Desenvolvimento de filamentos de PLA e óxido de grafeno para melhoria termomecânica de peças produzidos por impressão 3D / Development of PLA and graphene oxide filaments for thermo-mechanical improvement of parts produced by 3D printing

Filamentos de nanocompósitos de PLA com óxido de grafeno foram produzidos para aplicação em impressão 3D do tipo modelagem por fusão e deposição. As peças impressas com os nanocompósitos apresentaram melhores propriedades mecânicas se comparadas às peças impressas com PLA puro. As propriedades térmicas dos nanocompósitos não apresentaram alteração frente ao PLA. Foram avaliados também corpos de prova produzidos por injeção a fim de compará-los com aqueles obtidos por impressão 3D

Polyacrylamide hydrogels for stone restoration: Effect of salt solutions on swelling/deswelling degree and dynamic correlation length

Hydrogels have prominent roles in many fields, being applied from the biomedical and pharmacological to engineering and chemical fields. Polyacrylamide (PAM) hydrogels with different crosslinking degree are synthesized and studied in this work by different analytical techniques. Swelling properties are characterized in water and in different aqueous salt solutions, and the results are correlated with the dynamic light scattering measurements of swollen hydrogels; it is demonstrated that gels are more swollen in salt solutions than in pure water. The dynamic correlation length in the swollen gel networks follows closely their mean linkage distance in accordance with De Gennes prescription. SEM observations show that the porous structure is associated with the variation of crosslinking agent amount. The cleaning process of artwork, in the cultural heritage field, can strongly benefit from the use of hydrogels. The desalting efficiency of the gel, when applied to salt contaminated stone surface for cleaning purpose, is tested and the ability of remove efflorescence is demonstrated

Polydimethylsiloxane Membranes Containing Multi-walled Carbon Nanotubes for Gas Separation

<div><p>Polydimethylsiloxane (PDMS) membranes with different concentrations of multi-walled carbon nanotubes were prepared in order to evaluate their gas separation performances. Mixed matrix membranes were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transformed infrared, positron annihilation lifetime and Raman spectroscopies and X-ray diffraction. The permeabilities to CO2, CH4, N2 and O2 were determined. No phase separation was noticed. For carbon nanotubes content of 1 wt%, it was shown a decrease in membrane permeability with slight increase in ideal selectivity, compared to pure PDMS. However, the increase in the filler load up to 6.7 wt% increased the free volume average size of the membranes, improving the contribution of the diffusion to the transport and decreasing ideal selectivities of CO2/CH4, CO2/N2 and O2/N2.</p></div

Otimização do processo de dispersão de nanotubos de carbono em poliuretano termorrígido

Resumo Neste trabalho foi desenvolvido um processo empregando misturador de alto cisalhamento e moinho de rolos para dispersar MWCNTs (multiwalled carbon nanotubes) puros e modificados em poliol visando a preparação de concentrados de 3% em massa. Condições otimizadas no trabalho permitiram a obtenção de suspensões com menor número e tamanho de agregados de MWCNTs. Compósitos contendo 0,5% em massa de MWCNTs foram preparados por diluição dos concentrados em poliol usando mistura mecânica seguida de cura. Resultados de microscopia indicaram que as melhores dispersões foram obtidas com os MWCNTs modificados, os quais permitiram um aumento na tensão na ruptura, no alongamento e uma melhor preservação da estabilidade térmica. Além disso, valores de condutividade elétrica sugerem que o compósito possa ser empregado para dissipação eletrostática. Dessa forma, os resultados obtidos demonstram que a modificação covalente da superfície dos MWCNTs e a utilização de estratégias eficientes de dispersão são essenciais para melhorar as propriedades finais dos nanocompósitos

Evaluation of the dispersion of carbon nanotubes in an elastomeric polyurethane and fatigue test

Abstract Two series of polyurethane (PU) and carbon nanotubes (CNT) based composites with 0.0, 0.25, 0.5 and 1.0 mass% of CNT were obtained from diluting a commercial masterbatch with 30 mass% CNT and using two different dispersion methods. The quality of the dispersions was assessed using optical microscopy, and scanning and transmission electron microscopies. These tests showed that high controlled shear stress is necessary to produce composites with nanoscale dispersion: the elastic modulus improved by an average of 38% in the case of the high-shear dispersed materials in comparison with the neat polymer. A specific fatigue test conducted by dynamic mechanical analysis was first used in this work to compare the neat PU with the CNT/PU nanocomposites. The number of cycles to failure increased from 2700 for the neat polymer to 3200 for the 0.5 mass% CNT based nanocomposite; the elongation at failure increased by 145% in the test conditions

Theoretical study of solvent and temperature effects on the behaviour of poly(ethylene oxide) (PEO).

Molecular mechanics and molecular dynamics simulations were applied in order to study the behaviour of poly ethylene. oxide PEO in different temperatures and solvents. It was found that over the temperature range of 50?500 K the equilibrium structure of PEO is folded. Both kinetic and potential energies increase with temperature. The behaviour of PEO . in two different solvents ? CHCl ? s5 and H O ? s80 ? was found to be similar, with the folded structure observed 32 in equilibrium. The solvation energy calculated using the GBrSA model yielded essentially the same value in CHCl and H2O

Carbon nanotube/dendrimer hybrids as electrodes for supercapacitors.

Carbon nanotubes (CNTs) were surface-modified by a glycodendrimer with four glucose units (4-Gl). Electrodes for supercapacitors based on CNT/4-Gl hybrids were used for the first time in this work. The preparation was conducted by casting eight alternating bilayers of two types of modified multiwalled carbon nanotubes (MWCNTs), MWCNT-COOH/4-Gl and MWCNT-NH2/4- Gl, from aqueous dispersions (pH= 6). The electrodes showed good cohesion, dimensional stability, and a homogeneous nanoscale structure because the carbon nanotube/dendrimer layers interact electrostatically. The supercapacitor was stacked with a separator embedded with a 1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid electrolyte. The device with 20 wt% of dendrimer with respect to CNT content in the electrodes achieved a remarkable increase of 600 % in capacitance compared with the capacitance without the dendrimer