Showing papers on "Intrinsic viscosity published in 2004"

Deep Eutectic Solvents Formed between Choline Chloride and Carboxylic Acids: Versatile Alternatives to Ionic Liquids

Abstract: Deep Eutectic Solvents (DES) can be formed between a variety of quaternary ammonium salts and carboxylic acids. The physical properties are significantly affected by the structure of the carboxylic acid but the phase behavior of the mixtures can be simply modeled by taking account of the mole fraction of carboxylic acid in the mixture. The physical properties such as viscosity, conductivity, and surface tension of these DES are similar to ambient temperature ionic liquids and insight into the cause of these properties is gained using hole-theory. It is shown that the conductivity and viscosity of these liquids is controlled by ion mobility and the availability of voids of suitable dimensions, and this is consistent with the fluidity of other ionic liquids and molten salts. The DES are also shown to be good solvents for metal oxides, which could have potential application for metal extraction.

Correlations of solution rheology with electrospun fiber formation of linear and branched polyesters

Abstract: The implications of the entanglement concentration (Ce) on the electrospinning process for a series of linear and branched poly(ethylene terephthalate-co-ethylene isophthalate) (PET-co-PEI) copolymers with weight-average molecular weights (Mw) ranging from 11 700 to 106 000 g/mol and branching index values (g‘) from 1.0 to 0.43 were investigated. Analyzing the dependence of specific viscosity (ηsp) on concentration enabled the determination of the semidilute unentangled, semidilute entangled, and concentrated regimes for the PET-co-PEI solutions. Linear and branched copolymers were electrospun from semidilute unentangled, semidilute entangled, and concentrated solutions under identical conditions to determine the effects of concentration regime and molecular topology on electrospun fiber morphology. The dependence of the fiber diameter and morphology on the zero shear rate viscosity (η0) and normalized concentration (C/Ce) was determined. For copolyesters with molecular weights well above the entanglement...

Viscosimetry of Polymers and Polyelectrolytes

Abstract: 1 Introduction and Objective.- 2 Basic Concepts.- 3 Execution of Viscosity Measurements.- 4 The Intrinsic Viscosity.- 5 Parameters Affecting the Intrinsic Viscosity.- 6 Viscosimetric Determination of the Molar Mass.- 7 Determination of the Polymer Coil Dimensions from the Intrinsic Viscosity.- 8 A Deeper Insight Into Viscosimetry.- 9 List of References.- 10 Subject Index.

Synthesis and Characterization of Biodegradable Low Molecular Weight Aliphatic Polyesters and Their Use in Protein-Delivery Systems

Abstract: Poly(lactic acid) (PLA) and poly(lactic-co- GA) (PLGA) with low molecular weights were synthesized by a one-step polycondensation of lactic acid (LA) with glycolic acid (GA) molecules using stannous octoate as a catalyst at 160°C. A high yield (80%) of all the polymers was obtained in the study. The PLA and PLGA copolymers were characterized by 1 H-NMR, GPC, and DSC measure- ments, etc. We elaborated HSA-loaded microspheres based on PLA and PLGA copolymers with different monomer ratios (LA/GA 85:15, 75:25, 65:35, and 50:50) by the sol- vent-extraction method based on the formation of double w/o/w emulsion. Microspheres were characterized in terms of the morphology, size, and encapsulation efficiency (E.E.). The highest E.E. (69.3%) of HSA was obtained for HSA- loaded PLGA (65/35) microspheres among all the formula- tions. In vitro matrix degradation and protein release of these microspheres were performed in phosphate-buffer saline (PBS; 154 mM, pH 7.4). The degradation profiles were char- acterized by measuring the loss of the microsphere mass and the decrease of the polymer intrinsic viscosity. The release profiles were investigated from the measurement of the protein presented in the release medium at various intervals. It was shown that the matrix degradation and protein-re- lease profiles were highly LA/GA ratio-dependent. It is suggested that these matrix polymers may be optimized as carriers in protein- and peptide-delivery systems for differ- ent purposes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1848 -1856, 2004

Recycled poly(ethylene terephthalate) chain extension by a reactive extrusion process

