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Search Results: 1 - 10 of 224836 matches for " Marcos L. Dias "
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Extens?o de Cadeia em Poli(Naftalato de Etileno) pelo Fosfito de Trifenila
Dias, Marcos L.;Silva, Alexandre P. F.;
Polímeros , 2001, DOI: 10.1590/S0104-14282001000300008
Abstract: the reactive processing of poly(ethylene naphthalate) (pen) in presence of triphenylphosphite (tpp) was investigated. an internal mixer coupled to a torque rheometer was used to monitor changes of molecular mass and temperature during processing. the torque curves revealed that chain extension reactions took place. during the processing, there is an increase in the molecular weight of the polyester, which reaches a maximum and then decreases due to molecular degradation, accelerated by the presence of chain extention by-products. the intensity of the chain extention reaction increases when tpp content, temperature and shear rate rise. chain extension and degradation rate are slower in pen than in poly(ethylene terephthalate). the presence of low molecular weight by-products of chain extension in pen causes changes in the tg, due to plasticization effects, and increase the crystallization rate.
Extens o de Cadeia em Poli(Naftalato de Etileno) pelo Fosfito de Trifenila
Dias Marcos L.,Silva Alexandre P. F.
Polímeros , 2001,
Abstract: O processamento reativo de poli(naftalato de etileno) (PEN) na presen a de fostito de trifenila (TPP) em um misturador interno acoplado ao re metro de torque foi investigado. O acompanhamento do torque e da temperatura durante o processamento revelou a ocorrência de rea es de extens o de cadeia. A massa molecular do poliéster aumentou com o tempo de processamento, passando por um máximo, após o qual come a a decrescer como resultado de degrada o molecular acelerada pela presen a de subprodutos da extens o de cadeia. A intensidade das rea es de extens o de cadeia aumenta com o aumento do teor de TPP, da temperatura e do cisalhamento. Tanto a extens o de cadeia quanto a degrada o ocorrem mais lentamente para o PEN que para o poli(tereftalato de etileno). A presen a de TPP no material provoca modifica es na Tg, devido a um efeito de plastifica o, e aumenta a velocidade de cristaliza o.
Morphology and Thermal Properties of Core-Shell PVA/PLA Ultrafine Fibers Produced by Coaxial Electrospinning  [PDF]
Raquel P. Gon?alves, Flavia F. F. da Silva, Paulo H. S. Picciani, Marcos L. Dias
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.62022
Abstract: Coaxial electrospinning process was used to produce biodegradable membranes made of coreshell fibers of a poly(lactic acid) (PLA) shell and a poly(vinyl alcohol) (PVA) core. Scanning electron microscopy analyses of these structures showed that the PLA shell can present certain porosity depending on the process condition. FTIR-ATR and contact angle measurements also suggested imprisonment of the PVA core within the PLA shell. This type of structure was also confirmed by means of transmissions electron microscopy. The morphology of these fibers was dependent on the flow rate of both core and shell solutions, and homogeneous and smooth surface was only attained when the flow rate of the external PLA solution was 4 times the flow rate of the internal PVA solution. The increase in the PLA solution flow rate increases the diameter of the core-shell fiber which reaches up to 1.7 μm. Nevertheless, fibers with smaller average diameter could also be produced (200 nm). These core-shell fibers presented improved hydrophilicity as compared with monolithic PLA fibers.
Efeitos estéricos e eletr?nicos de substituintes alquilas em catalisadores titanocênicos solúveis na polimeriza??o sindioespecífica de estireno
Pereira, Brasilio C. A.;Klein, Stanlei I.;Dias, Marcos L.;
Polímeros , 1999, DOI: 10.1590/S0104-14281999000400019
Abstract: titanocenes are known to be soluble, stereospecific catalysts for the polymerisation of prochiral olefins such as styrene. in this work we shall describe the relations between polystyrene cracteristics and the structure of the catalyst precursor, namely those of the family (rcp)2ticl2 (r = h, ethyl, iso-propyl, n-propyl, sec-butyl, n-butyl, iso-amyl e ciclohexyl). all catalysts were found to be active for the production of polystyrene at temperatures above zero degrees centigrade. the syndiotacticity of the polymers were found to be dependent on the side chain at the aromatic rings of the titanocene, and onthe temperature of polymerisation. the relationship between steric and electronic factors within the catalyst precursors and the polymerisation products shall be presented and discussed.
