Measurement Of Molecular Weight Distribution Research Articles

OZONE-BASED ADVANCED OXIDATION PROCESSES IN NUCLEAR LAUNDRY WATER TREATMENT

The efficiency of ozone treatment in the degradation of organic compounds of nuclear laundry water is presented. Ozonation experiments were performed in different combinations of pH, hydrogen peroxide and ultraviolet radiation. The degradation of non-ionic surfactant and other organic compounds was analysed by chemical oxygen demand, total organic carbon, biochemical oxygen demand and the molecular weight distribution measurements. The optimal degradation circumstances were found to be at pH 7 with ozone, UV radiation and hydrogen peroxide addition. The transfer of ozone increased substantially thus resulting in decreased treatment time compared to our previous experiments. The reductions of chemical oxygen demand, total organic carbon and biochemical oxygen demand were about 46%, 32% and 70%, respectively.

Mechanism Involved in the Evolution of Physically Irreversible Fouling in Microfiltration and Ultrafiltration Membranes Used for Drinking Water Treatment

Control of membrane fouling is important for more efficient use of membranes in water treatment. Control of physically irreversible fouling, which is defined as fouling that requires chemical cleaning to be cancelled, is particularly important for reduction of operation cost in a membrane process. In this study, a long-term filtration experiment using three different types of MF and UF membranes was carried out at an existing water purification plant, and the evolution of physically irreversible fouling was investigated. The experimental results demonstrated that the extent of physically irreversible fouling differed significantly depending on the membrane type. Cleaning of the fouled membranes with various chemical reagents demonstrated that organic matter was mainly responsible for physically irreversible fouling. Organic matter that had caused physically irreversible fouling in the long-term operation was desorbed from the fouled membranes and was subjected to Fourier transform infrared and 13C nuclear magnetic resonance analyses. These analyses revealed that carbohydrates were dominant in the membrane foulant regardless of the type of membrane. Based on measurements of molecular weight distribution of organic matter in the feedwater and the permeates from the membranes, a two-step fouling mechanism is proposed to explain the dominance of carbohydrates in the foulant: hydrophobic (humic-like) components with small molecular weight are first adsorbed on the membrane and, consequently, narrow the size of micro-pores of membranes, and then hydrophilic (carbohydrate-like) compounds with larger molecular weight plug the narrowed pores or the hydrophilic compounds are adsorbed onto the membrane surface conditioned by the hydrophobic components.

Desorption and Ionization of Heavy Petroleum Molecules and Measurement of Molecular Weight Distributions

Field desorption (FD) ionization is studied for the measurement of the molecular weight distribution of heavy petroleum, vacuum residua, and asphaltene derived from them. Hydrocarbon polymers, heavy petroleum distillation cuts, and chemical and solubility fractions of heavy petroleums were examined to determine the ionization efficiency. FD showed effective ionization of molecules of a wide molecular weight range (300−5000 Da) with different chemical compositions (saturates versus aromatics) and solubility (maltene versus asphaltene) properties. Electrospray ionization (ESI) was explored and compared with FD. Previous studies had shown that ESI is selective toward the ionization of polar molecules (mostly basic and acidic molecules) while FD is a more universal ionization method. The comparison revealed general agreement between the two techniques. Small variation in the molecular weight distribution of polar and nonpolar molecules was observed. ESI yields lower average molecular weights. The difference i...

Effects of retained natural organic matter (NOM) on NOM rejection and membrane flux decline with nanofiltration and ultrafiltration

Two natural source waters containing natural organic matter (NOM) with different physical and chemical characteristics were dead-end filtered using five types of membranes having different material and geometric properties. In this study retained dissolved organic carbon (DOC) per unit membrane area is introduced as a better parameter compared to permeate volume, time, and delivered DOC to provide a reasonable comparison of NOM rejection and flux-decline trends. Retained DOC/NOM was calculated, which influences NOM concentration polarization at the membrane interface, and transport measurements of NOM rejection and flux decline were made. Molecular weight (MW) distribution measurements (by size exclusion chromatography) were used to calculate the average MW of the NOM. This persuasively demonstrated that the nominal molecular weight cut-off (MWCO) of a membrane is not the unique predictor of rejection characteristics for NOM composites. The charge density of NOM from the source waters was measured to estimate its effects on NOM rejection and flux decline during filtration. The contact angle of the membranes was used to determine hydrophobic interactions between NOM and membrane. All filtration measurements were performed at approximately the same permeate flow rate in order to minimize artifacts from mass transfer at the membrane interface. ESNA having a nominal MWCO of 200 Daltons showed NOM rejection greater than 95% and flux decline lower than 10% under a condition of a retained DOC of 0.5 mg C/cm 2 for the feed source waters. The other membranes having larger membrane pores (nominal MWCOs ranging from 8,000 to 20,000 Daltons) than the ESNA showed NOM rejection ranging from 68% to 86% and flux decline ranging from 5% to 17% at the same retained DOC for the waters.

