Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 896
Filtrar
1.
J Chromatogr A ; 1609: 460448, 2020 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-31421793

RESUMO

In this work, we reported a simple two-step method for the synthesis of magnetic mesoporous epoxy resin (MMER), including one-pot template-free hydrothermal synthesis of nanoscale amine-functionalized magnetic nanoparticles (MN-NH2) and initiator-free ring-opening polymerization of epoxy resin. The resultant MMER was characterized in detail by transmission electron microscope (TEM), Fourier transform-infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), thermogravimetic analysis (TGA) and magnetization curves. These results demonstrated successful synthesis of MMER with sufficient magnetic property and excellent thermal stability. The epoxy resin was covalent bonding MN-NH2 on and synthesized by hydrophobic monomers, so the MMER exhibited excellent adsorption quantity for hydrophobic bile acids. The MMER was used as magnetic solid-phase extraction (MSPE) sorbent, and combined with liquid chromatography-tandem mass spectrometry to extract and monitor 11 kinds of bile acids from serum sample. The proposed MSPE combined with LC-MS/MS method exhibited low limit of detection between 0.1 and 5 ng mL-1. In blank serum sample, 9 kinds of bile acids were detected, and ranged from -2.29 ng mL-1 to 6.86 ng mL-1. In standard addition recovery test, the recovery values of detectable bile acids ranged 102.4% to 108.5%, 96.0% to 104.0% and 82.3% to 103.3% when spiked with 0.2, 2.0 and 20 ng mL-1, respectively. The intra- and inter-day precision (n = 6) ranged 3.7% to 5.9% and 7.0% to 9.5%, respectively. The above results demonstrated that the MSPE combined with LC-MS/MS method was accurate and effective for quantitative determination of bile acids from complex biological samples.


Assuntos
Ácidos e Sais Biliares/sangue , Ácidos e Sais Biliares/isolamento & purificação , Resinas Epóxi/química , Fenômenos Magnéticos , Polimerização , Adsorção , Cromatografia Líquida , Humanos , Limite de Detecção , Nanopartículas/química , Nanopartículas/ultraestrutura , Porosidade , Extração em Fase Sólida , Soluções , Espectroscopia de Infravermelho com Transformada de Fourier , Espectrometria de Massas em Tandem
2.
J Appl Oral Sci ; 28: e20190005, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31800870

RESUMO

other: Chitosan is a natural, biocompatible chelating substance with potential for dental use. This study compared the effects of final canal irrigation with chitosan and EDTA on dentin microhardness, sealer dentin tubules penetration capacity, and push-out strength. METHODOLOGY: Fifty canine roots were distributed according to the final irrigation protocol (n=10): G1- 15% EDTA with conventional irrigation; G2- 15% EDTA with Endovac; G3- 0.2% chitosan with conventional irrigation; G4- 0.2% chitosan with Endovac; and G5- without irrigation. Specimens were obturated (AH Plus) and sectioned in 3 slices per root third. The first slice was used for microhardness and sealer penetration assessments under a laser confocal microscope. The second was utilized in a push-out strength test. The third slice was discarded. Data were analyzed using 2-way ANOVA and Tukey's post hoc test (α<0.05). Failure mode was determined at x40 magnification. RESULTS: Microhardness reduction was more significant in groups G2 and G4 (p<0.05). Sealer penetration through dentin was significantly greater in group G2 (p<0.05). There was no significant difference between groups G1, G3, and G4 (p>0.05). In general, all experimental groups presented similar bond resistance (p>0.05) that significantly differed from the control (p<0.001). Mixed type failures were predominant. CONCLUSIONS: In general, 0.2% chitosan and 15% EDTA solutions act in a similar manner with regard to the variables studied. The use of Endovac potentiates the effect of these solutions.


