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Morphology Development (morphology + development)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Effect of Concentration Gradient on the Morphology Development in Polymer Solutions Undergoing Thermally Induced Phase Separation

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2007
Bai Tao Jiang
Abstract Anisotropic porous polymeric materials fabricated from the phase separation method via spinodal decomposition are used in various practical engineering applications. We studied the formation of anisotropic porous polymeric materials numerically, by imposing an initial linear concentration gradient across a model polymer solution. The initial concentration gradient is placed at three different regions of the polymer sample for comparison purposes. All the simulation results are in good agreement with published experimental observations, which are reported from the applications of porous polymeric membranes. The structure development shows that an anisotropic porous morphology forms when an initial linear concentration gradient is applied to the model polymer solution. [source]

Morphology development of PC/PE blends during compounding in a twin-screw extruder

POLYMER ENGINEERING & SCIENCE, Issue 1 2007
Bo Yin
The morphological development of a polycarbonate/polyethylene (PC/PE) blend in a twin-screw extruder was studied using a scanning electron microscope (SEM). The effects of extrusion temperature, viscosity ratio (the ratio of the viscosity of the dispersed phase to that of the matrix), and the screw configuration on the morphology of the PC/PE blend during the extrusion were discussed in detail. It was found that the morphology of the dispersed particles and the interfacial adhesion between the dispersed phase and matrix were both influenced by the extrusion temperature. The dispersed phase had a spheroidal shape and a small size during the high temperature processing, and an irregular shape and a large size when it was processed at low temperature. The PC phase with a lower viscosity was easier to disperse and also to coalesce. Therefore, the deformation of the low-viscosity dispersed phase during the processing was more intense than that of the high-viscosity dispersed phase. By comparing the effects of the different screw configurations on the morphology development of the PC/PE blend, it was found that the melting and breaking up of the dispersed phase were mainly affected in the initial blending stages by the number of the kneading blocks. While a kneading block with a 90 degree staggering angle was used, the size of the dispersed particles decreased and the long fibers were shortened, the large particles were drawn by the additional kneading zone. Finally, all of these structures were completely changed to the short fibers. POLYM. ENG. SCI., 47:14,25, 2007. © 2006 Society of Plastics Engineers [source]

Morphology development during blending of immiscible polymers in screw extruders

POLYMER ENGINEERING & SCIENCE, Issue 6 2002
Sandeep Tyagi
The present work reports evolution of morphology from initial (presence of striation) to final (droplet formation) stages in a single-screw extruder. Morphology development during the blending process controls the final size of the dispersed phase, which in turn significantly affects the properties of the blends. The experiments were carried out using a 70/30 wt% polypropylene/ethylene vinyl acetate (PP/EVA) blend; samples were collected along the length of the screw, by screw pullout experiment, to analyze the size and size distribution of the dispersed phase present both as striated layers and subsequently as droplets. Average size of the dispersed phase and standard deviation were taken into account to monitor the morphology evolution along the length of the screw. Pre-breakup morphology development was studied by analyzing the sample collected from the feed zone of the extruder in terms of upper and lower layers along the cross section of screw channel. Examination of micrographs revealed the existence of pattern of ordered striations along the length of the melting zone containing striations from average size of 1000 ,m down to 50 ,m decreasing rapidly along the length of the screw. The breakup process was captured at the start of compression zone where step-up in the shear as well as elongational flow was applied due to decrease in the channel depth along the compression zone. The observed droplet size formed by the breakup of filaments is found to be in accordance with theory. The final droplet size is found to be governed by the emulsification process occurring as a result of stretching, breakup and coalescence in the metering section of the screw and is in the order of 2 ,m. [source]

Photoinitiated polymerization in bicontinuous microemulsions: Fluorescence monitoring

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2006
C. Peinado
Abstract The photopolymerization of bicontinuous microemulsions was simultaneously monitored with differential scanning calorimetry and fluorescence. The kinetics and mechanism of the reaction were studied throughout the entire photopolymerization reaction. The role played by the surfactant in the kinetics and morphology was studied. The nature of the surfactant changed the autoacceleration process and final conversion. The behavior was explained as a result of the differences in the interfacial properties. Anionic cetyltrimethylammonium bromide (CTAB) gave rise to a more flexible interfacial film than anionic sodium dodecyl sulfate (SDS), resulting in competition between the intramolecular and intermolecular reactions in the former systems. As cyclization did not contribute to the increase in the degree of crosslinking, SDS photopolymerization gave solids with a more rigid microstructure. Fluorescence methodology was applied to monitor bicontinuous microemulsion polymerization and to reveal the microstructure and morphology development during photopolymerization. The microemulsion composition was designed to prepare nanoporous, crosslinked materials. Even though the nanostructure of the precursor microemulsions was not retained because of phase separation during polymerization, mesoporous solids were obtained. Their morphologies depended on the nature of the surfactant, and membranes with open cells were successfully prepared with CTAB, whereas more complex morphologies resulted with SDS. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5291,5303, 2006 [source]

