bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogel composites of neutral and slightly charged poly (acrylamide) gels with incorporated bentonite. Interaction with salt, linear polyelectrolytes and ionic surfactants
Authors: Starodoubtsev Serguei G. , Churochkina Natalia A. , Dembo Alexander T. , Khokhlov Alexei R.
Published: March 2011

The swelling behavior in the solutions of sodium chloride, linear polyelectrolytes and ionic surfactants of the composites based on clay mineral bentonite (BENT) embedded in neutral and slightly charged poly(acrylamide) (PAAm) gels is studied. Negatively charged flat clay particles incorporated into polymer gel adsorb oppositely charged surfactant and linear polyelectrolyte and attract the charged chains of cationic polymer matrix. The results of SAXS study manifest the formation of lamella structure of the cationic surfactant adsorbed by the clay plates. The gels loaded with the clay show a strong response to changes in the nature and the composition of the ionic environment.
Polymer gel/organic dye complexes in aqueous salt solutions
Authors: Nasimova I. R. , Makhaeva E. E. , Khokhlov A. R.
Published: March 2011

The present work is devoted to the study of the complex formation of polymer gel with organic dye and their properties in the aqueous salt solutions. Two systems were studied: 1) polyelectrolyte gel based on poly(diallyldimethylammonium chloride) and water soluble oppositely charged organic dyes (alizarin red S and catechol violet) and 2) organogel based on poly(N‐vinylcaprolactam) and dithizone. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depends on the dye concentration. In the case of PVCa gel in organic media the dye absorption takes place.

The main attention has been concentrated on the study of the behaviour of gel/dye complex immersed in the salt solution if dye is the chelating ligand for metal ions. It was shown that polyelectrolyte gels generally form stable complexes with oppositely charged dyes.

The behaviour of PVCa‐dithizone‐chloroform system was studied in AgNO3 aqueous solution. The release of dithizone to the external aqueous solution of AgNO3 reservoir is completely suppressed.

Absorption spectra of gel/dye and gel/dye/metal ion systems were studied. It was shown that metal ions penetrate inside the gel phase and the dye/metal ion complexes form within the gel. The dependence of the optical density for the systems of gel/dye/metal ion on the salt concentration is observed.
Theory of supercrystalline structures in mixtures of ABC triblock and ab, bc, and ac diblock copolymers
Authors: Birshtein Tatiana M. , Polotsky Alexey A. , Amoskov Victor M.
Published: March 2011

Theoretical analysis of the ability of forming mixed supercrystalline structures in the mixtures of ABC triblock copolymer with ab, bc, and ac diblock copolymers in the strong segregation limit is carried out. Effects of combined phase and microphase segregation are analysed. The possibility of changing the initial superstructure is demonstrated.
Polyelectrolyte gel elasticity in poor solvent
Authors: Johner A. , Vilgis T. A. , Joanny J. F.
Published: March 2011

Polyelectrolytes in poor solvents are expected to show a necklace structure where collapsed polymer pearls are linked by stretched polymer strands. This prediction by Kantor and Kardar worked out by Dobrynin Rubinstein and Obukhov Macromol. 1996,29,2974 has mainly be confirmed by computer simulations of Dobrynin; Darinskii; Holm and Kremer. We study the unwinding of pearls under an external force. Polyelectrolyte gels in poor solvents are then discussed, mainly on the basis of single chain elasticity following Katchalsky.
Competition between liquid‐crystalline ordering and glassy freezing in melts of semiflexible polymers: A monte carlo simulation
Authors: Paul W. , Weber H. , Binder K.
Published: March 2011

We present results of a Monte Carlo simulation of dense melts of semi‐flexible polymers using the bond‐fluctuation model. The chosen Hamiltonian increases the chain stiffness upon cooling which in turn leads to glass‐transition like freezing of the polymer mobility. Employing an efficient simulation algorithm, which is able to equilibrate the simulated systems to lower temperature than the Rouse‐type algorithm showing the glassy freezing, we are able to observe an isotropic‐nematic phase transition. This transition lies above the glass transition temperature one would extrapolate from the observed freezing behavior.
Molecular dynamics studies of anchored polyelectrolytes
Authors: Csajka Félix S. , van Der Linden Catharina C. , Seidel Christian
Published: March 2011

We study polyelectrolytes end‐grafted to a surface in a model which includes counterions explicitly and treats the full long‐range Coulomb interaction. For strongly charged polyelectrolytes the counterions are localized inside the brush and electroneutrality is satisfied locally. Under these conditions, we find that the brush thickness is linearly proportional to the chain length and the grafting density. The counterion distribution is strongly inhomogeneous, and counterion condensation can be observed although the Bjerrum length is smaller than the average bond length. Varying the Bjerrum length we find a non‐monotonic behaviour of the brush height. Counterion diffusion is anisotropic, and is enhanced at higher grafting densities. For partially charged polyelectrolytes we obtain a crossover from quasi‐neutral behaviour to the strongly charged behaviour reported above.
Computer simulation of globules with microstructure
Authors: Ivanov Victor A. , Chertovich Alexander V. , Lazutin Alexei A. , Shusharina Nadezhda P. , Khalatur Pavel G. , Khokhlov Alexei R.
Published: March 2011