Assuntos
Quelantes/química , Quitosana/química , Colagem Dentária/métodos , Dentina/efeitos dos fármacos , Ácido Edético/química , Irrigantes do Canal Radicular/química , Análise de Variância , Resinas Epóxi/química , Testes de Dureza , Humanos , Teste de Materiais , Microscopia Confocal , Pessoa de Meia-Idade , Valores de Referência , Reprodutibilidade dos Testes , Materiais Restauradores do Canal Radicular/química , Resistência ao Cisalhamento , Propriedades de Superfície/efeitos dos fármacos
3.
Histochem Cell Biol ; 153(2): 121-127, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31848702

RESUMO

Epoxy-embedded semithin sections are useful for the analysis of cell and tissue organization, as well as for the processing of samples for transmission electron microscopy. Because only a very limited number of staining protocols have been developed for epoxy-embedded sections; semithin sections are used infrequently compared to conventional paraffin sections. Here, we describe a simple and reproducible polychromatic protocol for the routine staining of epoxy-embedded semithin sections by adapting Twort's staining method (mixture of neutral red and fast green FCF). The method can be used for the visualization of cellular organization as well as for the detection of elastic and collagen fibers. The proposed protocol demonstrated the best results for samples fixed for transmission electron microscopy, which suggests, as we demonstrated here, that this staining protocol can also be used for correlative light and electron microscopy.


Assuntos
Resinas Epóxi/química , Técnicas Histológicas , Tetróxido de Ósmio/química , Coloração e Rotulagem , Animais , Glutaral/química , Camundongos , Camundongos Endogâmicos BALB C , Microscopia Eletrônica , Coelhos
4.
Mater Sci Eng C Mater Biol Appl ; 105: 110108, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31546415

RESUMO

Hydrophilic epoxy resin-based monoliths were employed as cell culture substrates. The monoliths were made of a porous material with a bicontinuous structure that consisted of a porous channel and a resin skeleton. Monolith disks were prepared with a skinless surface through polymerization-induced spinodal decomposition-type phase separation. The pore sizes, which were well controlled by the polymerization temperature, ranged from 70 to 380 nm. The quantity of protein adsorbed per unit area and the early-stage adhesion of HepG2 cells on the monolith substrates were independent of pore size, meaning they were not affected by surface topology. Long-term cell adhesion, as indicated by adherent cell number and shape, as well as liver-specific gene expression were significantly affected by pore size. In terms of cell shape, number, and gene expression, pores of approximately 200 nm were most suitable for HepG2 cell growth. These results highlight the importance of monolith morphology for use as a cell culture substrate. The well-controlled morphology demonstrated in this work indicates monoliths are capable of supporting growth for various types of cells in a range of applications.


Assuntos
Adesão Celular , Resinas Epóxi/química , Teste de Materiais , Células Hep G2 , Humanos , Interações Hidrofóbicas e Hidrofílicas
5.
Braz Oral Res ; 33: e042, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31508725

RESUMO

This study evaluated the cytotoxicity and biocompatibility of a new bioceramic endodontic sealer (i.e., Sealer Plus BC) in comparison with those of MTA Fillapex and AH Plus. L929 fibroblasts were cultured and Alamar Blue was used to evaluate cell viability of diluted extracts (1:50, 1:100, and 1:200) from each sealer at 24 h. Polyethylene tubes that were filled with material or empty (as a control) were implanted in the subcutaneous tissue of rats. The rats were killed after 7 and 30 d (n = 8), and the tubes were removed for histological analysis. Parametric data was analyzed using a one-way ANOVA test, and nonparametric data was analyzed via the Kruskal-Wallis test followed by the Dunn test (p < 0.05). A reduction in cell viability was observed in the extracts that were more diluted for Sealer Plus BC when compared to that of Control and AH Plus (p < 0.05). However, the 1:50 dilution of the Sealer Plus BC was similar to that of the Control (p > 0.05). Conversely, more diluted extracts of MTA Fillapex (1:200) and AH Plus (1:100 and 1:200) were similar to the Control (p > 0.05). Histological analysis performed at 7 d did not indicate any significant difference between tissue response for all materials, and the fibrous capsule was thick (p > 0.05). At 30 d, Sealer Plus BC was similar to the Control (p > 0.05) and MTA Fillapex and AH Plus exhibited greater inflammation than the Control (p < 0.05). The fibrous capsule was thin for the Control and for most specimens of Sealer Plus BC and AH Plus. Thus, Sealer Plus BC is biocompatible when compared to MTA Fillapex and AH Plus, and it is less cytotoxic when less-diluted extracts are used.