Abstract: A commercial-scale reactive extrusion processing system for recycled poly(ethylene terephthalate) (PET) flakes with an added chain extender, pyromellitic dianhydride (PMDA), was investigated. The PMDA concentration was varied with the intention of reaching a higher recycled PET intrinsic viscosity ([η]). The effect of changing the extruder residence time on the system's stability and the recycled PET [η] was also investigated. Reactive extruded PET with a PMDA concentration up to 0.3 wt% was found to have a higher [η] and lower carboxyl content than recycled PET processed in a normal extrusion system. A shift in [η] of about 0.18 dl/g was obtained with a 0.3 wt% PMDA concentration. A PMDA concentration above 0.3 wt% produced chemical, thermal and hydrodynamic instability in the system, causing crosslinking reactions and gel formation. The reactive extrusion system was stable at low residence time (45 s) and moderate (0.15 wt%) PMDA concentration; however, using 0.2 wt% PMDA produced higher reactive extruded recycled PET [η] with lower carboxyl content than other PMDA concentration levels examined. Residence times higher than 45 s produced higher reactive extruded recycled PET [η]. Reactive extruded recycled PET was also tested for mechanical properties. Polym. Eng. Sci. 44:1579–1587, 2004. © 2004 Society of Plastics Engineers.

Triple-Detector GPC Characterization and Processing Behavior of Long-Chain-Branched Polyethylene Prepared by Solution Polymerization With Constrained Geometry Catalyst

Abstract: Fourteen long-chain branched (LCB) polyethylene (PE) samples were prepared by a constrained geometry catalyst. The PE samples had average branching frequencies of 0.06–0.98 branches per polymer chain, as determined by the nuclear magnetic resonance spectroscopy (13C NMR). These samples, as well as five linear PEs were characterized using a gel permeation chromatography (GPC) coupled with online three-angle laser light scattering (LS), differential refractive index (DRI), and viscosity (CV) detectors. The root mean-square radius of gyration ( 〈 r g 2 〉 1 / 2 ) , intrinsic viscosity ([η]), and molecular mass (M) of the PEs were measured for each elution fraction. Based on the comparison of the long-chain branching (LCB) PEs with their linear counterparts and the Zimm–Stockmayer equation, the distributions of long-chain branch frequency (LCBF) and density (LCBD) as function of molecular mass were estimated. It was found that although the LCBF increased with the increase of molecular mass, the LCBD showed a maximum value in the medium molecular mass range for most of the PE samples. The average LCBD data from the GPC analysis were in good agreement with the 13C NMR measurements. The rheological properties and processing behavior of these samples were also assessed. While the long chain branching showed significant effects on the modulus and viscosity, it did not improve the processing. Compared to linear PE, polymer melt flow instabilities such as sharkskin, stick-slip and gross melt fracture developed in extrusion of LCB PEs occurred at lower wall shear stresses and apparent shear rates.

How Conductivities and Viscosities of PC-DEC and PC-EC Solutions of LiBF4 , LiPF6 , LiBOB, Et4 NBF 4 , and Et4 NPF 6 Differ and Why

Abstract: Electrolytes of LiBF 4 , LiPF 6 , LiBOB, Et 4 NBF 4 , and Et 4 NPF 6 in propylene carbonate-diethyl carbonate (PC-DEC) and propylene carbonate-ethylene carbonate (PC-EC) binary solvents were compared for their electrolytic conductivity (K) and viscosity (η) to assist their application to the batteries and capacitors and to understand the mechanisms underlying the differences in these properties. For η, the Li + -salts resulted in considerably higher values than the Et 4 N + -salts, and the influence of an anion was such that the larger its size, the higher the η of the electrolyte. Correspondingly, κ of the Et 4 N + -electrolytes was substantially higher than the Li + -electrolytes, and a larger anion was accompanied by a lower K, except for electrolytes at the low-η end. Toward this end, the order of K tended to be in reverse: the K of an electrolyte with a larger anion rose relative to one with a smaller anion. All evidence presented leads to the conclusion that the η, and thereby the K, of the electrolytes are dominantly affected by the number of unassociated Li + ions through their solvation by the carbonate solvent molecules, the different anions of the Li-salts exerting their influence only through altering the number by their different powers for associating with the Li + .

Variability in starch physicochemical and functional properties of yam (Dioscorea sp) cultivated in Ivory Coast