We present recent data of our Monte Carlo computer simulation study of properties of AB‐copolymer globules which depend strongly on the primary sequence of A and B monomeric units. Different primary sequences have been studied: random, random‐block, regular and designed ones by using some particular spatial conformation of a homopolymer chain (we have compared here three models: proteinlike copolymers, AB‐copolymers modeling membrane proteins and ABC‐copolymers modeling proteins with active enzymatic center). We have found several evidences for the fact that an AB‐copolymer chain with a primary sequence prepared on the basis of a particular conformation of a homopolymer chain by some “coloring” procedure preserves the “memory” about its “parent” spatial conformation. Analyzing the power spectra of AB‐sequences, we find the existence of long‐range power‐law correlations for the copolymers with specially designed primary sequences.
Collapse of diblock copolymer in poor solvent. Molecular dynamics study
Authors: Neelov Igor , Niemela Satu , Sundholm Franciska , Skrifvars Mikael
Published: March 2011

The modification of unsaturated polyesters (UPE) by poly (ethylene glycol) (PEG) end groups [1] and the computer simulation of the collapse of a single molecule of a diblock copolymer AB consisting of PEG (A) and UPE (B) blocks [2] were reported recently by us. In the present paper the static and dynamic characteristics of the final collapsed structure were investigated by a molecular dynamics simulation. The structure and the local dynamic of collapsed homopolymers (AA and BB) were studied also. The initial conformations in all cases were taken near completely extended ones. The final structures of the diblocks are similar to the structure of a core (UPE) and shell (PEG) model. The differences in torsion angle distributions between diblock and homopolymer are maximal for the CCOC dihedral angles (both in UPE and PEG blocks). The orientational order of the COC vectors (‘chords’ along backbone of polymer chain) inside both blocks is larger in the diblock than in the homopolymer. Local orientational mobility of the COC vector and the translational mobility of the monomers is larger in the diblock than in the homopolymers for both blocks.
Creep rate spectroscopy: High‐resolution analysis of relaxations and prediction of anomalies in mechanical behavior of solids
Authors: Bershtein Vladimir A. , Yakushev Pavel N. , Peschanskaya Nina N.
Published: March 2011

An original laser‐interferometric creep rate spectroscopy method was applied to analysis of molecular motion in some polymers, composites and interpenetrating polymer networks. Its potentials for study of nanoscale dynamic/compositional heterogeneity in complex systems, of a peculiar relaxation behavior of polymer binder in composites, and for prediction of temperature anomalies in strength are demonstrated.
Characterization of polymers in particulate systems
Authors: Glass H. J. , De Graaf M. J. M.
Published: March 2011

Small amounts of polymers (ca. 1 wt.‐%) are often used in the processing of ceramics to bond the particles. The purpose is to enhance mechanical properties, notably the strength, of intermediate or green products obtained after consolidation of the powder. In this paper, the influence of polymers on mechanical properties of green (Mn, Zn)‐ferrite products is investigated. Frequently used polymers are methyl methacrylate ‐ ethyl acrylate copolymer and poly(vinyl alcohol) (PVA). Because PVA generally produces low‐strength compacts and is sensitive to moisture, a blend of the copolymer and PVA was used. The glass transition temperatures (Tg) of the polymers and green products were determined. The good correspondence between the Tg's indicates that the polymers dominate the mechanical behaviour when tensile stresses are applied. In practice, compacts usually have an axisymmetric shape and are subject to diametral compression during handling. Therefore, ring‐shaped compacts were crushed at different velocities. The crushing velocity has a strong influence on the compact strength when the copolymer is used and only a small effect when the compact contains the PVA blend. This indicates that the copolymer can absorb a rapid buildup of stress through plastic deformation. By contrast, the rate of plastic deformation in the PVA blend is relatively slow. Further insight is obtained by subjecting rectangular compacts to three‐point bending. By interpreting the experimental data with a mechanical model, the deformation of compacts containing acrylic is found to be elasto‐plastic. With compacts containing the PVA blend, a yield point is observed. This indicates that elasto‐plastic deformation is preceded by elastic deformation.
Tensile deformation behaviour of the polymer phase of flexible polyurethane foams and polyurethane elastomers
Authors: van Der Heide Evert , van Asselen Otto L.J. , Ingenbleek Gerwin W. H. , Putman Constant A. J.
Published: March 2011

The change in micromorphology of the polymer phase (single strut) of a flexible polyurethane foam during deformation has been investigated by attenuated total reflection infrared spectroscopy ‐ linear dichroism and by atomic force microscopy. Deformation and, therefore, orientation take place mainly in the soft rubbery phase. This two‐phase elastic deformation process has been translated into a mathematical model, which correctly predicts the shape of a single‐strut stress‐strain curve. The theory also predicts the ultimate shape of stress‐strain curves of polyurethane elastomers at various hard phase contents and of low‐density polyethylene at various temperatures. Deviations from the elastic behaviour could be ascribed to yielding in combination with the rubbery behaviour.
Fracture of notched polypropylene specimens under creep conditions
Authors: Kučera Jaroslav , Nezbedová Eva
Published: March 2011

