bluuebunny/crossref_metadata_2025 huggingface dataset:
Design strategies for integrated protein purification processes: challenges, progress and outlook
Authors: Nfor Beckley K , Ahamed Tangir , van Dedem Gijs WK , van der Wielen Luuk AM , van de Sandt Emile JAX , Eppink Michel HM , Ottens Marcel
Published: December 2007

The key to successful and efficient protein purification is the selection of the most appropriate purification techniques and their combination in a logical way to obtain the desired purification in the minimum number of steps. However, the rationalization of protein purification process development is faced with a number of challenges. In this paper, the challenges in protein purification process development are captured. The state‐of‐the‐art in protein purification process synthesis and design is reviewed and the strengths and weaknesses of the current strategies highlighted. Finally, views on the future directions of protein purification process development are presented. Copyright © 2007 Society of Chemical Industry
Ozonation of humic acid in water
Authors: Miao Hengfeng , Tao Wenyi
Published: December 2007

BACKGROUND: Humic acids (HAs) are heterogeneous macromolecules widely dispersed in natural waters, which display significant resistance to biodegradation. Removal of HA by ozone and its related reaction mechanisms are investigated.

RESULTS: Ozonation of HA showed a significant reduction of UV254, Color436 and had the capability of mineralizing the TOC to CO2 and improving the biodegradability. Fourier trandform infrared (FT‐IR) spectra, elemental composition analysis and high performance size exclusion chromatography (HPSEC) revealed that ozonation could not only change the structure characteristics but modify the molecular size distribution of HA. Volatile compounds detected by gas chromatography‐mass spectroscopy (GC‐MS) showed that ozonation brought out 43 different organics, which were identified as mainly: aldehydes, ketones, aromatics, carboxylic acids and alcohols.

CONCLUSION: Ozonation of HA could be elucidated by the followed mechanism: ozonation with its direct and indirect pathway hydroxylated the HA in water, and polyhydroxy HA was further oxidized to bond rupture leading to the change of molecular structure and size distribution of HA, trimming out a series of small molecular volatile compounds. The volatile compounds with electron denoting group could be further oxidized to acids and esters, and even totally mineralized to CO2. Copyright © 2007 Society of Chemical Industry
Role of OH− in the low temperature hydrothermal synthesis of ZnO nanorods
Authors: Song Jaejin , Baek Seonghoon , Lee Jonghyuck , Lim Sangwoo
Published: December 2007

BACKGROUND: ZnO nanorods, which have a wide range of applications, were grown on a Si substrate by low temperature hydrothermal synthesis. An understanding of the reaction mechanism of ZnO nanorods is crucial to control their growth kinetics. Therefore, the effect of OH− concentration in a zinc sulfate solution on the growth of ZnO nanorods was investigated in order to better understand the growth mechanism of ZnO nanorods.

RESULTS: The growth rate and diameter of ZnO nanorods were increased by increasing the pH of the zinc sulfate solution from 10.4 to 10.6, and the highest growth rate, 850 nm h−1, was observed when the nanorods were grown in a solution with a pH of 10.6. However, further increase in the pH of the solution decreased the growth rate, due to the simultaneous dissolution of ZnO nanorods by OH−. The amount of OH− consumed by the dissolution of ZnO and other subreactions was minimized in a solution with a pH of 10.6. The intensity of c‐axis (0001) orientation was the highest in the solution with a pH of 10.6.

CONCLUSION: It is concluded that the concentration of OH− plays a critical role in the hydrothermal synthesis of ZnO nanorods, and that the suppression of OH− subreactions increases the growth rate of ZnO nanorods. From the changes in the length and diameter of ZnO nanorods with synthesis time, it is suggested that the nucleation of ZnO nanocrystals occurs in the first 30 min, from which the growth of nanorods then proceeds. Copyright © 2007 Society of Chemical Industry
Cross‐cultural development of an abridged job insecurity measure
Authors: Lee Cynthia , Bobko Philip , Ashford Susan , Chen Zhen Xiong , Ren Xiaopeng
Published: December 2007

Using four samples from the United States and China, we developed two theoretically based abridged job insecurity (JI) scales to address researcher concerns with the length of the original 57‐item scale. These two scales contained all the components of the scale originally developed and validated by Ashford et al., 1989. Our abridged scale has 37 items (18 items for job features, 16 items for total job, and 3 items for powerlessness). We further developed a bare‐bones scale with only 25 items (10 items for job features, 12 items for total job, and 3 items for powerlessness). Results show that the content and construct validities of both the abridged and the bare‐bones scales are highly similar to the original JI scale. Our results provide support for the use of either the abridged or the bare‐bones JI scales. Copyright © 2007 John Wiley & Sons, Ltd.
Getting to the core of core self‐evaluation: a review and recommendations
Authors: Johnson Russell E. , Rosen Christopher C. , Levy Paul E.
Published: December 2007

