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A new approach for the kinetic modelling of non-linear free-radical polymerizations and its application to poly(Vinyl-acetate) bulk and solution manufacturing processes

Dias, Rolando; Costa, Mário Rui
Fonte: 2nd IUPAC-Sponsored International Symposium on Free Radical Polymerization: Kinetics and Mechanisms Publicador: 2nd IUPAC-Sponsored International Symposium on Free Radical Polymerization: Kinetics and Mechanisms
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
66.56%
A New Approach for the Kinetic Modelling of Non-Linear Free-Radical Polymerizations and its Application to Poly(Vinyl-Acetate) Bulk and Solution Manufacturing Processes

Decyl acetate synthesis by enzyme catalysis in sc-CO2

Rebocho, Sílvia F.; Ribeiro, Adriano S.; Ferreira, Olga; Oliveira, Manuela V.; Vidinha, Pedro; Barreiros, Susana; Macedo, Eugénia A.; Loureiro, José M.
Fonte: CHEMPOR Publicador: CHEMPOR
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.68%
The synthesis of decyl acetate, from the transesterification of vinyl acetate with decanol, was studied in a high-pressure experimental set-up, equipped with a variable volume batch reactor, operating isothermally at 35 ºC and 100 bar, using CO2 in supercritical conditions as solvent, and Candida antarctica lipase B (CALB), immobilized on the macroporous resin Lewatit B (Novozym 435®), as catalyst. The enzymatic content was determined for each particle size of the catalyst. It was shown that the smallest particles have a larger specific amount of enzyme, and the results indicate that the enzyme is located in an external shell of the particle, following an “egg-shell” model type, with a thickness of ca. 60 μm (assuming a homogeneous distribution), independent of the particle size. Both external and internal mass transfer resistances were evaluated. External resistances were easily eliminated by stirring and internal diffusional limitations can be considered as negligible. The effect of the feed concentration of substrates on the initial reaction rate was also studied. It was observed that, above a certain concentration of decanol in excess relatively to vinyl acetate, the reaction is inhibited by the alcohol. On the contrary...

Development of a Continuous Emulsion Copolymerization Process in a Tubular Reactor

CARVALHO, Antonio C. S. M.; CHICOMA, Dennis L.; SAYER, Claudia; GIUDICI, Reinaldo
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.56%
This contribution describes the development of a continuous emulsion copolymerization processs for vinyl acetate and n-butyl acrylate in a tubular reactor. Special features of this reactor include the use of oscillatory (pulsed) flow and internals (sieve plates) to prevent polymer fouling and promote good radial mixing, along with a controlled amount of axial mixing. The copolymer system studied (vinyl acetate and butyl acrylate) is strongly prone to composition drift due to very different reactivity ratios. An axially dispersed plug flow model, based on classical free radical copolymerization kinetics, was developed for this process and used successfully to optimize the lateral feeding profile to reduce compositional drift. An energy balance was included in the model equations to predict the effect of temperature variations on the process. The model predictions were validated with experimental data for monomer conversion, copolymer composition, average particle size, and temperature measured along the reactor length.

Modeling Vinyl Acetate and n-Butyl Acrylate Emulsion Copolymerization Process

LEONARDO, Marcelo F.; OLIVEIRA, Eder D.; GIUDICI, Reinaldo
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.56%
This work presents a mathematical model for the vinyl acetate and n-butyl acrylate emulsion copolymerization process in batch reactors. The model is able to explain the effects of simultaneous changes in emulsifier concentration, initiator concentration, monomer-to-water ratio, and monomer feed composition on monomer conversion, copolymer composition and, to lesser extent, average particle size evolution histories. The main features of the system, such as the increase in the rate of polymerization as temperature, emulsifier, and initiator concentrations increase are correctly represented by the model. The model accounts for the basic features of the process and may be useful for practical applications, despite its simplicity and a reduced number of adjustable parameters.