Prepara??o e caracteriza??o de estruturas porosas de poli(3-hidroxibutirato)
Sader, Márcia S.;Ferreira, Marysilvia;Dias, Marcos L.;
Polímeros , 2006, DOI: 10.1590/S0104-14282006000100006
Abstract: three-dimensional polymeric scaffolds have been widely employed as support in tissue engineering to reconstruct damaged or lost tissue. in this study porous structures were obtained using p(3hb) solution with five concentrations of sieved sodium chloride 50, 60, 70, 80 and 90 wt %, with particles size in the range of 75 - 150, 53 - 75 and 38 - 53 μm. thermal properties of the samples were investigated by differential scanning calorimetry and thermo gravimetric analysis, while the morphology was observed by scanning electron microscopy. asymmetric porous structures were formed for salt concentrations of 50, 60 and in some cases 70wt%. additionally, porosity increased as the salt weight fraction was increased and pore diameter increased as the salt particle size increased. x-ray diffraction analysis showed that salt concentration and granulometry did not influence the crystalline characteristics of the porous matrices when compared with the dense polymer film obtained by casting of a solution without salt. the scaffolds promote the spontaneous deposition of a calcium phosphate layer, indicating bioactivity.
Efeitos estéricos e eletr nicos de substituintes alquilas em catalisadores titanocênicos solúveis na polimeriza o sindioespecífica de estireno
Pereira Brasilio C. A.,Klein Stanlei I.,Dias Marcos L.
Polímeros , 1999,
Abstract: Titanocenos s o catalisadores solúveis conhecidos para a polimerisa o estereoespecífica de olefinas pró-quirais como o estireno. Nesse trabalho descrevemos as rela es entre as características do poliestireno e a estrutura do precursor do catalisador, de fato aqueles da família (RCp)2TiCl2 (R = H, etila, iso-propila, n-propila, sec-butila, n-butila, iso-amila e ciclohexila). Todos os catalisadores s o ativos para a produ o de poliestireno acima de zero graus centígrados. A sindiotaticidade dos polímeros s o dependentes da cadeia lateral dos anéis aromáticos do titanoceno e da temperatura da polimeriza o. A rela o entre os fatores estéricos e eletr nicos do precursor do catalisador e os produtos de polimeriza o s o apresentados e discutidos.
Thermal and Crystallization Behavior of PLA/PLLA-Grafting Cellulose Nanocrystal  [PDF]
Erika M. Inácio, Diego H. S. Souza, Marcos L. Dias
Materials Sciences and Applications (MSA) , 2020, DOI: 10.4236/msa.2020.111004
Abstract: PLLA-modified cellulose nanocrystals (CNC) were produced from commercial CNC by tin-catalyzed polymerization of lactide in presence of CNC. FTIR spectroscopy demonstrated that the result of the reaction produced the grafting of PLLA chains onto CNC surface (CNC-g-PLLA). Films of poly(lactic acid) (PLA) and PLA/CNC nanocomposites (with non-modified CNC and CNC-g-PLLA) containing 0.5% and 5% (w/w) of the nanofillers were prepared by casting in chloroform solution and the crystallization behavior and thermal properties investigated. All nano-composites had similar thermal stability when analyzed by TGA analyses under an inert nitrogen atmosphere. Addition of both types of CNC influenced crystallization, the higher crystallization rate being observed for 5% (w/w) CNC. Nanocomposites with 5% (w/w) CNC-g-PLLA had the strain resistance of PLA improved in the rubbery state. PLLA-modification of CNC surface increased the crystallization of PLA in PLA/CNC nanocomposites and improved the rigidity at temperatures above the glass transition, properties which are desirable for hot drinking application.
