Orientador: Newton Dias Filho / Resumo: Pensando na sustentabilidade, a introdução de fibras naturais em substituição às sintéticas no reforço de matrizes poliméricas, faz-se necessária entre outras coisas devido à preservação do meio ambiente, redução de custos, sem que comprometa a qualidade final do material. Esse projeto tem o objetivo de obter as características mecânicas e térmicas de materiais compósitos a base de resina epoxídica curada DGEBA/TETA com a adição de porcentagens específicas de fibras de buriti. A fibra escolhida foi o buriti, pela abundância no Mato Grosso do Sul, buscando um desenvolvimento sócio econômico para a região e a matriz escolhida foi a epóxi DGEBA/TETA por ser a resina mais utilizada no mundo. Foram utilizadas fibras com diâmetro de 0,17mm e comprimento de 30mm em porcentagens em massa de 1%,5%,10%,15% e 17,6% do total do compósito. A caracterização mecânica foi realizada através de ensaios de tração. Após a ruptura dos corpos de prova foi verificado com uso da Microscopia Eletrônica de Varredura (MEV),a formação de microvazios através dos ensaios de Termogravimetria (TGA) e Calorimetria Diferencial de Varredura (DSC) foram verificadas a degradação e temperatura de transição vítrea (Tg) dos compósitos. O compósito com a adição de 5% em massa de fibras apresentou um aumento de 11,98% (60,12 para 67,32 MPa) no limite de resistência a tração (LRT) e de 8,21% no módulo de elasticidade (E) (901,06 para 977,82 Mpa) em relação a resina pura, acima de 5% as propriedades permaneceram consta... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Thinking about sustainability, the introduction of natural fibers instead of synthetic fibers in the reinforcement of polymer matrices, is necessary among other things due to the preservation of the environment, cost reduction without compromising the final quality of the material. This project aims to obtain the mechanical and thermal characteristics of composite materials based on cured DGEBA / TETA epoxy resin with the addition of specific percentages of buriti fibers. The fiber was buriti, due to the abundance in Mato Grosso do Sul, seeking a socioeconomic development for the region and the chosen matrix was the epoxy DGEBA / TETA as the most used resin in the world. Fibers with a diameter of 0.17mm and a length of 30mm were used in mass percentages of 1%, 5%, 10%, 15% and 17,6% of the total composite. The mechanical characterization was performed through tensile tests. After the rupture of the specimens was verified with the use of Scanning Electron Microscopy (SEM), the microgravity formation through the Thermogravimetry (TGA) and Differential Scanning Calorimetry (DSC) tests showed the degradation and glass transition temperature ( Tg) of the composites. The composite with the addition of 5% by mass of fibers presented an increase of 11.98% (60.12 to 67.32 MPa) at the tensile strength limit (LRT) and 8.21% in the modulus of elasticity ( E) (901.06 to 977.82 MPa) relative to pure resin, above 5% the properties remained constant. However, the Limit of Resistance to crack... (Complete abstract click electronic access below) / Mestre

Lignin, the second most abundant biopolymer on earth, is potentially a replaceable source for bulky fuels and chemical feedstocks. There have been numerous reports on methods for the oxidative cleavage of β-O-4 linkages but relatively few reports of how those methods affect other linkages that are present in lignin. We investigated how the β-1 and β-5 linkages respond under oxidative conditions proposed for lignin deconstruction based on their effect on β-O-4 linkages. Mechanochemical treatment of lignin can greatly improve the yield of monomer products and we applied a mechanochemical approach, using powerful ring-and-puck milling to promote lignin degradation. Along with similar production of monomers in a much shorter period than what we observed in previous ball-milling process, much more unexpected reactions were taking place during the current mechanochemical process. Lignin is a promising feedstock for epoxy resins since lignin-derived aromatic monomers usually bear hydroxyl and carboxyl groups. We are working on utilizing these mono-aromatic compounds and highly-functionalized-lignin as precursors for preparation of epoxy thermosets. We are interested in investigating the properties of thermosets by utilizing the actual isolated monomer streams from raw lignin. We expect to observe attractive thermal and mechanical properties from these lignin-derived epoxy thermosets compare to that of the commercialized but currently limited-used BPA-based epoxy resins.