Compatible blends of thermoplastic starch and hydrolyzed ethylene-vinyl acetate copolymers

Da Roz, A. L.; Ferreira, A. M.; Yamaji, F. M.; Carvalho, Antonio José Felix de
Fonte: ELSEVIER SCI LTD; OXFORD Publicador: ELSEVIER SCI LTD; OXFORD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
66.87%
Ethylene-vinyl acetate copolymer (EVA) with 19% of vinyl acetate and its derivatives modified by hydrolysis of 50 and 100% of the initial vinyl acetate groups were used to produce blends with thermoplastic starch (TPS) plasticized with 30 wt% glycerol. The blends were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy. X-ray diffraction, water absorption, stress-strain mechanical tests, dynamic mechanical analysis and thermogravimetric analysis. In contrast to the blends with unmodified EVA. those made with hydrolyzed EVA were compatible, as demonstrated by the brittle fracture surface analysis and the results of thermal and mechanical tests. The mechanical characteristics and water absorption of the TPS were improved even with a small addition (2.5 wt%) of hydrolyzed EVA. The glass transition temperature rose with the degree of hydrolysis of EVA by 40 and 50 degrees, for the EVA with 50 and 100% hydrolysis, respectively. The addition of hydrolyzed EVA proved to be an interesting approach to improving TPS properties, even when very small quantities were used, such as 2.5 wt%. (C) 2012 Elsevier Ltd. All rights reserved.; State of Sao Paulo Research Foundation (FAPESP); State of Sao Paulo Research Foundation (FAPESP); National Council for Scientific and Technological Development (CNPq); National Council for Scientific and Technological Development (CNPq); CAPES PNPD [02880/09]; CAPES PNPD

Análise da viabilidade técnica da utilização do copolímero etileno acetato de vinila (EVA) descartado pela indústria calçadista em misturas asfálticas (processo seco); Analysis of the technical feasibility of the use of the ethylene vinyl acetate copolymer (EVA) discarded for the footwear industry in asphalt mixtures (dry process)

Ildefonso, Jesner Sereni
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 07/02/2007 PT
Relevância na Pesquisa
66.56%
A presente dissertação teve por objetivo analisar o comportamento de misturas asfálticas modificadas, pelo processo seco, com o copolímero etileno acetato de vinila (EVA), resíduo sólido descartado pela indústria calçadista. Em razão das características do EVA, acredita-se que ele possa melhorar as características mecânicas de misturas asfálticas e a resistência ao desgaste. A maioria dos pesquisadores tem direcionado seus esforços em estudos de misturas asfálticas modificadas pelo processo úmido, porém, devido à natureza do resíduo analisado neste trabalho, optou-se pelo processo seco, que demanda menos energia por não necessitar de moagem do material. A pesquisa compreendeu o estudo de amostras de misturas asfálticas não envelhecidas e com envelhecimento de duas e quatro horas em estufa, com moldagem de corpos-de-prova para realização dos ensaios de resistência à tração por compressão diametral estática, módulo de resiliência por compressão diametral, fluência por compressão uniaxial estática e dinâmica, vida de fadiga e desgaste por abrasão (ensaio Cantabro). Os resultados mostram que a utilização deste resíduo aumentou a resistência das misturas à fadiga e ao desgaste de forma significativa...

Desenvolvimento de processo contínuo de copolimerização em emulsão em reator tubular.; Development of a continuous emulsion copolymerization process in a tubular reactor.

Carvalho, Antônio Carlos Sallarés de Mattos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/03/2008 PT
Relevância na Pesquisa
46.56%
Os processos industriais de polimerização em emulsão são normalmente realizados em reatores batelada ou semi batelada ou em tanques agitados contínuos (CSTR). Os reatores contínuos têm a vantagem de terem menor porte e de propiciarem melhor controle de qualidade do produto através da redução de variações de batelada a batelada. Além disso, as oscilações periódicas autosustentadas na conversão de monômero e no tamanho da partícula, que são normalmente observadas em reatores do tipo CSTR, podem ser minimizadas em reatores tubulares mediante o uso de dispositivos de mistura estáticos adequados combinados com escoamento pulsado (oscilatório). O objetivo deste trabalho é apresentar o desenvolvimento de uma copolimerização em emulsão de acetato de vinila e acrilato de butila em uma coluna pulsada com pratos perfurados (CPPP). A fim de aumentar a sua flexibilidade operacional, a coluna é composta de 5 seções, cada uma apresentando controles independentes de alimentação lateral e temperatura. Dependendo da estratégia de alimentação de monômero, pode-se notar uma deriva de composição durante o processo de copolimerização em emulsão do acetato de vinila e acrilato de butila devido às grandes diferenças entre estes monômeros em suas razões de reatividade e nas solubilidades na fase aquosa. Neste caso...

