous scaffolds were successfully prepared by using electrospinning technique. Equisetum arvense extract (EE) and nanohydroxyapatite (nHA) in different quantities were loaded into PLA solution to fabricate composite nanofibrous webs under various electrospinning conditions. Uniform nanofibers were obtained with an average diameter of 157 ± 47 nm in the case of those containing the herbal extract. Characterization of the webs was carried out by means of Fourier transform infrared (FTIR) spectroscopy, field emission‐scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectroscopy (EDX), and differential scanning calorimetry (DSC) techniques. Mechanical properties, porosity, and contact angle of the prepared webs were also determined. Releasing behavior was investigated in phosphate buffer solution (pH 7.2) medium. Moreover, cell studies and osteogenic capacity were assessed in vitro using human adipose tissue‐derived mesenchymal stem cell (AT‐MSC). Evaluations of cell attachment, spreading, and proliferation of AT‐MSC were done by SEM observation and thiazolyl blue (MTT) assay. Osteogenic differentiation capability of AT‐MSC on the nanofibrous webs was analyzed by alkaline phosphatase activity and calcium content assay. It was found that with the addition of nHA and EE to PLA nanofibrous webs, their surface hydrophobicity was reduced while the tensile strength and Young's modulus were increased satisfactorily. Regarding the samples containing EE and nHA, cellular adhesion was observed with flattened normal morphology. Osteogenic differentiation of AT‐MSC on PLA/nHA/EE webs showed the highest mineralization capacity after 3 weeks which, was about 1.8 and 3 times higher than that of PLA/nHA and tissue culture polystyrene as control, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45343.     

Comparison of pristine and polyaniline‐grafted MWCNTs as conductive sensor elements for phase change materials: Thermal conductivity trend analysis

Phase change materials (PCMs) function based on latent heat stored on or released from a substance over a slim temperature range. Multiwalled carbon nanotubes (MWCNTs) and polyaniline are important elements in sensor devices. In this work, pristine and polyaniline‐grafted MWCNTs (PANI‐g‐MWCNTs) were applied as conductive carbon‐based fillers to make PCMs based on paraffin. The attachment of PANI to the surface of MWCNTs was proved by Fourier transform Infrared analysis. Dispersion of MWCNTs in paraffin was studied by wide‐angle X‐ray scattering. Heating and solidification of PCM nanocomposites were investigated by differential scanning calorimetry, while variation in nanostructure of PCMs during heating/solidification process was evaluated by rheological measurements. It was found that after 30 min of sonication, the samples filled with 1 wt % MWCNTs have melting and solidification temperatures of 29 and 42 °C, respectively. It was also found that PANI attachment to MWCNTs significantly changes thermal conductivity behavior of PCM nanocomposites. The developed MWCNTs‐based sensor elements responded sharply at low MWCNTs content, and experienced an almost steady trend in conductivity at higher contents, while PANI‐g‐MWCNTs sensor followed an inverse trend. This contradictory behavior brought insight for understanding the response of PCMs against thermal fluctuations. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45389.     

Estimation of Mixing Ratio for Saturated Air over Water

The role that water vapor plays in atmospheric phenomena is extremely important. Saturation of moist air at a given temperature and pressure occurs if its mixing ratio is such that the moist air can coexist in a stable condition with an associated condensed phase at the same temperature and pressure. The saturation mixing ratio is useful to calculate the relative humidity which is a ratio, expressed in percent, of the amount of water vapor in the air (actual mixing ratio) compared to the amount of water vapor the air can hold (saturation mixing ratio). In this work, an attempt has been made to develop a simple‐to‐use Arrhenius‐type function to estimate the mixing ratio for saturated air over water as a function of pressure and temperature. Estimations have been found to be in excellent agreement with the data reported in the literature, with the average absolute deviation being around 0.4 %.