Parametric Studies on the Grafting of Poly(Methyl Methacrylate) onto Organophilic Montmorillonite Using Silylated Clay Platelets

Poly(methyl methacrylate) (PMMA)/organophilic montmorillonite (Cloisite 30B) nanocomposites were synthesized by the chemical grafting of PMMA onto Cloisite 30B via solution polymerization of methyl methacrylate (MMA) with vinyl-modified organoclay. The effects of different parameters such as clay weight percent (CWP), solvent per monomer volume ratio, and dispersion time on the properties of the PMMA grafted Cloisite 30B were investigated using the Taguchi experimental design method. This method gives a much-reduced variance for the experiments with optimum setting of control parameters and provides a set of minimum experiments compared to the conventional methods. Qualitative evidence for the chemical grafting of the PMMA onto Cloisite 30B was confirmed by Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) was used to investigate interlayer changes of the clay in the grafted nanoplatelets. The exfoliated/intercalated morphology of the nanocomposites was confirmed by XRD. Furthermore, thermal properties were measured by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). Statistical analysis of results revealed that clay weight percent and solvent per monomer ratio had significant effects on the properties of final products. The percent of grafted PMMA and storage modulus of PMMA/30B nanocomposites decreased with increasing clay content due to better dispersion of the clay at lower loadings. On the other hand, because of a tendency to formation of homopolymer and oligomers at higher solvent loadings; the percent of grafted PMMA, storage modulus and glass transition temperature of PMMA/30B nanocomposites decreased with an increase in solvent per monomer volume ratio. However, the obtained PMMA/30B nanocomposites at the optimum conditions, was exhibited a higher glass transition temperature, higher storage modulus and better thermal stability than the pure PMMA.     

Optical soliton perturbation with spatio-temporal dispersion in parabolic and dual-power law media by semi-inverse variational principle

This paper studies the perturbed optical solitons with parabolic and dual-power law nonlinearities in presence of spatio-temporal dispersion. The semi-inverse variational principle is applied to extract an analytical 1-soliton solution to the governing equation. There are constraint conditions that naturally fall out for the existence of these solitons.     

Ascorbic Acid and Salicylic Acid Mitigate NaCl Stress in Caralluma tuberculata Calli

Plants exposed to salt stress undergo biochemical and morphological changes even at cellular level. Such changes also include activation of antioxidant enzymes to scavenge reactive oxygen species, while morphological changes are determined as deformation of membranes and organelles. Present investigation substantiates this phenomenon for Caralluma tuberculata calli when exposed to NaCl stress at different concentrations. Elevated levels of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) in NaCl-stressed calli dwindled upon application of non-enzymatic antioxidants; ascorbic acid (AA) and salicylic acid (SA). Many fold increased enzymes concentrations trimmed down even below as present in the control calli. Electron microscopic images accentuated several cellular changes upon NaCl stress such as plasmolysed plasma membrane, disruption of nuclear membrane, increased numbers of nucleoli, alteration in shape and lamellar membrane system in plastid, and increased number of plastoglobuli. The cells retrieved their normal structure upon exposure to non-enzymatic antioxidants. The results of the present experiments conclude that NaCl aggravate oxidative molecules that eventually alleviate antioxidant enzymatic system. Furthermore, the salt stress knocked down by applying ascorbic acid and salicylic acid manifested by normal enzyme level and restoration of cellular structure.     

Semiconductor nanoparticles for photoinitiation of free radical polymerization in aqueous and organic media

Photoinduced free radical polymerization of vinyl monomers by using semiconductor inorganic nanoparticles (NPs) is investigated. Zinc oxide and iron‐doped zinc oxide were used as photosensitive compounds to initiate the polymerization of acrylamide as a water‐soluble monomer in aqueous environment and methyl methacrylate as an oil‐soluble monomer in organic media under UV‐light irradiation. The method uses photochemically generated electrons and holes from the NPs to form initiating hydroxyl radicals in aqueous media, while tertiary amines and iodonium salt served as coinitiator in organic media. The initiation mechanism in organic media involves hydrogen abstraction or reduction processes via charge carriers, respectively. The kinetic of the polymerization in both environments was studied by means of a photo‐differential scanning calorimetry. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1500–1507     

Rectangular Tubular Steel Columns Loaded Biaxially

An inelastic analysis of rectangular tubular steel columns subjected to a constant axial load and a gradually increasing biaxial end moment is presented. Analytical thrust-moment-curvature relationships are given for the cross section with bilinear material stress-strain characteristics. An iterative procedure based on column deflection curves is used to predict moment-deflection curves up to collapse, and numerical examples are given for square and rectangular tubular steel columns. The interaction of biaxial moments, as well as the effect of strain-hardening, is explained for the non-proportional loading considered. The technique can be modified for beam-columns with other types of end moments.     

Determination of Trace Elements in Integrated Human Diet for Dietary Assessment

Abstract

Neutron activation analysis in combination with atomic absorption spectrometry was utilized for the determination of 21 elements in integrated diet samples of the inhabitants of the Rawalpindi/Islamabad area. The study was carried out to determine prevailing concentration levels of trace elements nutrition, inadequacy, imbalances and toxicity. This data will serve as baseline values and will be helpful to monitor the degree of future contamination from foreign chemicals. The dietary intake values were also estimated and compared with the reported daily intake values. In general, the diets studied are adequate source of nutrient elements. The toxic elements intake through all the diet samples are within the safety limits.     

Hepatic toxicity of nickel chloride in mice

The present study is to evaluate the toxic effects of nickel (Ni) on the liver structure of male mice. Male Balb/c mice weighing 30–32 g, 50 days old, were treated orally with 1–16 mg/kg (body wt.) NiCl₂. The body weight, liver weight, histological examination of liver, and DNA ladder for apoptosis were studied. Ni induced increases in apoptotis and severity of necrosis. Liver weight and body weight decreased with increasing dose. Histological changes in the liver included hepatocyte degeneration, nuclear pycnosis, cellular swelling, and congestion of blood vessels. There was a marked difference in these changes among the different treatments of Ni concentrations in addition to the intensity of histological changes which were, however, influenced by the extent of the exposure period. It has been concluded that nickel caused apoptotis in liver of male mice.