Large Molar Mass Research Articles

Extracting wood lignin without dissolving or degrading cellulose: investigations on the use of food additive-derived ionic liquids

Biodegradable plastics and biocompatible composites, generated from renewable biomass feedstock, are regarded as promising materials that could replace synthetic polymers and reduce global dependence on fossil fuel sources. Wood cellulose, the most abundant biopolymer on earth, holds great potential as a renewable biomass feedstock for the future. To unlock the entire scope of potential benefits of this feedstock, the wood components—namely cellulose, hemicellulose and lignin—need to be separated and processed individually. Current methods to separate wood components, such as Kraft pulping for example, suffer considerable drawbacks and cannot be considered environmentally benign. This work investigates the use of food-additive derived ionic liquids (ILs) for separating wood lignin, studying the influence of selected process parameters, such as extraction time, extraction temperature, IL moisture content, wood particle size, wood species, IL cation species, solvent composition, and IL recyclability on the lignin extraction efficiency. The lignin extract and the wood residues were characterised viainfrared spectroscopy, elemental analysis, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, and gel permeation chromatography. An extraction efficiency of e = 0.43 of wood lignin was achieved in one gentle extraction step (T = 373 K, t = 2 h), and it was found that the presence of a co-solvent increased the extraction efficiency to e = 0.60. Gentle conditions during IL treatment did not decrease the crystallinity of the wood sample, and the extracted lignin had both a larger molar mass and a more uniform molar mass distribution, compared to commercially available Kraft lignin.

Evaluation of Assam Bora Rice Starch as Plasma Volume Expander by Polymer Analysis

Water soluble polysaccharides are currently finding increasing use as a basis material for plasma volume expander. In clinical setting it is desirable to have a precise knowledge of steric and chemical structure, since these affect the pharmacokinetics and pharmacology of plasma volume expander. Branch component of starch amylopectin is very similar in structure to glycogen, the reserve polysaccharide of animal and therefore is liable to be compatible with body tissue. The knowledge of weight average molecular mass, degree of branching, osmotic pressure and coil dimension are essential, since low molecular mass do not have desirable effect and large molar mass have undesirable effect. Assam Bora rice starch was characterized by polymer analysis for use as plasma volume expander. Characterization involves the determination of FTIR spectra, degree of branching by H1 NMR, osmotic pressure by internal measurement technique, establishment of Mark-Houwink relationship and determination of Molecular weight - viscosity relationship.

Separation of small organic ions from salts by ion‐exchange membrane in electrodialysis

AbstractElectrodialysis (ED) can be applied in the food and fermentation industry for separating inorganic salts and organic ions from other fractions. However, the separation efficiency for small organic ions should be understood in detail. In this article, the membrane selectivity and transport mechanism of small organic ions from mixed salts by ion‐exchange membranes are theoretically and experimentally investigated. First of all, the influence of current density on the solute flux (organic ions and inorganic ions) and on membrane selectivity (between organic ions and inorganic ions and between different organic ions) in ED has been studied. The selectivity was shown to be influenced by changing the applied current density. It was observed that separation of inorganic ions from organic solutes was feasible, but the selectivity was dependent on the size, charge, and functional groups of the organic ions. Furthermore, results imply that binary organic anions with larger molar mass (>130, i.e., aspartate and tartrate) can be adsorbed onto the membrane free volume and hence form a charged double layer, which affects membrane selectivity. Finally, competition between small organic and inorganic ions is discussed by comparison of the concentration profiles and current efficiencies of the different anions. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Aggregate Structure in Heavy Crude Oil: Using a Dissipative Particle Dynamics Based Mesoscale Platform

Heavy crude oil consists of thousands of compounds and much of them have a fairly large relative molar mass and complex structure. It is hard to learn the dynamic behavior of this fluid system at all atom models. The present study aims at constructing a mesoscale platform to explore aggregate behavior of asphaltenes in heavy crude oil. The aggregate structure in heavy crude oils was investigated by introducing rigid body fragments, which represents the significant presence of structures of fused aromatic rings in fractions such as asphaltenes and resins into dissipative particle dynamics (DPD). Another pressing task about how to determine the structure of the average model molecules and conservative force parameters was discussed in detail. With some regularity concerning the number of rings, the distribution of side chains and heteroatoms in average model molecules are revealed. Finally, we integrated the modified DPD program, model molecules, and the parameters selected for the preliminarily simulation ...

