Effect Of Average Molecular Weight Research Articles

Dewatering Oil Sands Mature Fine Tailings (MFTs) with Poly(acrylamide-co-diallyldimethylammonium chloride): Effect of Average Molecular Weight and Copolymer Composition

Copolymers of acrylamide and cationic comonomers such as diallyldimethylammonium chloride can effectively dewater solid suspensions containing negatively charged fine particles. A good example of such suspensions is oil sands mature fine tailings (MFTs). However, little is known about the impact of the microstructure of copolymers in dewatering performance. In this study, we used a surface response methodology to systematically assess the impact of chemical composition and average molecular weight of poly(acrylamide-co-diallyldimethylammonium chloride) in dewatering MFTs. We controlled the chemical composition and average molecular weight of the copolymers by manipulating feed monomer/comonomer ratios and initiator concentration. We found both the copolymer composition and the molecular weight averages were statistically significant variables for initial settling rates and supernatant turbidities of flocculated MFTs. However, capillary suction time and resistance to filtration depended only on copolymer c...

Crystallinity of Electrospun and Centrifugal Spun Polycaprolactone Fibers: A Comparative Study

Crystalline properties of semicrystalline polymers are very important parameters that can influence the application area. The internal structure, like the mentioned crystalline properties, of polymers can be influenced by the production technology itself and by changing technology parameters. The present work is devoted to testing of electrospun and centrifugal spun fibrous and nanofibrous materials and compare them to foils and granules made from the same raw polymer. The test setup reveals the structural differences caused by the production technology. Effects of average molecular weight are also exhibited. The applied biodegradable and biocompatible polymer is polycaprolactone (PCL) as it is a widespread material for medical purposes. The crystallinity of PCL has significant effect on rate of degradation that is an important parameter for a biodegradable material and determines the applicability. The results of differential scanning calorimetry (DSC) showed that, at the degree of crystallinity, there is a minor difference between the electrospun and centrifugal spun fibrous materials. However, the significant influence of polymer molecular weight was exhibited. The morphology of the fibrous materials, represented by fiber diameter, also did not demonstrate any connection to final measured crystallinity degree of the tested materials.

Hydroxypropyl Sulfonated Lignin as Dye Dispersant: Effect of Average Molecular Weight

Sulfonated lignin obtained from pulping waste liquor is a nontoxic and renewable polymer that can be used as a dispersant in the dyeing industry. In order to reveal the effect of the lignin dispersant’s molecular weights on disperse dye, three hydroxypropyl sulfonated alkali lignin (HSL) samples with different molecular weights were obtained by controlling the dosage of etherification to cross-link lignin molecules. The molecular weight of HSL can be adjusted from 8,100 to 14,830 Da. More than 80% of phenolic hydroxyl groups of HSL samples were blocked by etherification compared to that of AL and which decrease with increasing molecular weight. The increasing molecular weight of HSL causes a considerable reduction in the staining effect of HSL on fiber since the adsorption amount of HSL on the fiber decreases by reducing the phenolic hydroxyl group. HSL with Mw of 11,020 Da contains 2.10 mmol·g–1 of the sulfonic group and as low as 0.46 mmol·g–1 of the phenolic hydroxyl group (compared to 2.32 mmol·g–1 of...

Viscosity and creep compliance of polyoxymethylene copolymers of various average molecular weights

The effect of average molecular weight (Mw ) of polyoxymethylene (POM) on melt viscosity and solid state creep compliance were investigated. Viscosity follows the power function of Mw. Creep compliance results indicate that time-temperature superposition applies to POM copolymers. Creep compliance in ashort time (0.25 s) is independent of Mw, but in a longer time (10 years) it follows an inverse power law relation with Mw, up to a critical value of Mw = 81 100, where creep compliance becomes independent of Mw. At intermediate time (17 min), similar to short one, no effect on susceptibility to creep compliance was observed. It was also stated that the activation energy is independent of Mw.