Síntesse de novos estabilizantes poliméricos do tipo poli(álcool vinilico-co-neo decanoato de vinila) para utilização na copolimerização em miniemulsão do acetato de vinila (VAc) com o neo-nonanoato de vinila (VEOVA-9); Synthesis of new poly(vinyl alcohol-co-vinyl neodecanoate) based polymeric stabilizers, to be used in the miniemulsion copolymerizatin of vinyl acetate (VAc) with vinyl neononanoate (VEOVA-9).

Oliveira, Mauricio Pinheiro de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 30/04/2010 PT
Relevância na Pesquisa
66.92%
Devido à importância industrial e tecnológica dos látices estabilizados com poli(álcool vinílico)/PVA e a dificuldade encontrada na etapa de polimerização em emulsão, na presença de monômeros hidrofóbicos e de PVA's com alto grau de hidrólise (>92%), a síntese de novos estabilizantes poliméricos derivados de PVA para utilização em reações de polimerização em emulsão e em miniemulsão se torna muito atraente e desafiadora. O objetivo principal deste trabalho foi sintetizar novos estabilizantes poliméricos do tipo poli(álcool vinílico-co-neodecanoato de vinila)/PVA-VV com alto grau de hidrólise e conseqüentemente com propriedades diferenciadas, para serem utilizados como estabilizantes nas reações de polimerização em emulsão e em miniemulsão do acetato de vinila (VAc) com o neo-nonanoato de vinila (VEOVA-9), visando a obtenção de adesivos com propriedades diferenciadas para colagem de madeiras. Os novos estabilizantes poliméricos foram obtidos em duas etapas: i) copolimerização em solução do VAc com o neo-decanoato de vinila (VEOVA-10); ii) hidrólise alcalina (NaOH/Metanol) do poli(acetato de vinila-coneodecanoato de vinila). As miniemulsões de VAc com VEOVA-9 com diferentes tipos de estabilizantes poliméricos foram preparadas em um homogeneizador de alta pressão do tipo "Manton Gaulin". Foi estudado o efeito dos estabilizantes poliméricos (PVA e PVA-VV) na etapa de emulsificação (diâmetro médio das gotas...

Síntese e caracterização de látices híbridos de poli(acetato de vinila)/montmorilonita - PVAc/MMT para aplicação como adesivos; Synthesis and characterization of poly(vinyl acetate)/montmorillonite - PVAc/MMT hybrid latexes for use as adhesives

Cazotti, Jaime Caetano
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/06/2011 PT
Relevância na Pesquisa
66.73%
Este projeto de mestrado teve como objetivo a obtenção de látices híbridos constituídos de poli(acetato de vinila) (PVAc) e argila montmorilonita (MMT). O homopolímero de acetato de vinila foi sintetizado através da técnica de polimerização em emulsão na presença de diferentes tipos de argila, sendo empregada uma argila sódica (Na-MMT) e três argilas modificadas (o-MMT) com diferentes sais quaternários de amônio. Poli(álcool vinílico) (PVOH) foi utilizado como colóide protetor e persulfato de amônio (APS) como iniciador. Foi estudada a melhor condição para incorporação da argila na matriz polimérica, visando a esfoliação desta nanocarga, resultando desta maneira na formação de nanocompósitos com propriedades diferenciadas. A influência da presença das argilas foi avaliada em termos da velocidade de consumo de monômero, a qual foi acompanhada por gravimetria. Os látices foram caracterizados quanto ao diâmetro médio de partícula e polidispersidade pela técnica de espalhamento de luz (LS). O teor de coágulos do látex foi calculado por análise gravimétrica e a viscosidade analisada em um viscosímetro rotacional. Os filmes nanocompósitos foram caracterizados pelas técnicas de análise dinâmico-mecânica (DMA)...