Dependence of the interfacial reaction and morphology development on the functionality of the reactive precursors in reactive blending

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Z. Yin
Abstract PMMA containing 50 wt% of anthracene-labeled PMMA chains end-capped by a phthalic anhydride group (anth-PMMA-anh) has been melt blended at 180°C with PS containing 33 wt% of chains end-capped by an aliphatic primary amine (PS-NH2) and PS bearing 3.5 pendant amine groups (as an average) along the chains (PS-co-PSNH2), respectively. The reactive chains have been synthesized by atom transfer radical polymerization. Conversion of anth-PMMA-anh into PS-b-PMMA and PS-g-PMMA copolymers has been monitored by SEC with a UV detector. The interfacial reaction mainly occurs in the initial melting and softening stage (<1.0 min.), although at a rate which strongly depends on the number of reactive groups attached to PS chains, the higher conversion being observed for the PS-co-PSNH2 containing blends. The phase morphology depends on the architecture of the in-situ formed copolymer. Indeed, a coarser phase dispersion is observed in case of the graft copolymer compared to the diblock. [source]

Nylon 66/clay nanocomposite structure development in a twin screw extruder,

POLYMER ENGINEERING & SCIENCE, Issue 4 2009
Bin Lin
Nylon 66/clay nanocomposites were prepared in a Berstorff ZE25A UTX Ultra-glide corotating twin screw extruder at 270°C. Two types of extruder configurations with different mixing sections were used. One comprised two kneading block sections in the screws (KB only) and the other had a combination of a multi-process-element (MPE) section and a kneading block section. Samples at eight different locations along the extruder screw were obtained and analyzed using scanning electron microscope and transmission electron microscope to examine the morphology development of clay inside nylon down the length of the extruder. It is found that the clay aggregates are quickly broken into smaller tactoids (micron size) and then even much smaller clay bundles (nanometer size) and single clay platelets in the first mixing section. The structure changes in the second mixing section are much less significant. X-ray diffraction (XRD) analysis of the nanocomposite products showed small, or disappearance of, characteristic XRD (001) peaks, which indicates partial exfoliation, or complete exfoliation, respectively, of clay inside nylon matrix. Differential scanning calorimetry nonisothermal study shows that the crystallization temperature of the nanocomposites has increased around 17°C when compared with neat nylon 66. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Morphology development of PC/PE blends during compounding in a twin-screw extruder

Influence of the processing conditions on a two-phase reactive blend system: EVA/PP thermoplastic vulcanizate

POLYMER ENGINEERING & SCIENCE, Issue 11 2002
Catherine Joubert
The elaboration of a TPV based on copolymer of ethylene and vinyl acetate (EVA) and polypropylene (PP) as thermoplastic phase was investigated in a batch mixer. The crosslinking reaction is carried out through a transesterification reaction between ester groups of EVA and alcoxysilane groups of the crosslinker agent tetrapropoxyorthosilicate (TPOS). The main advantage of this crosslinking reaction is that it can be well controlled and suitable for different processing conditions. The aim of the present study is to get a better understanding of the dispersion mechanism and of the phase inversion of the EVA major phase during its dynamic vulcanization into the PP minor phase. It was proved that the initial viscosity ratio, , = ,pp/,EVA, between EVA and PP plays an important part in the morphology development of the reactive blend. The viscosity ratio must be close to the critical ratio expressed by Utracki's model of phase inversion mechanism. Furthermore, the influence of different processing parameters on the variation of the morphology and on the mechanical properties of the ultimate TPV was investigated. The main conclusion of this study is that the characteristic time of crosslinking must be of the same order than the time of mixing. Indeed, better mechanical properties are obtained when a progressive phase inversion occurred and when it is controlled by rheological aspects and transient morphology equilibrium of the two phases and not by the mechanical fragmentation of the crosslinked EVA. For example, in our experimental conditions (concerning the amounts of catalyst and crosslinker reagents), high shear rates can be avoided ( < 80 s,1) as the self-heating of the blend under shear considerably increases (,T , 50°C for = 225 s,1), leading to faster kinetics and consequently to a phase inversion controlled by the fragmentation of the crosslinked EVA phase. [source]