<p>U ovoj doktorskoj disertaciji je ispitan uticaj montmorilonita i<br />termoplastičnih segmentiranih poliuretana na kinetiku reakcija<br />umrežavanja, strukturu i svojstva funkcionalnih hibridnih<br />materijala na osnovu epoksidnih smola. Pripremljene su dve<br />serije uzoraka hibridnih materijala: prva na osnovu epoksidne<br />smole sa različitim sadržajem organski modifikovanog<br />montmorilonita (0, 1, 3, 5 i 10 mas.%) umrežene sa<br />umreživačem Jeffamine D-230; druga serija je sintetisana na<br />osnovu epoksidne smole, sa različitim sadržajem (10, 15 i 20<br />mas.%) termoplastičnog poliuretanskog elastomera sa<br />različitim sadržajem tvrdih segmenata (20, 25 i 30 mas.%)<br />sintetisanih na osnovu alifatičnog polikarbonatnog diola i<br />heksametilendiizocijanata i produživača lanca butandiola, kao<br />i katalizatora dibutiltin dilaurata; kao i bez dodatog elastomera<br />umrežene sa diaminom Jeffamine D-2000. Umrežavanje<br />reaktivnih sistema sa projektovanim sirovinskim sastavom je<br />praćeno diferencijalnom skenirajućom kalorimetrijom (DSC).<br />Modeli izokonverzije primenjeni su da se ustanovi da li<br />dodatak punila utiče na reakciju umrežavanja hibridnih<br />materijala. Sintetisani materijali su analizirani dinamičkomehaničkom<br />analizom (DMA), mikroskopijom atomskih sila<br />(AFM), kao i TG-DSC i TG-MS metodama i određena su<br />mehanička svojstva (zatezna čvrstoća, prekidno izduženje i<br />tvrdoća po &Scaron;oru A). Epoksidni materijal sa 10 mas.% organski<br />modifikovanog montmorilonita ima značajno niže vrednosti<br />energija aktivacije za definisane stepene reagovanja, čime je<br />potvrđen katalitički efekat gline sa slojevitom strukturom kada<br />je prisutna u reakcionoj sme&scaron;i u dovoljnoj količini. Uticaj<br />otežane difuzije pri kraju reakcije je izraženiji u prisustvu<br />montmorilonita, čime je pokazano da njegovo prisustvo utiče<br />na ceo mehanizam umrežavanja. Utvrđeno je da na vrednosti<br />G&#39;, pored udela montmorilonita, utiče i stepen dispergovanja<br />čestica unutar polimerne matrice. Zaključeno je da dodatak<br />punila do 3 mas. % utiče povoljno na ispitana mehanička<br />svojstva, dok pri sadržaju od 5 i 10 mas. % dolazi do<br />aglomeracije čestica punila, &scaron;to negativno utiče na ispitana<br />svojstva, osim tvrdoće, koja se povećava linearno sa dodatkom<br />punila montmorilonita. Na osnovu rezultata TG analize<br />zaključeno je da je sa porastom udela montmorilonita u<br />epoksidnoj matrici termička stabilnost uzoraka ispitivanih u<br />atmosferi vazduha neznatno pobolj&scaron;ana, dok u inertnoj<br />atmosferi nema uticaja na termičku stabilnost, niti na<br />mehanizam raspada hibridnih materijala na osnovu epoksidnih<br />smola sa različitim udelima montmorilonita. Kod sistema kod<br />kojih je dodavan termoplastični poliuretanski elastomer,<br />zaključeno je da pri većem sadržaju segmentiranih poliuretana<br />u epoksidnoj matrici (10 i 15 mas.%) proces umrežavanja<br />započinje na nižim temperaturama i maksimalna brzina se<br />ostvaruje na nižim temperaturama, a najveća vrednost<br />promena ukupne entalpije reakcije umrežavanja je određena za<br />hibridni materijal sa poliuretanom koji u svojoj strukturi ima<br />30 mas.% tvrdih segmenata. Zatezna čvrstoća hibridnih<br />materijala raste sa porastom udela tvrdih segmenata u strukturi<br />poliuretana, kao i sa porastom masenog udela poliuretanskog<br />elastomera u epoksidnoj matrici. Dodatkom termoplastičnih<br />segmentiranih poliuretana značajno je povećano prekidno<br />izduženje epoksidnih smola. Sa porastom udela tvrdih<br />segmenata kod poliuretana dodatih u istom masenom procentu<br />u epoksidnu matricu, tvrdoća raste. Ustanovljeno je da na<br />konačna svojstva hibridnih materijala utiče izbor polaznih<br />komponenti, način ume&scaron;avanja punila u matricu i uslovi pri<br />kojima se vr&scaron;i umrežavanje. Zaključeno je da je dobro<br />poznavanje kinetičkih parametara reakcije umrežavanja važno<br />za pravilan odabir optimalnih uslova za proizvodnju i preradu<br />hibridnih materijala u industrijskim uslovima.