bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractBiaxially 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

AbstractApplying 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

AbstractApplying 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

AbstractA 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

AbstractTo 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

AbstractPhotoinitiated 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

AbstractThe 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

AbstractHighly 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

AbstractDue 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

AbstractResidual 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

AbstractThe 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

AbstractThe 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

AbstractIt 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

AbstractA 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

AbstractBiologically‐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.