Abstract: An Erratum has been published for this article in Journal Of the Science of Food and Agriculture 85(5), 889 (2005). Native starches were extracted from 21 cultivars of four yam species representative of the yam population of Ivory Coast. They were first characterized for their proximate composition, starch physico-chemical properties (amylose content, particle size distribution, crystallinity, thermal properties and intrinsic viscosity). Some functional properties (swelling, solubility and pasting behaviour and paste clarity) were then determined. Analysis of variance and principal component analysis showed that three homogenous groups could be distinguished, mainly based on starch physico-chemical properties. The first group contained all yam starches of the D alata and the D cayenensis-rotundata complex species. It was characterized by a large diameter grain (approximately 25 µm), a high amylose content (around 25% db), a high intrinsic viscosity (mean of 190 cm3 g−1), and a high apparent viscosity and clarity of the paste. The second group contained the D esculenta varieties, characterized by a small granule size (diameter 6 µm), a low intrinsic viscosity (121 cm3 g−1), a high gelatinization enthalpy change (19 J g−1) and a low paste viscosity. The D dumetorum sample differed from the D esculenta group by having a pure A-type crystalline form and an opaque paste. A multiple regression showed that the volume fraction of the dispersed phase and native granule size (or amylose content) could account for close to 80% of the variability of paste apparent viscosity. Gel clarity appeared mainly linked to granule size, small granules from D dumetorum and D esculenta giving the most opaque gels. Copyright © 2004 Society of Chemical Industry

Temperature dependence of density, thermal expansion coefficient and shear viscosity of supercooled glycerol as a reflection of its structure

Abstract: The relationship of the microstructure of supercooled, highly viscous glycerol to the temperature dependence of its density, thermal expansion coefficient, and shear viscosity are discussed. The character of this temperature dependence at the transition from low viscosity state to the solid amorphous state (solidified state without nuclei) is described with help of function ψ, which can be interpreted as the effective number of degrees of freedom responsible for the change of viscosity of glycerol over a broad range; these degrees of freedom are those related to the α-relaxation process. It is shown that the change in effective activation energy of the viscosity is completely determined by the parameter ψ. The change in the shear viscosity of glycerol due to the influence of the solid-phase nuclei is considered. It is shown that the introduction of the parameter φ, equal to the specific volume occupied by the nuclei of the solid phase, together with ψ provides a natural explanation of the temperature depe...

Morphologies and conformation transition of lentinan in aqueous NaOH solution.

Abstract: Molecular morphologies and conformation transition of lentinan, a β-(13)-D-glucan from Lentinus edodes, were studied in aqueous NaOH solution by atomic force microscopy (AFM), viscometry, multiangle laser light scattering, and optical rotation measurements. The results revealed that lentinan exists as triple-helical chains and as single random-coil chains at NaOH concentration lower than 0.05M and higher than 0.08M, respectively. Moreover, the dramatic changes in weight-average molecular weight Mw, radius of gyration 〈s2〉1/2, intrinsic viscosity [η], as well as specific optical rotation at 589 nm [α]589 occurred in a narrow range of NaOH concentration between 0.05 and 0.08M NaOH, indicating that the helix–coil conformation transition of lentinan was carried out more easily than that of native schizophyllan and scleroglucan, and was irreversible. For the first time, we confirmed that the denatured lentinan molecule, which was dissolved in 0.15M NaOH to be disrupted into single coil chains, could be renatured as triple helical chain by dialyzing against abundant water in the regenerated cellulose tube at ambient temperature (15°C). In view of the AFM image, lentinan in aqueous solution exhibited the linear, circular, and branched species of triple helix compared with native linear schizophyllan or scleroglucan. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004

Evaluation of hydrophobically associated polyacrylamide-containing aqueous fluids and their potential use in petroleum recovery

Abstract: Acrylamide and tridecyl acrylate copolymers were synthesized by micellar copolymerization to obtain water-soluble, hydrophobically modified polymers. Rheological properties of the obtained polymer solutions were evaluated and compared to those of solutions of a commercial polyacrylamide currently used in the petroleum industry. The behavior of the copolymer solutions was studied as a function of the variation of hydrophobic monomer content incorporated in the copolymer as well as the salt content of the aqueous medium, for diluted and semi-diluted regimens. Comparative studies of such effects on the intrinsic viscosity and the critical concentration of those polymers were conducted. The increase in hydrophobic monomer content produced a sudden increase in the bulk and absolute viscosity of the polymeric solutions, a trend that was more intense from a certain concentration typical for each polymer. Salt addition led to lower bulk viscosity caused by a stronger interaction among hydrophobic groups, resulting from minimized exposure of such groups and water. The same effect was observed for the critical concentration. A comparison of the synthesized polymers with industrial polyacrylamide showed that the synthesized polymers were characterized by advantageously high shear strength and high salt resistance. However, in the absence of salts, higher copolymer amounts were needed to prepare solutions whose viscosity was the same as that of commercial polyacrylamide. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3686–3692, 2004

Online Monitoring of Controlled Radical Polymerization: Nitroxide-Mediated Gradient Copolymerization

