Characterization of depolymerized residues from extremely low acid hydrolysis (ELA) of sugarcane bagasse cellulose: Effects of degree of polymerization, crystallinity and crystallite size on thermal decomposition

Sugarcane bagasse cellulose was subjected to the extremely low acid (ELA) hydrolysis in 0.07% H2SO4 at 190, 210 and 225 degrees C for various times. The cellulose residues from this process were characterized by TGA, XRD, GPC, FIR and SEM. A kinetic study of thermal decomposition of the residues was also carried out, using the ASTM and Kissinger methods. The thermal studies revealed that residues of cellulose hydrolyzed at 190, 210 and 225 degrees C for 80,40 and 8 min have initial decomposition temperature and activation energy for the main decomposition step similar to those of Avicel PH-101. XRD studies confirmed this finding by showing that these cellulose residues are similar to Avicel in crystallinity index and crystallite size in relation to the 110 and 200 planes. FTIR spectra revealed no significant changes in the cellulose chemical structure and analysis of SEM micrographs demonstrated that the particle size of the cellulose residues hydrolyzed at 190 and 210 degrees C were similar to that of Avicel. (C) 2011 Elsevier B.V. All rights reserved.

Chemical Modifications in Styrene-Butadiene Rubber after Microwave Devulcanization

Microwave devulcanization has been studied as a method for elastomer recycling, which is based on the conversion of the reticulated and infusible structure of thermosetting rubbers in free polymeric chains able to be remolded by thermomechanical processing in recycling operations for the manufacture of other products. Elastomeric wastes are often irregularly discarded in nature, producing serious environmental damage, and their mechanical recycling is still considered a challenge. Thus, the development of alternatives for elastomer recycling is directly related to the actions of sustainable development and economic benefits to companies that pay to discard their wastes. The aim of this work is to evaluate the chemical modifications occurring in styrene butadiene rubber (SBR) after microwave devulcanization. Compounds of SBR were vulcanized in the presence of vulcanization agents and variable amounts of carbon black, and then the rubbers were milled and submitted to microwave treatment. Only the SBR with high carbon black content shows some portion of devulcanized material. However, the rubber with lower content of carbon black which was devulcanized by microwave radiation shows an increase in cross-link density. The microwave treatment also causes cross-link breaks mainly in polysulfidic bonds as well as decomposition of chemical groups containing sulfur attached to the chemical structure of SBR, while. the chemical bonds of higher energy such as monosulfidic bonds remain preserved. The improvement of the microwave method for rubber devulcanization represents a way for viable recycling of thermosetting rubbers.

Fiber Post Cementation Strategies: Effect of Mechanical Cycling on Push-out Bond Strength and Cement Polymerization Stress

Purpose: To evaluate the effect of mechanical cycling and cementation strategies on the push-out bond strength between fiber posts and root dentin and the polymerization stresses produced using three resin cements. Materials and Methods: Eighty bovine mandibular teeth were sectioned to a length of 16 mm, prepared to 12 mm, and embedded in self-curing acrylic resin. The specimens were then distributed into 8 groups (n = 10): Gr1 - Scotchbond Multi Purpose + RelyX ARC; Gr2 - Scotchbond Multi Purpose + RelyX ARC + mechanical cycling; Gr3 - AdheSE + Multilink Automix; Gr4 - AdheSE + Multilink Automix + mechanical cycling; Gr5 - phosphoric acid + RelyX U100 (self-adhesive cement); Gr6 - phosphoric acid+ RelyX U100 + mechanical cycling; Gr7 - RelyX U100; Gr8 - RelyX U100 + mechanical cycling. The values obtained from the push-out bond strength test were submitted to two-way ANOVA and Tukey's test (p = 0.05), while the values obtained from the polymerization stress test were subjected to one-way ANOVA and Tukey's test (alpha = 0.05). Results: Mechanical cycling did not affect the bond strength values (p = 0.236), while cementation strategies affected the push-out bond strength (p < 0.001). Luting with RelyX U100 and Scotch Bond Multi Purpose + RelyX ARC yielded higher push-out bond strength values. The polymerization stress results were affected by the factor "cement" (p = 0.0104): the self-adhesive cement RelyX U100 exhibited the lowest values, RelyX ARC resulted in the highest values, while Multi link Automix presented values statistically similar to the other two cements. Conclusion: The self-adhesive cement appears to be a good alternative for luting fiber posts due to the high push-out bond strengths and lower polymerization stress values.