Production Variance in Purified Carboxymethyl Cellulose (CMC) Manufacture

AbstractThis study investigates the variance in industrial production of carboxymethyl cellulose (CMC). Initially it was thought that the product exhibited excessive quality variations. However careful viscosity and molecular weight distribution measurements on both the raw material and the final product, supplemented with online quality measurements, showed that the product variations were less severe than originally thought. The most probable reason for this unfounded quality concern is due to imperfect routine measurements coupled with a limited reporting of the subsequent offline laboratory analysis. The situation where the routine quality analysis plays as much a role in the uncertainty as the production itself is believed to be of general relevance for the chemical processing industries.

Characterization of polyesters by matrix-assisted laser desorption/ionization and Fourier transform mass spectrometry.

Two homopolyesters, poly(neopentyl glycol-alt-isophthalic acid) and poly(hexanediol-alt-azelaic acid), and two copolyesters, poly(dipropoxylated bisphenol-A-alt-(isophthalic acid-co-adipic acid)) and poly(neopentyl glycol-alt-(adipic acid-co-isophthalic acid)) were analyzed by internal source matrix assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS). The high resolution and high mass accuracy provided by FTMS greatly facilitate the characterization of the polyester and copolyester samples. Isobaric resolution allows the ion abundances of overlapping isotopic envelopes to be assessed. Repeat units were confirmed and end functionality assigned. Single shot mass spectra of the entire polymeric distribution demonstrate that the dynamic range of this internal MALDI source instrument and the analyzer cell exceeds performance of those previously reported for higher field instruments. Corrections of space charge mass shift effects are demonstrated for the analytes using an external calibrant and (subsequent to confirmation of structure) via internal calibration which removes ambiguity due to space charge differences in calibrant and analyte spectra. Capillary gel permeation chromatography was used to prepare low polydispersity samples from a high polydispersity polyester, improving the measurement of molecular weight distribution two-fold while retaining the benefits of high resolution mass spectrometry for elucidation of oligomer identity.

Product property and production rate control of styrene polymerization

Abstract A multivariable multi-rate nonlinear model predictive control (NMPC) strategy is applied to styrene polymerization. The NMPC algorithm incorporates a multi-rate Extended Kalman Filter (EKF) to handle state variable and parameter estimation. A fundamental model is developed for the styrene polymerization CSTR, and control of polymer properties such as number average molecular weight (NAMW) and polydispersity is considered. These properties characterize the final polymer distribution and are strong indicators of the polymer qualities of interest. Production rate control is also demonstrated. Temperature measurements are available frequently while laboratory measurements of concentration and molecular weight distribution are available infrequently with substantial time delays between sampling and analysis. Observability analysis of the augmented system provides guidelines for the design of the augmented disturbance model for use in estimation using the multi-rate EKF. The observability analysis links measurement sets and corresponding observable disturbance models, and shows that measurements of moments of the polymer distribution are essential for good estimation and control. The CSTR is operated at an open-loop unstable steady state. Control simulations are performed under conditions of plant-model structural mismatch and in the presence of parameter uncertainty and disturbances, and the proposed multi-rate NMPC algorithm is shown to provide superior performance compared to linear multi-rate and nonlinear single-rate MPC algorithms. The major contributions of this work are the development of the multi-rate estimator and the measurement design study based on the observability analysis.