Synthesis, characterization, and metal adsorption properties of tannin–phenol–formaldehyde resins produced using tannin from dried fruit of Terminalia chebula (Aralu)

AbstractIn this study, tannin extracted from Terminalia chebula (Aralu) was used to produce tannin–phenol–formaldehyde resins. They were produced to obtain resins with different tannin to phenol ratio in an attempt to optimize the ion exchange capacities of resins produced. The resins made were sulfonated to improve their properties further. Bivalent cations, such as Zn2+, Pb2+, Ca2+, Mg2+, and Cu2+, were used to estimate the adsorption properties of both unsulfonated and sulfonated resins. The glass transitions of representative resins were estimated using differential scanning calorimeter thermograms. Fourier transform infrared spectroscopic analysis was used to gauge changes on resins by sulfonation and adsorption of cations. The glass transition values of unsulfonated, sulfonated, and metal‐adsorbed sulfonated resins showed a similar increasing trend with the increase of phenol content in the resin. The glass transition temperature values reach a plateau beyond the tannin/phenol ratio of 1 : 0.5, indicating the formation of large molar masses facilitating entanglements beyond that ratio. The phenol ratio of 1 : 0.5 has shown the highest adsorption capacity for all the metal ions used. The highest adsorption capacity was shown for sulfonated tannin–phenol–formaldehyde resin with the tannin/phenol ratio of 1 : 0.5 for Pb2+, which is 0.610 meq/g. The adsorption equilibrium data obtained using the column technique were found fitting Freundlich isotherm. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Characteristics of transitional multicomponent gaseous and drop-laden mixing layers from direct numerical simulation: Composition effects

Transitional states are obtained by exercising a model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer at larger Reynolds numbers, Re, than in a previous study. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete dynamic and thermodynamic coupling between phases is included. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass, is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of their PDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices, resulting into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions, and the effects of the initial mass loading and initial free-stream gas temperature are explored. For reference, simulations are also performed for gaseous multicomponent mixing layers for which the effect of Re is investigated in the direct-numerical-simulation–accessible regime. The results encompass examination of the global layer characteristics, flow visualizations, and homogeneous-plane statistics at transition. Comparisons are performed with previous pretransitional MC-liquid simulations and with transitional single-component (SC) liquid-drop-laden mixing layer studies. Contrasting to pretransitional MC flows, the vorticity and drop organization depend on the initial gas temperature, this being due to drop/turbulence coupling. The vapor-composition mean molar mass and standard deviation distributions strongly correlate with the initial liquid-composition PDF. Unlike in pretransitional situations, regions of large composition standard deviation no longer necessarily coincide with those of large mean molar mass. The rotational and composition characteristics are all liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The classical energy cascade is found to be of similar strength, but the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation for MC flows. The kinetic energy and dissipation are liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The gas composition, of which the first four moments are calculated, is shown to be close to, but distinct from, a SGPDF. Eulerian and Lagrangian statistics of gas-phase quantities show that the different observation framework may affect the perception of the flow.

Dissociation Mechanism of HNIW Ions Investigated by Chemical Ionization and Electron Impact Mass Spectroscopy

AbstractChemical Ionization (CI) with Collision‐Induced Dissociation (CID) spectroscopy and Electron Impacting (EI) with metastable Mass analyzed Ion Kinetic Energy (MIKE) spectroscopy have been applied to study ionic dissociations of Hexanitrohexaazaisowurtzitane (HNIW). Similarities and differences between EI/MIKE and CI/CID mass spectra of HNIW were analyzed. In EI mass spectra, the ions [HNIW−n NO2]+ (n=2–5), such as the ion at m/z 347, were less frequent (1–2% relative abundance), but in CI mass spectra, these ions were very abundant. For some ions of large molar mass from HNIW, their dissociations pathways from parent ions to daughter ions were built according to CID and MIKE spectra. Molecular ions of HNIW with a protonated nitro group at five‐member ring seem more stable than at six‐member ring. The HNIW ions losing five of six nitro groups are very stable based on CID spectra, which agrees with some research results for thermal decomposition of HNIW in literature.