The kinetics of slow crack growth of isotactic polypropylene (Vestolen PP P 9022) was observed in single‐edge‐notched specimens under a constant tensile load and at a temperature of 95°C. The notch opening under different stress levels was measured as a function of time. Two types of specimens (perpendicular and parallel to the extrusion direction) were examined. The development of the processing zone and the crack advance was observed after unloading at surfaces introduced along and across the crack plane. Optical and scanning electron microscopy was used for these observations. Morphologies of the processing zone as a function of loading time and stress level were assessed. The relationships between (i) stress and time to rupture for ductile and brittle region and (ii) minimal notch opening rate δ0 and stress intensity K10 were expressed quantitatively. A pronounced effect of the orientation on the crack propagation was established. The time to break of specimens taken along the extrusion direction was about 20% higher than that of the specimens taken in the cross direction.
Deformation of thermotropic liquid crystalline polymer droplets dispersed in a polyamide
Authors: Seo Yongsok
Published: March 2011

The deformation of dispersed droplets of a thermotropic liquid crystalline polymer in a polyamide (nylon 6) matrix was studied by morphological observation. An immiscible binary blend and compatibilized ternary blends were studied. For the uncompatibilized blend, the morphology of the blends was that of a typical immiscible blend showing poor adhesion and no deformation of the dispersed phase. For the compatibilized blend, deformation of the dispersed TLCP phase was observed even if the viscosity of the matrix was lower than that of the TLCP phase. Compatibilizer addition improved the interfacial adhesion, hence enabled TLCP droplets to be deformed. A simple mechanism for the deformation of TLCP droplets was presented considering characteristic rheological properties of the TLCP melt.
Biaxial stretching of pet films: A molecular description
Authors: Tassin Jean‐François , Vigny Murielle , Veyrat Didier
Published: March 2011

Biaxially oriented poly(ethylene terephthalate) films were prepared under well defined stretching conditions in order to mimic the three stages of the industrial inverse drawing process. Molecular orientation has been characterized through X‐ray diffraction and infrared dichroism. The main orientation mechanisms in the constant‐speed drawing of an amorphous film as well as in the constant‐force transverse drawing of monodrawn samples are described. It is shown that relaxation phenomena dominate the orientation of an amorphous sample. Reorientation along the second drawing direction involves rotation of crystalline blocks along the draw direction and further crystalline growth. The high‐temperature heating stage leads to an almost four‐fold increase in the size of the crystallites. The orientation of the amorphous phase is controlled by the mechanisms occurring during crystallization (relaxation followed by extension).
Scanning force microscopy experiments probing micromechanical properties on polymer surfaces using harmonically modulated friction techniques I. Principles of operation
Authors: Sturm Heinz
Published: March 2011

Applying a high‐frequency lateral vibration between the sample surface and the tip of a scanning force microscope (SFM), a harmonically modulated lateral (friction) force image can be obtained using lock‐in techniques. The principles of operation are explained, in particular the dramatic decrease of image artefacts generally caused by topography cross‐talk and laser beam interference. Flat interfaces between the two immiscible polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), are prepared on a sodium chloride single crystal from the melt. These samples are used to evaluate the appropriate model for the tip‐sample interaction geometry. The relationship between frictional and normal force does not follow Amonton's law. This shows that a single‐asperity interaction between the tip and sample surface can be considered. Using the new technique, local measurements of shear strength and Young's modulus can be performed.
Scanning force microscopy experiments probing micromechanical properties on polymer surfaces using harmonically modulated friction techniques II. Investigations of heterogeneous systems
Authors: Sturm Heinz , Schulz Eckhard , Munz Martin
Published: March 2011

Applying a high‐frequency lateral vibration between tip and sample in a scanning force microscope (SFM), a harmonically modulated lateral (friction) force image can be obtained using lock‐in techniques. Harmonically modulated lateral force microscopy (HM‐LFM) offers several advantages compared with standard lateral force microscopy (LFM). After a brief investigation of the scan velocity dependence of LFM and HM‐LFM, two samples were investigated. First, the surface of a poly(acrylonitrile‐co‐styrene)/polybutadiene blend (ABS) was used to demonstrate the ability of the new technique to decrease the stick effects of the SFM tip. Second, an interface between two chemically very similar polymers was prepared by melting polypropylene (PP) and poly(propene‐block‐ethene) (PP‐block‐PE) films on each other. After cutting, the surface roughness of this sample was very high. It is shown that only HM‐LFM clearly resolves the local micromechanical properties without artefacts.
Multifunctional polyurethane network structures
Authors: Fedderly Jeffry J. , Lee Gilbert F. , Lee John D. , Hartmann Bruce , Dušek Karel , Šomvársky Ján , Smrčková Miroslava
Published: March 2011

A series of thirteen polyurethanes were synthesized using blends of monofunctional, difunctional, and trifunctional poly(propylene oxides) reacted with 4,4'‐diphenylmethane diisocyanate in a stoichiometric ratio. Experimental measurements were made of glass transition temperature, sol fraction, and dynamic mechanical properties. Computer simulations based on the theory of branching processes were made on the same systems. The glass transition temperature was correlated with the number average functionality of the components. Dynamic mechanical data was fitted to the Havriliak‐Negami model. A correlation was demonstrated between the measured rubbery modulus and the concentration of elastically active network chains.
Enthalpy recovery in polymeric glasses: Does a correlation exist between the empirical (T‐N‐M) relationship parameters and the glass structures?
Authors: Saiter J. M. , Denis G. , Grenet J.
Published: March 2011