The theory of core self‐evaluation (CSE) has provided organizational scholars with a framework for describing disposition‐based effects on work attitudes and behaviors. Although the CSE construct has been useful for predicting various phenomena, there are potential weaknesses concerning how it is conceptualized and used. We review limitations regarding CSE theory, its measurement, and specific traits, and provide recommendations for addressing them. Key recommendations include strengthening the theory underlying CSE, specifying CSE as an aggregate construct with causal indicators, representing CSE as a multidimensional construct rather than a scale score, and incorporating a trait that reflects approach motivation. Theoretical and empirical evidence that relate to our recommendations are presented. Copyright © 2007 John Wiley & Sons, Ltd.
Extraction, separation, and detection methods for phenolic acids and flavonoids
Authors: Stalikas Constantine D.
Published: December 2007

The impetus for developing analytical methods for phenolic compounds in natural products has proved to be multifaceted. Hundreds of publications on the analysis of this category of compounds have appeared over the past two decades. Traditional and more advanced techniques have come to prominence for sample preparation, separation, detection, and identification. This review provides an updated and extensive overview of methods and their applications in natural product matrices and samples of biological origin. In addition, it critically appraises recent developments and trends, and provides selected representative bibliographic examples.
Validation of a capillary zone electrophoresis method for the comparative determination of etoricoxib in pharmaceutical formulations
Authors: Dalmora Sérgio Luiz , da Silva Sangoi Maximiliano , da Silva Lucélia Magalhães , Oliveira Macedo Rui , Barth Thiago
Published: December 2007

A CZE method was developed and validated for the analysis of etoricoxib in pharmaceutical dosage forms, using prilocaine as an internal standard. The CZE method was carried out on a fused‐silica capillary (50 μm id, effective length 40 cm). The BGE consisted of 25 mM tris‐phosphate solution at pH 2.5. The capillary temperature was maintained at 35°C, the applied voltage was 25 kV, the injection was performed using the pressure mode at 50 mbar for 5 s, with detection at 234 nm using a photodiode array detector. The method was linear in the range of 2–150 μg/mL (r2= 0.9999). The specificity and stability‐indicating capability were proven through the degradation studies and showing also that there was no interference of the excipients of the formulation. The accuracy was 99.49% with RSD of 0.66%. The limits of quantitation and detection were 2 and 0.58 μg/mL, respectively. Moreover, method validation demonstrated acceptable results for the precision, sensitivity, and robustness. The proposed method was successfully applied for the quantitative analysis of etoricoxib pharmaceutical formulations, and the results compared to the HPLC and LC‐MS/MS methods, showing nonsignificant difference (p>0.05).
Simultaneous determination of 15 marker constituents in various Radix Astragali preparations by solid‐phase extraction and high‐performance liquid chromatography
Authors: Qi Lian‐Wen , Yu Qing‐Tao , Yi Ling , Ren Mei‐Ting , Wen Xiao‐Dong , Wang Yu‐Xia , Li Ping
Published: December 2007

An improved quality control method was developed to simultaneously determine 15 major constituents (eight flavonoids and seven saponins) in various Radix Astragali preparations, using SPE for pretreatment of samples, HPLC with diode‐array and evaporative light scattering detectors (DAD‐ELSD) for quantification in one run, and HPLC‐ESI‐TOF/MS for definite identification of compounds in preparations. Optimum separations were obtained with a ZORBAX C18 column, using a gradient elution with 0.3% aqueous formic acid and ACN. This established method was fully validated with respect to linearity, precision, repeatability, and accuracy, and was successfully applied to quantify the 15 compounds in 19 commercial samples, including 3 dosage forms, i. e., oral solution, injection, concentrated granule, and its processed products of Radix Astragali. The results demonstrated that many factors might result in significant differences in quality of the final preparations, including crude drugs, pretreatment processes, manufacturing procedure, storage conditions, etc. Then the developed method provided a reasonable and powerful manner to ensure the efficacy, safety, and batch‐to‐batch uniformity of Radix Astragali products by standardizing each procedure, and thus should be proposed as quality control for the clinical use and modernization of herbal preparations.
Solid‐phase microextraction for the determination of benzoylureas in orange juice using liquid chromatography combined with post‐column photochemically induced fluorimetry derivatization and fluorescence detection
Authors: Parrilla Vázquez Piedad , Mughari Ahmed R. , Martínez Galera María
Published: December 2007

A solid‐phase microextraction (SPME) method has been developed for the determination of six benzoylureas (diflubenzuron, triflumuron, hexaflumuron, teflubenzuron, lufenuron, and flufenoxuron) in natural orange juice based on the direct immersion mode of a 60 μm polydimethylsiloxane/divinylbenzene fiber. An orange juice was obtained from blended, homogenized, and diluted ecological natural orange juice samples. An aliquot of 3 mL of a spiked sample was extracted under optimum SPME conditions. The determination of benzoylureas was carried out using HPLC combined with post‐column photochemically induced fluorimetry derivatization and fluorescence detection. The limits of quantification obtained in matrix were within the range of 0.02 to 0.04 mg/kg and these limits are lower than the maximum residue levels established in Spanish regulations for all pesticides in this study. Recoveries in juice samples ranged between 85 and 110% and relative standard deviations between 1.8 and 7.4%.
GC/MS of terpenes in walnut‐tree leaves after accelerated solvent extraction
Authors: Fojtová Jitka , Lojková Lea , Kubáň Vlastimil
Published: December 2007