Polimerização de acetato de vinila em emulsão de modo contínuo em coluna pulsada de pratos perfurados.; Continuous emulsion polymerization of vinyl acetate in pulsed sieve plate column.

Palma, Mauri Sergio Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 24/06/2002 PT
Relevância na Pesquisa
66.77%
Processos industriais de polimerização em emulsão são usualmente realizados em reatores tipo tanque agitado em batelada (ou semi-batelada) ou em contínuo (CSTR). Reatores contínuos tem a vantagem de serem comparativamente de menor porte, e propiciarem melhor controle da qualidade do produto pela redução de variações de batelada a batelada. Reatores tipo CSTR podem exibir oscilações periódicas e autosustentadas de conversão, de tamanho e concentração de partículas. Estas oscilações podem ser minimizadas nos reatores tubulares pulsados devido à diminuição da dispersão axial em relação aos reatores do tipo CSTR. Na presente tese, desenvolveu-se um novo tipo de reator tubular, a Coluna Pulsada de Pratos Perfurados, CPPP, para uso no processo de polimerização contínua do acetato de vinila em emulsão. O reator é operado com escoamento pulsado e contém pratos perfurados como dispositivos internos. Inicialmente foram realizados ensaios de distribuição de tempos de residência, em um reator montado em vidro, com o objetivo de caracterizar o escoamento no reator CPPP quanto ao grau de mistura axial. Os dados foram interpretados usando o modelo de escoamento pistonado com dispersão axial. Valores do coeficiente de dispersão axial foram medidos e correlacionados para diferentes condições de freqüência e amplitude de pulsação...

Training on synthetic ethylene-vinyl acetate bench model allows novice medical students to acquire suture skills

Denadai, Rafael; Saad-Hossne, Rogerio; Oshiiwa, Marie; Bastos, Erika Malheiros
Fonte: Acta Cirúrgica Brasileira Publicador: Acta Cirúrgica Brasileira
Tipo: Artigo de Revista Científica Formato: 271-278
ENG
Relevância na Pesquisa
46.68%
PURPOSE: To assess the acquisition of suture skills by training on ethylene-vinyl acetate bench model in novice medical students.METHODS: Sixteen medical students without previous surgery experience (novices) were randomly divided into two groups. During one hour group A trained sutures on ethylene-vinyl acetate (EVA) bench model with feedback of instructors, while group B (control) received a faculty-directed training based on books and instructional videos. All students underwent a both pre-and post-tests to perform two-and three-dimensional sutures on ox tongue. All recorded performances were evaluated by two blinded evaluators, using the Global Rating Scale.RESULTS: Although both groups have had a better performance (p<0.05) in the post-test when compared with the pre-test, the analysis of post-test showed that group A (EVA) had a better performance (p<0.05) when compared with group B (control).CONCLUSION: The ethylene vinyl acetate bench model allowed the novice students to acquire suture skills faster when compared to the traditional model of teaching.; OBJETIVO: Avaliar a aquisição das habilidades de sutura com o treinamento no modelo de bancada de etileno vinil acetato em acadêmicos de medicina. MÉTODOS: Dezesseis estudantes de medicina iniciantes na prática cirúrgica foram divididos aleatoriamente em dois grupos. Durante uma hora o grupo A treinou diferentes suturas no modelo de bancada de etileno vinil acetato (EVA) com feedback dos instrutores...