Assuntos
Cimentos para Ossos/química , Hidróxido de Cálcio/química , Cerâmica/química , Materiais Restauradores do Canal Radicular/química , Compostos de Alumínio/química , Animais , Materiais Biocompatíveis , Cimentos para Ossos/farmacologia , Cimentos para Ossos/toxicidade , Compostos de Cálcio/química , Hidróxido de Cálcio/farmacologia , Hidróxido de Cálcio/toxicidade , Sobrevivência Celular/efeitos dos fármacos , Células Cultivadas/efeitos dos fármacos , Combinação de Medicamentos , Resinas Epóxi/química , Fibroblastos/efeitos dos fármacos , Técnicas In Vitro , Inflamação , Masculino , Teste de Materiais , Óxidos/química , Ratos Wistar , Materiais Restauradores do Canal Radicular/toxicidade , Silicatos/química , Tela Subcutânea/patologia
6.
J Appl Oral Sci ; 27: e20180556, 2019 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-31508791

RESUMO

OBJECTIVE: To evaluate the effect of ultrasonic and sonic activation on physicochemical properties of AH Plus, MTA Fillapex, ADSeal, GuttaFlow Bioseal, and GuttaFlow 2 sealers. METHODOLOGY: Three experimental groups were formed: no activation (NA), ultrasonic activation (UA), and sonic activation (SA). The sealers were manipulated according to the manufacturers' instructions. A 3-mL syringe was adapted to receive 1 mL of sealer. Activation was performed with a 20/.01 ultrasonic insert (20 s/1W) in the UA group. A size 35.04 sonic tip was used (20 s/10,000 cycles/min-1) in the SA group. The molds for physicochemical analysis were filled and evaluated according to ANSI/ADA specification no. 57: setting time (ST), flow (FL), dimensional change (DC), solubility (SB), and radiopacity (RD). Statistical analysis was performed by Kruskal-Wallis, one-way ANOVA, and Tukey's tests (P<0.05). RESULTS: Regarding ST, only AH Plus and GuttaFlow 2 in the NA group met the ANSI/ADA standards. All FL values were greater than 20 mm in diameter, as determined by ANSI/ADA. The tested sealers and protocols did not comply with the ANSI/ADA standards for DC. As for SB, only MTA Fillapex, regardless of the activation protocol, did not follow the ANSI/ADA standards. All of the investigated sealers, regardless of the activation protocol, presented radiographic density higher than 3 mm Al, as proposed by ANSI/ADA. CONCLUSIONS: UA and SA promoted changes in the physicochemical properties of the evaluated root canal sealers, mainly in ST and F. Thus, it is important to evaluate the physicochemical properties of endodontic sealers associated with activation techniques prior to clinical application in order to determine whether the properties follow the parameters set by ANSI/ADA, ensuring safety and quality of root canal filling.


Assuntos
Compostos de Alumínio/química , Compostos de Cálcio/química , Dimetilpolisiloxanos/química , Resinas Epóxi/química , Guta-Percha/química , Óxidos/química , Materiais Restauradores do Canal Radicular/química , Silicatos/química , Ondas Ultrassônicas , Análise de Variância , Combinação de Medicamentos , Teste de Materiais , Valores de Referência , Reprodutibilidade dos Testes , Solubilidade , Estatísticas não Paramétricas , Propriedades de Superfície , Fatores de Tempo
7.
Molecules ; 24(18)2019 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-31505884

