Maria do Carmo Gonçalves

Asymmetric polysulfone and polyethersulfone membranes: effects of thermodynamic conditions during formation on their performance

Abstract Membranes of polysulfone (PSU) and polyethersulfone (PES) were prepared from ternary and quaternary mixtures containing N , N -dimethylformamide (DMF) as solvent, water as non-solvent, and acetone (AC) as additive. The conditions for phase inversion and the desired phase separation mechanisms were selected on the basis of the phase behavior determined for the solvent/non-solvent/polymer systems. The influences of the composition of the casting solution, of the support, and of film thickness on structure and permeation properties of the membranes were analyzed by scanning electron microscopy (SEM) plus flux and separation experiments. The mechanisms of phase inversion that should prevail under the different conditions according to the measured phase diagrams were corroborated by means of light scattering experiments.

In situ compatibilization of polyamide 6/natural rubber blends with maleic anhydride

The rheology, thermal and dynamic-mechanical properties and phase morphology of blends of polyamide 6 with natural rubber (NR) are explored. The objective was to investigate in situ formation of a graft copolymer between NR and polyamide 6 during processing. Addition of maleic anhydride (MA) to the rubber was done prior to blending with polyamide 6. During processing MA can react with both NR and polyamide 6 leading to the graft copolymer formation. Molau test was used to confirm this graft copolymer formation. Rheology and thermal properties as well as dynamic-mechanical analysis also indicated the graftization. Blend morphology analysis showed a significant reduction in particle size as the MA was added to the rubber.

Silicon oxycarbide glasses from silicone networks

Abstract Rubbers resulting from the hydrosilylation reaction between poly(methylsiloxane), and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcycletetrasiloxane, have been pyrolyzed to silicon oxycarbide ceramics, with ceramic yield varying as a function of the mixture composition. The rubber–ceramic conversion process was investigated by 13 C and 29 Si nuclear magnetic resonance and infrared spectroscopies, thermogravimetric analysis and density measurements. The composition of the ceramic products was determined by elemental and X-ray fluorescence analyses and their structural characterization was done by 29 Si solid-state magic angle spinning nuclear magnetic resonance. The structure of the ceramic products is, actually, a mixture of SiO 4 , SiCO 3 , SiC 2 O 2 , SiC 3 O, SiC 4 sites randomly distributed in the bulk. The C–C/SiC x O 4− x composites were prepared by infiltration of the siloxane mixture into the bidirectionally reinforced carbon plate. The composites obtained after pyrolysis showed an improved resistance to oxidation in relation to untreated carbon plates.

Polypropylene/polyamide-6 blends: influence of compatibilizing agent on interface domains

Abstract The influence of maleic anhydride grafted polypropylene (PP-g-MA) at the interface of immiscible polypropylene (PP)/polyamide-6 (PA6) blends was studied by infrared spectroscopy, differential scanning calorimetry and transmission and scanning electron microscopy. The formation of a new copolymer at the interface between the domains and the matrix was investigated. The characterization of the interfacial copolymer was accomplished by carbonyl vibration of the imide group at 1674 cm−1. The reduction of water absorption and the thermoanalysis experiments corroborated the imide linkage between the amino end groups of PA6 and the carboxylic groups of PP-g-MA. The modification of the PA6 particle size and the formation of the interfacial layer were characterized by microscopy and related to the reaction of the interfacial components.

Surface modification of cotton nanocrystals with a silane agent

The research herewith aims at obtaining cellulose nanocrystals with a reduced hydrophilic surface character using a silane with isocyanate groups (isocyanatepropyltriethoxysilane), which are very reactive to hydroxyl groups and thus, are readily able to react with the low quantity of free hydroxyl groups present in the cellulose nanocrystal surfaces, therefore, promoting surface modification. Cellulose nanocrystals were obtained by hydrochloric acid hydrolysis of cotton fiber and were characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and solid state 29Si nuclear magnetic resonance (NMR) and their morphologies were investigated by scanning and transmission electron microscopy techniques. The nanocrystals presented a needle-like geometry with a 10 nm approximate diameter and a 166 nm average length. FTIR, 29Si NMR and silicon mapping images showed that nanocrystal surface chemical modification was successfully achieved. Also, the results confirm that the chemical modification occurred mainly at the nanocrystal surface, keeping the morphological integrity of the nanocrystals. The applied methodology for surface modification of the cellulose nanocrystals provided nanofillers with more appropriate surface characteristics that allow the dispersion in polymeric matrices and the adhesion at filler-matrix interface to be obtained. This may result in a better performance of these nanocrystals as reinforcing agents of hydrophobic polymer matrices.