Terpenes,e. g.(+)‐α‐pinene, (–)‐camphene, (–)‐(‐pinene, myrcene,R‐(+)‐limonene, eucalyptol, (±)‐linalool, (–)‐bornyl acetate, (–)‐trans‐caryophyllene, and α‐humulene were determined in leaves of walnut trees from the Juglandaceae family (walnut tree, royal (J. regiaL.), black (J. nigraL.), and Siebold (J. sieboldiana, var. Cordiformis Lam.) using gas chromatography with mass spectrometric detection. Terpenes were repeatedly (3 cycles, 5 min each) extracted from leaves of walnut trees by accelerated (pressurized) solvent extraction (ASE) 150 bar and 120°C. The efficiency of ASE extraction was superior to that of steam distillation, solvent extraction according to Soxhlet, sonication, and extraction by agitation. Differences in relative concentrations and distribution of terpenes were studied in dependence on the species of walnut tree and on different locations.
The impact of singlet oxygen on lipid oxidation
Authors: Van Dyck Stefaan
Published: December 2007

Oxidation plays a fundamental role in the reduction of the quality of fats, oils and many other principal ingredients in food or animal feed. A significant amount of research data is available on the impact of autoxidation caused by the most abundant and stable form of oxygen: triplet oxygen (3O2). An alternative oxidation process occurs when lipids are exposed to a light source, even at low temperatures. Many molecules are able to absorb energy from light after which this energy is transferred to an oxygen molecule. This process leads to the conversion of the most abundant triplet oxygen into the more reactive singlet oxygen (1O2). Both types of oxygen react very differently with lipids and other nutrients due to the dissimilarity in their fundamental chemical structure. This allows researchers to study the different possible oxidation pathways and consequently to develop potential strategies to delay oxidation for the improvement of shelf life.
Structural Changes of Casein Micelles in a Calcium Gradient Film
Authors: Gebhardt Ronald , Burghammer Manfred , Riekel Christian , Roth Stephan Volkher , Müller‐Buschbaum Peter
Published: December 2007

Calcium gradients are prepared by sequentially filling a micropipette with casein solutions of varying calcium concentration and spreading them on glass slides. The casein film is formed by a solution casting process, which results in a macroscopically rough surface. Microbeam grazing incidence small‐angle X‐ray scattering (µGISAXS) is used to investigate the lateral size distribution of three main components in casein films: casein micelles, casein mini‐micelles, and micellar calcium phosphate. At length scales within the beam size the film surface is flat and detection of size distribution in a macroscopic casein gradient becomes accessible. The model used to analyze the data is based on a set of three log‐normal distributed particle sizes. Increasing calcium concentration causes a decrease in casein micelle diameter while the size of casein mini‐micelles increases and micellar calcium phosphate particles remain unchanged.

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Measurement of Spin Diffusion Coefficients in Glassy Polymers: Failure of a Simple Scaling Law
Authors: Meurer Bernard , Weill Gilbert
Published: December 2007

For a series of polymers, the spin diffusion coefficients D do not scale as predicted from a simple expression based on regularly spaced nuclei. We compare D for PVA and polystyrene with their side group either protonated or deuterated. For polystyrene, D is considerably reduced from 600–800 to 65 nm2 · s−1. For PVA, D is already small for the fully protonated chain and is only slightly reduced from 170 to 130 nm2 · s−1. This indicates that the rapidly rotating methyl group does not contribute appreciably to spin diffusion between neighboring chains and confirms that the mean proton density is not the pertinent parameter to control D.

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Copolyesters Containing Terephthalic and Bio‐Based Furanic Units by Melt‐Polycondensation
Authors: Abid Majdi , Kamoun Wided , Gharbi Rachid El , Fradet Alain
Published: December 2007

5,5′‐Isopropylidene‐bis(ethyl 2‐furoate), a monomer prepared from bio‐based ethyl 2‐furoate, was reacted with dimethyl terephthalate and ethan‐1,2‐diol (ED) by melt polycondensation in order to obtain copolyesters containing both terephthalate and furoate units. The conventional two‐step method involving (i) the formation of a hydroxyethyl‐terminated oligomer by reaction of starting diester mixture with excess ED and (ii) a polycondensation step with elimination of ED was used to obtain high molar mass copolyesters. Copolymers of various compositions were synthesized and characterized by 1H NMR, DSC, and TGA. For all compositions, the degree of randomness, determined by 1H NMR, was close to 1, reflecting a random distribution of terephthalic and furanic ester units in polymer chains. The resulting materials are amorphous polymers (Tg = 70–80 °C) with good thermal stability.