RESUMO

Most of the current amine hardeners are petro-sourced and only a few studies have focused on the research of bio-based substitutes. Hence, in an eco-friendly context, our team proposed the design of bio-based amine monomers with aromatic structures. This work described the use of the reductive amination with imine intermediate in order to obtain bio-based pluri-functional amines exhibiting low viscosity. The effect of the nature of initial aldehyde reactant on the hardener properties was studied, as well as the reaction conditions. Then, these pluri-functional amines were added to petro-sourced (diglycidyl ether of bisphenol A, DGEBA) or bio-based (diglycidyl ether of vanillin alcohol, DGEVA) epoxy monomers to form thermosets by step growth polymerization. Due to their low viscosity, the epoxy-amine mixtures were easily homogenized and cured more rapidly compared to the use of more viscous hardeners (<0.6 Pa s at 22 °C). After curing, the thermo-mechanical properties of the epoxy thermosets were determined and compared. The isophthalatetetramine (IPTA) hardener, with a higher number of amine active H, led to thermosets with higher thermo-mechanical properties (glass transition temperatures (Tg and Tα) were around 95 °C for DGEBA-based thermosets against 60 °C for DGEVA-based thermosets) than materials from benzylamine (BDA) or furfurylamine (FDA) that contained less active hydrogens (Tg and Tα around 77 °C for DGEBA-based thermosets and Tg and Tα around 45 °C for DGEVA-based thermosets). By comparing to industrial hardener references, IPTA possesses six active hydrogens which obtain high cross-linked systems, similar to industrial references, and longer molecular length due to the presence of two alkyl chains, leading respectively to high mechanical strength with lower Tg.


Assuntos
Aldeídos/química , Aminas/química , Resinas Epóxi/química , Polímeros/química , Resinas Epóxi/síntese química , Polímeros/síntese química , Temperatura , Resistência à Tração , Viscosidade
8.
Molecules ; 24(18)2019 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-31527461

RESUMO

The effects of thermoplastic polyimide (PI) and polypropylene (PP) fibers and areal density of toughened layer on interlaminar fracture toughness and impact performance of carbon fiber/epoxy (CF/EP) laminated composites were studied. Mode I interlaminar fracture toughness (GIC) was analyzed via double cantilever beam (DCB) tests. When comparing for the toughener type, PI played a positive role in enhancing the mode-I fracture toughness, while PP was not effective due to the less fiber bridge formed during composite curing. The toughening effects of areal density of PI were further investigated by end notched flexure (ENF) testing and low velocity impact testing to better understand the toughening mechanisms. The results revealed that the toughening effect reached its best effectiveness when the areal density of toughened layer was 30 g/m2. Compared with the control group, GIC and GIIC of CF/EP laminated composite were increased by 98.49% and 84.07%, and Fmax and Ee were enhanced by 92.38% and 299.08% under low velocity impact. There is no obvious delamination phenomenon on the surface of laminates after low velocity impact, indicating the improved interlaminar and impact performance of laminated composite.


Assuntos
Fibra de Carbono/química , Resinas Epóxi/química , Fibra de Carbono/ultraestrutura , Teste de Materiais , Fenômenos Mecânicos
9.
Braz Oral Res ; 33: e057, 2019 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-31365704

RESUMO

The aim of this study was to evaluate the effect of peracetic acid (PAA) as a single irrigant on the smear layer, on the intraradicular dentinal bond strength, and on the penetrability of an epoxy-based resin sealer into the dentinal tubules. A total of 120 roots were distributed into 4 groups according to the irrigant used in root canal preparation: 1% PAA (PAA); 2.5% NaOCl followed by final irrigation with 17% EDTA and 2.5% NaOCl (NaOCl-EDTA-NaOCl); 2.5% NaOCl (NaOCl); and saline solution (SS). The smear layer was evaluated using scanning electron microscopy. The bond strength of an epoxy-based resin sealer (AH Plus) to root dentin was evaluated by the push-out test and penetrability of the sealer into dentinal tubules was observed by confocal laser microscopy. The results were analyzed by the Kruskal-Wallis and the Dunn post-test (α = 0.05). The use of 1% PAA as single root canal irrigant provided smear layer removal and improved the penetrability and bond strength of AH Plus to root dentin in a manner similar to that of the NaOCl-EDTA-NaOCl group (p > 0.05). The NaOCl and SS groups had higher values of smear layer and lower values of sealer penetrability and dentin bond strength than the PAA and NaOCl-EDTA-NaOCl groups (p < 0.05). Thus, 1% PAA has the potential to be used as a single irrigant in root canals.