Improvements in Polysaccharides for use as Blood Plasma Expanders

AbstractModern blood plasma volume expanders consist of water‐soluble polysaccharides that are compatible with the human body. They are more effective for the treatment of intravasal volume deficiency compared to synthetic polymers. These colloidal blood plasma volume expanders, for example pullulan, dextran or hydroxyethyl starch (HES) are used in blood isotonic electrolyte solutions. HES has the lowest tendency to remain in the liver or other organs of the human body in comparison to other expanders.The knowledge of the molar mass and coil dimensions as well as their distribution are essential, since products of low molar masses do not have the desired effect and parts of large molar masses can lead to an anaphylactic shock. Injection of HES enhances the microcirculation and leads to a better oxygen transport into the tissue and the muscle. Because of this, HES was identified as a doping agent in 02/2002. In addition to this it will be shown that starch acetates have an even better physiological compatibility and are an interesting alternative to HES. We will present investigations on the shelf life of a new acetyl starch, which may be an alternative to the blood plasma expanders used to date.

Facile Manufacture and Storage of Poly(methylhydrogenosiloxane)s

This paper describes the ring-opening polymerization of 2,4,6,8-tetramethylcyclotetrasiloxane (D4H) in miniemulsion, using mono- and diphosphonic acid surfactants. In the simplest formulation conditions, polymerization proceeds in less than 15 min to generate linear poly(methylhydrogenosiloxane) (PMHS) of large molar masses (typical number-average of 25 kg/mol), of low polydispersities (around 2), and in good yields (up to 94%). Molar masses can be tuned at will since for similar conversions but increasing times, varies between 10 and 30 kg/mol. After 4 h reaction, some redistribution reactions start to proceed, responsible for PMHS chains switching into macrocycles. It was shown that rising the pH to stop the polymerization and breaking the emulsion with excess of alun salt induced hydrolysis/condensation reactions, which rapidly convert the polymer chains into an unwished macrogel. Rather, extracting the polymer by simple centrifugation and using the diacid surfactant induce a physical gelling that very efficiently suppresses side reactions, as shown by minor evolution of the molar mass distribution for 10 months.

Importance of Solubility in the Sample Preparation of Poly(ethylene terephthalate) for MALDI TOFMS

The role of solubility in the sample preparation process for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is demonstrated for oligomeric and medium molar mass poly(ethylene terephthalate) (PET). For low molar mass oligomers (PET-1), minor discrimination effects were observed when the sample was not completely in solution. MALDI spectra of medium molar mass PET, representative of the entire molar mass distribution, were obtained only when a good solvent for PET was used, such as 1,1,1,3,3,3-hexafluoro-2-propanol (commonly referred to as HFIP), as the sample preparation solvent and dithranol as the matrix. The azeotropic composition of 70:30 CH(2)Cl(2)/HFIP better solubilizes the more nonpolar matrixes, which enables more latitude in selecting sample preparation conditions than pure HFIP. Segregation effects were observed when the azeotrope mixture was diluted with tetrahydrofuran, resulting in large molar mass distribution discrimination effects in the MALDI spectra. Dilution with CH(2)Cl(2) resulted in a significant decrease in the overall signal intensity for the entire polymer distribution. With each attempt to dilute the azeotrope, the sample after solvent evaporation was visibly heterogeneous, which resulted in shot-to-shot variability. Both examples demonstrate the importance of constant solvent composition during solvent evaporation. The compatibility of matrix and polymer was explored using relative HPLC retention times. Consistent with previous work in our laboratories, it was found that the matrix/polymer combination that has the closest match of retention time resulted in the best MALDI signal intensity.