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Macromol. Mater. Eng. 12/2007
Authors: Volz Marissa , Walther Paul , Ziener Ulrich , Landfester Katharina
Published: December 2007

Cover: Thermally instable azoinitiators were embedded within a polymer particle by using the miniemulsion process and afterwards quickly decomposed by thermal treatment below the glass temperature of the polymer. The resulting nitrogen gas overpressure inside the particles leads to a disruption of the polymer particle and a possible sudden release of encapsulated substances. Further details can be found in the article by M. Volz, P. Walther, U. Ziener, and K. Landfester* on page 1237.
A Smart Polymer with Ion‐Induced Negative Shift of the Lower Critical Solution Temperature for Phase Transition
Authors: Mi Peng , Chu Liang‐Yin , Ju Xiao‐Jie , Niu Catherine Hui
Published: December 2007

A novel thermo‐responsive smart copolymer that can selectively respond to specific ions, poly[(N‐isopropylacrylamide)‐co‐(benzo‐15‐crown‐5‐acrylamide)], has been synthesized and characterized. The copolymer exhibits a negative shift of the lower critical solution temperature (LCST) for phase transition that is specifically responsive to certain alkali metal ions. The order of significance of the LCST shift that is induced by ions is K+ > Cs+ > Na+ > Li+. The greater the number of crown ether units in the copolymer, or the larger the ion concentration, the higher the sensitivity and selectivity of the copolymer for cation recognition. Because of its novel ion‐responsive characteristics, the proposed smart copolymer is a promising new candidate material for sensors, actuators, switches, and so on.

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Surface‐Active Gold Nanoparticles with Mixed Polymer Brushes as Surfactants in the Preparation of Polystyrene Colloid Particles
Authors: Liu Li , Zhang Jian , Wu Chenglin , Zhao Hanying
Published: December 2007

Gold nanoparticles with hydrophobic polystyrene (PS) and hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) mixed polymer brushes are prepared. Different morphologies of the nanoparticles can be observed in chloroform (a common solvent for both of the polymers) and water (a precipitant for PS and a good solvent for PPEGMA). The nanoparticles can be used as surfactants in Pickering suspension polymerization. Upon addition of nanoparticles to a mixture of oil and water, the nanoparticles locate at the interface and the size of the oil droplets gets smaller. After polymerization of styrene oil droplets PS colloid particles with gold nanoparticles on the surface can be obtained.

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Modification of Polymer Substrates with Low Surface Free Energy Material by Low‐Temperature Cured Polybenzoxazine
Authors: Liao Chun‐Syong , Wu Jiann‐Shing , Wang Chih‐Feng , Chang Feng‐Chih
Published: December 2007

The B‐ala/AIBN PBZ system has a high extent of ring‐opening of oxazine because phenol‐containing oligomers are formed at the early stage of the curing process. As a result, the B‐ala/AIBN PBZ system possesses a relatively stronger intramolecular hydrogen bonding and lower surface energy than the pure B‐ala system at low temperature curing. In this context, poly(4‐vinyl pyridine), poly(4‐vinyl phenol) thin films and polycarbonate substrates, which lack liquid resistance, possess low surface free energy after modification with B‐ala/AIBN = 5/1 PBZ.

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Acid‐Degradable Core‐Crosslinked Micelles Prepared from Thermosensitive Glycopolymers Synthesized via RAFT Polymerization
Authors: Zhang Ling , Bernard Julien , Davis Thomas P. , Barner‐Kowollik Christopher , Stenzel Martina H.
Published: December 2007

A thermoresponsive block copolymer, namely poly(acryloyl glucosamine)‐block‐poly(N‐isopropylacryamide) (PAGA180‐b‐PNIPAAM350) was simultaneously self‐assembled and crosslinked in aqueous medium via RAFT polymerization at 60 °C to afford core‐crosslinked micelles exhibiting a glycopolymer corona and a PNIPAAM stimuli‐responsive core. An acid‐labile crosslinking agent, 3,9‐divinyl‐2,4,8,10‐tetraoxaspiro[5.5]undecane, was employed to generate thermosensitive and acid‐degradable core‐shell nanoparticles. Stable against degradation at pH = 6 and 8.2, the resulting core crosslinked micelles readily hydrolyzed into well‐defined free block copolymers at lower pH (30 min and 12 h respectively at pH = 2 and 4).

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New Falling Film Reactor for Melt Polycondensation Process
Authors: Xi Zhenghao , Zhao Ling , Liu Zhaoyan
Published: December 2007

Summary: A grid falling film tower (GFFT) has been invented as an ideal polycondensation reactor. In this reactor, polymer melt flows through multi‐layers grids from top to bottom to form falling film owing to gravity without agitation and shear; large gas‐liquid interfacial area is generated; the grids are perpendicular between adjacent layers to ensure film renewal and to achieve uniformly flowing. The fluid flow in this reactor has little back‐mixing and dead zone, which is near to plug flow. All melts are under the state of thin film which avoids the negative effect of hydrostatic head on the mass transfer impetus. Furthermore, the GFFT has wide operation flexibility as well as adjustable configuration parameters to meet different demands. A pilot scale GFFT with the height of 4.0 meters has been applied to polyester polycondensation process. The intrinsic viscosity of polyethylene terephthalate increased from 0.45 dl/g to 0.8–0.9 dl/g successfully. GFFT is supposed to be an universal apparatus for many devolatilization processes.
Recent Advances in Modern Static Devolatilization
Authors: Wäckerlin Manfred , Nising Philip
Published: December 2007