Measurement and mathematical modeling of molecular weight and chemical composition distributions of ethylene/-olefin copolymers synthesized with a heterogeneous Ziegler-Natta catalyst

The distributions of molecular weight and chemical composition of two linear low-density poly-ethylene resins synthesized with Ziegler-Natta catalysts were analyzed with several microstructural characterization techniques and the results were used to investigate the nature of the active site types present on the catalyst. Deconvolution of the molecular weight distribution measured by gel permeation chromatography and of the chemical composition distribution measured by either crystallization analysis fractionation or temperature rising elution fractionation or temperature rising elution fractionation leads to consistent results that indicate the presence of multiple active site types on the catalyst. This shows that these fractionation techniques, when combined with adequate mathematical models, are powerful tools to understand the behavior of Ziegler-Natta catalysts and structural properties of the produced resins.

Grafting Kinetics of Vinyl Neodecanoate onto Polybutadiene

The kinetics and mechanism of the bulk free-radical polymerization of vinyl neodecanoate in the presence of polybutadiene are studied in a series of rate and molecular weight distribution measurements over the temperature range 50−90 °C. The polymerization of the vinyl ester is greatly retarded by the presence of polybutadiene. The dependences of the rates and molecular weight distributions on the ratio of monomer to the amount of polybutadiene are quantitatively in accord with a retardative chain transfer mechanism, whereby an alkanoate radical undergoes hydrogen transfer with polybutadiene, leaving an unreactive radical species (probably allylic in character) which cannot propagate and instead undergoes termination with another radical. The data yield Arrhenius parameters for the transfer to polybutadiene as ktr,P = 106.9 dm3 mol-1 s-1 exp(−27.6 kJ mol-1), which, although subject to high uncertainty, are consistent with the rate-determining step being either (a) diffusion to a hindered butadiene unit of the chain end of an alkanoate macroradical or (b) the actual (chemically controlled) hydrogen transfer event, which would then have to have an unusually low activation energy.

Determination of Propagation Rate Coefficient of Free-Radical Polymerization of N-Vinylcarbazole by Pulsed-Laser Polymerization

Pulsed-laser polymerization in conjunction with molecular weight distribution measurement was adopted for determining the propagation rate coefficient kp in the free radical solution polymerization of N-vinylcarbazole (VCZ). A photoinitiator which absorbs up to ca. 410 nm was selected to exclude the excitation of VCZ. We measured the effects of light intensity, pulse frequency and the concentration of VCZ on the rate coefficients. The value kp=4.16×103 L mol−1 s−1 was obtained in benzene at 30°C. The values of kp were well fitted by the Arrhenius equation in the range of 30–70°C. The values evaluated by using the non-linear least-squares fitting for determination of Arrhenius parameters were A=2.20×108 L mol−1 s−1 and EA=27.4 kJ mol−1. We obtained the 95% joint confidence interval for the Arrhenius parameters.

Ageing phenomena of chitosan and chitosan–diclofenac sodium system detected by low-frequency dielectric spectroscopy

The use of natural polymers for design of dosage form has received considerable attention recently, especially from the safety point of view. Among these polymers, chitosan shows very interesting biological, chemical and physical properties which makes it possible to use chitosan for various pharmaceutical applications. Microcrystalline chitosan (MCCh) is a special multifunctional polymeric material existing in the form of either of gelatinous water dispersion or a powder.Thermal ageing of chitosan and chitosan–diclofenac sodium mixture have been studied using low-frequency dielectric measurements. The ageing was carried out by annealing in ambient atmosphere in the temperature range between 25°C and 100°C. The dielectric losses in the aged samples proved to decrease by about one order of magnitude. The additional measurements of molecular weight distribution and infrared absorption were also carried out for better understanding of nature of the ageing phenomena. Partial evacuation of water, cross-linking and improvement of structural order may be suggested to be a result of thermal ageing of the investigated materials.

