Nanoconfinement revealed in degradation and relaxation studies of two structurally different polystyrene-clay systems

Degradation and relaxation studies have been performed on two polystyrene (PS)-montmorillonite clay nanocomposites, one of which has an intercalated PS-clay structure and the other an exfoliated PS-clay brush structure. Compared to virgin PS, both nanostructured materials have demonstrated the following similarities: (a) a high yield of alpha-methylstyrene in the degradation products as measured by infrared spectroscopy; (b) larger values of the activation energy of the thermal degradation as determined by isoconversional kinetic analysis of thermogravimetric data; and (c) larger values of the activation energy for the glass transition as found from the frequency dependence of the glass transition temperature measured by multifrequency temperature-modulated differential scanning calorimetry. These effects are taken as structure independent manifestations of nanoconfinement of the PS chains in the PS-clay materials. Heat capacity measurements have been employed to evaluate the size of the cooperatively rearranging region, VCRR, that is found to be structure dependent. Compared to its value in virgin PS, VCRR has markedly increased in the exfoliated PS-clay brush system but remained practically unchanged in the intercalated PS-clay system.     

Die Wirkung von Jod auf Phenole und deren Anwendung zur volumetrischen Bestimmung

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Synergistic effects of organo‐sepiolite and zinc borate on the fire retardancy of polypropylene

Polypropylene (PP)/sepiolite/zinc borate (BZn) composites were prepared by melt extrusion after pre‐modification of sepiolite with cetyltrimethylammonium bromide. The synergistic effects of organo‐sepiolite (OSEP) and BZn on the fire retardancy of PP were studied. X‐ray diffraction and transmission electron microscopy were used to characterize the morphology of the composite. Thermogravimetric analysis, cone calorimetric analysis, limiting oxygen index, and the UL‐94 protocol (Demaisheng technology Co. Ltd.,Shenzhen,China) were used to assess the thermal stability and fire retardancy of the composites. The fire retardancy of PP was greatly improved by introducing OSEP and BZn. The reduction in peak heat release rate for PP/BZn composites at 10% BZn loading is 62% compared with pristine PP, but increased to 78% for PP/10%BZn/10%OSEP composite. Other fire retardant parameters were also improved. The fire performance index of PP/10%BZn/10%OSEP composite was 0.045 sm²/kW compared with 0.014 sm²/kW of pristine PP. The average mass loss rate was 12.1 g/sec/m² for the composite with both additives compared with 30.1 g/sec/m² for pristine PP; the smoke production rate decreased by 37% from 0.117 m²/s of pristine PP to 0.074 m²/s of PP/OSEP/BZn. The char residue of composite increased from 0.6% in pristine PP to 12.19% in the composite. The limiting oxygen index increased from 17.1 in pristine PP to 20.8 in the composite: all the samples could obtain a UL‐94 horizontal burn rating. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of nano cadmium sulfide on combustion and thermal decomposition of polystryene and poly(methyl methacrylate)

Cadmium sulfide nano particles, both hollow spheres (CdS‐HS) and rods (CdS‐NR), were synthesized by ultrasonic and solvothermal processes, respectively, and characterized by XRD and SEM. The effect of the two kinds of nano particles on flammability was investigated using the cone calorimeter and microscale combustion calorimeter. The incorporation of small amount of CdS nano particles (1 wt.%, 3 wt.%, 5 wt.%) leads to a reduction in the peak heat release rate (PHRR) compared to pristine PS; CdS‐NR is more efficient in reducing the PHRR. CdS nano particles are less effective in reducing the PHRR of PMMA. Thermal stability of PS/CdS and PMMA/CdS nanocomposites was studied by TGA. The TGA results show that the addition of the nano particles mainly increases thermal stability of PS and PMMA at high temperatures. Copyright © 2014 John Wiley & Sons, Ltd.     