Summary: The present paper deals with state‐of‐the‐art static devolatilization technology for polymer melts. Recent results obtained by CFD‐studies as well as by experimental testing at pilot scale are presented for the devolatilization of technical thermoplasts like polystyrene, poly (methyl methacrylate) and polycarbonate. It is shown that with the correct design of preheater and devolatilization chamber, volatiles like monomers and solvents can be efficiently removed from the polymer melt, both from the economical and technological point of view. As design criteria for the preheater, maldistribution and heat transfer efficiency are explained in detail.
Process Intensification of Emulsion Polymerization in the Continuous Taylor Reactor
Authors: Rüttgers Dana , Negoita Iuliana , Pauer Werner , Moritz Hans‐Ulrich
Published: December 2007

Summary: Process intensification is investigated by the emulsion polymerization of styrene in the continuous Taylor reactor. The result is an increase in space time yield up to a factor 200 in comparison to a semi‐batch polymerization process. This is obtained by a fast emulsion polymerization with a mean residence time, which is reduced to 60 seconds. The article presented the results of the process and the economical aspects of the Taylor reactor plant.
Characterization of Mixing Efficiency in Polymerization Reactors Using Competitive‐Parallel Reactions
Authors: Kunowa Kathrin , Schmidt‐Lehr Sebastian , Pauer Werner , Moritz Hans‐Ulrich , Schwede Christian
Published: December 2007

Summary: In this article particular attention is paid to processes of mixing fluids with different viscosities relevant for polymerization where the reaction is fast and mixing is the limiting factor. Apart from this, mixing fluids with different viscosities is still one of the challenging tasks in industrial chemistry. Therefore, the characterization of mixing elements is another important topic.

Two different multiple chemical reactions, based on the principle of competitive‐parallel reactions, were used and compared to investigate (micro)mixing efficiency in polymerization reactors. The well‐known Villermaux‐Dushman reaction and the third Bourne reaction were applied. The observed product distribution represents the quantity of segregation of the fluid which gives in turn information about the dependency on certain parameters like type and speed of stirrer, dosing period, feed position, and the viscosity of the fluid.

The results from semibatch and continuous stirred tank reactors and two different stirrers, Rushton and INTERMIG® impeller, are discussed.
Model Based Operation of Polymer Processes – What has to be Done?
Authors: Bausa Jens
Published: December 2007

Summary:In the last two decades, simulation technology had a large influence on process industries. Today, modern numerical methods, powerful personal computers and convenient software packages facilitate the solution of complex chemical engineering problems on the basis of rigorous process models at every office workplace. However, although in many cases process models are available from the process design step, model based operation of production plants can only be found rarely. Changing this situation would significantly contribute to the cost effectiveness of many production plants.

This contribution focuses on the model based operation of polymer processes which are for some reasons not perfectly suited for model application: Polymer process models tend to be complex, meaningful online measurements are expensive and not always reliable, many polymer processes are performed in batch instead of steady‐state and for most polymer plants, due to the smaller throughput, the economic impact of model application is much smaller than compared to for instance a steam cracker.

When model based operation is considered, it has to be recognized that there is not one single approach but many different alternatives of which maybe only a single one will lead to a sustainable economical improvement of the process. From many successfully applied concepts for model based plant operation it can be clearly identified that always trying to implement the most complex solution (e.g. nonlinear closed‐loop online optimization) is neither possible nor reasonable but that plant specific tailor‐made solutions are necessary.
Influence of Reaction Pressure on Semibatch Esterification Process of Poly(ethylene terephthalate) Synthesis
Authors: Patel Himanshu , Feix Gunter , Schomäcker Reinhard
Published: December 2007

Summary: Influence of esterification pressure on oligomeric properties was studied by using a semibatch reactor. Esterification model for semibatch process was further improved by considering EG reflux in the column. It was observed that increasing the reaction pressure decreases EG/water ratio in the column while increasing the EG/TPA feed ratio increases EG/water ratio in the column. By controlling the EG reflux in a semibatch reactor, it is possible to generate oligomers with similar oligomeric properties observed at different stages of continuous process.
Estimation of Kinetic Parameters for the Polar‐Modified Anionic Solution Copolymerization of 1,3‐Butadiene and Styrene
Authors: McIntosh W. Carl , Hamann Evemarie , Oertel Ronald , Bartke Michael
Published: December 2007

Summary: The application of the terminal copolymerization model to polar modified anionic initiated 1,3‐butadiene/styrene systems in hydrocarbon solvent requires the determination of twelve kinetic model parameters. These include frequency factors (kxY,∞), activation energies (ExY) and live chain end association numbers (nxY) for all four possible combinations of live chain end termini and free monomer. The individual determination of all twelve parameters requires an enormous numerical effort and a large number of experiments. A method for estimating parameters with a minimum number of kinetic batch experiments in an industrial environment will be demonstrated.
Steady State Simulation of Ethylene Polymerization Using Multiple‐Site Coordination Catalysts
Authors: Valencia Francisco Pérez , Soares Joao B.P.
Published: December 2007

Summary: Simulation models are important tools for the development and optimization of polymerization processes because they can describe catalyst performance and polymer properties as a function of polymerization kinetics and process conditions. As the polyolefin industry moves towards the production of resins with more complex microstructures, these models become essential for process understanding and product design. A simulation model has been developed for the polymerization of ethylene in a process with n reactors working in series. The model can predict raw material conversions and product properties like the molecular weight distribution (MWD) coupled with short chain branching distribution (SCBD), melt index, density and fluff morphology. Model parameters have been obtained from laboratory data. The model predictions are in good agreement with experimental results.
Modeling Polycondensation of Lactic Acid
Authors: Harshe Yogesh M. , Storti Giuseppe , Morbidelli Massimo , Gelosa Simone , Moscatelli Davide
Published: December 2007