Influence of Non-Starch Polysaccharides Structure on the Metabolisable Energy of U.K. Wheat Fed to Poultry

With the inclusion of wheat in European poultry diets at 600 g/kg, or more, there is increasing concern that its apparent metabolisable energy (AME) is more variable than would be predicted by conventional analysis. Twelve samples of wheat with a range of AME values (8·34–13·74 MJ/kg dry matter when fed to broiler chicks aged 11–14 d at 750 g/kg diet) were used to investigate the causes of this variability. AME was not correlated with the amount of total water-soluble non-starch polysaccharide (sNSP), soluble arabinoxylan (the major polysaccharide contributing to NSP) or (1→3, 1→4)-β-glucan released from the grain or with the viscosity of aqueous extracts. Surprisingly,in vitroviscosity was negatively related to soluble (r2=0·61) and total (r2=0·82) arabinoxylan. This was thought to be due to the slow, but cumulative, action of endogenous hydrolases in the stored grain. Soluble NSP from each wheat was characterised by measurement of molecular weight distribution and the structural features of arabinoxylan determined from the amount and nature of the oligosaccharides released following treatment with an endo-xylanase. Oligomer molecular weight was determined by matrix-assisted laser desorption/ionisation time of flight mass spectrometry and structure by NMR. Multivariate analysis of the 32 variables measured provided a three-term model able to explain approximately 0·80 of the variation between wheat samples: AME=8·07+11·16(XRAX)+30·67(AX-6)−0·355(sNSP) Two terms (XRAX, the proportion of arabinoxylan resistant to hydrolysis by xylanase and AX-6, the properties of branched six-sugar present in hydrolysates) reflected the degree of branching of arabinoxylan and were positively associated with AME while the third term, the amount of sNSP present, was negatively related.

Optimization of Molecular-Weight Distribution Using Batch-to-Batch Adjustments

A batch-to-batch optimization methodology for producing a desired molecular-weight distribution (MWD) using an approximate model is presented. The method uses fundamental polymer knowledge in order to simplify an otherwise complicated optimization problem and provide significant freedom in manipulated variable selection. A measurement of the MWD at the end of the batch is used to update manipulated variable trajectories for the next batch, thus iterating into a good operating policy. The optimization approach is then extended for use as an on-line control method. To achieve this, it was necessary to address the modeling of highly correlated measurement error typically observed in the MWD measurements. A multivariable statistical process control (MSPC) monitoring scheme is developed for deciding when a new batch optimization is required. The optimizer remains on, but dormant, while the desired MWD is being produced, and it re-optimizes the process quickly if the process changes and a poor quality polymer is produced. The combined MSPC/batch-to-batch optimizer is demonstrated on a simulated semi-batch polystyrene reactor.

低角度レーザー光散乱検出器を用いたサイズ排除クロマトグラフィーによるヒアルロン酸の分子量分布測定

低角度レーザー光散乱検出器 (LALLS) を用いたサイズ排除クロマトグラフィー (SEC/LALLS) により, 市販化粧品用粉末及び医薬品用注射剤中のヒアルロン酸 (HA) の平均分子量 (Mw) と分子量分布を測定した。用いたカラムは網目状に架橋された親水性樹脂からなるTSK gel G6000PWXL (30cm) を4本連結し, これに移動相として0.2M硫酸ナトリウム水溶液を毎分1.0mlで流した。このSEC条件によりHAの保持時間と分子量の間にはSECの原理に見合った適切な関係が得られた。70℃での加熱処理によるHAの低分子化の過程については高分子量になるにつれて分解率が高くなることを認めた。測定した8種の化粧品用HA粉末のMwと粘度平均分子量は良く一致した。HA含有注射剤からの前処理は移動相に希釈するだけであり, この溶液を直接SECに注入した。今回測定した8種の化粧品用HA粉末と4種の医薬品用HA注射剤の中では, 注射剤からのHAが最も低い分子量分散度を示した。SEC/LALLSはHAとこの関連製剤の分子量分布測定に有用であることがわかった。

Further Application of a Procedure for Molecular Weight and Molecular Weight Distribution Measurement of Polydisperse Polymers from Their Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectra

A recently reported off-line procedure to estimate molecular weight (MW) averages and molecular weight distribution (MWD) index, also for polydisperse polymers, directly from their matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra was applied here to poly(bisphenol A-carbonate) (PC), a poly(ether-sulfone) resin (PES), and poly(dimethylphenylene oxide) (PDMPO), all having a wide polydispersity index. The MW and MWD obtained values were compared with those determined by GPC or supplied by makers. A structural characterization of these polymers was also performed by examining their MALDI-TOF mass spectra.