Assuntos
Cavidade Pulpar/efeitos dos fármacos , Dentina/efeitos dos fármacos , Resinas Epóxi/química , Ácido Peracético/química , Materiais Restauradores do Canal Radicular/química , Irrigantes do Canal Radicular/química , Camada de Esfregaço/química , Colagem Dentária/métodos , Cavidade Pulpar/química , Dentina/química , Ácido Edético/química , Humanos , Teste de Materiais , Microscopia Confocal , Microscopia Eletrônica de Varredura , Valores de Referência , Reprodutibilidade dos Testes , Hipoclorito de Sódio/química
10.
Molecules ; 24(15)2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31344801

RESUMO

In this work, bamboo fibers are chemically modified with NaOH solution of 1, 4, and 7 wt% concentrations at room temperature, respectively, and subsequently the untreated and treated fibers are prepared with epoxy resin for unidirectional composites by hot pressing molding technique. Tensile and micro-bond tests are conducted on the composite specimens to obtain mechanical properties, such as tensile strength and modulus, elongation at break, and interfacial strength. Besides, scanning electron microscopy (SEM) is employed to perform morphological observations for constituent damages. In addition, the influence of alkali concentration on the thermal performance of epoxy-based composites is examined by using differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. It is found that composite tensile strength reaches the maximum when the alkali concentration is 4%, increased by 45.24% compared with untreated composites. The composite elongation at break increases on increasing the concentration. Inversely, the composite modulus decreases as the concentration increases. Besides, the results demonstrate that the chemical treatment on the fiber surface could improve interface adhesion, as observed from its topography by SEM. Micro-bond test reveals that there is maximum interfacial shear strength when the alkali concentration is 4%, which increases by 100.30% in comparison with the untreated samples. In case of thermal properties, the DSC analysis indicates that the glass transition temperature is maximized at 4% alkali concentration, which is increased by 12.95%, compared to those from unmodified fibers. In addition, TG results show that the 4% concentration also facilitates thermal stability improvement, indicative of superior interfacial bonding.


Assuntos
Fenômenos Químicos , Compostos de Epóxi/química , Sasa/química , Resinas Epóxi/química , Fenômenos Mecânicos , Propriedades de Superfície , Termogravimetria
11.
Molecules ; 24(12)2019 Jun 18.
Artigo em Inglês | MEDLINE | ID: mdl-31216672

RESUMO

In this paper, we studied the aggregation of amphiphilic polymer epoxy-terminated polydimethylsiloxane (PDMS-E) grafted gelatin (PGG) in water induced by methanol, ethanol, 2-propanol, acetone, tetrahydrofuran (THF), and 1,4-dioxane. The aggregation pattern of the polymer was monitored by infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. It was revealed that the aggregate morphology showed clear dependence on the solvent polarity. The PGG aggregates had regular spherical morphology in polar solvents, including water, methanol, ethanol, 2-propanol, and acetone. The coating performance was evaluated by X-ray photoelectron spectroscopy and friction experiment, and PGG and acetone coating exhibited excellent coating performance on the surface of pigskin. Gel was formed in acetone and tetrahydrofuran (THF) with the slow evaporation of solvent, and this property can possibly be applied to industrial sewage treatment. White precipitate and soft film were formed in non-polar 1,4-dioxane.


Assuntos
Resinas Epóxi/química , Gelatina/química , Siloxanas/química , Solventes/química , Técnicas de Química Sintética , Gelatina/ultraestrutura , Polímeros/química , Análise Espectral , Tensoativos/química
12.
Braz Oral Res ; 33: e049, 2019 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-31141039

RESUMO

The aim of the present study was to assess the penetration capacity of two endodontic cements, Endosequence BC Sealer and AH Plus, in artificial lateral canals. Twenty-six two-rooted, maxillary first premolars were instrumented to size 40.06 using K3 files. In each root, six lateral canals of two diameters (0.06 and 0.10 mm) were created with a working length of 2, 4, and 6 mm. The specimens were randomly divided into two groups according to the endodontic cement to be used (Endosequence BC Sealer and AH Plus) and obturated by the single-cone technique. The specimens were imaged by digital periapical radiography and scores from 0 to 4 were attributed according to the degree of penetration by sealers into the lateral canals. Data were analyzed statistically by Kruskal-Wallis and Student-Newman-Keuls tests, and a significance level of p < 0.05 was adopted. No significant difference was observed between the two endodontic cements used to fill the simulated lateral canals (p > 0.05). The diameter of lateral canals only influenced the capacity of the Endosequence BC Sealer in filling the canals, and presented greater penetration in the lateral canals of diameter 0.10 mm (p < 0.05). We concluded that the bioceramic endodontic cement Endosequence BC Sealer presented similar ability as AH Plus to fill simulated lateral canals.