Steam reforming of ethanol for hydrogen production on Co/CeO²-ZRO² catalysts prepared by polymerization method

Catalysts containing 10%Co supported on CexZr1-xO2 (0 < x < 1) were applied to ethanol steam reforming reactions. The catalysts were characterized by Raman spectroscopy, XANES-H-2 and DRS-UV-Vis. The catalytic tests were conducted at 673, 773 and 873 K, with molar ratios of H2O:ethanol = 3:1. The ethanol conversion and H-2 selectivity were temperature dependent and the association of CeO2 with ZrO2 in the support led to show a low formation of CO, due to the higher mobility of oxygen. (C) 2012 Elsevier B.V. All rights reserved.

Indirect doping of microstructures fabricated by two-photon polymerization with gold nanoparticles

Nanoplasmonics and metamaterials sciences are rapidly growing due to their contributions to photonic devices fabrication with applications ranging from biomedicine to photovoltaic cells. Noble metal nanoparticles incorporated into polymer matrix have great potential for such applications due to their distinctive optical properties. However, methods to indirectly incorporate metal nanoparticles into polymeric microstructures are still on demand. Here we report on the fabrication of two-photon polymerized microstructures doped with gold nanoparticles through an indirect doping process, so they do not interfere in the two-photon polymerization (2PP) process. Such microstructures present a strong emission, arising from gold nanoparticles fluorescence. The microstructures produced are potential candidates for nanoplasmonics and metamaterials devices applications and the nanoparticles production method can be applied in many samples, heated simultaneously, opening the possibility for large scale processes. (C) 2012 Optical Society of America

Reversible polymerization of novel monomers bearing furan and plant oil moieties: a double click exploitation of renewable resources

Monomers based on plant oil derivatives bearing furan heterocycles appended through thiol-ene click chemistry were prepared and, subsequently, polymerized via a second type of click reaction, i. e. the Diels-Alder (DA) polycondensation between furan and maleimide complementary moieties. Two basic approaches were considered for these DA polymerizations, namely (i) the use of monomers with two terminal furan rings in conjunction with bismaleimides (AA + BB systems) and (ii) the use of a protected AB monomer incorporating both furan and maleimide end groups. This study clearly showed that both strategies were successful, albeit with different outcomes, in terms of the nature of the ensuing products. The application of the retro-DA reaction to these polymers confirmed their thermoreversible character, i. e. the clean-cut return to their respective starting monomers, opening the way to original macromolecular materials with interesting applications, like mendability and recyclability.

Emission features of microstructures fabricated by two-photon polymerization containing three organic dyes

Fabrication of microstructures containing active compounds, such as fluorescent dyes and nanoparticles have been exploited in the last few years, aiming at applications from photonics to biology. Here we fabricate, using two-photon polymerization, microstructures containing the fluorescent dyes Stilbene 420, Disodium Fluorescein and Rhodamine B. The produced microstructures, containing dyes at specific sites, present good structural integrity and a broad fluorescence spectrum, from about 350 nm until 700 nm. Such spectrum can be tuned by using different excitation wavelengths and selecting the excitation position in the microstructure. These results are interesting for designing multi-doped structures, presenting tunable and broad fluorescence spectrum. (C)2012 Optical Society of America

Regioregular improvement on the oxidative polymerization of poly-3-octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat-to-tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl3 is a one-pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl3 addition rate and reaction temperature, poly-3-octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat-to-tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Influence of the base and diluent methacrylate monomers on the polymerization stress and its determinants