Separation and purification of flavonoids from Artemisia annua L.by polyethylene glycol-ammonium sulfate aqueous two-phase system

An aqueous two- phase system of PEG- ( NH4) 2SO4was used to extract flavonoids from the crude ethanol extract of Artemisia annua L..The effects of average molecular weight of PEG, mass percent of ( NH4) 2SO4, mass percent of PEG, pH and temperature on partition coefficient and extraction rate of flavonoids were explored by single factor experiments, then the extraction condition of flavonoids was further optimized by orthogonal method.Then the optimum conditions were obtained as follows: An aqueous two- phase system of 30% PEG600 and 25% ( NH4) 2SO4, pH of 3 and temperature of 45℃.Under the optimal extraction conditions, flavonoids from Artemisia annua L.was mainly distributed in the upper phase with a partition coefficient of 21.86 and the extraction rate of 96.33%.

フェノール樹脂の改質に関する研究 [V] 改質材として用いたN-p-ヒドロキシフェニルマレイミド/n-ブチルアクリレート共重合体の分子量の影響

フェノール樹脂の改質に関する研究 [V] 改質材として用いたN-p-ヒドロキシフェニルマレイミド/n-ブチルアクリレート共重合体の分子量の影響

Recovery of antibiotics by aqueous two-phase partition ?Partitioning behavior of pure acetylspiramycin solution in polyethylene glycol/potassium phosphate aqueous two-phase systems

The effects of average molecular weight of PEG, concentrations of PEG and KH2PO4 and pH on the partition equilibrium of acetylspiramycin in PEG/KH2PO4 aqueous two-phase systems were studied in detail. The partition coefficients of acetylspiramycin in PEG/ KH2PO4 systems were measured at room temperature 25 °C. It was found that acetylspiramycin partitioned unevenly in the aqueous two-phase systems composed of PEG and KH2PO4 and could be purified by this technique. A suitable phase-forming system (pH=6.7, 12w/w% PEG2000, 11w/w% KH2PO4) was found out after partition coefficient (Kp=42) , extraction ratio (η=96%) and recovery ratio(R=98.8%) were investigated comprehensively in this paper.

Glass Transition in Poly(vinylpyrrolidone): Effect of Molecular Weight and Diluents

AbstractAmorphous poly(vinylpyrrolidone) (PVP) varying in molecular weight (MW) (10 000, 24 000, and 40 000) was used to study the effect of molecular weight on the glass transition temperature (Tg). Tg was measured by differential scanning calorimetry (DSC). Blends with several diluents (water, butylamine, glycine, hexanal, xylose, glucose, and lysine) were also analyzed and the effect of blend composition on Tg was evaluated. The effect of average molecular weight and of composition in the blends of PVP‐plasticizer on Tg was well described by previously reported relationships developed for synthetic polymers. The quantitative results obtained can be used for formulation of mixtures with known Tg and for prediction of their behavior in storage.

Effects of Average Molecular Weight and Concentration of Polymer Additive on Friction and Wear

Tribological behavior with oils containing PMAs differing in average molecular weight, Mw, is examined in sliding concentrated contacts. At low loads, low PMA Mw or higher concentrations of PMA have a beneficial effect on wear, but at high loads are detrimental. The beneficial effect is attributed to EHD film formation. The most important parameter is the number of PMA molecules per unit oil volume. The prowear action can be explained by the fact that PMA molecules may accumulate in the inlet region of the contact. The polymer accumulation may block the base oil entering the contact leading to oil starvation which in turn leads to severe contacts and increases in wear. This anamalous behavior may result from the competition between the prowear action and oil film formation.

Phase Equilibria of Quasi-Ternary Systems Consisting of Multicomponent Polymers in a Binary Solvent Mixture III. Effects of Average Molecular Weight and Molecular Weight Distribution of the Original Polymer

The effects of average molecular weight and molecular weight distribution MWD of the original polymer on the phase equilibrium of quasi-ternary systems consisting of multicomponent polymers, solvent 1 and solvent 2 were studied by computer experiments. For this purpose, polymers having strict monodispersity, Poisson (the weight-average molar volume ratio of the polymer to the solvents, Xw=300), Schulz–Zimm (Xw=150—6000, the ratio of the Xw to number-average molar volume ratio of the polymer to the solvents, Xw/Xn=1.03—5.0), and Wesslau (Xw=300, Xw/Xn=2.0—8.0) type molecular weight distributions were utilized. A small, but significant difference was observed for coexistence curves and other characteristic parameters between strictly monodisperse polymer and the Schulz–Zimm polymer (Xw/Xn=1.03). As Xw of the original polymer, Xwo, decreases, the partition coefficient σ, phase volume ratio R, and the polymer volume fraction in a polymer-rich phase vp(2) increases, and the MWD of the polymers in both phases becomes sharp. As Xw/Xn of the original polymer (Xwo/Xwo) decreases, σ, R, and vp(2) increase for a small relative amount of polymer in a polymer-rich phase ρp, but in larger ρp region, σ, R, and vp(2) decrease with Xwo/Xwo.