To characterize the enthalpy recovery which appears during physical aging in glassy materials and especially in glassy polymers, the empirical Tool‐Narayanaswamy‐Moynihan (TNM) relationship for the relaxation time is widely used. This relationship depends essentially on three parameters, the apparent activation energy Δh*, the non linearity parameter x and the fictive temperature Tf. Even if a great amount of data (x, Δ*) can be found in the literature, no direct correlation between the values of these parameters and the engaged structures are available. On the one hand, using some polymers like Poly(ethylene terephthalate), Polymethyl(α‐n‐alkyl)acrylates and three dimensional epoxy networks for which structural changes are controlled and on the other hand, using some recently published results concerning other materials including inorganic polymers (Ge‐Se and Ge‐Te glasses), we show that it is possible to propose some interesting tendencies. In particular it is shown that the value of x depends on the intermolecular strength for organic polymers and on the connectivity for inorganic polymer.
Simulation of conversion profiles and temperature distributions within dimethacrylate thick material during photopolymerization
Authors: Lecamp Laurence , Lebaudy Philippe , Youssef Boulos , Bunel Claude
Published: March 2011

Photoinitiated polymerization of multifunctional monomers is an usual method to prepare highly crosslinked networks which have a wide variety of applications. This method leads to high reaction rates and the resulting exothermic effect of this reaction can be the cause of defects in the final material. The heterogeneities alter greatly the physical properties of ultimate products, particularly the optical ones, what causes problems in the design of thick and optically perfect materials. The knowledge of the conversion profile and the temperature distribution within the material during the photopolymerization is useful for the process optimization. Unfortunately, these parameters cannot be measured during the process. Thus, we decided to simulate them. Firstly, the necessary parameters (like conversion and reaction rate) were measured on thin material in isothermal conditions by photocalorimetry. Secondly, these kinetic data were used in a computational calculation to obtain the conversion profile and the temperature distribution within dimethacrylate thick material. The calculated temperature and conversion‐time curves are in good agreement with the experimental curves determined under the same conditions.
Poly (phenylmethylsilane) obtained by electrochemical reduction in a divided cell containing a polymeric membrane
Authors: Dabek Roman , Cervantes Jorge , Zizumbo Arturo
Published: March 2011

The electrochemical synthesis of poly(phenylmethylsilane) was carried out in a divided cell using a polymeric anion‐exchange membrane. The solution contained phenylmethydichlorosilane (PhMeSiCl2), mixed solvent tetrahydrofuran + hexamethylphosphoramide, with tetrabutylammonium perchlorate as support electrolyte. The electrodes were stainless steel as the cathode, stainless steel as the sacrificial anode or platinum as the resistant anode. Poly(phenylmethylsilane) was obtained in yields from 1.5 to 4.5 % from phenylmethyldichlorosilane concentrations equal or higher than 1 M. The number‐average molecular mass Mn of poly(phenylmethylsilane) was in the range from 5600 to 9500. A monomodal molecular weight distribution was obtained with a polydipersity Index of 2. The spectra of 1H, 13C, 29Si MMR and IR were determined. From the 29Si NMR analysis, the poly(phenylmethylsilane) showed a clear difference in the tacticity related to the chemical synthesis of the same polymer. The UV spectra showed a strong absorption in a 331 to 335 nm characteristic for the poly(phenylmethylsilane).
Time‐dependent nonlinear optical properties of pyroelectric liquid crystalline polymers
Authors: Örtegren Jonas , Busson Philippe , Gedde Ulf W. , Hult Anders , Eriksson Anders , Lindgren Mikael , Arntzén Per‐Otto , Hermann David S. , Rudquist Per , Lagerwall Sven T.
Published: March 2011

Highly oriented pyroelectric liquid‐crystalline polymers were prepared by photopolymerization under the influence of a static electric field from binary mixtures of two acrylate monomers exhibiting chiral smectic C mesomorphism. Both monomers contained nitro groups to yield second order nonlinear optical properties (second harmonic generation) and one of the monomers had two functional groups to yield a crosslinked polymer. The room temperature second order nonlinear susceptibility of the polymers showed during the first two hours a 10 % decrease after which it remained constant during the next 48 days. At elevated temperatures there was a significant difference in the nonlinear optical properties over time between crosslinked and uncrosslinked polymers. The uncrosslinked polymer showed a pronounced loss of second order nonlinear optical activity with time at ≥38°C. The crosslinked polymer showed a much smaller and basically a temperature independent decrease rate in the second order nonlinear optical properties at all the ageing temperatures (23‐130°C). Both the loss in mesogen order parameter, very evident for the uncrosslinked polymer, and conformational changes occurring within the mesogens (β mechanism), may account for the observations made.
Characterization of the dynamic properties of binary polypropylene blends via the hysteresis measurement method
Authors: Raue Frank , Ehrenstein Gottfried W.
Published: March 2011