The aim of this study was to evaluate the effect of the association between bisphenol-A diglycidyl dimethacrylate (BisGMA) or its ethoxylated version (BisEMA) with diluents derived from the ethylene glycol dimethacrylate (EGDMA), with increasing number of ethylene glycol units (1: EGDMA, 2: DEGDMA, 3: TEGDMA, or 4: TETGDMA), or trimethylol propane trimethacrylate (TMPTMA) or 1,10-decanediol dimethacrylate (D3MA) on polymerization stress, volumetric shrinkage, degree of conversion, maximum rate of polymerization (Rpmax), and elastic modulus of experimental composites. BisGMA containing formulations presented lower shrinkage and stress but higher modulus and Rpmax than those containing BisEMA. TMPTMA presented the lowest stress among all diluents, as a result of lower conversion. EGDMA, DEGDMA, TEGDMA, and TETGDMA presented similar polymerization stress which was higher than the stress presented by D3MA and TMPTMA. D3MA presented similar conversion when copolymerized with both base monomers. The other diluents presented higher conversion when associated with BisEMA. EGDMA showed similar shrinkage compared with DEGDMA and higher than the other diluents. The lower conversion achieved by TMPTMA did not jeopardize its elastic modulus, similar to the other diluents. Despite the similar conversion presented by D3MA in comparison with EGDMA and DEGDMA, its lower elastic modulus may limit its use. Rather than proposing new materials, this study provides a systematic evaluation of off the shelf monomers and their effects on stress development, as highlighted by the analysis of conversion, shrinkage and modulus, to aid the optimization of commercially available materials. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

OPTIMIZATION AND CONTROL OF A CONTINUOUS POLYMERIZATION REACTOR

This work studies the optimization and control of a styrene polymerization reactor. The proposed strategy deals with the case where, because of market conditions and equipment deterioration, the optimal operating point of the continuous reactor is modified significantly along the operation time and the control system has to search for this optimum point, besides keeping the reactor system stable at any possible point. The approach considered here consists of three layers: the Real Time Optimization (RTO), the Model Predictive Control (MPC) and a Target Calculation (TC) that coordinates the communication between the two other layers and guarantees the stability of the whole structure. The proposed algorithm is simulated with the phenomenological model of a styrene polymerization reactor, which has been widely used as a benchmark for process control. The complete optimization structure for the styrene process including disturbances rejection is developed. The simulation results show the robustness of the proposed strategy and the capability to deal with disturbances while the economic objective is optimized.

Optimization and control of a continuous polymerization reactor

This work studies the optimization and control of a styrene polymerization reactor. The proposed strategy deals with the case where, because of market conditions and equipment deterioration, the optimal operating point of the continuous reactor is modified significantly along the operation time and the control system has to search for this optimum point, besides keeping the reactor system stable at any possible point. The approach considered here consists of three layers: the Real Time Optimization (RTO), the Model Predictive Control (MPC) and a Target Calculation (TC) that coordinates the communication between the two other layers and guarantees the stability of the whole structure. The proposed algorithm is simulated with the phenomenological model of a styrene polymerization reactor, which has been widely used as a benchmark for process control. The complete optimization structure for the styrene process including disturbances rejection is developed. The simulation results show the robustness of the proposed strategy and the capability to deal with disturbances while the economic objective is optimized.

Nanopartikel durch Strukturfixierung mizellarer Assoziate aus amphiphilen, endgruppenfunktionalisierten Diblockcopolymeren

Nanopartikel durch Strukturfixierung mizellarer Assoziate aus amphiphilen, endgruppenfunktionalisierten Diblockcopolymeren Zwei unterschiedliche Diblockcopolymersysteme mit Molmassen unterhalb von Mw = 10 000 g/mol wurden über anionische Polymerisation synthetisiert. Ein hetero-telecheles a,w-Poly(dimethylsiloxan)-b-Poly(ethylenoxid) (PDMS-PEO) Diblockcopolymer wurde mit einer Methacrylatendgruppe am PDMS und entweder einer Benzyl-, Hydroxy- oder Carboxylatendgruppe am PEO funktionalisiert. Ein Poly(butadien)-b-Poly(ethylenoxid) (PB-PEO) Diblockcopolymer wurde am PEO ebenfalls entweder mit einer Benzyl-, Hydroxy- oder Carboxylatendgruppe funktionalisiert. In selektiven Lösungsmitteln wie Wasser oder Methanol bilden beide Diblockcopolymersysteme supramolekulare Strukturen mit sphärischer, zylindrischer oder toroider Geometrie aus, die mit statischer und dynamischer Lichtstreuung in Lösung und mit Rasterkraftmikroskopie (AFM) und Transmissionselektronenmikroskopie (TEM) auf der Oberfläche untersucht wurden. Durch Zusatz eines Vernetzers und Initiators wurden die selbstassoziierenden Mizellen des PDMS-PEO Diblockcopolymers permanent durch radikalische Polymerisation mit UV-Licht fixiert. Mizellen des PB-PEO Diblockcopolymers wurden über Bestrahlung mit gamma-Strahlen permanent fixiert. Die Untersuchung der resultierenden Nanopartikel beider Diblockcopolymersysteme mit AFM und TEM zeigte, daß diese sogar in nicht selektiven Lösungsmitteln wie Tetrahydrofuran formstabil bleiben.