Summary: A mathematical model for the polycondensation of lactic acid accounting for water removal by diffusion is developed. The corresponding kinetic parameters are estimated by performing experiments under different sets of reaction conditions in open system. The model results are compared with the experimental ones and, after validating the model, parametric simulations are further carried out to understand the effects of operating conditions such as reaction temperature, catalyst activity, and reaction pressure.
A Novel Production Route for Nylon‐6:. Aspects of Catalysis and Process Development
Authors: Meuldijk J. , van Dijk A. J. M. , Duchateau R. , Koning C. E.
Published: December 2007

Summary: A novel production route for nylon‐6 out of 6‐aminocapronitrile has been investigated. Hydrolysis of 6‐aminocapronitrile using a solid porous ZrO2 catalyst is the key step in this novel route. Nylon‐6 with a number average molecular weight of 10 · 103 g · mol−1 can be produced from the hydrolyzed 6‐aminocapronitrile. The reactor set up for the polycondensation can in broad outline be the same as the continuously operated reactor used for the ε‐caprolactam based production of nylon‐6. For the hydrolysis of 6‐aminocapronitrile a number of parallel batchwise operated loop reactors is recommended. A fixed bed of catalyst particles is part of each recirculation loop. Intraparticle mass transport limitation can be avoided by using catalyst particles made of a shell of active ZrO2 and a massive inert core. An annual production of 50 · 106 kg nylon‐6 demands for 5.3 m3 zirconia.
Ethylene/1‐Butene Copolymerization over Heterogeneous Metallocene Catalyst
Authors: van Grieken Rafael , Martín Carlos , Moreno Jovita , Prieto Oscar , Bravo Jose M.
Published: December 2007

Summary: Nowadays, bimodal polyethylene obtained in a two step cascade process is a matter of intensive research in polyolefin field. In the second stage of this process, a high molecular weight ethylene‐α‐olefin copolymer is formed over the homopolymer produced in the first step. In this work, a study of reaction variables on this second step using an heterogeneous metallocene catalyst was carried out. The effect of reaction temperature (70–85 °C) and comonomer concentration (0–0.32 mol/l) was evaluated. Polymerization results showed that activity increases with temperature and 1‐butene initial concentration. Moreover, higher comonomer concentrations and lower temperatures involve higher short chain branching (SCB). Copolymers characterization indicated that melt temperature and density values have a lineal decrease with the SCB content in the polymer, regardless of the reaction temperature. As well, for every temperature, higher comonomer concentrations do not seem to affect to molecular weight, whereas a decrease of crystallinity was observed, which may explain the increase of catalyst activity.
Fe2+ Catalyzed Synthesis of Radiation Grafted Functional Membranes and Application in Fuel Cells and Ion Recovery
Authors: Schmidt Christian , Schmidt‐Naake Gudrun
Published: December 2007

Summary: 1‐Vinylimidazole is grafted onto Poly(ethylene‐alt‐tetrafluoroethylen (ETFE) by means of pre‐irradiation technique with electron beam doses between 50 and 150 kGy. The degree of grafting is significantly increased to values of up to 115% by addition of 20‐50 mmol/L of an Fe2+ salt that facilitates the decomposition of the peroxide structures within the irradiated films. The obtained mechanically stable and flexible ETFE‐graft‐poly(1‐vinylimidazole) membranes exhibit a homogenous distribution of the graft polymer for degrees of grafting greater than 50 wt.‐% and show thermal stability up to 250 °C. The applicability of these membranes as anhydrous proton conducting material when doped with phosphoric acid and the complexation capability for Cu2+ ions is demonstrated.
Sorption and Swelling of Poly(D,L‐lactic acid) and Poly(lactic‐co‐glycolic acid) in Supercritical CO2
Authors: Pini Ronny , Storti Giuseppe , Mazzotti Marco , Tai Hongyun , Shakesheff Kevin M. , Howdle Steven M.
Published: December 2007

Summary: The equilibrium sorption and swelling behavior in supercritical CO2 of poly(D,L‐lactic acid) and poly(lactic‐co‐glycolic acid) has been studied at a temperature of 35 °C and at pressures up to 200 bar. Sorption was measured through a gravimetric technique and swelling by visualization. From these data, the behavior of the different polymers can be compared. In terms of partial molar volume of CO2 in the polymer matrix, all the polymers exhibit a behavior typical of rubbery systems. The experimental results have been modeled using the Sanchez‐Lacombe equation of state, which is able to represent the actual behavior of the polymer‐CO2 systems with reasonable accuracy.
Dispersion Polymerization of Methyl Methacrylate in Supercritical Carbon Dioxide: Control of Molecular Weight Distribution by Adjusting Particle Surface Area
Authors: Mueller Philipp A. , Storti Giuseppe , Morbidelli Massimo , Mantelis Charalampos A. , Meyer Thierry
Published: December 2007