Due to the poor impact behavior of polypropylene (PP) at low temperatures, blending PP with an elastomeric phase is a common way to improve some of the characteristic quantities. The property profile of thermoplastic elastomers strongly depends on the content of the elastomeric component. For applications under dynamic loading conditions, the corresponding material behavior is of importance. In order to reduce long testing times with constant amplitude loading, the hysteresis measurement method, which evaluates the hysteresis loop and makes use of a stepwise load increase procedure (SLIP), was developed. Binary blends based on PP were compounded with either ethylene‐propylene‐dien‐rubber (EPDM), metallocene polymerized polyethylene (mPE), or styrene‐ethylene‐butylene‐styrene block copolymer (SEBS) as the elastomeric phase. Static and dynamic tests under tensile and pressure conditions were performed in order to evaluate the influence of the type of elastomeric phase on the properties of these blends. It is shown how the hysteresis measurement method can be used to determine dynamic load limits for the application of these blends and of other polymers. Some properties improved slightly when using mPE.
Characterization of deformation in injection molded parts after packing and cooling
Authors: Jung Jung Hoon , Lee Seok Won , Youn Jae Ryoun
Published: March 2011

Residual stresses which are developed in injection molded parts affect dimensional accuracy and mechanical properties of the final products. To predict the residual stresses in injection molded parts, three stages of injection molding, i. e., filling, packing, and cooling, must be taken into consideration for the thermal and flow analyses. Flow field anaysis for filling and postfilling stages has been carried out by using the control volume based FEM/FDM hybrid method. The generalized Hele‐Shaw flow is assumed. Compressibility of the Polymer melt is considered during packing and cooling stages. Modified Cross model is employed to reflect the dependency of the viscosity upon shear rate and temperature. An equation of state proposed by Tait offers an efficient means to describe pvt‐relationship of the polymer. Variations in temperature and pressure fields are obtained over all stages by the numerical flow analysis and used as input data for the stress analysis of the part. Plane stress elements, such as shell elements, are used for finite element stress analysis of injection molded parts with appropriate boundary conditions both in the mold and after ejected from the mold. The numerical analysis yields useful information which is relevant to the mechanical properties of the final products, e. g., residual stress distribution, shape of deformation, displacement field, and strain distribution.
Dehydration‐induced structural relaxation effects in poly(methyl methacrylate)
Authors: Kalogeras Ioannis M. , Vassilikou‐Dova Aglaia
Published: March 2011

The Thermally Stimulated Depolarization (TSD) dielectric technique and Dielectric Relaxation Spectroscopy (DRS) have been used in order to investigate aging phenomena in poly(methyl methacrylate) (PMMA). Earlier TSD studies on amorphous PMMA report peculiar dielectric relaxation signals within the range of the glass transition (at ∼378 K) and the secondary relaxation (∼230 K). In the present study, an intense TSD current relaxation band maximizing around 310 K is tentatively attributed to the molecular mobility due to a residual free volume below the glass transition temperature, Tg, that allows structural recovery at the free volume released from the desorption of H2O molecules during evacuation. Limited motions in the main backbone provoke dipole (re)orientation of the ester carbonyl pendant groups with an activation energy E=0.85±0.05 eV, being responsible for the latter dielectric relaxation effect. Alternative attributions based on the short‐range jump relaxation of electric charges and boundary effects are also discussed.
A TSD current dielectric investigation of the effects of xanthene and perylene dye incorporation in PMMA
Authors: Kalogeras Ioannis M. , Vassilikou‐Dova Aglaia
Published: March 2011

The potentials of developing tunable lasers with the use of photostable dyes, incorporated at solid‐state hosts of high optical quality, have attracted considerable scientific interest. A critical factor determining the optical response of the dye is related to the extend to which its intrinsic physical and chemical properties are maintained in the environment provided. The thermally stimulated depolarization (TSD) current technique has been employed in order to investigate possible interactions between the typical thermoplastic carrier PMMA and dispersed xanthene and perylene derivatives. The dielectric β‐relaxation of PMMA, related to the (re)orientation of the polar ester carbonyl side groups, exhibits a broad distribution in the relaxation times that remains unaffected by the presence of the dye molecules. The result is supportive of the model considering the chromophores being encapsulated in the polymer without strong (chemical) bonding, in agreement with the observed laser behavior. Further aspects of the dielectric response are discussed in terms of the specific sample preparation procedures and structural relaxation phenomena occurring in PMMA.
Dynamic characterization of surface topography of plastic films
Authors: Boutaous M'Hamed , Bourgin Patrick
Published: March 2011

It is well known that surface roughness plays an important role on the handling and winding of flexible polymer films such as PET which is widely used in various applications. In order to characterize the surface topography of such materials, an air layer is squeezed between a rigid smooth substrate and a film sample. For that purpose a novel experimental set‐up has been built. Using an interferometric method and image processing, we have observed the evolution of the air layer thickness and measured its reduction for several configurations and squeezing pressures. It is found that the reduction of the central air layer thickness follows a linear law versus time allowing a parameter, called “dynamic roughness”, to be defined. This parameter, which characterizes the kinetics of the air layer being squeezed, represents the dynamic manifestation of the influence on the flow of more conventional “static” parameters representative of the film roughness. We have developed a theoretical model based on the hypothesis of perfectly flexible film samples and on the concept of equivalent smooth surfaces. The predictions are in good agreement with the experimental results and for each film tested the value of the characteristic parameter associated to its “dynamic roughness” is determined.
Polyimide‐epoxy alloys prepared via micro‐modification: Water sorption and diffusion
Authors: Jain Sanjeev , Saktimayi Rajani , Dubey Madhu , Nema Suresh Kumar
Published: March 2011