Adrenoleukodystrophy: case report and aspects relevant to the otorhinolaryngologist
Queiroz, Maria Carolina Souza,Barros, Emilia L. de,Antunes, Marcos L,Garcia, Roberta Ismael Dias
International Archives of Otorhinolaryngology , 2009,
Abstract: Introduction: Adrenoleukodystrophy is a genetic disease with heritage standard bound to X, which consists of an alteration of the metabolism and causes an accumulation of fatty acids of a very large chain (AGCML) associated to demyelinization of axons and adrenal insufficiency. It may initially manifest with alterations of behavior, hearing, vision, speech, writing, gait, and in the more advanced cases, it results in generalized hypertension, loss of cognitive and motor functions and dysphagia. The diagnosis is confirmed by dosing the AGCML's plasmatic levels, findings of the Magnetic Resonance and karyotype. Case Report: We report the case of A.V.F., 5 years old, sent to the otorhinolaryngology service for school and communication difficulties of auditory evaluation. The audiometry confirmed a bilateral moderate hearing loss. Some months after he evolved with progressive loss of vision, worsening of writing and aggressiveness, and was then forwarded to the neuropediatrician with the hypothesis of neurodegenerative disease. Magnetic Resonance was carried out and showed extensive parieto-occipital lesions. His diagnosis was confirmed through karyotype performed by a geneticist with an immediate beginning of the treatment. Approximately 1 year after the beginning of the symptoms, he presented with severe oropharyngeal dysphagia and silent bronchoaspiration diagnosed by the video-deglutogram exam. Final Comments: Today with gastrotomy. So far, there is no therapy defined for adrenoleukodystrophy. The otorhinolaryngologist must know this disease because, as well as in the case described above, he/she is one of the first professionals.
Adrenoleucodistrofia: relato de caso e aspectos relevantes ao otorrinolaringologista
Queiroz, Maria Carolina Souza,Barros, Emilia L. de,Antunes, Marcos L,Garcia, Roberta Ismael Dias
Arquivos Internacionais de Otorrinolaringologia , 2009,
Abstract: Introdu o: A adrenoleucodistrofia é uma doen a genética com padr o de heran a ligado ao X, que consiste numa altera o do metabolismo ocasionando um acúmulo de ácidos graxos de cadeia muito longa (AGCML) associados à desmieliniza o dos ax nios e insuficiência adrenal. Pode manifestar-se inicialmente com altera es de comportamento, da audi o, da vis o, da fala, da escrita, da marcha e nos casos mais avan ados cursa com hipertonia generalizada, perda das fun es cognitivas, motoras e disfagia. O diagnóstico é confirmado dosando-se os níveis plasmáticos dos AGCML, achados na ressonancia magnética e cariótipo. Relato do Caso: Relatamos o caso de A.V.F., 5anos, encaminhado ao servi o de otorrinolaringologia por dificuldades na escola e de comunica o para avalia o auditiva. A audiometria evidenciou uma perda auditiva moderada bilateral. Alguns meses depois evoluiu com perda progressiva da vis o, piora da escrita e agressividade, na ocasi o encaminhado ao neuropediatra com a hipótese de doen a neurodegenerativa. Foi realizada ressonancia evidenciando les es extensas parieto occipitais. Seu diagnóstico foi confirmado através de cariótipo realizado pelo geneticista com início imediato do tratamento. Aproximadamente 1 ano após início dos sintomas apresentou disfagia orofaríngea grave e broncoaspira o silente diagnosticado pelo videodeglutograma. Comentários Finais: Atualmente com gastrostomia. N o existe uma terapia definida até o momento para a adrenoleucodistrofia. Cabe ao otorrinolaringologista conhecer esta doen a pois, assim como no caso acima descrito, é um dos primeiros profissionais a ser consultado, podendo contribuir para o diagnóstico precoce beneficiando o paciente e auxiliando na identifica o dos portadores.
Intercalation compounds involving inorganic layered structures
Anais da Academia Brasileira de Ciências , 2000, DOI: 10.1590/S0001-37652000000100006
Abstract: two-dimensional inorganic networks can shown intracrystalline reactivity, i.e., simple ions, large species as keggin ions, organic species, coordination compounds or organometallics can be incorporated in the interlayer region. the host-guest interaction usually causes changes in their chemical, catalytic, electronic and optical properties. the isolation of materials with interesting properties and making use of soft chemistry routes have given rise the possibility of industrial and technological applications of these compounds. we have been using several synthetic approaches to intercalate porphyrins and phthalocyanines into inorganic materials: smectite clays, layered double hydroxides and layered niobates. the isolated materials have been characterized by elemental and thermal analysis, x-ray diffraction, surface area measurements, scanning electronic microscopy, electronic and resonance raman spectroscopies and epr. the degree of layer stacking and the charge density of the matrices as well their acid-base nature were considered in our studies on the interaction between the macrocycles and inorganic hosts.
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