Summary: Experiments of methyl methacrylate dispersion polymerization are carried out in a reaction calorimeter using PDMS‐mMA as surfactant. Different stabilizer concentrations from 0 to 10 wt% with respect to monomer have been considered in order to control particle morphology. The analysis by scanning electron microscopy reveals a definite decrease of the total particle surface area at decreasing stabilizer concentration. At the same time, the analysis of the polymer microstructure by gel permeation chromatography shows a trend of the average molecular weight towards smaller values. In particular, a second mode at low molecular weights has been observed leading to bimodal molecular weight distributions. The experimental results are compared with simulation results obtained through a detailed kinetic model developed in previous studies.1 The key role of the radical exchange between continuous and dispersed phases is confirmed.
Effect of 1‐Hexene Comonomer on Polyethylene Particle Growth and Kinetic Profiles
Authors: van Grieken Rafael , Carrero Alicia , Suarez Inmaculada , Paredes Beatriz
Published: December 2007

Summary: The polymer growth and the microstructure of the final polymer are greatly affected by mass transfer, especially in the early stages of polymerization. In the present work, the catalytic system (nBuCp)2ZrCl2/MAO immobilized over SiO2‐Al2O3 has been tested in ethylene‐1‐hexene copolymerizations using different amounts of comonomer. The catalytic activity shows a positive comonomer effect up to 1‐hexene concentration of 0.724 mol/L since larger amounts of 1‐hexene lead to a decrease in the activity. Copolymer properties analyzed by 13C NMR, GPC, CRYSTAF and DSC point to the presence of important amorphous regions in the growing polymer chains as the 1‐hexene concentration increases.

In order to study the incorporation of 1‐hexene during ethylene polymerization, several experiments were performed with 0.194 mol/L of 1‐hexene, 5 bar of ethylene pressure and different polymerization times. The incorporation of 1‐hexene decreases slightly at polymerization times above 20 minutes. From cross‐sectioned SEM images it can be concluded that the presence of 1‐hexene helps catalyst fragmentation which could be related with the filter effect proposed by Fink.
Adaption of the Mechanism of Emulsion Polymerization to New Experimental Results
Authors: Tauer Klaus , Hernández Hugo F. , Kozempel Steffen , Lazareva Olga , Nazaran Pantea
Published: December 2007

Summary: New experimental investigations of the 'classical' batch ab‐initio emulsion polymerization of styrene reveal the important role of monomer droplets for the whole process. Monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low molecular weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles (monomer or radicals) strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).
Nucleation in Emulsion Polymerization: Another Step towards Non‐Micellar Nucleation Theory
Authors: Nazaran Pantea , Tauer Klaus
Published: December 2007

Summary: Comprehensive experimental results of the nucleation stage of styrene emulsion polymerization in the absence as well as in the presence of emulsifier at different concentrations are presented. In addition, the influence of initiator type and presence of seed particles are studied. The nucleation mechanism is verified by means of on‐line monitoring of the optical transmission and the conductivity of the aqueous phase. Results prove that micelles do not alter the nucleation mechanism which comprises the initiation of water soluble oligomers in the aqueous phase followed by their aggregation into colloidally stable latex particles. Surfactants assist with nucleation as they lower the activation free energy of particle formation. Contrary, in the presence of seed particles above a critical volume fraction the formation of new particles can be suppressed.
Brownian Dynamics Simulation Studies on Radical Capture in Emulsion Polymerization
Authors: Hernández Hugo F. , Tauer Klaus
Published: December 2007

Summary: A computer simulation method based on the solution of the equations of Brownian motion is used to study the process of radical capture in emulsion polymerization. The effect of the size of the radical was studied, showing that as the radical grows its mobility is reduced (its diffusion coefficient decreases), and this leads to lower collision rates. The distance between the radicals and the surface of the particles at the moment of radical generation was found to be a very important factor in radical capture, with an increase of several orders of magnitude in the collision rate as the radical is generated closer to the particle surface. The effect of process temperature and interfacial barriers to radical capture on the collision rate and on the collision efficiency, defined as the ratio of successful radical captures to the total number of radical‐particle collisions, is also analyzed. In the presence of an energy barrier, multiple collisions are observed, having an important effect on capture kinetics. The results obtained evidence the complexity involved in emulsion polymerization and demonstrates the capability of Brownian Dynamics simulation as a powerful tool for the study and understanding of such complex systems.
Kinetic Study of the Copolymerisation of Ethylene with a Single Site Catalyst in Propane Slurry Polymerisation
Authors: Kröner Sebastian , Eloranta Kirsi , Bergstra Michiel F. , Bartke Michael
Published: December 2007

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1‐hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5‐litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1‐hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1‐hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.
High‐Solids Content Waterborne Polymer‐Clay Nanocomposites
Authors: Diaconu Gabriela , Asua José M. , Paulis Maria , Leiza Jose R.
Published: December 2007