</p> / <p>In this thesis the influence of clay fillers and thermoplastic<br />segmented polyurethanes on the curing kinetics, structure and<br />properties of functional hybrid materials based on epoxy resins<br />was assessed. Two sets of hybrid material samples were<br />prepared. First type of samples was based on epoxy resin with<br />a different content of organically modified montmorillonite (0,<br />1, 3, 5 and 10 wt. %) and crosslinking with hardener Jeffamine<br />D-230. Second type of samples was based on epoxy resin,<br />having different content (10, 15 and 20 wt. %) of thermoplastic<br />segmented polyurethane with different content of hard<br />segments (20, 25 and 30 wt. %) based on aliphatic<br />polycarbonate macrodiols and hexamethylene diisocyanate,<br />with chain extender 1,4-butanediol and the catalyst, dibutyltin<br />dilaurate, and also a sample without added elastomeric<br />polyurethane and crosslinking with hardener Jeffamine D-<br />2000. The curing of the hybrid materials based on epoxy resins<br />systems were investigated by non-isothermal differential<br />scanning calorimetry (DSC). The kinetic study by<br />isoconversion models has been carried out using data from<br />DSC. The synthesized materials were analyzed by dynamicmechanical<br />analysis (DMA), atomic force microscopy (AFM)<br />as well as TG-DSC and TG-MS methods and mechanical<br />properties (tensile strength, elongation and hardness at Shore<br />A) were determined. Epoxy based hybrid material with 10 wt.<br />% of the organically modified montmorillonite has<br />significantly lower activation energy values for the defined<br />reaction rates, thereby confirming the catalytic effect of the<br />clay with the layered structure when present in the reaction<br />mixture in sufficient quantity. The diffusion effects at the end<br />of the reaction are more pronounced in the presence of<br />montmorillonite, which indicates that its presence affects the<br />entire curing mechanism. It was found that G&#39;, along with<br />montmorillonite content, is affected by the degree of particle<br />dispersion inside the polymer matrix. It was concluded that the<br />addition of montmorillonite up to 3 wt. % improves<br />investigated mechanical properties, while the samples with 5<br />and 10 wt. % of montmorillonite resulted in agglomeration of<br />the filler particles, which negatively influenced the<br />investigated properties, except for the hardness which<br />increases linearly with the addition of montmorillonite. TG<br />analysis shows that the increase of montmorillonite content in<br />the epoxy matrix slightly improves the thermal stability in the<br />air, while in the inert atmosphere there is no influence on the<br />thermal stability nor on the mechanism of the decomposition<br />of epoxy based hybrid materials. In the system with a<br />thermoplastic polyurethane filler, it was concluded that hybrid<br />materials with a higher content of segmented polyurethane (10<br />and 15 wt. %), curing process starts at lower temperatures and<br />the maximum speed is achieved at lower temperatures and the<br />highest value of changes in total enthalpy of the crosslinking<br />reaction is determined for the epoxy hybrid material with<br />polyurethanes containing 30 wt. % of hard segments. Tensile<br />strength of hybrid materials increases with the increase of hard<br />segments content in the polyurethane elastomer as well as with<br />the increase of polyurethane content in the epoxy matrix. The<br />addition of thermoplastic segmented polyurethanes<br />significantly increased the elongation at break of prepared<br />epoxy resins hybrid materials. The increase of the hard<br />segments content in polyurethane, in the same ratio, improves<br />hardness of epoxy based hybrid material. It was concluded that<br />the final properties of hybrid materials are influenced by the<br />selection of initial compounds, methods of processing and the<br />curing conditions. It was concluded, as well that knowing the<br />kinetic parameters of curing reaction is important for the<br />proper selection of optimal parameters for production and<br />processing of hybrid materials in industrial conditions.</p>

M. Tech. Polymer Technology. / Studies the effects of incorporating epoxidised soybean oil (ESO) in a standard bisphenol A-type epoxy resin (EP) cured by both amine and anhydride hardeners. The EP/ESO ratio was set for 100/0, 75/25, 50/50, 25/75 and 0/100 (wt./wt.). The investigations performed covered the curing, rheology (gelling), and thermomechanical analysis and thermogravimetric analysis of the sample produced.