Abstract: A comprehensive characterization of the controlled radical copolymerization of styrene and n-butyl acrylate comonomers is obtained by using a recently introduced method termed automatic continuous online monitoring of polymerization reactions (ACOMP). By simultaneously monitoring and combining signals from a continuously diluted reactor stream, light scattering, viscosity, differential refractive index, and UV absorption were used, in a model-independent fashion, to follow the weight-average molecular weight Mw, weight-average intrinsic viscosity [η]w, the concentrations of each comonomer, and hence also the evolution of the average instantaneous and cumulative compositions along the chains as comonomers were consumed. The “composition profile” along the chain will largely influence the copolymer properties, and it is suggested that gradient copolymers might also be termed “profiled copolymers”, which then includes di- and multiblock polymers. Invoking the Mayo−Lewis model allowed sequence length averages...

Identification of rheological and structural characteristics of foamable poly(ethylene terephthalate) by reactive extrusion

Abstract: The reactivity and efficiency of five low molecular weight multifunctional anhydride and epoxy compounds as chemical modifiers of a bottle grade poly(ethylene terephthalate) (PET) resin were evaluated by reactive extrusion under controlled conditions. The two dianhydrides and the three epoxy compounds were used at concentrations based on stoichiometry derived from the measured carboxyl and hydroxyl end group contents of the base resin. Measures of melt viscosity, melt strength, intrinsic viscosity and carboxyl group content were used as criteria of the extent of the modification. Correlations of die pressure with extrudate swell during extrusion, and melt flow index (MFI) with melt strength by off-line testing of the extrudates permitted the ranking of the modifiers according to their chain-extending/branching efficiency. For some systems molecular weight increases (related to die pressure/MFI/intrinsic viscosity) accompanied by broadening of the molecular weight distribution (related to die swell/melt strength) were considered excessive. Extrusion foaming experiments with one particular dianhydride modifier that increased the intrinsic viscosity of the resin from 0.71 to 0.9 dl g−1 indicate that production of low-density foams by a process involving one-step reactive modification/gas injection foaming is feasible, at conditions not significantly different from those employed in the simple reactive modification of the PET resin. The rheological and structural parameters determined in this work may be used as criteria to specify PET foamable compositions in terms of types and concentrations of modifiers. Copyright © 2004 Society of Chemical Industry

Impact Resistant Polyolefin Compositions

Abstract: Olefin polymer composition comprising (by weight, unless otherwise specified): A) 60 - 95% of a propylene homopolymer or copoloymer having a Polydispersity Index (P.I.) value of from 4.6 to 10 and a content of isotactic pentads (mmmm), measured by 13C NMR on the fraction insoluble in xylene at 25 °C, higher than 98 molar; B) 5 - 40% of a copolymer of ethylene containing from 40% to 70% of propylene or C4-C10 α-olefins) or of combinations thereof, and optionally minor proportions of a diene; said composition having a Temperature Rising Elution Fractionation (TREF) profile, obtained by fractionation in xylene and collection of fractions at temperatures of 40 °C, 80°C and 90 °C, in which the ethylene content Y of the fraction collected at 90 °C satisfies the following relation (I): Y≤ -0.8 + 0.035X + 0.0091X2 wherein X is the ethylene content of the fraction collected at 40 °C and both X and Y are expressed in percent by weight, and a value of intrinsic viscosity [η] of the fraction soluble in xylene at 25 °C of from 1.8 to 4.2 dl/g.

Water-swellable polyelectrolyte microgels polymerized in an inverse microemulsion using a nonionic surfactant

Abstract: A series of poly(dimethylacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid) microgels slightly crosslinked by methylene-bis-acrylamide (MBA) were polymerized in a novel inverse microemulsion polymerization (IMEP) system. To determine a suitable composition of the IMEP system, the phase diagram of a pseudoternary system was made. The pseudoternary polymerization system consisted of n-hexane, a nonionic surfactant (polyoxyethylene oleyl ether, C18En), and an aqueous monomer solution. Polymerization was performed in a single-phase reversed micelle solution. The reversed micelles were about 50 nm in diameter, as determined by FF-TEM. The viscometric characteristics of the polymers extracted from the IMEP system were studied in 3 mM sodium chloride aqueous solution. The intrinsic viscosity values for the noncrosslinked and crosslinked (0.1 mol% MBA was incorporated) samples were 25 and 7.4 dl/g, respectively. The overlap concentration ( c ∗ ) of crosslinked polymer microgel occurred at c[η]=1 in the solvent. When the volume fraction (φ) of the microgel was 0.7, the value of the apparent yield stress of the microgel solution was observed. These results show that the microgel has a significant thickening effect above c ∗ due to friction between the microgel particles. It is assumed that the microgels polymerized in a confined space retain the shape or size of the nanosized reactor with a diameter on the order of 50 nm.