Photo-Fries rearrangements of 1-naphthyl (R)-2-phenylpropanoate in poly(vinyl acetate) and ethyl acetate: influence of medium polarity and polymer relaxation on motions of singlet radical pairs

Xu,Jinqi; George,Mathew; Weiss,Richard G.
Fonte: Academia Brasileira de Ciências Publicador: Academia Brasileira de Ciências
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2006 EN
Relevância na Pesquisa
46.75%
Both the regio- and stereo-chemistries of the photoreactions of 1-naphthyl (R)-2-phenylpropanoate have been investigated in poly(vinyl acetate) films in their glassy (at 5ºC) and melted (at 50ºC) states and in ethyl acetate. These results are compared with those from irradiations in polyethylene films and in n-hexane. The regioselectivity of the intermediate 1-naphthoxy/(R)-2-phenylpropanoyl radical pair combinations is much higher in both the melt and glassy states of poly(vinyl acetate) films than that in the melt state of completely amorphous polyethylene films, but the stereoselectivity of intermediate prochiral 1-naphthoxy/1-phenylethyl radical pair combinations is much lower in poly(vinyl acetate). The results emphasize the need to control the ratio between the rates of radical tumbling and translation, as well as the ratio between the rates of in-cage motions and cage-escape, if high stereo- and regio-selectivities of combination products are to be achieved. A mechanistic picture of how the radicals of the intermediate pairs are affected by and interact with the various media is advanced.

Training on synthetic ethylene-vinyl acetate bench model allows novice medical students to acquire suture skills

Denadai,Rafael; Saad-Hossne,Rogério; Oshiiwa,Marie; Bastos,Érika Malheiros
Fonte: Sociedade Brasileira para o Desenvolvimento da Pesquisa em Cirurgia Publicador: Sociedade Brasileira para o Desenvolvimento da Pesquisa em Cirurgia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2012 EN
Relevância na Pesquisa
46.68%
PURPOSE: To assess the acquisition of suture skills by training on ethylene-vinyl acetate bench model in novice medical students. METHODS: Sixteen medical students without previous surgery experience (novices) were randomly divided into two groups. During one hour group A trained sutures on ethylene-vinyl acetate (EVA) bench model with feedback of instructors, while group B (control) received a faculty-directed training based on books and instructional videos. All students underwent a both pre-and post-tests to perform two-and three-dimensional sutures on ox tongue. All recorded performances were evaluated by two blinded evaluators, using the Global Rating Scale. RESULTS: Although both groups have had a better performance (p<0.05) in the post-test when compared with the pre-test, the analysis of post-test showed that group A (EVA) had a better performance (p<0.05) when compared with group B (control). CONCLUSION: The ethylene vinyl acetate bench model allowed the novice students to acquire suture skills faster when compared to the traditional model of teaching.

Kinetic and structural features of furan compounds as inhibitors of the radical polymerization of vinyl acetate

Vega,Rebeca; Rieumont,Jacques
Fonte: Associação Brasileira de Polímeros Publicador: Associação Brasileira de Polímeros
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/1997 EN
Relevância na Pesquisa
66.62%
Some furan compounds bearing a double bond in the side group have been examined as inhibitors of the radical polymerization of vinyl acetate initiated by AIBN in ethyl acetate at 60 ºC. The inhibition effect was found to follow the order: furfurylidenacetone > furylacrolein > furanacrylic acid > furylacrylmorpholinamide as a consequence of the greater stabilization of the radical formed. The site of radical attack can be considered either as the C-5 position of the furan ring or as the double bond of the side group. The compounds taken as models such as 5-methylfuranacrylic acid and furfurylidenbutanal indicate that both positions can participate in the inhibitory process.

Degradation of vinyl acetate by soil, sewage, sludge, and the newly isolated aerobic bacterium V2.