Fabrication of transparent and ultraviolet shielding composite films based on graphene oxide and cellulose acetate.

Graphene oxide (GO) has been considered a promising filler material for building polymeric nanocomposites because of its excellent dispersibility and high surface area. In this work, we present the fabrication and characterization of transparent and ultraviolet (UV) shielding composite films based on GO and cellulose acetate (CA). GO sheets were found to be well-dispersed throughout the CA matrix, providing smooth and homogeneous composite films. Moreover, the GO sheets were completely embedded within the CA matrix and no presence of this nanomaterial was found at the surface. Nevertheless, CAGO composite films offered an improved high energy light-shielding capacity when compared to pristine CA films. Particularly for UVC irradiation, the CAGO film containing 0.50wt% GO displayed a UV-shielding capacity of 57%, combined with 79% optical transparency under visible light. These CAGO composite films can be potentially applied as transparent UV-protective coatings for packing biomedical, pharmaceutical, and food products.

Poly(Ethylene Glycol) as a Compatibilizer for Poly(Lactic Acid)/Thermoplastic Starch Blends

A new route to prepare poly(lactic acid) (PLA)/thermoplastic starch (TPS) blends is described in this work using poly(ethylene glycol) (PEG), a non-toxic polymer, as a compatibilizer. The influence of PEG on the morphology and properties of PLA/TPS blends was studied. The blends were processed using a twin-screw micro-compounder and a micro-injector. The morphologies were analyzed by scanning and transmission electron microscopies and the material properties were evaluated by dynamic-mechanical, differential scanning calorimetry, thermogravimetric analysis and mechanical tests. PLA/TPS blends presented large TPS phase size distribution and low adhesion between phases which was responsible for the lower elastic modulus of this blend when compared to pure PLA. The addition of PEG resulted in the increase of PLA crystallization, due to its plasticizing effect, and improvement of the interfacial interaction between TPS and PLA matrix. Results show that incorporation of PEG increased the impact strength of the ternary blend and that the elastic modulus remained similar to the PLA/TPS blend.

Structural and morphological investigations of β-cyclodextrin-coated silver nanoparticles.

This paper describes the synthesis of silver nanoparticles using an aqueous silver nitrate solution in the presence of glucose as a reducing agent, sodium hydroxide as a reaction catalyst and β-CD as a stabilizer. The structure and the morphology associated to the stabilizing layer around the silver nanoparticles were investigated. Raman spectroscopy confirmed the nanoparticle surface modification by β-CD, demonstrating the interaction between the β-CD rim hydroxyl groups and the AgNP surface. Transmission electron microscopy images showed an average 28.0nm diameter pseudo-spherical nanoparticles. Apart from this, a novel characterization of the β-CD layer surrounding the nanoparticles was carried out by using complementary analytical electron microscopy based on electron spectroscopy imaging in the transmission microscope. Mapping images revealed the presence of carbon and oxygen, demonstrating the existence of a uniform and interacting β-CD layer covering the nanoparticles. The antibacterial activity was also investigated and the β-CD-coated silver nanoparticles showed a promising bactericidal activity against the microorganism Escherichia coli.

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

A new practical experiment involving silver and gold nanoparticle syntheses was introduced in an inorganic chemistry laboratory course for undergraduate students at the Institute of Chemistry, UNICAMP. The nanoparticles were synthesized by the reduction of silver nitrate and tetrachloroauric acid with sodium borohydride and sodium citrate in an aqueous medium. Stabilities of the suspensions were tested using several different reactants including sodium chloride, polyvinylpyrrolidone, polyvinyl alcohol and cistamine. Changes in optical properties were observed by electronic spectra and also by transmission electronic microscopy, which also yielded data for estimating particle size.

Comparative AFM and TEM investigation of the morphology of nylon6-rubber blends

Abstract In the present paper, blends of nylon6 with rubber were cut by means of microtoming for the AFM investigation of bulk morphology using phase contrast imaging. This investigation was compared to the results of a TEM analysis. The cutting procedure used in the preparation of the samples did not affect the morphology of the rubber particles, since the topography of the area analyzed did not affect the contrast between hard and soft phases in AFM phase contrast imaging. The values of particle average diameter and particle aspect ratio of rubber particles in the nylon6 matrix are similar in AFM and TEM analyses, showing that both techniques can be used to distinguish phase morphology of polymer blends. It was also possible to detect an elongation of the rubber particles in the nylon6/SEBS-g-MA sample, caused by flow direction of the blend injection process.