Pressure dependence of melt viscosity in the system NaAlSi3O8-CaMgSi2O6

Abstract: The effect of pressure on melt viscosity was investigated in the system NaAlSi3O8-CaMgSi2O6 (Ab-Di) at pressures from 0.1 to 400 MPa using a parallel plate viscometer. The new measurements in the high viscosity range of 108.5 −1011 Pa·s are consistent with previous data obtained at higher temperature (lower viscosity) in that the pressure dependence changes from positive for the polymerized Ab melt to negative for the depolymerized Di melt. However, a pressure independent viscosity is observed at much higher Ab contents at low temperature (70–90 mol%) than at high temperature (<30 mol%, Brearley et al. 1986). Hence, the sign of the pressure dependence of viscosity changes from positive to negative with increasing temperature for intermediate compositions along the join. The apparent activation volume ( V a ), which is derived from the pressure derivative of log viscosity using an Arrhenian relationship, decreases systematically with temperature for Di-rich compositions, e.g., for the Di melt from 52.0 ± 2.7 cm3/mol at 1020 K to 24.8 ± 6.6 cm3/mol at 1057 K. To model the P - T dependence of viscosity, we propose a modification of the commonly used equation based on Adam-Gibbs theory as ![Formula][1] where A AG, B AG, and C AG are fit parameters and S conf is the configurational entropy. The parameter C AG can be interpreted as the volume change of a structural unit during transition from one stable configuration to another one. The new approach excellently reproduces the experimental viscosity data for Di melts over a wide range of temperature. A modified Vogel-Fulcher-Tamman equation also describes the data with a similar reproducibility, but one additional fit parameter is needed. Experimental viscosity data for Ab melts scatter too much at given P-T to be fitted by a unique model. To calculate viscosities of stoichiometric Ab melt at elevated pressure and temperature, we suggest that the C AG parameter determined in our study be combined with published viscosity equations for ambient pressure. [1]: /embed/tex-math-1.gif

Charge density effects in salt-free polyelectrolyte solution rheology

Abstract: Solution rheology of 2-vinyl pyridine and N-methyl-2-vinyl pyridinium chloride random copolymers in ethylene glycol was studied over wide ranges of concentration and effective charge. The fraction of quaternized monomers α and the fraction of monomers bearing an effective charge f of these copolymers were measured using counterion titration and dielectric spectroscopy, respectively. Ethylene glycol is a good solvent for neutral poly(2-vinyl pyridine), with very few ionic impurities. The viscosity η and relaxation time T of dilute and semidilute unentangled solutions exhibit the scaling with concentration and effective charge expected by the Dobrynin model. Reduced viscosity data are independent of concentration in dilute solution, giving an intrinsic viscosity that depends on effective charge, and the experimental data obey the Fuoss law in the semidilute unentangled regime. Scaling concentration with the overlap concentration (c/c*) reduces these data to common curves, and c* ∼ f -12/7 as predicted by the Dobrynin model, where f is the fraction of monomers bearing an effective charge. While the overlap concentration depends strongly on effective charge until counterion condensation occurs, the entanglement concentration c e is surprisingly insensitive to effective charge, indicating that entanglement effects are not understood using the Dobrynin model. The terminal modulus G = η/τ depends only on the number density of chains G = ckT/N for c* c e independent of the effective charge.

Segment-Based Eyring−NRTL Viscosity Model for Mixtures Containing Polymers

Abstract: A multicomponent liquid mixture viscosity model based on the Eyring and nonrandom two-liquid (NRTL) theories was recently presented and evaluated over the entire concentration range using data from several polymer−solvent systems. In this paper, the original component-based Eyring−NRTL viscosity model is transformed to a segment-based Eyring−NRTL viscosity model for polymer−solvent and polymer−polymer systems. The segment-based approach provides a more physically realistic model for large molecules when diffusion and flow is viewed to occur by a sequence of individual segment jumps into vacancies rather than jumps of the entire large molecule. Evaluation of a segment-based Eyring−NRTL model with polyisobutylene−isooctane mixture viscosity data demonstrates an improvement in the correlation capability over the Mn range of 900−1 200 000. Additional evaluations with polystyrene in styrene, poly(ethylene glycol) in oxolane (THF), poly(dimethylsiloxane)s in pentamer, and poly(dimethylsiloxane) blends provide f...