Nieder, M; Sunarko, B; Meyer, O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1990 EN
Relevância na Pesquisa
46.99%
Vinyl acetate is subject to microbial degradation in the environment and by pure cultures. It was hydrolyzed by samples of soil, sludge, and sewage at rates of up to 6.38 and 1 mmol/h per g (dry weight) under aerobic and anaerobic conditions, respectively. Four yeasts and thirteen bacteria that feed aerobically on vinyl acetate were isolated. The pathway of vinyl acetate degradation was studied in bacterium V2. Vinyl acetate was degraded to acetate as follows: vinyl acetate + NAD(P)+----2 acetate + NAD(P)H + H+. The acetate was then converted to acetyl coenzyme A and oxidized through the tricarboxylic acid cycle and the glyoxylate bypass. The key enzyme of the pathway is vinyl acetate esterase, which hydrolyzed the ester to acetate and vinyl alcohol. The latter isomerized spontaneously to acetaldehyde and was then converted to acetate. The acetaldehyde was disproportionated into ethanol and acetate. The enzymes involved in the metabolism of vinyl acetate were studied in extracts. Vinyl acetate esterase (Km = 6.13 mM) was also active with indoxyl acetate (Km = 0.98 mM), providing the basis for a convenient spectrophotometric test. Substrates of aldehyde dehydrogenase were formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde. The enzyme was equally active with NAD+ or NADP+. Alcohol dehydrogenase was active with ethanol (Km = 0.24 mM)...

Influence of Matrix Polarity on the Properties of Ethylene Vinyl Acetate–Carbon Nanofiller Nanocomposites

George, Jinu Jacob; Bhowmick, Anil K.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Publicado em 21/03/2009 EN
Relevância na Pesquisa
46.68%
A series of ethylene vinyl acetate (EVA) nanocomposites using four kinds of EVA with 40, 50, 60, and 70 wt% vinyl acetate (VA) contents and three different carbon-based nanofillers—expanded graphite (EG), multi-walled carbon nanotube (MWCNT), and carbon nanofiber (CNF) have been prepared via solution blending. The influence of the matrix polarity and the nature of nanofillers on the morphology and properties of EVA nanocomposites have been investigated. It is observed that the sample with lowest vinyl acetate content exhibits highest mechanical properties. However, the enhancement in mechanical properties with the incorporation of various nanofillers is the highest for EVA with high VA content. This trend has been followed in both dynamic mechanical properties and thermal conductivity of the nanocomposites. EVA copolymer undergoes a transition from partial to complete amorphousness between 40 and 50 wt% VA content, and this changes the dispersion of the nanofillers. The high VA-containing polymers show more affinity toward fillers due to the large free volume available and allow easy dispersion of nanofillers in the amorphous rubbery phase, as confirmed from the morphological studies. The thermal stability of the nanocomposites is also influenced by the type of nanofiller.

A comparative study of biodegradation of vinyl acetate by environmental strains

Greń, Izabela; Gąszczak, Agnieszka; Guzik, Urszula; Bartelmus, Grażyna; Łabużek, Sylwia
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.87%
Four Gram-negative strains, E3_2001, EC1_2004, EC3_3502 and EC2_3502, previously isolated from soil samples, were subjected to comparative studies in order to select the best vinyl acetate degrader for waste gas treatment. Comparison of biochemical and physiological tests as well as the results of fatty acids analyses were comparable with the results of 16S rRNA gene sequence analyses. The isolated strains were identified as Pseudomonas putida EC3_2001, Pseudomonas putida EC1_2004, Achromobacter xylosoxidans EC3_3502 and Agrobacterium sp. EC2_3502 strains. Two additional strains, Pseudomonas fluorescens PCM 2123 and Stenotrophomonas malthophilia KB2, were used as controls. All described strains were able to use vinyl acetate as the only source of carbon and energy under aerobic as well as oxygen deficiency conditions. Esterase, alcohol dehydrogenase and aldehyde dehydrogenase were involved in vinyl acetate decomposition under aerobic conditions. Shorter degradation times of vinyl acetate were associated with accumulation of acetic acid, acetaldehyde and ethanol as intermediates in the culture fluids of EC3_2001 and KB2 strains. Complete aerobic degradation of vinyl acetate combined with a low increase in biomass was observed for EC3_2001 and EC1_2004 strains. In conclusion...