Thesis (Ph.D.) -- Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

Thesis (Ph.D.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

Made available in DSpace on 2014-06-11T19:31:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2001-02-08Bitstream added on 2014-06-13T20:02:15Z : No. of bitstreams: 1 rasquin_lc_dr_arafo.pdf: 3893563 bytes, checksum: 878343df876b4142fa2d487eea60d577 (MD5) / O objetivo do presente estudo foi o de avaliar comparativamente, dois cimentos obturadores de canal radicular à base de resina epóxica, AH Plus e Sealer Plus, através de duas diferentes metodologias. 1. Teste in vivo - Avaliação histopatológica em dentes de cães. Foram utilizados 36 canais radiculares de dentes pré-molares superiores e inferiores de 2 cães, com vitalidade pulpar, os quais, após o preparo biomecânico coadjuvado pela irrigação/aspiração e inundação com solução de hipoclorito de sódio a 1% (Líquido de Dakin), foram obturados pela técnica clássica complementada pela condensação lateral ativa, empregando os cimentos Sealer Plus (Grupo I) e AH Plus (Grupo II). Decorridos 90 dias após a obturação, os animais foram sacrificados por sobredose anestésica, as maxilas e mandíbulas removidas e fixadas em formol a 10%, durante 48 horas. Após processamento histológico de rotina, os cortes foram corados pela hematoxilina e eosina, pelo tricrômico de Mallory e Brown e Brenn. A análise histopatológica evidenciou que o cimento AH Plus, quanto à compatibilidade biológica, mostrou-se superior ao Sealer Plus, sendo o cimento que melhor permitiu a deposição de tecido mineralizado à nível apical, oferecendo um selamento quase completo na maioria dos casos, com infiltrado inflamatório ausente e quando presente era suave no tecido intersticial e/ou junto ao material obturador, assim como na região periapical. Já, com o cimento Sealer Plus, ocorreu predominantemente, selamento parcial, porém sempre acompanhado de infiltrado inflamatório de grau suave, no tecido intersticial, porém, mais concentrado, junto ao cimento obturador. Quando o material obturador era observado na região periapical, o infiltrado inflamatório apresentava-se, classificado como de grau moderado, concentrado próximo ao... . / The scope of the present study was to evaluate comparativily, two root canal resin - based sealers - AH Plus and Sealer Plus through two different methodologies. 1. In vivo study - Histopathological evaluation in teeth of dogs. 36 root canals of lower and upper bicuspide teeth of 2 dogs with vital pulp, which after biomechanic preparation utilizing sodium hypochloride solution at 1% (Milton solution) were filling by classical technique complemented by active lateral condensation, using Sealer Plus (Group I) and AH Plus (Group II). 90 days after treatment, the animals were sacrificed by overdose anesthetical. After histopathological processing of routine, the sections were stained with hematoxiline and eosine, Mallory Trichromic and Brown and Brenn. The histopathological analysis had evidenced that the AH Plus sealer shows more biological compatibility in relation to the Sealer Plus being the sealer that shows more good deposition of mineralized tissue to the apical level, offering an almost full apical sealing in the majority of the cases, with infiltrated inflammatory absent and when present was mild in the interstitial tissue and/or together to the material sealer, as well as in the periapical region. With the Sealer Plus, partial apical sealing occurred, however always followed by infiltrated inflammatory of mild degree in the intersticial tissue, however, more concentrated, together to the filling material when in the periapical region, the inflammatory infiltrated was presented, classified as of moderate degree. 2. In vitro study - With the objective to analyze pH and clearing of total calcium by periods that had varied from 0 to the 5 days, the filling materials. AH Plus and Sealer Plus had been manipulated according to the manufacturers instructions. Samples of each sealer were... (Complete abstract, click electronic address below).