The effect of molecular weight in the crystallization kinetics of glassy nylon 6

AbstractCrystallization of glassy nylon 6 has been investigated with differential scanning calorimetry and wide angle X‐ray diffraction in order to determine the effect of average molecular weight. Samples were prepared by quenching molten films between platens: chilled with liquid nitrogen. These films had number average molecular weights ranging from 10,000 to 42,000 and had polydispersity indices ranging from 2.0 to 3.1. Crystallization kinetics at large undercoolings were measured in terms of the systematic dependence of conversion half time, Avrami exponent and heat of crystallization. Number average molecular weight was observed to influence crystallization rate at large undercoolings through its effect on glass transition temperature. At intermediate undercoolings, molecular weight affected crystallization rate through terms other than the glass transition temperature. In addition, a dependence on the degree of order of the macromolecules, both prior to and after crystallization, was observed.

Effect of average molecular weight of the original polymer on the separation characteristics in successive solutional fractionation

AbstractWhen solutions of a polymer with a molecular weight distribution (MWD) having a great variety of the average molecular weights are solutionally fractionated, the effect of the average molecular weight on the phase separation features can be described by means of a hypothetical calculation technique. The Flory‐Huggins theory is employed as a basic principle for the simulation. The partition coefficient, σ, as well as the volume ratio of the polymer‐lean phase to the polymer‐rich phase, R, decrease with an increase in the average molecular weight of the original polymer under the same operating conditions, i.e., initial concentration, v, the concentration dependence of the polymer/solvent interaction parameter, p, and the amount of fraction, ϱ. The value of standard deviation, σ′, of MWD in the fraction is predominantly influenced by σ, irrespective of the average molecular weight and of MWD type in the original polymer.The fractions obtained by successive solutional fractionation (SSF) are approximately symmetric with respect to the peak and their MWD in the fractions, obtained under the same operating conditions, become broader with increasing weight‐average degree of polymerization X̄ of the original polymer. Very sharp fractions can be separated by SSF even if X̄ is varied over a tenfold range. The superiority of SSF over successive precipitational fractionation (SPF) is very apparent for large X̄ polymers.

Effect of average molecular weight of the original polymer on phase separation characteristics of multicomponent polymer/single solvent system

AbstractWhen solutions of a polymer with a molecular weight distribution (MWD) having a great variety of the average molecular weights are precipitationally fractionated, the effect of the average molecular weight on the phase separation features can be discussed by means of a hypothetical calculation technique.The FLORY‐HUGGINS‐FUJISHIRO theory was employed as a basic tenet for the simulation. The partition coefficient, σ, as well as the volume ratio of the polymer‐lean phase to the polymer‐rich phase, R, decrease with an increase in the average molecular weight of the original polymer under the same operating conditions, including initial concentration, vpo, the concentration dependence of the polymer/solvent interaction parameter, p, and the amount of fraction, p. The standard deviation of the fraction, σ', (Eq. (3)), for a given p reveals a maximum at a specific vpo. In the cases where the original polymers differ in the average molecular weight, but have the same X̄w/X̄n and where the original polymers have the same σ', the fractionation efficiency, defined by \documentclass{article}\pagestyle{empty}\begin{document}$ (\overline X _w /\overline X _n )/(\overline X _w^0 /\overline X _n^0 ) $\end{document}, is lowered with a decrease in the average molecular weight (suffix zero means the original polymer), i.e., the molecular weight distribution of the fractions, obtained under the same operating conditions, becomes broader. The average molecular weight of the original polymer affects insignificantly the characteristics, but the accuracy of estimating the MWD of the original polymer becomes inferior.