Enzymes involved in vinyl acetate decomposition by Pseudomonas fluorescens PCM 2123 strain

Szczyrba, Elżbieta; Greń, Izabela; Bartelmus, Grażyna
Fonte: The Institute of Microbiology, Academy of Sciences of the Czech Republic Publicador: The Institute of Microbiology, Academy of Sciences of the Czech Republic
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.63%
Esterases are widely used in food processing industry, but there is little information concerning enzymes involved in decompositions of esters contributing to pollution of environment. Vinyl acetate (an ester of vinyl alcohol and acetic acid) is a representative of volatile organic compounds (VOCs) in decomposition, of which hydrolyses and oxidoreductases are mainly involved. Their activities under periodically changing conditions of environment are essential for the removal of dangerous VOCs. Esterase and alcohol/aldehyde dehydrogenase activities were determined in crude cell extract from Pseudomonas fluorescens PMC 2123 after vinyl acetate induction. All examined enzymes exhibit their highest activity at 30–35 °C and pH 7.0–7.5. Esterase preferably hydrolyzed ester bonds with short fatty chains without plain differences for C2 or C4. Comparison of Km values for alcohol and aldehyde dehydrogenases for acetaldehyde suggested that this metabolite was preferentially oxidized than reduced. Activity of alcohol dehydrogenase reducing acetaldehyde to ethanol suggested that one mechanism of defense against the elevated concentration of toxic acetaldehyde could be its temporary reduction to ethanol. Esterase activity was inhibited by phenylmethanesulfonyl fluoride...

Addition-Fragmentation Kinetics of Fluorodithioformates (F-RAFT) in Styrene, Vinyl Acetate, and Ethylene Polymerization: An Ab Initio Investigation

Coote, Michelle; Izgorodina, Ekaterina; Cavigliasso, German; Roth, Marion; Busch, Markus; Barner-Kowollik, Christopher
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.68%
The kinetics and thermodynamics of the addition-fragmentation equilibrium in fluorodithioformate (S=C(F)SR; F-RAFT) mediated polymerization of styrene and vinyl acetate were investigated via high-level ab initio molecular orbital calculations. The fragmentation efficiencies of a wide range of leaving groups (R = C(CH3)2CN, CH2CN, C(CH3)2Ph, CH(Ph)CH3, CH2Ph, CH(COOCH3)CH3, CH2COOCH3, CH(OCOCH3), CH2-OCOCH3, C(CH3)3, CH2CH3, CH3) were also investigated. The calculations confirm earlier predictions, on the basis of thermodynamic considerations alone, that these agents are likely to function as genuine multipurpose RAFT agents. Thus, stable propagating radicals (as in styrene polymerization) are capable of adding to the RAFT agent with high rate coefficients (1.8 × 106 L mol-1 s-1 at 333.15 K), comparable to those observed with normal dithioesters such as S=C(CH3)SR (3.8 × 106 L mol-1 s-1). Concurrently, unstable propagating radicals (as in vinyl acetate polymerization) are capable of undergoing fragmentation with significantly higher rate coefficients (1.7 × 104 s-1) than that for S=C(CH3)SR (8.4 s-1) and are not expected to be rate retarded. On the basis of an examination of leaving group abilities and known reinitiation rate coefficients...

Substituent Effects in Xanthate-Mediated Polymerization of Vinyl Acetate: Ab Initio Evidence for an Alternative Fragmentation Pathway

Coote, Michelle; Radom, Leo
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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High-level ab initio calculations have been performed for the addition and fragmentation steps in reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl acetate. The RAFT agents considered were a series of xanthates of the form S=C(O-Z′)S-R, where Z′ = methyl, ethyl, iso-propyl, and tert-butyl and R = CH2OCOCH3 and CH3. The results indicate that increasing substitution within the Z′ group stabilizes the RAFT adduct radical, thereby reducing the rate of fragmentation of the S-R bond. For the model vinyl acetate system, there is an additional substantial reduction in rate for the bulkier iso-propyl and tert-butyl substituents (compared with methyl and ethyl) associated with a sterically induced conformational change in the transition structures. However, the calculated S-R fragmentation rate for Z′ = tert-butyl is still not low enough to explain the experimentally observed rate retardation in this system. Instead, the rate retardation appears to be the result of the preferred fragmentation of the O-C bond in the tert-butoxy group of the RAFT adduct. This fragmentation pathway is not normally favored in RAFT polymerization. However, in this particular system, the combination of the vinyl acetate radical being a poor homolytic leaving group...