A novel polyimide‐epoxy or PI‐EP alloys are prepared by the modification of polyamic acid in the concentration range of 1.54×10−6 to 1.54×10−2 mol/L. The methanol sorption for these alloys at 24 hrs and at equilibrium conditions are determined and the residual solvent in fully cyclized polyimides were calculated. The presence of the residual solvent is visualized in fully imidized polymer and a structure containing partly imidized amic acid moiety is proposed and their concentration (in percentage) is calculated. The water sorption for these alloys at 24 hrs and at equilibrium conditions and the values of the water diffusion coefficient are determined from absorption isotherms. The PI‐EP alloys have shown comparatively lower water sorption and higher diffusion coefficient than the unmodified polyimide. The mechanistic aspects of water sorption and diffusion are discussed.
Production of biological polymers from organic wastes
Authors: Chua H. , Yu P. H. F.
Published: March 2011

Biologically‐produced polymers, from microbial fermentation are naturally biodegradable and are potential environment‐friendly substitutes for some synthetic plastics. However, broader applications are restricted by the high production costs and limitations in physical and mechanical properties. In this study, activated sludge bacteria in a conventional wastewater treatment system treating a wastewater that contained organic pollutants, were induced by nitrogen deficiency to accumulate intracellular storage polymers, which can be extracted as a low‐cost source of biodegradable plastics. Chromatographic analysis of the extracted polymers revealed a composition of poly‐hydroxyalkanoate and a number of related co‐polymers. Alcaligene spp. in the activated sludge microbial consortium was identified as the main genus accumulated these polymers. When the C:N ratio was increased from 20 to 140, the specific polymer yield increased to a maximum of 0.39 g polymer/g dry cell while specific growth yield decreased to 0.26 g dry cell/g carbonaceous matter consumed. The highest overall polymer production yield of 0.11 g polymer/g carbonaceous matter consumed was achieved when the C:N ratio was maintained at a nitrogen‐deficient level of 100. The specific polymer yield in the isolated Alcaligene spp. cells were as high as 0.7 g polymer/g dry cell mass. The composition of the co‐polymers, and hence the physical and mechanical properties, could be controlled by manipulating the influent organic compositions.
Conversion of food industrial wastes into bioplastics with municipal activated sludge
Authors: Yu Peter H. , Chua Hong , Huang Phoeby Ai‐Ling
Published: March 2011

Plastics have become an integral part of our contemporary life because of many desirable properties including durability and resistance to degradation. However, these non‐degradable, petrochemicals‐derived plastics accumulate in the environment at a rate of 25 million tons per year. Recently there is an interest in the development of a class of microbially produced bioplastics, e.g., polyhydroxyalkanoates (PHAs) which retain the desired physical and chemical properties of conventional synthetic plastics. Broader usage of biodegradable plastics in packaging and disposable products as a solution to the environmental problem would heavily depend on further reduction of costs and the discovery of novel biodegradable plastics with improved properties. In this paper, the microbial production of PHAs by activated sludge utilizing food industrial wastes is reported. The melting points of the products as well as the co‐polymer composition of the products investigated by GC and NMR were compared. By use of activated sludge to convert the carbon source into PHAs not only environment‐friendly bioplastics are produce, but also part of the problem of the disposal of municipal activated sludge is solved. The selection of food industrial waste as carbon resource can also further reduce the cost of production of PHAs.
Dynamic mechanical behaviour of styrene/butadiene copolymers and their blends
Authors: Rek Vesna , Grgurić Tamara H. , Jelčić Želimir , Hace Drago
Published: March 2011

The dynamic mechanical behaviour of high impact polystyrene (PS‐HI), styrene/butadiene/styrene block copolymer (SBS) and PS‐HI + SBS blends were investigated. Dynamic mechanical analysis (DMA) was performed in the temperature range −100°C to 100°C. The primary viscoelastic functions were determined. The copolymers PS‐HI and SBS as well as PS‐HI+SBS blends were investigated in creep‐fatigue regime and relaxation at temperatures 25, 30, 35, 40 and 45°C. Dynamic mechanical behavior of PS‐HI, SBS and PS‐HI + SBS blends depends on the copolymer and blends composition, the hard phase content, time and temperature. With the decrement of the hard phase PS concentration, the loss tangent of the soft phase increases while the loss tangent of the hard phase and the storage modulus decrease. All samples have a single Tg of the hard phase and a single Tg of the soft phase. The glass transition temperatures decrease as the content of the PS phase decreases. At the constant load the creep values increase and those of creep modulus decrease over a period of time, for all examined samples. These effects are more pronounced in samples with lower content of hard phase and at higher temperatures. The time‐temperature correspondence principle was applied to create master curves for the reference temperature 25°C for the creep modulus of PS‐HI, SBS and PS‐HI + SBS blends on a time scale far outside of the range measured by DMA experiments. These results enable us to predict the useful life of our copolymers and their blends in a wide range of time and temperature.
A novel crystalline structure ‐ poly(tetrafluoroethylene) spherulitic crystal and its crystallization kinetics
Authors: Wang Xiao Qun , Han Jie Cai , Du Shan Yi
Published: March 2011