Kinetische Untersuchungen zur Synthese von Blockcopolymeren mit Methacrylatsegmenten durch neue anionische Polymerisationssysteme

Ein metallfreies Reaktionssystem mit Bis(triphenylphosphoranyliden)ammonium-Kationen als Gegenionen sowie das Additiv Lithium-2-methoxyethoxid wurden auf ihre Eignung zur anionischen Synthese von Blockcopolymeren mit (Meth)acrylatsegmenten bei moderaten Temperaturen im Strömungsrohr-Reaktor untersucht. Das metallfreie System ist zur lebenden Polymerisation von Methacrylaten in THF mit engen Molekulargewichtsverteilungen bei Reaktionszeiten < 1 s bis zu Temperaturen von 0 °C geeignet. In Gegenwart von Metallionen (Li+) findet eine Verlangsamung der Polymerisation unter Verlust der Reaktionskontrolle statt, Lithiumenolate verursachen nun breite, multimodale Molekulargewichtsverteilungen. Eine lebende Polymerisation von Acrylaten ist nicht möglich, massenspektroskopische Untersuchungen der Produkte weisen auf einen komplexen Reaktionsmechanismus mit Abbruch- und Übertragungsreaktionen hin. Die Synthese von Poly(styrol)-block-Poly(1,4-butadien)-block-Poly(methylmethacrylat)-Copolymeren in Toluol ist mit Lithium-2-methoxyethoxid als Additiv für die MMA-Polymerisation bei moderaten Mischtemperaturen (T < 0 °C) im Strömungsrohr-Reaktor möglich, die Effektivität des Wechselschritts von Polybutadien zu PMMA beträgt im Durchschnitt ca. 50 %. Untersuchungen verschiedener Reaktionsparameter, wie z.B. der Endfunktionalisierung des Polybutadiens mit 1,1-Diphenylethylen und der Temperatur während der Verkappung und der MMA-Polymerisation, geben keine eindeutigen Hinweise auf die Ursache dieses Phänomens. MALDI-TOF-Massenspektren des unreagierten Polybutadien Precursors zeigen die Anlagerung von 1-3 Molekülen Methylmethacrylat und keinen Abbruch durch Backbiting, was auf die Ausbildung stabiler Aggregate hindeutet.

5-substituted triazolinyls as novel counter radicals in controlled radical polymerization

The work is devoted to synthesis of new triazolinyl stable radical derivatives with different substituents at the 5-position of the triazolinyl ring. Obtained results showed great influence of these substituents on the stability of the radical. Electron-rich aromatic substituents at this position stabilize the radical while electron-poor aromatics decrease the stability of the triazolinyl. The triazolinyl radicals synthesized were used as additives for kinetic investigations of controlled radical polymerization of styrene and methylmethacrylate (MMA). The studies performed showed that the more stable radicals provide better control for the polymerization of styrene. In the same time certain instability of the radical is required for realization of controlled polymerization of methylmethacrylate. Based on the kinetic investigations controlled radical polymerization of a variety of monomers including 4-vinylpyridine (4-VP), ethylmethacrylate (EMA), 2,2,2-trifluoroethylmethacrylate (FEMA) and n-butylmethacrylate (BMA)was successfully carried out. Polystyrene and polymethylmethacrylate macroinitiators prepared by triazolinyl mediated controlled radical polymerization were efficiently reinitiated in the presence of a variety of monomers leading to the formation of block copolymers. Using this method PS-b-P-4-VP, PMMA-b-PS, PMMA-b-PBMA, PMMA-b-PFEMA, and PMMA-b-Poly-tert-butylacrylate were successfully synthesized. The results obtained during this work showed the efficiency and flexibility of the method allowing preparation of a range of advanced macromolecular structures.