Assuntos
Fosfatos de Cálcio/química , Cerâmica/química , Cavidade Pulpar/efeitos dos fármacos , Resinas Epóxi/química , Óxidos/química , Materiais Restauradores do Canal Radicular/química , Silicatos/química , Combinação de Medicamentos , Humanos , Teste de Materiais , Distribuição Aleatória , Valores de Referência , Reprodutibilidade dos Testes , Obturação do Canal Radicular/métodos , Estatísticas não Paramétricas
13.
Molecules ; 24(9)2019 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-31083463

RESUMO

Epoxy materials have attracted attention for many applications that require fireproof performance; however, the utilization of hazardous reagents brings about potential damage to human health. Eugenol and cardanol are renewable, harmless resources (according to ECHA) that allow the achievement of synthesis of novel phosphorylated epoxy monomers to be used as reactive flame retardants. These epoxy building blocks are characterized by 1H NMR and 31P NMR (nuclear magnetic resonance) and reacted with a benzylic diamine to give bio-based flame-retardant thermosets. Compared to DGEBA (Bisphenol A Diglycidyl Ether)-based material, these biobased thermosets differ by their cross-linking ratio, the nature of the phosphorylated function and the presence of an aliphatic chain. Eugenol has led to thermosets with higher glass transition temperatures due to a higher aromatic density. The flame-retardant properties were tested by thermogravimetric analyses (TGA), a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. These analyses demonstrated the efficiency of phosphorus by reducing significantly the peak heat release rate (pHRR), the total heat release (THR) and the effective heat of combustion (EHC). Moreover, the cone calorimeter test exhibited an intumescent phenomenon with the residues of phosphorylated eugenol thermosets. Lastly, the higher flame inhibition potential was highlighted for the phosphonate thermoset.


Assuntos
Eugenol/química , Retardadores de Chama , Fenóis/química , Calorimetria , Resinas Epóxi/química
14.
Molecules ; 24(10)2019 May 16.
Artigo em Inglês | MEDLINE | ID: mdl-31100841

RESUMO

The need for affordable systems that are capable of regulating the temperature of living or storage spaces has increased the interest in exploring phase change materials (PCMs) for latent heat thermal energy storage (LHTES). This study investigates n-nonadecane (C19H40) and n-eicosane (C20H42) as alkane hydrocarbons/paraffins for LHTES applications. An epoxy resin is used as the support matrix medium to mitigate paraffin leakage, and a thickening agent is utilized to suppress phase separation during the curing process. In order to enhance the thermal conductivity of the epoxy-paraffin composite, conductive agents including carbon nanofibers (CNFs), carbon nanotubes (CNTs), boron nitride (BN) microparticles, or boron nitride nanotubes (BNNTs) are incorporated in different gravimetric ratios. Enhancements in latent heat, thermal conductivity, and heat transfer are realized with the addition of the thermal fillers. The sample composition with 10 wt.% BN shows excellent reversibility upon extended heating-cooling cycles and adequate viscosity for template casting as well as direct three-dimensional (3D) printing on fabrics, demonstrating the feasibility for facile integration onto liners/containers for thermal regulation purposes.