Spherulitic crystals of Poly(tetrafluoroethylene) (PTFE), for the first time, are observed in a kind of PTFE composite, and are verified by polarized optic microscopy (POM). Differential scanning calorimetry (DSC) is used to study the isothermal crystallization kinetics of PTFE matrix at different temperatures. The result shows that Avrami parameter is near 3, which may be elucidated that PTFE crystallizes three‐dimensionally from preexisting nuclei. The result is in accordance with scanning electric microscopy (SEM) and POM observation of the crystalline morphology of PTFE. Compared with the rate of one‐dimension crystallization, the rate of three‐dimension crystallization is lower. So the three‐dimension crystallization is easier to control than the one‐dimension crystallization of PTFE.
Thermal stabilization of polypyromellitimide films
Authors: Martsinkevich A. A. , Prokopchuk N. R. , Krutko E. T.
Published: March 2011

The paper is devoted to the modification of the polyimide based on pyromellitic dianhydride and 4,4'‐diaminodiphenyloxide with phosphoric and boric anhydrides. It is demonstrated that, due to the use of phosphorus‐ and boron‐containing polyamidoacid compositions for casting the polyimide films, one can significantly increase their heat resistance without substantial expenditures while, at the same time, preserving the film‐forming ability and mechanical properties of the polyimide.
Severe persistent bone marrow failure following therapy with 2‐chlorodeoxyadenosine for relapsing juvenile xanthogranuloma of the brain
Authors: Yamada Kayo , Yasui Masahiro , Sawada Akihisa , Inoue Masami , Nakayama Masahiro , Kawa Keisei
Published: March 2011

2‐Chlorodeoxyadenosine (2‐CdA) has been successfully used in children to treat refractory Langerhans cell histiocytosis and juvenile xanthogranuloma (JXG) as salvage therapy. Although 2‐CdA is generally well‐tolerated, with temporary myelosuppression as the primary dose‐limiting toxicity, prolonged myelosuppressive, and immunosuppressive effects have been reported. We describe an adolescent patient with refractory multiple central nervous system JXG, with the lesion size markedly reduced after treatment with 2‐CdA. However, severe transfusion‐dependent bone marrow failure developed after five courses of 2‐CdA. He underwent successful bone marrow transplantation from his HLA compatible sister with reduced intensity conditioning. Pediatr Blood Cancer 2012; 58: 300–302. © 2011 Wiley Periodicals, Inc.
Synthetic aliphatic biodegradable poly(butylene succinate)/clay nanocomposite foams with high blowing ratio and their physical characteristics
Authors: Lim Sang‐Kyun , Lee Jung‐Joon , Jang Suk‐Goo , Lee Seok‐In , Lee Kwang‐Hee , Choi Hyoung Jin , Chin In‐Joo
Published: March 2011

Poly(butylene succinate) (PBS)/organoclay nanocomposites were prepared by both solution blending and melt mixing methods. In addition, nanocomposites of PBS/organoclay were also prepared by a two‐step process where the solution blended mixture is subsequently compounded in the melt state using a torque rheometer (SOAM method). We then investigated thermal and mechanical properties of the PBS/organoclay nanocomposite at first and determined an optimum organoclay content for the preparation of nanocomposite foams. All PBS/organoclay nanocomposite foams are found to possess closed spherical‐shaped cells without any rupture when examined by an optical microscopy. The blowing ratio also increased with the increase in the blowing temperature and time, with the maximum blowing ratio of 19. Furthermore, the addition of a small amount of organoclay is found to allow the cell size to follow Gaussian distribution. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
The nanostructure and dewetting of block copolymer thin films annealed in different neutral solvents
Authors: Ningrum Eva Oktavia , Lin Wei‐Ting , Lo Chieh‐Tsung
Published: March 2011

The morphology of polystyrene‐b‐poly(2‐vinyl pyridine) thin films annealed under various neutral solvents was investigated. The morphological transition depends on the vapor pressure of the solvent, the quantity of the solvent in the film, and annealing time. We introduced the volume fraction of solvent in a film (Q) to correlate these factors to the morphology. At low Q, the amount of solvent that penetrates into the film is limited and it cannot induce enough chain mobility. Thus, thin film shows short stripes or a worm‐like structure. At high Q, the great diffusion of solvent into the film facilitates polymer mobility, leading to an ordered structure. Our results also suggested that the dewetting mechanism of thin film depends on Q. At low Q, dewetting develops via the nucleation and growth. At high Q, the condensation of solvent on the surface removes some polymer and dewetting is dominated by spinodal mechanism. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Crystallization behavior of biodegradable poly(L‐lactide)/multiwalled carbon nanotubes nanocomposites from the amorphous state
Authors: Zhao Yuanyuan , Qiu Zhaobin , Yan Shouke , Yang Wantai
Published: March 2011