Online light scattering measurements: A method to assess morphology development of polymer blends in a twin-screw extruder

POLYMER ENGINEERING & SCIENCE, Issue 10 2002
G. Schlatter
Light scattering has proved itself an efficient technique to determine particle diameters in heterogeneous dilute dispersions in the micrometer range. Extrusion of polymer blends is expected to give rise to very small particles, typically in the range from hundreds of nanometers to tens of micrometers. A light scattering device developed in our laboratory has been used to study the morphology of polymer blends obtained in a twin-screw extruder. The main advantage of this technique is the immediate response obtained without any surface or interface modification that can occur during the sample preparation by using more conventional techniques like electron microscopy. To show the possible applications of this light scattering device, preliminary tests have been carried out. First, we present a comparison between experimental measurements and theoretical results for dilute systems. Second, we have investigated the effect of shear flow on the droplet deformation. Finally, we have studied the variations of the light scattering pattern for a reactive blend. [source]

Morphology development during blending of immiscible polymers in screw extruders

Evolution of structure in the softening/melting regime of miscible polymer mixing

POLYMER ENGINEERING & SCIENCE, Issue 6 2001
Heidi E. Burch
Structure development in the softening/melting processing regime is investigated using the model miscible blend poly(styrene-co-acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fourier-transform infrared spectroscopy is used to help determine the normalized sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale(s) present in the blend at short mixing times. Results of these experiments indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that this multimodality is due to the operation of the Scott/Macosko sheeting mechanism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixing model, which postulates the formation of a striated mixture while ignoring the softening/melting regime. [source]

Morphological and fractal studies of polypropylene/poly(ethene-1-octene) blends during melt mixing using scanning electron microscopy

POLYMER INTERNATIONAL, Issue 3 2008
Xinhua Xu
Abstract BACKGROUND: Polymer blending creates new materials with enhanced mechanical, chemical or optical properties, with the exact properties being determined by the type of morphology and the phase dimension of the blend. In order to control blend properties, morphology development during processing needs to be understood. The formation and evolution of polypropylene/poly(ethylene-1-octene) (PP/POE) blend morphology during blending are qualitatively represented by a series of time-dependent scanning electron microscopy (SEM) patterns. The area diameter and its distribution of dispersed phase domains are discussed in detail. In order to characterize the formation and evolution of phase morphology quantitatively, two fractal dimensions, Ds and Dd, and their corresponding scaling functions are introduced to analyze the SEM patterns. RESULTS: The evolution of the area diameter indicates that the major reduction in phase domain size occurs during the initial stage of melt mixing, and the domain sizes show an increasing trend due to coalescence with increasing mixing times. The distribution in dispersed phase dimension obeys a log-normal distribution, and the two fractal dimensions are effective to describe the phase morphology: Ds for dispersed phase dimension and Dd for the distribution in it. CONCLUSIONS: The fractal dimensions Ds and Dd can be used quantitatively to characterize the evolutional self-similarity of phase morphology and the competition of breakup and coalescence of dispersed phase domains. It is shown that the fractal dimensions and scaling laws are useful to describe the phase morphology development at various mixing times to a certain extent. Copyright © 2007 Society of Chemical Industry [source]

Syndiotactic poly(propylene)/organoclay nanocomposite fibers: influence of the nano-filler and the compatibilizer on the fiber properties

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2005
Zita Mlynar, íková
Abstract Melt spinning of nanocomposites prepared from syndiotactic poly(propylene) (sPP) and organolayered silicate (M-ODA), containing bound octadecyl ammonium chains, was investigated. The influence of the nano-filler reinforcement and the role of the addition of maleic anhydride grafted isotactic poly(propylene) (iPP-g-MA) as compatibilizer with respect to the fiber proportion was examined. The presence of nano-filler, the drawing ratio, and the compatibilizer addition afforded increased tenacity of the fibers. Only in the presence of the compatibilizer high drawing ratio of the sPP nanocomposite fibers was achieved. Transmission electron microscopy (TEM) was applied to monitor morphology development during nanocomposite fiber spinning in the presence and the absence of the compatibilizer. Copyright © 2005 John Wiley & Sons, Ltd. [source]