A reação entre resinas epóxi e polialquileno glicóis gera um aduto de elevado peso molecular que pode ter aplicações em diferentes segmentos, tais como polímeros usados na composição base de fluidos de têmpera, viscosificantes para lubrificantes e desemulsificantes de petróleo. As condições envolvendo a formação destes adutos possuem referências limitadas na literatura aberta e basicamente envolvem um polialquileno glicol com diferentes funcionalidades, tipicamente duas hidroxilas reagindo com os grupos epóxi presentes na resina epóxi que tipicamente possui funcionalidade igual a dois, a uma temperatura ao redor de 120°C na presença de catalisador de hidróxido de potássio (KOH). O presente trabalho avaliou a formação destes adutos considerando um delineamento experimental de resolução III onde as variáveis de controle foram temperatura, velocidade de agitação do meio reacional, velocidade de adição de resina epóxi, concentração de catalisador e relação molar entre a resina epóxi e o polialquileno glicol. Ao total onze experimentos foram realizados de acordo com o planejamento experimental e incluindo triplicata para avaliação do erro experimental. Diferenças significativas nas características físico químicas dos produtos obtidos tais como viscosidade, teor de epóxi residual e de performance de desemulsificação foram encontradas. Dois produtos apresentaram gelificação. Com um bom nível de confiabilidade estatística pode-se dizer que o peso molecular ponderal médio é influenciado principalmente pelo teor de catalisador seguido da temperatura e proporção molar entre resina epóxi e polialquileno glicol nesta ordem de importância. Com menor nível de significância a conversão é influenciada positivamente com respeito ao incremento do teor de catalisador e da temperatura e pela redução na proporção molar entre resina epóxi e polialquileno glicol. Apesar de terem sido atingidos elevados níveis de conversão de resina epóxi na maioria dos experimentos, pelas analises de GPC foi observado uma grande proporção de polialquileno glicol livre residual nos produtos. Pode-se observar também uma fraca correlação estatística positiva entre a qualidade da separação petróleo-água com respeito à conversão e ao peso molecular numérico médio dos produtos. / The reaction between epoxy resins and polyalkylene glycols generates an adduct of high molecular weight that may have applications in several sectors such as polymers for metal quenchant fluids, demulsifiers and viscosifiers for lubricating oil. The conditions involving the formation of these adducts have limited references in the open literature and basically it involves a polyalkylene glycol having different functionalities, typically two hydroxyl groups reacting with the epoxy groups present in the epoxy resin with typical functionality equal to two at a temperature around 120°C and in the presence of catalyst, potassium hydroxide (KOH). This study evaluated the formation of these adducts considering a resolution III experiment design where the controllable variables were temperature, stirring speed of the reaction medium, rate of addition of epoxy resin, catalyst concentration and molar ratio between the epoxy resin and polyalkylene glycol . In total eleven experiments were carried out according to the experimental design, including three replications at the center point to evaluate the experimental error. Significant differences in chemical and physical characteristics such as viscosity, residual epoxy content and performance of demulsification were found between the synthesized materials. Two products showed gelation. With a good level of statistical reliability it can be considered that the weight average molecular weight is mainly influenced by the amount of catalyst followed by temperature and mole ratio of epoxy resin to polyalkylene glycol in this order of importance. With lower significance level conversion is influenced positively with respect to the increment of the catalyst amount and temperature and by the decrease in molar ratio of epoxy resin and polyalkylene glycol. Despite achieving high levels of conversion of epoxy resin in most of the experiments, by GPC analysis it was observed a large proportion of free residual polyalkylene glycol in the products. It can be observed also a slight positive statistical correlation between the quality of oil-water separation with respect to conversion and number average molecular weight of the products.