Crystallization behavior of biodegradable poly(L‐lactide) (PLLA) and its nanocomposites at different carboxyl‐functionalized multiwalled carbon nanotubes (f‐MWNTs) contents from the amorphous state was studied in detail in this work. For the isothermal cold crystallization, the presence of f‐MWNTs enhances the isothermal cold crystallization of PLLA in the nanocomposites compared with that of neat PLLA at the same crystallization temperature; moreover, the overall cold crystallization rate of PLLA increases with increasing the f‐MWNTs content in the PLLA matrix while the crystallization mechanism does not change. For the nonisothermal crystallization, the f‐MWNTs also accelerate the crystallization process of PLLA. In addition, the activation energies of nonisothermal cold crystallization process were calculated using both the Kissinger and Friedman methods. The cold crystallization activation energies of PLLA are higher in the nanocomposites than in neat PLLA, indicating that the addition of f‐MWNTs into the PLLA matrix acts as a physical hindrance to retard crystallization. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Nonisothermal melt‐crystallization behavior of calcium phosphate/poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) nanocomposite microspheres
Authors: Duan Bin , Wang Min , Zhou Wen‐You , Cheung Wai‐Lam
Published: March 2011

Microspheres consisting of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) polymer matrix and calcium phosphate (Ca‐P) nanoparticles were made using the solid‐in‐oil‐in‐water (S/O/W) emulsion solvent evaporation technique. Amorphous Ca‐P nanoparticles with the calcium to phosphate ratio of 1.5 were relatively well distributed in microspheres. The nonisothermal crystallization behavior of Ca‐P/PHBV nanocomposite with different Ca‐P contents (0–20%) was studied through differential scanning calorimetry using different cooling rates. During nonisothermal crystallization, the presence of Ca‐P nanoparticles resulted in an increase in crystallization rate and the nucleation activity of the nanocomposite also increased with increasing Ca‐P content. Various models were applied to investigate nonisothermal crystallization kinetics. All approaches, except for the Ozawa model, could successfully describe the nonisothermal crystallization behavior of PHBV and Ca‐P/PHBV nanocomposite. The effective activation energy for nonisothermal crystallization was calculated using the differential isoconversional method proposed by Friedman. The morphology of PHBV spherulites in nanocomposite was also studied using polarized optical microscopy. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers
Synthesis and photochemical properties of novel pentamethylated norbornadiene containing polyimides
Authors: Oueslati Ahmed , Ben Romdhane Hatem , Martin Vincent , Schiets Fréderic , Mercier Régis , Chaâbouni Refaât
Published: March 2011

A novel pentamethylated norbornadiene (NBD) based dianhydride, α,α′‐bis‐(3,4,5,6,7‐pentamethylcyclopenta‐2,4‐dienyl)meta‐xylene‐1,2‐dianhydride (3), was prepared from α,α′‐bis‐(pentamethylcyclopentadienyl)meta‐xylene (1) and acetylene dicarboxylic acid. The bis‐adduct formed via Diels–Alder reaction afforded tetra‐acid (2), which was chemically cyclodehydrated to lead the targeted dianhydride (3). New polyimides containing NBD moieties in the main chain were prepared from the dianhydride monomer (3) and various aromatic diamines. The chemical structure of the polymers was confirmed by both 1H and 13C NMR analysis. Their Molecular weights were also measured by SEC. All of these polyimides are soluble at room temperature in common organic solvents, such as chloroform, dichloromethane, THF, DMSO, DMF, and NMP, and show good thermal stabilities. The photochemical isomerization of the NBD into quadricyclane (QC) was investigated by UV/vis spectrophotometry from polymer films using visible sunlight as irradiation source. It was found that the kinetic rate of the conversion NBD‐QC which proceeded smoothly is a first kinetic order. The stored energies released by the transformation of QC groups into NBD ones of the irradiated polymer films were also evaluated by DSC measurement and were found to be around 90 kJ mol−1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
Anionic polymerization of MMA and renewable methylene butyrolactones by resorbable potassium salts
Authors: Hu Yangjian , Gustafson Laura O. , Zhu Hongping , Chen Eugene Y.‐X.
Published: March 2011

Three resorbable potassium salts of hydride (K[H]), enolate Me2CC(OiPr)OK (K[E]), and allyl K[1,3‐(SiMe3)2C3H3] (K[A]) have been investigated for controlled anionic polymerization of methyl methacrylate (MMA) and its cyclic analogs, naturally renewable methylene butyrolactones including α‐methylene‐γ‐butyrolactone (MBL) and γ‐methyl‐α‐methylene‐γ‐butyrolactone (MMBL). When used alone at ambient temperature in toluene, these salts exhibit no (K[H]) to low (K[A]) to modest (K[E]) polymerization activity. Mixing of K[H] and Al(C6F5)3 leads to the formation of an “ate” complex, K+[HAl(C6F5)3]−, which has been structurally characterized by X‐ray diffraction; this complex has a high polymerization activity producing atactic PMMA, but addition of another equiv of Al(C6F5)3 further enhances both the rate and the efficiency of the polymerization, now producing syndiotactic PMMA with a narrow molecular weight (MW) distribution of 1.04. The K[H]/2Al(C6F5)3 system also exhibits high activity for polymerization of (M)MBL. In sharp contrast, addition of Al(C6F5)3 to K[A] shuts down the polymerization at various temperatures. The most active, controlled, and syndioselective polymerization system in this series is K[E]/2Al(C6F5)3. Accordingly, the polymerization control and kinetics of this most effective system have been examined in more detail. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011