Summary: Waterborne polymer clay nanocomposites (WPCN) were prepared by emulsion and miniemulsion copolymerization of butyl acrylate and methyl methacrylate with enhanced mechanical, thermal and barrier properties for coating applications. Emulsion polymerization was used to synthesize WPCN using pristine Na‐MMT (sodium montmorillonite) and miniemulsion polymerization to prepare the WPCNs when the pristine clay was organically modified and hence its incorporation into the polymerization loci was not guaranteed by the conventional emulsion polymerization technique. Both techniques allowed preparing stable nanocomposite latexes of BA/MMA copolymers with partially exfoliated morphologies as demonstrated by wide X‐ray difraction (WAXD) and transmission electron microscope (TEM) measurements. Furthermore, latexes with solids contents up to 45 wt% and manageable viscosities were prepared for the first time using seeded semibatch emulsion polymerization.
Sorption and Diffusion of Propylene and Ethylene in Heterophasic Polypropylene Copolymers
Authors: Bartke Michael , Kröner Sebastian , Wittebrock Annette , Reichert Karl‐Heinz , Illiopoulus Ilias , Dittrich Christoph Johannes
Published: December 2007

Summary: Sorption experiments of ethylene and propylene in different polypropylene powder samples, both homopolymer and heterophasic copolymers with different rubber content, have been carried out in a high‐pressure magnetic suspension balance at 10 bars pressure and 70 °C. The gross solubilities measured can be well correlated with the rubber content of the polymer samples. Solubility of ethylene and propylene in the rubber phase differ from solubility in the amorphous fraction of the homopolymer, especially the concentration ratio of propylene to ethylene differs significantly between rubber phase and amorphous fraction of the homopolymer. From the slope of monomer uptake, information on kinetics of mass‐transfer can be gained. No significant differences were observed in terms of mass‐transfer for ethylene and propylene. With increasing rubber content, effective diffusion coefficients increased slightly. By combined sorption studies with powder samples and compressed films, information about both effective diffusion coefficients and the effective length scale of diffusion could be gained. It could be shown, that the particle radius is not the characteristic length of diffusion in the studied powder samples. Mass transfer of nearly all samples could be described by a constant diffusion length of 120 to 130 µm, independently on particle size. This indicates that the effective scale of diffusion in polymer particles is in between microparticle and macroparticle scale used in classical particle modeling.
Mathematical Modeling of the Grafting of Maleic Anhydride onto Polypropylene
Authors: Giudici Reinaldo
Published: December 2007

Summary: A kinetic model for the free radical grafting of maleic anhydride (MAH) onto polypropylene (PP) was developed. The model is able to predict the effect of MAH and initiator concentrations on the grafting degree as well as the changes in the polymer molecular weight distribution during the grafting process. Simulation results are validated by comparison with data from different sources, showing that the model is able to represent reasonably the main trends of the experimentally measured variables both in batch (internal mixer, static film) and in continuous processing (twin‐screw extruder), under different conditions. Model predictions are also compared well with a Monte Carlo simulation previously presented in the literature for the same process.
RAFT Polymerization ‐ Investigation of the Initialization Period and Determination of the Transfer Coefficients
Authors: Drache Marco , Schmidt‐Naake Gudrun
Published: December 2007

Summary: The rate of activation of the initial RAFT agent is very important with regard to effective control of the polymerization. The initialization period of Benzyl Dithiobenzoate RAFT mediated bulk polymerization of styrene at 120 °C was investigated at different RAFT agent and initiator concentrations. The concentration of the RAFT agent and the monomer concentration in the initial phase of the RAFT polymerization were determined experimentally by Size Exclusion Chromatography (SEC). We characterized the RAFT initialization following the concept of Rizzardo et al.1,2 by determination of the transfer coefficients. For the determination of the transfer coefficients from the experimental data a Monte Carlo simulation was developed by us.
Molecular Weight Control in Emulsion Polymerization by Catalytic Chain Transfer: A Reaction Engineering Approach
Authors: Smeets Niels M.B. , Meda Ujwal S. , Heuts Johan P.A. , Keurentjes Jos T.F. , van Herk Alex M. , Meuldijk Jan
Published: December 2007

Summary: For the application of catalytic chain transfer in (mini)emulsion polymerization, catalyst partitioning and deactivation are key parameters that govern the actual catalyst concentration at the locus of polymerization and consequently the final molecular weight distribution. A global model, based on the Mayo equation, catalyst partitioning and deactivation was developed. The influence of several reaction parameters on the instantaneous number average molecular weight was quantified.
Analysis of Nitroxide‐Mediated Polymerization of Styrene by Soft‐Ionization‐MS – A Challenging Task
Authors: Dempwolf Wibke , Flakus Silke , Schmidt‐Naake Gudrun
Published: December 2007

Summary: A suitable method to synthesize well defined polymers with different architectures is the application of functionalized alkoxyamines in the controlled radical polymerization. The analysis of such nitroxide capped polymers by MALDI‐ TOF‐MS is complex. Unexpected results of the mass analysis of our polymers lead us to study the influence of the structure of the analyte and the experimental conditions of the measurements in detail. In addition to common nitroxides like TEMPO, TEMPO‐derivates, TIPNO and BIPNO, other alkoxyamines with special structure requirements were synthesized. These alkoxyamines were tested in different MALDI experiments. Supported by a comparison with other methods we postulate a fragmentation mechanism inside the nitroxide‐group which takes place during the MALDI measurement. To the best of our knowledge such a fragmentation of the nitroxide‐group itself during a MALDI‐TOF experiment has not been described before.