Biopitch-based general purpose carbon fibers: Processing and properties

Eucalyptus tar pitches are generated on a large scale in Brazil as by-products of the charcoal manufacturing industry. They present a macromolecular structure constituted mainly of phenolic, guaiacyl, and siringyl units common to lignin. The low aromaticity (60–70%), high O/C atomic ratios (0.20–0.27%), and large molar mass distribution are peculiar features which make biopitches behave far differently from fossil pitches. In the present work, eucalyptus tar pitches are evaluated as precursors of general purpose carbon fibers (GPCF) through a four-step process: pitch pre-treatment and melt spinning, and fiber stabilization and carbonization. Homogeneous isotropic fibers with a diameter of 27 μm were obtained. The fibers had an apparent density of 1.84 g/cm 3, an electrical resistivity of 2 × 10 −4 Ω m, a tensile strength of 130 MPa, and a tensile modulus of 14 GPa. Although the tensile properties advise against using the produced fibers as structural reinforcement, other properties give rise to different potential applications, as for example in the manufacture of activated carbon fibers or felts for electrical insulation.

Real time monitoring of lipoplex molar mass, size and density

Time-resolved multiangle laser light scattering (TR-MALLS) is used to monitor the temporal variation of DNA/cationic liposome lipoplex molar masses and geometric sizes throughout the complexation process. The measured molar masses and geometric sizes are in turn used to estimate lipoplex density. The DNA/cationic lipid charge ratio is found to be the primary factor governing lipoplex formation kinetics and the final lipoplex molar mass, geometric size and density. Charge ratios near unity lead to a growing kinetic regime in which initially formed primary lipoplexes undergo further aggregation eventually forming large molar mass lipoplexes of high density, while charge ratios very far from unity yield low molar mass lipoplexes of lower density. It is also noted that solvent composition can play a significant role in the lipoplex formation process with lipoplexes formed in ion-containing media being larger and denser than those formed in dextrose solution.

Bioperformance Improvement: Small Particles and Optimal Polymorphs

The average molar mass of active substances in crop protection as well as in pharmaceuticals has grown almost tenfold in the last century. In general, large molar masses are a drawback when looking at bioavailability. There are several strategies to overcome the problem of low bioavailability. Two of those strategies will be discussed in this paper: (i) Increasing the dissolution rate of the solids by increasing the specific surface and (ii) increasing the solubility by choosing an optimal polymorph or an amorphous substance. It will be shown what physicochemical measurements are useful to predict which excipients will stabilize suspensions of particles as small as 500 nm. In relation to optimal polymorphs, the importance of the optimal choice will be highlighted and examples of reliable stabilization of the amorphous form will be given.

Stability of colloidal silica, sikron and polystyrene latex influenced by the adsorption of polycations of different charge density

In order to describe the influence of cationic polyelectrolytes (PEs) on the stability and flocculation of dispersed particles the adsorption of statistic copolymers of diallyl-dimethyl-ammonium-chloride (DADMAC) and of N-methyl- N-vinylacetamide (NMVA) and of the corresponding homopolymers was investigated on particles of colloidal silica, quartz powder Sikron and polystyrene latex. The adsorbed amounts and the hydrodynamic thicknesses of the polymer layers and furthermore the surface charge densities and the electrophoretic mobilities of the bare and covered particles have been measured. On silica and latex the adsorbed amounts and the layer thicknesses increase with ionic strength and pH (only silica), with decreasing chain charge density of the polycations and at high electrolyte concentration with the molar mass of the polymers. The zero point of charge (zpc), and the shape of the zeta potential-pH plots vary with the coverage of the surface by the polycations. The zpc-values are independent of the ionic strength. Zeta potentials, diffusion coefficients and flocculation rates measured in dependence of the adsorbed amount of the different charged copolymers at various salt concentration and pH demonstrate fast flocculation by van der Waals attraction at small zeta potentials because of screening of the repulsive surface charges at high ionic strength and by adsorbed polycations. Additional with high molecular polycations slow mosaic flocculation is observed at low PE concentrations at still higher surface charge and slow bridging flocculation at approach of plateau adsorption. Stabilization is accomplished at low salt concentration at full coverage by electrostatic repulsion because of charge reversal. At large ionic strength high molar mass PEs are necessary to stabilize the particles sterically by osmotic repulsion of the long tails. For Sikron particles optimum flocculation is obtained at about 30% of plateau adsorption of poly(diallyl-dimethyl-ammonium-chloride) (PDADMAC) and the size of the flocs increase with molar mass.