97/00197 The effect of benzoyl peroxide on solvent liquefaction of coal

Gel permeation chromatography was applied to the measurement of molecular weight distribution of the preasphaltenes in liquefied products from Victorian brown coal. When polar solvents such as N-methyl-2-pyrrolidone were used as elution solvents, two major peaks were separately observed at different retention times, reflecting the polarity of their components. By applying a new calibration method to the polar and non-polar components in the preasphaltenes, using a novolak phenol resin and polystyrenes respectively, the molecular weights of both components were estimated to be distributed around 103. According to the present evaluation, a high liquefaction temperature was found to be effective in reducing the polar components in the preasphaltenes.

Investigation of statistical, block and graft copolymerizations using nmr‐sensitive initiators and macroinitiators

Abstract13C‐ and 31P‐NMR studies on polymers and copolymers derived from 13C‐enriched AIBN, 13C‐enriched dibenzyl ketone and diphenyl‐2,4,6‐trimethylbenzoylphosphine oxide (Lucrin TPO) are reported. They provide information about the influence of solvent on the initiation step in copolymerization reactions, the selectivity of diphenylphosphinyl radicals and the chemical behavior of radicals derived from dibenzyl ketone. In addition, NMR, molecular weight and molecular weight distribution measurements on polymers obtained from polymerizations of methyl methacrylate conducted in the presence of stilbene indicate that stilbene or radicals derived from it may be able to moderate MMA polymerizations.

Chromatographic characterization of preasphaltenes in liquefied products from Victorian brown coal

Gel permeation chromatography was applied to the measurement of molecular weight distribution of the preasphaltenes in liquefied products from Victorian brown coal. When polar solvents such as N-methyl-2-pyrrolidone were used as elution solvents, two major peaks were separately observed at different retention times, reflecting the polarity of their components. By applying a new calibration method to the polar and non-polar components in the preasphaltenes, using a novolak phenol resin and polystyrenes respectively, the molecular weights of both components were estimated to be distributed around 10 3. According to the present evaluation, a high liquefaction temperature was found to be effective in reducing the polar components in the preasphaltenes.

Critically evaluated rate coefficients for free‐radical polymerization, 1. Propagation rate coefficient for styrene

AbstractPulsed‐laser polymerization (PLP) in conjugation with molecular weight distribution (MWD) measurement has emerged as the method of choice for determining the propagation rate coefficient kp in free‐radical polymerizations. Detailed guidelines for using this technique (including essential internal consistency checks) and reporting the results therefrom are given by the authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization. The results for PLP‐MWD kp measurements from many laboratories for bulk free‐radical polymerization of styrene at low conversions and ambient pressure are collated, and are in excellent agreement. They are therefore recommended as constituting a benchmark data set, one that is best fitted by (the confidence ellipsoid for the Arrhenius parameters is also given). These benchmark data are also used to evaluate the merits of several other methods for determining kp; it is found that appropriately calibrated electron paramagnetic resonance spectroscopy appears to yield reliable values of kp for styrene.

Time-of-Flight Secondary Ion Mass Spectrometric Measurements of Molecular Weight Distributions for Functionally Terminated Oligomers and Transferred Langmuir-Blodgett-Kuhn Monolayers

We report the first direct measurements of the molecular weight distribution in transferred condensed monolayers of amphiphilic oligomers determined by time-of-flight secondary ion mass spectrometry (TOFSIMS). Two α,ω-functional oligomers of poly(dimethylsiloxane) are investigated, comprising pentylamine and propylcarboxy end groups. Measurements are performed directly on condensed monolayer films transferred to silver-coated substrates using the Langmuir-Blodgett-Kuhn (LBK) technique. These results are compared to the original distributions measured on submonolayer thin films of the original oligomers prepared by spin coating onto silver-coated substrates and to molecular weight determinations provided by end group titration and size exclusion chromatography analyses. Different families of ions are found for the two different thin film preparation methods. A number of tentative assignments are proposed for these masses, based upon consideration of the effects of the LBK film deposition process and the influence of interactions between the end groups and the substrate. The molecular weight distributions for LBK films of both oligomers is found to be narrower and shifted to higher molecular weights than are those for the corresponding spin-coated films. The changes in molecular weight distribution observed are attributed to dissolution of lower molecular weight species into the aqueous subphase during the LBK film deposition process.