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Cement has been used in the world, presenting a wide versatility. However, due to its chemical nature, it is subject to several types of chemical damages, especially for agents of acidic nature. With the purpose of increase its life-time, new cement slurries have been modified with the addition of specific additives. The objective of this work is to modify cement slurries with epoxy resins, which promote higher resistance of those materials in relation to acid attacks. Three cement slurries were synthesized with epoxy resins (GY, PY-1 and PY-2) and a standard slurries, which was composed by cement and water (w/c = 0,5). The syntheses were performed according to the API recommendations. After 30 days of hydration, the samples were characterized by XDR, FTIR and thermal analysis (TG and DSC). The slurries characterization has suggested the presence of low amounts of portlandita (Ca(OH)2) in the slurry with the higher content of polymerized epoxy resin. The hydration processes of the cement slurries were studied by heat-conduction microcalorimetry. The energetic and enthalpic hydration data were all exothermic in nature. It was verified that the addition of the polymers delayed the processes of hydration of the slurries, decreasing the flow of heat released as a function of the amount of added resin. The cumulative heat release curves have shown the presence of multilinearity of the kinetic processes. The hydration microcalorimetric data were well fitted to the multistep Avrami kinetic model. A kinetic study of HCl interaction with the new slurries were performed by the batch methodology at 25, 35, 45 e 55°C. The Avrami kinetic model also appears to be the most efficient in describing the kinetic isotherms. It was observed that the kinetic constants of interaction of the acid with the slurries increased with the increase of temperature and decreased as a function of the amount of resin added in the slurries. The speed of reaction of the cement slurries with HCl was determined from the kinetic parameters obtained by the Avrami model. Speed reaction in the order of 10-3 mol.g.h-1 were found for the standard slurry and of the order of 10-5 mol.g.h-1 for the slurries with the epoxy resins. In general, the analysis of the kinetic parameters indicated that increasing the resin amount in the composition of the slurries reduced the reaction speed and increased the resistance of those slurries to the acid attack. / O cimento é um dos materiais mais utilizados no mundo, apresentando uma larga versatilidade. No entanto, devido à sua natureza química, está sujeito a vários tipos de desgastes, especialmente por agentes de natureza ácida. Com a finalidade de prolongar o tempo de vida útil desse material, buscam-se novas formulações de pastas de cimento através da adição de aditivos específicos. O objetivo deste trabalho é a modificação de pastas de cimento com resinas epóxi, as quais promovem maior resistência desses materiais frente aos ataques ácidos. Foram sintetizadas três pastas de cimento com resinas epóxi (GY, PY-1 e PY-2) e uma pasta padrão, composta de cimento e água. Para preparação utilizaram-se dois tipos de resinas epóxi, uma do tipo bisfenol-A e seu endurecedor de isoforonodiamina (GY) e outra, uma combinação do bisfenol-F e do bisfenol-A com endurecedor de poliamidoamina (PY-1 e PY-2). Após 30 dias de hidratação, as amostras foram caracterizadas por DRX, FTIR e por análise térmica (TG e DSC). A caracterização das pastas sugeriu a presença de baixas quantidades de portlandita (Ca(OH)2) nas composições com maior porcentagem de resina epóxi. Os processos de hidratação das pastas de cimento foram estudados por calorimetria isotérmica. Os dados energéticos de entalpia de hidratação foram todos de natureza exotérmica. Foi verificado que a adição do polímero retardou o processo de hidratação das pastas, reduzindo o fluxo de calor liberado em função da porcentagem de resina adicionada. As curvas de liberação do fluxo de calor mostraram a presença de vários processos cinéticos distintos. Os dados de hidratação foram bem ajustados ao modelo cinético de Avrami. O estudo cinético de interação de HCl com as pastas de cimento foi realizado pelo método de batelada nas temperaturas de 25, 35, 45 e 55°C. O modelo cinético de Avrami também foi o que mais se mostrou eficiente em descrever as isotérmicas cinéticas. Foram observados que as constantes cinéticas de interação do ácido com as pastas aumentaram com o aumento da temperatura, e diminuíram em função do aumento da quantidade de polímero adicionado nas pastas. A velocidade de reação das pastas de cimento com o HCl foi estimada a partir dos parâmetros cinéticos obtidos pelo modelo de Avrami. Foram verificados valores de velocidade de reação da ordem de 10-3 mol.g.h-1 para a pasta padrão e da ordem de 10-5 mol.g.h-1 para as pastas aditivadas. Em geral, a análise dos parâmetros cinéticos indicou que o aumento da porcentagem de resina na composição das pastas reduziu a velocidade de reação e, aumentou a resistência dessas pastas ao ataque ácido.

No description available.