Assuntos
Compostos de Boro/química , Carbono/química , Resinas Epóxi/química , Temperatura Alta , Nanocompostos/química , Nanocompostos/ultraestrutura , Análise Espectral , Termodinâmica
15.
Ultramicroscopy ; 202: 44-50, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-30953993

RESUMO

In sample preparation of biological samples for electron microscopy, many types of embedding media are widely used. Unfortunately, none of them is perfectly resistant to beam induced damage. The article is focused on mass loss measuring of pure epoxy resin EMbed 812 that replaced Epon - the most widely used embedding resin for biological electron microscopy, in a form of ultrathin sections with thicknesses ranging from 30 to 100 nm. The STEM imaging was performed in a quantitative way which allowed us to estimate the mass loss directly up to the total dose of 3000 e-/nm2. For data acquisition we used SEM equipped with a commercial STEM detector working at a relatively low acceleration voltage of 30 kV. In this study we estimated the influence of various factors which can affect the endurance of the epoxy resin EMbed 812 ultrathin sections under an electron beam, such as the sample aging, differences between storing the samples in forms of ultrathin sections and whole blocks, ultrathin sections thicknesses, temperature of the sample, probe current, and one or two-sided carbon coating of ultrathin sections. The aim of this work is to investigate beam induced mass loss at electron energies of SEM and find out how to reduce the mass loss.


Assuntos
Resinas Epóxi/química , Microscopia Eletrônica de Transmissão e Varredura/métodos , Elétrons
16.
Int J Biol Macromol ; 132: 585-591, 2019 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-30914367

RESUMO

Organic onium hydroxide aqueous solutions (OHAS) are demonstrated to be potential solvents for the dissolution of lignin and its epoxidation. A series of OHAS has been assessed in terms of the solubility of soda lignin (SL) and Klason lignin (KL), which are moderately and rarely soluble in NaOH aq. soln., respectively. Tetrabutylphosphonium hydroxide ([P4444]OH) aqueous solution was found to exhibit a highest solubility, specifically 40 wt% of SL and 3.0 wt% of KL. The superior solubility of OHAS is comprehended to be due to weak interactions between OH anions and phosphonium cations, and hence OH anions interact effectively with lignin. Epoxidation of SL was achieved by simply adding epichlorohydrin to [P4444]OH aq. dissolving SL. Films of epoxidized SL were prepared by thermal curing with the aid of a crosslinking agent, and the films were found to possess high thermal stability of >250 °C and excellent ductility. The thermal and mechanical properties were controllable by the concentration of [P4444]Cl as an additive.


Assuntos
Resinas Epóxi/química , Lignina/química , Compostos Organofosforados/química , Água/química , Estabilidade de Medicamentos , Elasticidade , Solubilidade , Soluções , Temperatura , Viscosidade
17.
Mater Sci Eng C Mater Biol Appl ; 99: 940-950, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30889768

RESUMO

This study characterized the static and fatigue compressive properties of a new hybrid composite material made of synthetic and natural fibers with an epoxy matrix. The glass/flax/epoxy composite material was manufactured as a "sandwich structure" with a Type A configuration (i.e. [0G2/0F12/0G2] using unidirectional glass (G) and flax (F) fibers) and Type B configuration (i.e. [0G2/±45F12/0G2] using unidirectional glass (G) and ±45° oblique flax (F) fibers). Digital image correlation was used to obtain the static properties of compressive elastic modulus (Type A, 24.4 GPa; Type B, 14.7 GPa), ultimate compressive strength (Type A, 261.7 MPa; Type B, 231.9 MPa), and Poisson's ratio (Type A, 0.37; Type B, 0.58). Thermographic stress analysis was used to measure a high cycle fatigue strength (HCFS) of 53% (Type A and B) of ultimate compressive strength. Conventional experimental fatigue methods (i.e. stress vs. number of cycles to failure) yielded a HCFS of 56-61% (Type A) and 51-56% (Type B), as well as almost constant dynamic compressive moduli of 15 GPa (Type A) and 10 GPa (Type B) over the entire loading regime. This new composite material may have various potential applications, such as aerospace, automotive, biomechanics, sports, etc., based on the compressive properties measured.