Nanosized polymer carriers for metallocene catalysts in heterogeneous olefin polymerization

Das Ziel der vorgelegten Arbeit war die Synthese von definierten, sphärischen Polystyrolpartikeln im Größenbreichen von Nanometern, die als Träger für die Immobilisierung von Metallocenkatalysatoren verwendet werden sollten. Ein wichtiger Anspruch an das System war dabei die Möglichkeit einer homogene Verteilung des Metallocenes auf dem Träger and eine homogene Fragmentierung des geträgerten Katalysators während der Polymerisation im Polymerprodukt. Für diese Zielsetzung wurden unterschiedliche Polystyrolnanopartikel hergestellt. Die Polystyrolnanopartikel waren mit unterschiedlichen funktionellen Gruppen wie Polyethylenoxid- und Polypropylenoxidketten oder Hydroxygruppen auf der Oberfläche versehen, um den Metallocenkatalysator und den Cokatalysator MAO immobilisieren zu können. In verschiedenen Experimenten wurde der Einfluss dieser Polystyrolnanopartikel als Träger auf die Katalysatoreigenschaften wie Aktivität oder Produktivität und die Eigenschaften des produzierten Polyolefins wie z.B. Molekulargewicht und Morphologie untersucht. Im Vergleich zu den PS- Nanopartikeln wurden außerdem PS-Mikropartikel, Silica und Dendrimere als Träger in der heterogenen Olefinpolymerisation eingesetzt. Von all diesen Trägersystemen wurde das Fragmentierungsverhalten durch konfocale Fluoreszenzmikroskopie untersucht. Aus den erhaltenen Ergebnissen kann geschlossen werden, dass die hergestellten Polystyrolnanopartikel neuartige und leistungsfähige Träger für heterogene Polymerisationsprozesse darstellen. Die hergestellten Polystyrolnanopartikel besaßen eine wohldefinierte sphärische Struktur, die eine homogene Verteilung des immobilisierten Metallocenkatalysators und somit auch eine vollständige Fragmentierung des geträgerten Katalysators im hergestellten Polyolefin ermöglichte. Die Katalysatorsysteme, die aus den PS- Nanopartikeln und dem Metallocenkatalysator zusammengesetzt waren, wurden in verschiedenen Polymerisationen wie der Ethylen- oder Propylenhomopolymersation und der Copolymerisation von Ethen mit α- Olefinen getestet. Die Oberflächen- funktionalisierten PS Nanopartikel immobilisierten den Metallocenkatalysator ausreichend gut, so dass kein „Leachen“ (Ablösen) des Katalysators von der Trägeroberfläche festgestellt werden konnte und deshalb Polymer von sehr guter Morphologie erhalten wurde. Um die Fragmentierung des Katalysators und den inneren Aufbau des Polymers näher untersuchen zu können, wurde die konfocale Fluoreszenzmikroskopie für das PS- Nanopartikelträgersystem angewendet. Durch farbstoffmarkierte Trägerpartikel konnte die Verteilung des fragmentierten Katalysators innerhalb des Polymers sichtbar gemacht und analysiert werden. Dabei wurde festgestellt, dass sich PS- Nanopartikel und auch Dendrimere als Träger ähnlich verhalten wie Ziegler- Natta- Katalysatoren, die auf MgCl2 immobilisiert für die heterogene Olefinpolymerisation verwendet werden. Das Fragmentierungsverhalten der Silica oder PS- Mirkopartikel geträgerten Systeme entsprach dagegen dem schichtweisen Fragmentierungsverhalten wie es bereits von Fink und Mitarbeitern beschrieben wurde.