Micellization of triblock copolymers in a solvent selective for the middle block: Influence of the molar mass

The micellization thermodynamics and micelle structural parameters for polystyrene- b -poly(ethylene/butylene) b -polystyrene copolymers (SEBS) in n -octane were studied. This solvent is selective for the middle poly(ethylene/butylene) block of the copolymer. The copolymer samples have similar chemical composition and different molar mass. Standard thermodynamic functions of micellization (Δ G °, Δ H ° and Δ S °) were determined by light scattering. All the functions showed more negative values for the SEBS copolymer with a larger molar mass. The structural parameters of micelles formed by different triblock copolymers were determined from static light scattering and viscosity measurements. Micelle molar mass, association number and viscometric hydrodynamic radius increase with the length of the copolymer chain for a constant copolymer composition; however, the radius of gyration decreases. Finally, the results found for SEBS micelles in n -octane are compared to those found for SEBS micelles in 4-methyl-2-pentanone. The different behaviour found supports the idea that the micelles of a triblock copolymer in a selective so vent of the middle block will show a shell formed by loops of the middle block in order that the two outer blocks go into the micelle core and even some poorly solvated outer blocks could be extended out of the micelle.

Microstructure and mechanical properties of three-dimensional carbon/silicon carbide composites fabricated by chemical vapor infiltration

Three-dimensional carbon/silicon carbide composites were fabricated by chemical vapor infiltration, and the microstructure and mechanical properties were investigated. For the composites ( C SiC ) with no pyrolytic carbon interfacial layer, the mechanical properties (flexural strength, flexural elastic modulus, shear strength and fracture toughness) are increased with density of the composites. High density ( p = 2.1 g cm −3 ) C SiC composites exhibit high fracture toughness (16.5 MPa m 1 2 ) but brittle fracture behavior because of strong bonding between the fiber/matrix. Low density composites show non-catastrophic failure mode with bundle pull-out. The composites (C/PyC/SiC) with pyrolytic carbon interfacial layer exhibit good mechanical properties and a typical failure behavior involving fiber pull-out and brittle fracture of sub-bundle. Microstructural observations and theoretical analysis reveal that the tortuosity and bottleneck effect of the pores and large molar mass of reactant agent (methyltrichlorosilane) are three key issues to hinder the densification of composites. Cracks formed in the SiC matrix by thermal stress have two influences on the mechanical properties of the composites: to decrease mechanical properties and have some contribution on toughness and failure behavior by deflecting cracks.

Preparation and properties of flame-retardant polycarbonates and copolycarbonates from 3,3′,5,5′-tetrabromobisphenol AF and bisphenol A