Assuntos
Resinas Epóxi/química , Linho/química , Vidro/química , Processamento de Imagem Assistida por Computador , Teste de Materiais/métodos , Fenômenos Mecânicos , Estresse Mecânico , Termografia , Força Compressiva , Temperatura
18.
Molecules ; 24(5)2019 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-30845646

RESUMO

Microencapsulated phase change materials (MicroPCMs)-incorporated in epoxy composites have drawn increasing interest due to their promising application potential in the fields of thermal energy storage and temperature regulation. However, the study on the effect of MicroPCMs on their microstructure, thermal and viscoelastic properties is quite limited. Herein, a new type of smart epoxy composite incorporated with polyurea (PU)-shelled MicroPCMs was fabricated via solution casting method. Field emission-scanning electron microscope (FE-SEM) images revealed that the MicroPCMs were uniformly distributed in the epoxy matrix. The thermal stabilities, conductivities, phase change properties, and dynamic mechanical behaviors of the composite were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), thermal constant analyzer and infrared thermography. The results suggested that the heat storage ability of the composites was improved by increasing the MicroPCMs content. The thermal stability of MicroPCMs was found to be enhanced after incorporation into the matrix, and the MicroPCMs-incorporated epoxy composites showed a good thermal cycling reliability. Moreover, the incorporation of MicroPCMs reduced the composites' storage modulus but increased the glass transition temperature (Tg) as a result of their restriction to the chain motion of epoxy resin. Besides, a less marked heating effect for the composite was explored through infrared thermography analysis, demonstrating the good prospect for temperature regulation application.


Assuntos
Cápsulas/síntese química , Resinas Epóxi/química , Transição de Fase , Alcanos/química , Emulsões/química , Temperatura Alta , Cinética , Teste de Materiais/métodos , Fenômenos Mecânicos , Tamanho da Partícula , Reprodutibilidade dos Testes , Propriedades de Superfície , Temperatura , Termodinâmica
19.
J Med Syst ; 43(5): 120, 2019 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-30911843

RESUMO

The purpose for this study is to obtain a new composite manufacturing system based on Additive Manufacturing techniques that allows the creation of parts for the medical industry. These pieces will be resistant, lightweight and may have geometries more complex than those created with traditional systems of composite material. The new system is based on the union of two heads on a 3D Rep-Rap printer. One of the heads is an extruder head of thermoplastic Fused Filament Fabrication (FFF) and the other is a dosing head, based on the Robocasting technique, designed to be assembled on the 3D printer. Thermoplastics material and epoxy resin will be used. The alternate printing of both materials generates a piece of composite material. This new technique will allow to increase the structural properties of the piece in the XY plane. The new additive manufacturing system allows to obtain mechanical improvements both in the modulus of elasticity and in the tensile strength. Increase the modulus of elasticity of a value between 50 and 80% depending on the thermoplastic filament used. In the same way the tensile strength has increased between 50 and 60%. The improvement in the strength / weight ratio allows to this new additive manufacturing system to create medical pieces in which the lightness and resistance are its main characteristic, such as orthopedic prostheses.The results show that the use of FFF together with Robocasting, as a manufacturing process for end-use parts, generates an additional advantage that had not been considered until now. The combination of a thermoplastic and an epoxy resin opens a new path in the additive manufacturing since it allows creating pieces with new qualities without being conditioned by the design.


Assuntos
Impressão Tridimensional/instrumentação , Próteses e Implantes , Desenho Assistido por Computador , Elasticidade , Resinas Epóxi/química , Desenho de Equipamento , Humanos , Ortopedia , Poliésteres/química , Resistência à Tração
20.
Molecules ; 24(3)2019 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-30708980

RESUMO

Sample preparation is an important step when testing the mechanical properties of materials. Especially, when carbon nanotubes (CNT) are added to epoxy resin, the increase in viscosity complicates the casting of testing specimens. We present a vacuum casting approach for different geometries in order to produce specimens from functional nanocomposites that consist of epoxy matrix and oxidized multi-walled carbon nanotubes (MWCNTs). The nanocomposites were characterized with various mechanical tests that showed improved fracture toughness, bending and tensile properties performance by addition of oxidized MWCNTs. Strengthening mechanisms were analyzed by SEM images of fracture surfaces and in-situ imaging by digital image correlation (DIC).


Assuntos
Resinas Epóxi/química , Fenômenos Mecânicos , Nanocompostos/química , Nanotubos de Carbono/química , Vácuo , Teste de Materiais , Nanocompostos/ultraestrutura , Nanotubos de Carbono/ultraestrutura , Porosidade , Resistência à Tração , Viscosidade
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA