Rheology and morphology of polypropylene in situ grafted and blended with methyl methacrylate/n‐buthylacrylate copolymer

The rheology and morphology of polypropylene (PP) modified by grafting and blending with vinyl monomers were studied in this work. The PP powder was impregnated by mixture of methyl methacrylate (MMA)/n‐buthylacrylate (n‐BA) and copolymerized with azobisisobutyronitrile (AIBN) initiator. The simultaneous grafting and blending of PP with MMA‐co‐n‐BA copolymers were performed in a corotating, 40 L/D, twin‐screw extruder in the presence of dicumyl peroxide. The Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to verify the grafting level and dispersion state of MMA/n‐BA copolymer on PP matrix, respectively, and their rheological properties were studied. It is observed that MMA/n‐BA copolymer is finely dispersed in the PP matrix. In this way, PP can be grafted, blended, and simultaneously compatibilized with polar copolymers, as is seen in SEM images. The results showed that by increasing acrylate monomers grafting on to PP increased. The same trend was observed for AIBN initiator. The gel content of samples with 25% monomers showed an increased from 0.7% to 3.5% by increasing AIBN from 0.2% to 0.4%. The grafting reaction took place with chain scission of PP molecules and also cross‐linking reactions. The optimum grafting of 7.3% with lowest chain scission and cross‐linking were obtained for samples containing 15 wt% monomer and 0.3% AIBN initiator. J. VINYL ADDIT. TECHNOL., 21:290–298, 2015. © 2014 Society of Plastics Engineers     

Matrix viscoelasticity: Controlling factor in the rubber toughening of epoxy resins

Our limited success in toughening methylene dianiline (MDA)-cured Epon 828, using varying rubber types, led to a study of the role of the matrix viscoelasticity in the toughening process. Two rubber types, with different interfacial bonding capabilities, poly(n-butyl acrylate)/15 wt % acrylonitrile/2 wt % acrylic acid and poly(n-butylacrylate)/15 wt % acrylonitrile, were incorporated into systems containing varying amine concentrations to control crosslink density. Impact strengths of controls and rubber-modified compositions increased with excess amine concentrations up to 70%. The impact strengths for the poly(n-butyl acrylate)/15 wt % acrylonitrile/2 wt % acrylic acid rubber-modified compositions were greater than their equivalent controls, with the effect being greater at a lower crosslink density. This study confirmed that the matrix viscoelasticity is the controlling parameter in the toughening process. The degree of rubber–epoxy interfacial bonding is also an important parameter to consider, if the matrix viscoelasticity permits toughening. A modified stress response model was used to explain the toughening phenomenon.     

Application of numerical hill-climbing in control of systems via Liapunov's direct method

The procedure of determining the control effort which minimizes the forward difference of the quadratic function x(k)^TQx(k) combined with improving Q by numerical hill-climbing is investigated to determine the feasibility of establishing time sub-optimal control policies for both linear and nonlinear systems. For linear systems, Rosenbrock's hill-climbing procedure is more efficient for improving Q than the method of Hooke and Jeeves; moreover it yields policies closer to the optimum when the number of state variables exceeds six. The “best” value of Q obtained by hill-climbing depends on the initial choice of Q and the initial state of the system x(0). The evaluation, carried out with a linear gas absorber and a nonlinear continuous stirred tank reactor, shows that the combined sub-optimal procedure yields results close to time-optimal control with little computational effort.     

Mathematical Properties of the Moments of Truncated Dynamic Magnetic Resonance Spectra and Their Potential Application

The moments of truncated dynamic magnetic resonance spectra, M_n(L), are expanded in terms of power series of the integration range −L to +L. The expansion consists of three contributions: 1) an L-independent term that, for the first three moments (n=1 to 3), is independent of the motion and equals the corresponding moment, M_n, of the rigid powder spectrum; 2) a limited number of (positive) terms, diverging as L^k (k<n, odd), reflecting the broadening effect due to motion; these terms vanish for the first three moments and become nonzero, with motion-dependent coefficients, only from the fourth moment on; and 3) an infinite series of converging (negative) terms, in powers of 1/L^k (k is odd), reflecting the reduction of the moments due to the truncation of the spectra; these terms are motion dependent for all moments. The convergence properties of this series are discussed and expressions for the lower (truncated) moments in the slow and fast motion limits of a secular Hamiltonian are derived. For the slow motion limit, it is shown how the L-dependence of the moments can be used to estimate the magnetic and dynamic parameters. The procedure is demonstrated using computer-simulated spectra. In the fast motion regime, closed expressions are obtained in a similar form to those of the relaxation equations. The effect of natural line width and strong-collision dynamics on the various moments as well as that of nonsecular terms in the Hamiltonian are also briefly discussed.     

The effect of matrix composition on the properties of cellulosic fibers–polyethylene composites

The solution/precipitation method was used for the preparation of polyethylene (PE)/cellulosic fibers composites. Blends of modified linear low density PE [linear low density PE‐grafted maleic anhydride (LLDPE‐g‐MAH)] with low density PE (LDPE) were used as matrices for the aforementioned composites. Blends of LDPE with a copolymer of LDPE and acrylic acid (AA)/n‐butyl acrylate (n‐BA) [(AA/n‐BA)–LDPE] were also studied for the same purpose. The reinforcing effect of cellulosic fibers in terms of tensile strength is more enhanced when mixtures of the modified polar polymer with pure PE were used as matrices, as compared with that corresponding to matrices consisting of modified PE alone. Regarding the Izod impact strength, composites of LLDPE‐g‐MAH presented the best performance with an improvement of 135% in comparison with specimens consisting of LDPE matrix, whereas composites of (AA/n‐BA)‐LDPE matrix showed a modest improvement of their impact resistance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Simple Iterative Procedures for Quantum-Mechanical Bound States

Iterative methods are developed to obtain approximate solutions for bound states of quantum-mechanical systems. A sequence of 2 × 2 secular equations is solved, to yield a specified eigensolution to the N × N secular equation. Our simplest procedure ensures convergence only for certain states, but a generalisation appears to converge for any state. Some sample calculations are presented, both for model (anharmonic oscillator) systems and for a two-electron atom.     

Thermally safe operation of liquid-liquid semibatch reactors. Part I: Single kinetically controlled reactions with arbitrary reaction order

The thermally safe operation of an indirectly cooled semibatch reactor in which an exothermic reaction occurs corresponds to conditions of potentially very high effective reaction rate compared to the dosing rate of the coreactant, whose accumulation in the reaction system is consequently small. On this basis it is possible to build boundary diagrams in terms of suitable dimensionless parameters, which summarize all the possible thermal behaviors of the reactor and can be used for safe scaleup purposes.In this work the influence of reaction kinetics on the shape and location of boundary diagrams for a single liquid-liquid reaction in the slow regime is discussed. First of all, the theory of boundary diagrams, originally developed for (1,1) reaction order, is extended to a generic (n,m) rate of reaction expression. Then it is shown that in many practical systems, using boundary diagrams based on (1,1) reaction order can lead to both unsafe and unnecessary (from a safety point of view) low-production operating conditions. New boundary diagrams for a few (n,m) reaction orders are presented. Some rules-of-thumb are also discussed to identify in which cases a boundary diagram developed for a given (n,m) reaction order can be reasonably used to approximate the real kinetic behavior of the system of interest.Moreover, since building a boundary diagram for the specific kinetics considered can be necessary, a simple and general procedure for building such diagrams that can be easily implemented in a computer code is also presented.     

Composite materials based on polydimethylsiloxane and in situ generated silica by using the sol–gel technique

A polydimethylsiloxane-α,ω-diol with molar mass M_n = 43,000 has been synthesized by cationic polymerization of octamethylcyclotetrasiloxane and reinforced with silica. Two pathways were used for incorporation of silica in the polymeric matrix: ex situ by mechanical blending of a pretreated fumed silica and in situ by adding tetraethyl-orthosilicate (TEOS) as silica precursor in the polymer matrix followed by their hydrolysis and condensation (sol–gel technique). The procedure occurred in the absence of solvent. Composites with different contents of silica were prepared and investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The results were compared to those obtained on a model network based on the same polysiloxane without silica. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

A model for the controlled release of tri-n-butyltin fluoride from polymeric molluscicides and mosquito larvicides

Tri-n-butyltin fluoride (TBTF) is used as a controlled release mosquito larvicide and molluscicide. The Ecopro 1370, which was used in this work, is a commercially available larvicide containing 20% TBTF in low density polyethylene. The larvicide has a theoretical life of 3.7 years. The release mechanism was studied in water and yields a strange type IB release curve with an initial peak after 10 days, a minimum release at 13 days, and steady state release after 24 days. The strange release curve is due to the initial release of TBTF from the surface of the formation. The release is inhibited as water diffuses into the matrix where it reacts with the TBTF to form immobile tri-n-butyltin hydroxide. The latter dehydrates to bis(tri-n-butyltin) oxide which diffuses into the aqueous layer to yield the steady state system. A model containing three reaction zones can be used to explain these phenomena.     

Planar Entry Converging Flow During Extrusion of Polymer Melts

In this article, a planar entry converging flow during die extrusion of polymeric melts was analyzed and a differential equation of entry converging boundary streamline equation with rheological parameters and channel geometry is established. By applying limit theory, the entry converging boundary streamline equation in the case with different non-Newtonian index (n) was discussed, and the corresponding expressions of entry natural convergent half angle and convergent region length were derived. The entrant flow pattern might be described with the half angle of entry natural convergence (α₀) and the convergent region length (L _e ) of the melts, and α₀ and L _e were mainly a function of the entry elastic storage deformation energy (e) and n. The values of α₀ and L _e were calculated by means of these simplified expressions. It was found that the estimations of α₀ decrease nonlinearly white L _e increases linearly with an addition of e. Finally, a preliminary verification of the natural converging half angle equation was made. The results showed that the estimations of 2α₀ based on the experiments of a low-density-polyethylene (LDPE) and a high-density-polyethylene (HDPE) were close to the data reported in reference.     

High‐Temperature Deformation Mechanisms in Monolithic 3YTZP and 3YTZP Containing Single‐Walled Carbon Nanotubes

Monolithic 3YTZP and 3YTZP containing 2.5 vol% of single‐walled carbon nanotubes (SWCNT) were fabricated by Spark Plasma Sintering (SPS) at 1250°C. Microstructural characterization of the as‐fabricated 3YTZP/SWCNTs composite shows a homogeneous CNTs dispersion throughout the ceramic matrix. The specimens have been crept at temperatures between 1100°C and 1200°C in order to investigate the influence of the SWCNTs addition on high‐temperature deformation mechanisms in zirconia. Slightly higher stress exponent values are found for 3YTZP/SWCNTs nanocomposites (n~2.5) compared to monolithic 3YTZP (n~2.0). However, the activation energy in 3YTZP (Q = 715 ± 60 kJ/mol) experiences a reduction of about 25% by the addition of 2.5 vol% of SWCNTs (Q = 540 ± 40 kJ/mol). Scanning electron microscopy studies indicate that there is no microstructural evolution in crept specimens, and Raman spectroscopy measurements show that SWCNTs preserved their integrity during the creep tests. All these results seem to indicate that the high‐temperature deformation mechanism is grain‐boundary sliding (GBS) accommodated by grain‐boundary diffusion, which is influenced by yttrium segregation and the presence of SWCNTs at the grain boundary.     

Extraction and Preconcentration of Mercury(II) from Aqueous Solutions

Abstract

The extraction/preconcentration of mercury(II) from aqueous media using diphenyl-2-pyridylmethane (DPPM) in benzene has been studied. The factors influencing the extraction are optimized. An extractive preconcentration procedure has been proposed on the basis of its quantitative extraction in a single equilibration from 1 M hydrochloric acid solution containing 0.02 M potassium thiocyanate. Extracted mercury can be stripped almost completely into 10 M aqueous solutions of hydrochloric or perchloric acid. A mechanism has been proposed, and the extractable species is assumed to be HgCl_2—n (SCN) _n (DPPM)₂, where n = 1,2. Aqueous to organic volume ratios up to 100:1 can be used without loss of extraction efficiency, and the procedure can effectively be used in water pollution abatement studies.     

Highly regioselective,base-catalyzed,biginelli-type reaction of aldehyde,phenylacetone and urea/thiourea kinetic vs. thermodynamic control

An efficient one-pot regioselective synthesis of various novel 3,4-dihydropyrimidin-2(1H)-one (DHPMs) via a three-component Biginelli-type condensation of aldehyde, phenylacetone and urea/thiourea under two different based-catalyzed conditions is described. In kinetic control path, lithium N, N-diisopropylamide (LDA-20 mol % generated in situ from n-BuLi and diisopropylamine) was used as the base, in tetrahydroforane (THF) as the solvent at 0°C. Thermodynamic control path was run with NaH as the base, in EtOH as the solvent under reflux status. The simple procedure, mild base-catalytic reaction conditions, no column chromatography and good to high yields are important features of this protocol.     

PMMA composites of single‐walled carbon nanotubes‐graft‐PMMA

To facilitate the dispersion of single‐walled carbon nanotubes (SWCNT) into poly(methyl methacrylate) (PMMA), SWCNT were functionalized with a RAFT chain transfer agent, and PMMA was grafted from the SWCNT by reversible addition–fragmentation transfer (RAFT) polymerization to give SWCNT‐g‐PMMA containing 6 wt % PMMA. SWCNT‐g‐PMMA in the form of small bundles was dispersed into PMMA matrices. The SWCNT‐g‐PMMA filler increased the glass transition temperature (T_g) of the composite when the matrix molecular weight M_n was less than the graft molecular weight, but not when the matrix M_n was equal to or greater than the graft M_n. The threshold of electrical conductivity of the composites as a function of weight percent SWCNT increased from 0.2% when matrix M_n was less than graft M_n to about 1% when matrix M_n was greater than graft M_n. Dynamic mechanical analyses of the composites having graft M_n less than or equal to matrix M_n showed broader rubbery plateaus with increased SWCNT content but no significant differences between samples with different grafted PMMAs. The results indicate that lower M_n matrix wets the SWCNT‐g‐PMMA whereas higher M_n matrix does not wet the SWCNT‐g‐PMMA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39884.     

Generalized binary interaction parameters for hydrogen-heavy-n-alkane systems using Peng–Robinson equation of state

The Peng–Robinson equation of state (PR EOS) is used to model the vapor–liquid equilibria (VLE) of binary systems of hydrogen with five heavy-n-alkanes: n-decane (n-C₁₀H₂₂), n-hexadecane (n-C₁₆H₃₄), n-octacosane (n-C₂₈H₅₈), n-hexatriacontane (n-C₃₆H₇₄), and n-hexatetracontane (n-C₄₆H₉₄). Using literature experimental data for these systems, binary interaction parameters (BIPs) were calculated using the PR EOS coupled with three different alpha (α) functions (Soave, Twu, and Gasem). The calculated BIPs have been fitted to a generalized correlation that can be used to estimate the BIPs and model the VLE within the temperature range of 283.2–449.6?K, pressure range of 1.151–15.970?MPa, and hydrogen solubility range of 0.016–0.257?mole fraction. It is found that PR EOS combined with one specific form of α function is capable of reproducing the experimental VLE data with an overall %AARD of 1.1%.     

Controlled antibody release from a matrix of poly(ethylene-co-vinyl acetate) fractionated with a supercritical fluid

A new method is presented for controlling the rate of antibody (Ab) release from an inert matrix composed of poly(ethylene-co-vinyl acetate) (EVAc), a biocompatible polymer that is frequently used to achieve controlled release. Using supercritical propane, a parent EVAc sample (M_n = 70 kDa, M_w/M_n = 2.4) was separated into narrow fractions with a range of molecular weights (8.7 < M_n < 165 kDa, 1.4 < M_w/M_n < 1.7). Solid particles of Ab were dispersed in matrices composed of different polymer fractions and the rate of Ab release into buffered saline was measured. The rate of Ab release from the EVAc matrix depended on molecular weight: > 90% of the incorporated Ab was released from low molecular weight fractions (M_n < 40 kDa) during the first 5 days of release, while < 10% was released from the high molecular weight fraction (M_n > 160 kDa) during 14 days of release. No significant differences in polymer composition, glass-transition temperature, or crystallinity were identified in the different molecular weight fractions of EVAc. Mechanical properties of the polymer did depend on the molecular weight distribution, and correlated directly with Ab release rates. Because it permits rapid and reproducible fractionation of polymers, supercritical fluid extraction can be used to modify the performance of polymeric biomaterials. © 1993 John Wiley & Sons, Inc.     

Starch urea-formaldehyde matrix encapsulation. IV. Influence of solubility and physical state of encapsulant on rate and mechanism of release

The influence of the physical state and solubility of the encapsulant on the rate and mechanism of release and swelling of the cross-linked starch-urea formaldehyde (St-UF) matrix has been studied by encapsulating model organic compounds. The release and swelling data have been analyzed in terms of the generalized equation M_t/M_∞ = ktⁿ applicable for swellable controlled-release systems. This matrix system shows and an inverse relationship of release rate with the cross-link ratio for all the encapsulants studied. The solid encapsulants have n values in the range of 0.22–0.41, indicating a Fickian or anomalous mechanism. Further, the release rate increases with solubility of the encapsulant. The liquid encapsulants have n values in the range of 0.5–1.5, indicating Case II transport mechanism. The release rates for liquid encapsulants are lower by one to three orders of magnitude than those for solid encapsulants and are not influenced by encapsulant solubility. This indicates a polymer chain relaxation-controlled mechanism of release for liquid encapsulants. © 1993 John Wiley & Sons, Inc.     

Copper-mediated ATRP of MMA in DMSO from unprotected dextran macroinitiators

To easily perform atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in homogeneous medium from unprotected polysaccharidic macroinitiators, the ATRP of MMA carried out in dimethylsulfoxide has been firstly reinvestigated using Cu(I)Br as metal catalyst and ethyl 2-bromoisobutyrate as initiator. Two ligands, 2,2′-bipyridyne (Bpy) and N-(n-propyl)-2-pyridylmethanimine (n-Pr-PMI), have been compared, as well as the addition of Cu(II)Br₂ (10 molar % relative to Cu(I)Br) or the adjustment of experimental temperature (from 30 to 60 °C). Appropriate conditions were founded for both ligands to achieve a controlled ATRP. Bpy giving far much faster polymerization compared to n-Pr-PMI, n-Pr-MI was preferred as ligand for accurate tuning of the conversion. Experimental procedure was then applied to unprotected macroinitiators based on dextran to obtain amphiphilic poly(methyl methacrylate) grafted dextran. While homopolymerization was controlled in these conditions, parameters have to be adjusted for the hydrophilic unprotected macroinitiators to prevent gel formation and control ATRP.