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...
As aplicações comerciais e científicas das resinas epoxídicas dependem diretamente da combinação entre resina/endurecedor/acelerador, tornando-o um sistema reativo bastante complexo, cuja determinação dos seus parâmetros de cura é um problema multivariável de tempo, temperatura e concentração de reagentes. É necessário o conhecimento de suas etapas de cura e de seu mecanismo cinético para obtenção das melhores propriedades mecânicas, elétricas e térmicas, com a finalidade de conseguir uma resina epoxídica de alto desempenho. As técnicas analíticas comumente empregadas na determinação da cura de resinas epoxídicas como também de diversas outras resinas poliméricas são: a calorimetria exploratória diferencial (DSC) e a análise dinâmico-mecânica (DMA). Neste trabalho, dois sistemas reativos foram analisados: o primeiro, resultante da combinação de resina DGEBA com endurecedor à base de amina alifática; o segundo composto pela resina DGEBA reagida com endurecedor à base de anidrido e catalisado por amina terciária. É apresentada a metodologia empregada na determinação dos parâmetros cinéticos para os dois sistemas epóxi utilizando a análise por DSC isotérmica e não isotérmica, a técnica DMA isotérmica...
De modo geral, os ciclos de cura para resina epóxi demandam algumas horas e elevadas temperaturas. Em busca de novas soluções para a otimização de processos sem perda de qualidade, bem como a economia de energia, diversos processos de cura de resina epóxi não convencionais foram desenvolvidos ao longo dos anos. O uso de irradiação de micro-ondas teve início após a Segunda Guerra Mundial, com a invenção do RADAR. A radiação de micro-ondas é uma radiação não-ionizante, com bom poder de penetração e boa transferência de calor em materiais absorvedores, ou materiais com cargas absorvedoras. A frequência usualmente utilizada em trabalhos de pesquisa e desenvolvimento é de 2,45GHz, a mesma disponível nos equipamentos comerciais e industriais existentes. Para a cura de resinas epóxi não são necessárias alterações no sistema reativo, com iniciadores específicos sensíveis a micro-ondas. O "efeito micro-ondas" proporciona um aumento da velocidade de colisão entre os reagentes que, associada à energia absorvida pelo sistema reacional, acelera a reação de cura, possibilitando a cura de resinas de tempo de uso longo (superior a 24 horas, em temperatura ambiente) em questão de minutos. Neste estudo foi utilizado inicialmente um sistema epóxi do tipo DGEBA...
No presente trabalho, utilizou-se a calorimetria diferencial exploratória (DSC) para investigar a cinética da reação de cura de resinas epóxi produzidas a partir da reação do óleo de soja epoxidado (ESO), com os anidridos dodecenilsuccínico (DDS), maleico (MAL), ftálico (FTA), succínico (SUC) e hexahidroftálico (CH), atuando como agentes de cura, e na presença de aminas terciárias como a trietilamina (TEA), a N,N’-dimetilanilina (ARO) e a 1,4- diazobiciclo[2,2,2]octano (DABCO), atuando como catalisadores. A taxa de aquecimento, a natureza química e a estrutura do anidrido e das aminas influenciaram a reação de cura. Os métodos dinâmicos de Kissinger, Ozawa e de Barrett foram utilizados para calcular a energia de ativação dos sistemas onde se variou o anidrido. Observou-se que os anidridos mais reativos foram o DDS e maleico que apresentaram os menores valores de energias de ativação. No estudo da influência do catalisador, utilizou-se o método de Barrett para determinar as energias de ativação das reações com as diferentes aminas. A amina cicloaliafática (DABCO) foi a mais reativa obtendo-se o menor valor de energia de ativação (Ea = 51 kJ.mol–1) e fator pré- exponencial (ln A = 9 s–1).; In the present work...
The dielectric behavior of composite materials (epoxy resin - barium titanate and epoxy - CCTO) was analysed as a function of ceramic amount. Composites were prepared by mixing the components and pouring them into suitable moulds. In some compositions, the matrix was reduced by tetrahydrofuran (THF) incorporation. Samples containing various amounts of ceramic filler were examined by TG/DTA and scanning electron microscopy analysis. Dielectric measurements were performed from 20 Hz to 1 MHz and 30 to 120 °C. It was demonstrated that the epoxy - CCTO composites possessed higher permittivity than classic epoxy - BaTiO3 composites. However, the low resin permittivity prevailed in the composite dielectric performance.
The presence of residual endodontic sealer in the pulp chamber may cause discoloration of the dental crown and interfere with the adhesion of restorative materials. The aim of this study was to compare the efficacy of different solvents in removing residues of an epoxy resin-based sealer (AH Plus) from the dentin walls of the pulp chamber, by scanning electron microscopy (SEM). Forty-four bovine incisor dental crown fragments were treated with 17% EDTA and 2.5% NaOCl. Specimens received a coating of AH Plus and were left undisturbed for 5 min. Then, specimens were divided in four groups (n = 10) and cleaned with one of the following solutions: isopropyl alcohol, 95% ethanol, acetone solution, or amyl acetate solution. Negative controls (n = 2) did not receive AH Plus, while in positive controls (n = 2) the sealer was not removed. AH Plus removal was evaluated by SEM, and a score system was applied. Data were analyzed by Kruskal-Wallis and Dunn tests. None of the solutions tested was able to completely remove AH Plus from the dentin of the pulp chamber. Amyl acetate performed better than 95% ethanol and isopropyl alcohol (p < 0.05), but not better than acetone (p > 0.05) in removing the sealer from dentin. No significant differences were observed between acetone...
Epoxy resin is chosen for our present study owing to its exceptional combination of properties such as easy processing, high safety, excellent solvent and chemical resistance, toughness, low shrinkage on cure, good electrical, mechanical and corrosion resistance with excellent adhesion to many substrates. This versatility in formulation made epoxy resins widely applied for surface coatings, adhesives, laminates, composites, potting, painting materials, encapsulant for semiconductor and insulating material for electric devices. There are numerous paint/coating systems based
on epoxy resin available for corrosion and fouling prevention. They however are not completely satisfactory in field applications, where high corrosion, fouling and flame resistance are required. The demand for epoxy resin as corrosion/fouling resistant coatings is restricted mainly due to
its inferior characteristics like poor impact strength, high rigidity, and moisture absorbing nature besides inadequate flame retardant properties. It is for this reason that silicones and phosphorus-based compounds are used as modifier in this work by intercrosslinking network mechanism (ICN) to obtain epoxy resin with desired properties ideally suitable for field applications for preventing corrosion and fouling with flame retardantancy.
The present work involves the development of solvent free silicone/phosphorus modified epoxy coating systems...
Thin bonded concrete overlay are commonly used nowadays in repairing concrete structures. Nevertheless, the performance of the structural system (repaired structure) depends on the sound bond behaviour between old and new concretes. Frequently, adhesives based on epoxy resins provide this liaison. In this work the behaviour of three different types of based epoxy adhesives was observed in the bonding of different strength concrete class. Samples for backscattered scanning electron microscopy (BSE) were prepared from extracted pieces - containing the bonding layer - of non reinforced concrete slabs overlaid with thin bonded steel fibre reinforced concrete (SFRC) layer. Different features of each bonding layer epoxy resin type which may explain differentiate mechanical pull-off results as well as failure modes were observed. Micrographs obtained with BSE give clearly bond layer arrangement and minimum and maximum thickness, typical air voids porosity, presence of hydrated cement paste embedded in epoxy layer, mineral admixtures contained in epoxy, and also relevant micro fissures existing in concrete substrate.; Fundação para a Ciência e a Tecnologia (FCT) - PhD grant number SFRH/BD/11232/
2002.; Sika SA.; Companhia Geral de Cal e Cimento
SA (SECIL).; Degussa Construction Chemicals Portugal SA.; Pedreiras Bezerras.; Bekaert NV.
The use of polymeric materials in civil construction makes possible original bonding processes because they have good adhesion. Among the polymeric materials, the epoxies are the most advantageous in the application for concrete rehabilitation. In this paper the bond between fresh/hardener concrete was made using epoxy resins in aqueous solution, because in previous tests they obtained the best results. This study analyzes the incorporation of one filler in the epoxy resin, to understand until what quantity we can add without significant decrease of the adhesion. A conventional hardened concrete was used. Otherwise, two types of fresh concretes were used with the purpose to understand the influence of the strength class in adhesion. The evaluation of adhesion between fresh and hardened concrete was made using two shear tests - direct and slant. The results showed that the direct shear test is better than the slant because the mixed failure make easier the study of the adhesion. The incorporation of the filler is benefic and the optimal quantity of filler seems to be related with the concrete strength class.
Fonte: Universidade do MinhoPublicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2010Português
Relevância na Pesquisa
The use of polymeric materials in civil construction makes possible original bonding processes because they have good adhesion. In this paper the bond between fresh/hardened concrete was made using epoxy resins in aqueous solution. Also the incorporation of one filler in the epoxy resins was analyzed. This study had two phases. n the first were conducted two shear tests - slant and direct. In the second phase were produced concrete with different strength classes by varying the ratio W/C - 0.6, 0.55 and 0.3. The results for the first phased showed that the direct shear test was the most appropriated. It was found in both phases mixed failures (type II). The use of mineral fillers also proved beneficial. This study also demonstrated the importance of water in the adhesion. The best water-cement ratio was 0.55, revealing the best balance between the porosity and the amount of water.
Epoxy adhesives have been extensively used in structural strengthening. This leads to a great concern in assessing their long-term performance since epoxy resins present viscoelastic behaviour. This work aims to better understand the long-term behaviour of a specific epoxy adhesive due to the creep effects. Therefore, an experimental program comprising tensile creep tests was carried out, divided in two series: (i) series S1 - epoxy specimens subjected to different stress levels for a predefined initial age; and (ii) series S2 - epoxy specimens subjected to equal stress levels but loaded at different ages. The paper presents the main results obtained so far, highlights relevant and corresponding conclusions.
Externally bonded (EB) or Near-Surface-Mounted (NSM) composite reinforcements are
often bonded to a cementitious substrate by means of commercially available epoxies. These twocomponent-
resins are generally ‘cold-curing’ (at room temperature), having however the ability to cure
faster under elevated temperatures. One application requesting such an accelerated curing process is the
gradient anchorage for strengthening of concrete structures with prestressed CFRP laminates, based on a
purely concrete/epoxy/CFRP connection without any mechanical devices.
This paper resumes the investigation on several crucial thermo-mechanical parameters of different epoxy
resins, such as glass-transition temperatures, directional tensile strength and elastic modulus. It is for
instance demonstrated that an accelerated curing process or an increasing specimen age implicate a higher
glass transition temperature. Strength and stiffness development is faster in case high temperatures are
applied; the final values with growing age however are below the ones for specimens cured only at room
temperature. Initial mixing under vacuum on the other hand induces higher strength and stiffness values.
Eventually, it is shown that an accelerated curing of a cold-curing epoxy increases the porosity of the
Samples of epoxy resin (EP) based on the diglycidyl ether of bisphenol A (DGEBA), cured with nadic methyl anhydride (NMA) and mercaptan (CAPCURE 3-800), or amine-phenol (CAPCURE EH-30), respectively, SE 4 and SE 5, were prepared in the stoichiometric ratio determined by the supplier. The curing behaviour of the epoxy systems SE 4 and SE 5 was followed by DSC (Differential Scanning Calorimetry). These SE and their ingredients were analyzed using FTIR transmission techniques (KBr pellets, pyrolysis without control and controlled pyrolysis-FT-IR, the CONTROLPIR/FT-IR) for characterizing the curing agents (CA). The temperature range used for samples pyrolysis was found from TG (thermogravimetry). Thus, the FT-IR bands of liquid pyrolysate obtained by CONTROLPIR/FT-IR were evaluated, in comparison to the reference spectrum of CA. The characterization of CA was also possible, by the analysis of such SE with the TG/FT-IR technique.
Epoxy resins were first introduced about 10 years ago. Toxic effects, particularly dermatitis, have been frequently described. An investigation into the possible causes of pathological sequelae following the use of epoxy resin/amine mixtures has been undertaken. The cause of most cases of dermatitis and sensitization appears to be uncombined amine which is present in recent mixtures and persists in hardened resin for long periods. The results of experiments with two of the most commonly used resin/amine mixtures confirm this. Cold-cured resins are more dangerous and remain so even when hardened. A simple theory is suggested for the mechanism of the reaction between epoxy resins, amines, and biological systems. This theory leads logically to the handling precautions outlined.
A method of embedding biological specimens in araldite 502 (Ciba) has been developed for materials available in the United States. Araldite-embedded tissues are suitable for electron microscopy, but the cutting qualities of the resin necessitates more than routine attention during microtomy. The rather high viscosity of araldite 502 also seems to be an unnecessary handicap. The less viscous epoxy epon 812 (Shell) produces specimens with improved cutting qualities, and has several features—low shrinkage and absence of specimen damage during cure, minimal compression of sections, relative absence of electron beam-induced section damage, etc.—which recommends it as a routine embedding material. The hardness of the cured resin can be easily adjusted by several methods to suit the materials embedded in it. Several problems and advantages of working with sections of epoxy resins are also discussed.
A new, easy and cost-effective synthetic procedure for the preparation of thermosetting melamine-based epoxy resins is reported. By this innovative synthetic method, different kinds of resins can be obtained just by mixing the reagents in the presence of a catalyst without solvent and with mild curing conditions. Two types of resins were synthesized using melamine and a glycidyl derivative (resins I) or by adding a silane derivative (resin II). The resins were characterized by means of chemical-physical and thermal techniques. Experimental results show that all the prepared resins have a good thermal stability, but differ for their mechanical properties: resin I exhibits remarkable stiffness with a storage modulus value up to 830 MPa at room temperature, while lower storage moduli were found for resin II, indicating that the presence of silane groups could enhance the flexibility of these materials. The resins show a pot life higher than 30 min, which makes these resins good candidates for practical applications. The functionalization with silane terminations can be exploited in the formulation of hybrid organic-inorganic composite materials.
This work presents an application of optical fiber sensors based on Bragg gratings encapsulated in polymeric composite resin with glass fiber reinforcement. Three commercial epoxy resins were evaluated. The main objective of the study is to characterize the composites and investigate the feasibility of embedding the optical fiber sensors based on Bragg gratings in epoxy composite. In the characterization of the samples tensile tests were performed to evaluate the residual stress after the curing process. The residual stress was investigated by mains of a FBG sensor embedded in the composite. Additionally, tests were conducted to evaluate the glass transition temperature by DSC technique. The values of the axial tensile and simple flexural stress were investigated using a universal testing machine. In addition, tests were performed for evaluating the composite behavior when subjected to a fixed load and variable temperature ranging from 20 °C to the temperature limit of the glass transition of the composite. The results show a high level of integration of the FBGs with the epoxy composite. One of the results is promising for applications in a high power generator and in hostile environments working at temperatures up to 127 °C.; ANEEL; FINEP; CAPES; CNPQ; Fundação Araucária; Neste trabalho é apresentada uma aplicação de sensores à fibra ótica baseados em redes de Bragg encapsulados em compósito de resina polimérica com reforço de fibra de vidro. Foram avaliadas três resinas epóxi comerciais. O objetivo do trabalho é caracterizar os compósitos e investigar a viabilidade de embeber sensores a fibra ótica...
The aim of this work was to evaluate the adhesiveness of uncoated and zinc-electrogalvanized steel sheets used in the automotive industry. Three types of adhesives, one acrylic and two epoxy resins, were employed to join low carbon cold rolled steels, one uncoated and another electrogalvanized, both previously degreased or chemically pickled. Mechanical strength of the joints was evaluated by the T-peel and tensile strength tests. Steel grade, surface condition and heating below the cure temperatures did not influence the joints' mechanical strength. However, their shear strength decreased drastically as the test temperature increased. The exposure of the joints to an atmosphere with 90% relative humidity at 40 °C caused reduction of their shear strength. Epoxy adhesives showed higher mechanical strength, but exhibited higher degradation by humidity.