Brominated fluorine-containing homopolycarbonates and copolycarbonates of varied unit ratio were synthesized from 3,3′,5,5′-tetrabromobisphenol AF and bisphenol A polycondensed with trichloromethyl choloroformate and a phase-transfer catalyst at 25°C. All polycarbonates were examined with i.r. spectra, elemental analyses (EA), inherent viscosity, X-ray diffraction, solubility, contact angle, tensile stress, d.s.c., t.g.a. and LOI. Polycarbonates of moderate to large molar mass and inherent viscosities up to 0.77 dlg −1 were obtained in high yields with tetra- n-butylammonium bromide as a catalyst, sodium hydroxide as a base and 1,2-dichloroethane as medium. The homopolycarbonate of greatest inherent viscosity reflects that bisphenol A, having an electron-releasing group, increases nucleophilic properties of the phenolate anion. The X-ray diffraction diagram showed that all polycarbonates were essentially semicrystalline. Almost all polycarbonates, except the homopolycarbonate based on bisphenol A, were soluble in acetone, NMP, DMF, THF, chloroform, pyridine, nitrobenzene and 1,1,2,2-tetrachloroethane at room temperature. The contact angles of polycarbonates were found in the range 64–85°. The wettabilities of polycarbonates increased with increasing mass fraction of bromine atoms. The tensile stress shows that the films become more pliable with increasing fluorine atom content. The homopolycarbonate based on tetrabromobisphenol AF has the highes T g at 206°C. The t.g.a. curves show that T d 10% of polycarbonates was in the range 446–477°C in nitrogen. The LOI homopolycarbonates based on bisphenol A and tetrabromobisphenol AF were found at 25.5 and 93, respectively. The results show that homopolycarbonate and copolycarbonates containing tetrabromobisphenol AF have great thermal stability and flame retardancy.

The effect of ultrasound on the structure and properties of the water-soluble corn hull heteroxylan

Ultrasonic irradiation of a water-soluble corn hull xylan fraction in neutral and alkaline aqueous medium has been found to produce significant changes in its molecular properties. Degradation is first manifested by a decrease in the large molar mass component under generation of polymer chains with about the same size as those of the main molar mass component. The latter is slightly shifted to the lower molar mass region only at stronger irradiation conditions. Ultrasonication of the xylan in neutral aqueous medium at high ultrasound power and/or long irradiation caused no significant changes in its sugar composition, primary structure and viscoelastic properties.

Screening the physical properties of novel Pseudomonas exopolysaccharides by HPSEC with multi-angle light scattering and viscosity detection

The physical properties of three novel acidic exopolysaccharides obtained from P. marginalis types A, B and C, one from P. ‘gingen’, one from P. andropogenis and one from P. fluorescens have been partially characterized. These EPSs were chromatographed on three serially placed SE Shodex OH pak columns covering a molar mass range for pullulans from about 4 × 10 7 to 1 × 10 3. The mobile phase was 0.05 M NaNO 3. Physical measurements were performed on about 30 mg of sample for each EPS. The weight average molar mass of these EPSs ranged from about 0.71 to 2.85 × 10 6, the weight average intrinsic viscosity from 7.15 to 35.3 dl/ g and the radius of gyration from 62 to 123nm. The polydispersities of these EPSs ranged from 1.01 to 1.37. The large molar mass, size and viscosities of these EPSs may indicate that they have potential for use as thickeners, stabilizers, emulsifiers, and gelling agents in the food and non-food industries.

Polymerization of 1-methoxy-1-ethynylcyclohexane by transition metal catalysts

The polymerization of 1-methoxy-1-ethynylcyclohexane (MEC) was carried out by various transition metal catalysts. The catalysts MoCl5, MoCl4, and WCl6 gave a relatively low yield of polymer (≤ 16%). The catalytic activity of Mo-based chloride catalyst was greater than that of W-based chloride catalyst. However, catalyst tungsten carbene complex (I) gave a larger molar mass and higher yield in the presence of a Lewis acid such as AlCl3 than in the absence of a Lewis acid. The activity of the tungsten carbene complex was obviously affected by Lewis acidity. The catalyst PdCl2 was a very effective catalyst for the present polymerization and gave polymers in a high yield. The structure of the resulting poly(MEC) was identified by various instrumental methods as a conjugated polyene structure having an α-methoxycyclohexyl substituent. The poly(MEC)s were mostly light-brown powders and completely soluble in various organic solvents such as tetrahydrofuran (THF), chloroform (CHCl3), ethylacetate, n-butylacetate, dimethylformamide, benzene, xylene, dimethylacetamide, 1,4-dioxane, pyridine, and 1-methyl-2-pyrrolidinone. Thermogravimetric analysis showed that the polymer started to lose mass at 125°C and that maximum decomposition occurred at 418°C. The x-ray diffraction diagram shows that poly(MEC) has an amorphous structure. © 1997 John Wiley & Sons, Inc.