A theoretical study of the effect of intraventricular pulsations on the pathogenesis of hydrocephalus

Hydrocephalus, a condition which affects thousands of people annually in the US alone, arises as a result of a build-up of cerebrospinal fluid (CSF) in the brain’s ventricular cavity due to an imbalance between the rates of CSF production and absorption. Although the earliest known instances of hydrocephalus date back to the time of Hippocrates, the pathophysiology of hydrocephalus is still poorly understood, and is the subject of active debate in the literature. Recently, the pulsations of the cerebrospinal fluid have been suggested as a possible mechanism for ventricular expansion. In this paper, we attempt to determine the significance of these pulsations in the development of hydrocephalus by simulating their mechanical effects on the brain. The brain parenchyma is modelled as a fractional Zener viscoelastic solid, which extends the work previously presented in Sivaloganathan et al. [S. Sivaloganathan, M. Stastna, G. Tenti, J. Drake, A viscoelastic model of the brain parenchyma with pulsatile ventricular pressure, Appl. Math. Comput. 165 (2005) 687-698]. Explicit solutions for the displacement and stresses are obtained by solving the boundary value problems corresponding to the cases of infant and adult hydrocephalus. As expected, when the cranial vault is a rigid container, as in adult hydrocephalus, very small displacements are predicted.     

Fire retardancy of bis[2-(methacryloyloxy)ethyl] phosphate modified poly(methyl methacrylate) nanocomposites containing layered double hydroxide and montmorillonite

Copolymer nanocomposites were prepared by suspension copolymerization of bis[2-(methacryloyloxy)ethyl] phosphate and methyl methacrylate, together with bis(2-ethylhexyl) phosphate layered double hydroxide and a montmorillonite, Cloisite 93A. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of nanocomposites and the dispersion of additives in the polymer. The thermal stability of the nanocomposites has been assessed by thermogravimetric analysis and cone calorimetry has been used to study the fire properties. Bis[2-(methacryloyloxy)ethyl] phosphate not only copolymerized with MMA, but also aids in the dispersion of additives in PMMA. The copolymer nanocomposites have better dispersion and higher degradation temperature and more char mass than the corresponding PMMA nanocomposites. The largest peak reduction in the heat release rate of the copolymer nanocomposites are 52 and 65% for LDH and MMT additives, respectively.     

Further studies on polystyrene/cerium (IV) oxide system: melt blending and interaction with montmorillonite

In order to clarify questions raised from a recent study on the polymer/cerium (IV) oxide (CeO₂) system, polystyrene/CeO₂ was prepared by melt blending, which produces only microscale dispersed CeO₂. The incorporation of CeO₂ moderately enhances the thermal stability of the composites. Because of the limited surface area of microscale CeO₂ particles compared with nanoscale particles, the microscale dispersed CeO₂ induces negligible peak heat release rate reduction in cone calorimetry. Combination of CeO₂ with organoclay does not show any advantages with either microdispersion of nanodispersion of CeO₂ in polystyrene and polymethylmethacrylate matrices. In summary, the nanodispersion (i.e. surface area) of CeO₂ particles is a critical factor in fire retardancy of the composites. Copyright © 2013 John Wiley & Sons, Ltd.     

Novel mixed ligand coordination compounds of some rare earth metal cations containing acesulfamato/N,N-diethylnicotinamide

The mixed ligand coordination compounds containing acesulfamato and N,N -diethylnicotinamide biomolecules of some rare earth metal cations (Eu³⁺, Tb³⁺, Ho³⁺, Er³⁺ and Yb³⁺) were synthesized, and their structural properties were investigated. Possible structural formulas have been proposed by determining the chemical composition of molecules (elemental analysis), binding properties (infrared spectroscopy, mass analysis, solid-state UV-vis spectroscopy), thermal degradation properties (TGA / DTA curves). Based on the data collected, it is suggested that rare earth metal cations with a 3+ oxidation state have sextet coordination. The geometries of the structures were thought to be distorted octahedral. The charge balance of the coordination sphere is balanced by a monoanionic acesulfamato located outside the coordination sphere. When the thermal behaviours of the complexes were examined, it was determined that the compounds with Eu³⁺, Tb³⁺, and Yb³⁺ metal cations contained one hydrate water outside the coordination sphere. Hydrate waters do not exist in the Ho³⁺ and Er³⁺ metal cation-centred complexes. At the end of the thermal decomposition analysis of all complex structures, it was determined that they leave the relevant metal oxides in the reaction vessels as final decomposition products.