Paulo H. S. Picciani

Eletrofiação de Polímeros em Solução: parte I: fundamentação Teórica

The electrospinning technique has been known since the 1930s, but only with the advent of new nanotechnology applications this technique was re-discovered and became important for production of nanomaterials. The potential for obtaining different nanofibers with sizes ranging from 50 to 500 nm and micrometer length has been investigated for different materials, with promising results in different applications. The first part of this review is aimed at describing the fundamentals of the electrospinning process. We describe the influence of process variables such as applied field, working distance, speed of rotation of the collector and solution injecting flow rate. The variables associated to this system, such as type of solvent and polymer of interest, are also discussed.

Estudo das propriedades mecânicas e elétricas de fibras de curauá modificada com polianilina

Natural fibers have been employed as reinforcement filler in composite materials for the automobile industry. Among the natural fibers, the curaua fiber is promising due to its high mechanical resistance associated with low density values. In this work curaua fibers are chemically modified by a conducting polyaniline coating, with the aim of using this new conductive composite as pressure sensors. The composite material obtained was characterized using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and optical microscopy. The results demonstrated that the methodology adopted was efficient in forming a partial, but effective, coating of the fiber, thus leading to conducting paths along the whole fiber. The electro-mechanical properties of the fibers were also evaluated and the composites have potential for low cost pressure sensors. Furthermore, the modified fibers had good thermal stability and the partial coating allows the composite to be naturally degraded as an environmentally-friendly material.

Edible films and coatings based on biodegradable residues applied to acerolas (Malpighia punicifolia L.)

BACKGROUND This study aimed to produce and characterize edible films and coatings from fruit and vegetable residue (FVR) flour and potato peel (P) flour. Two coating approaches (immersion and film) were studied on the quality of acerolas. RESULTS Film-forming solutions (FFS) presented a viscoelastic behavior and a gelation process occurring at 70 °C. Maximum density (1.018 g cm(-3) ), viscosity (44.404 cP) and starch content were obtained for FFS based on 8% FVR flour with 4% P flour. This same film presented enhanced mechanical properties such as tensile strength and elongation at break (0.092 MPa and 36% respectively). Solubility of the films averaged 87%, demonstrating high hydrophilicity. Improved performance was obtained for film-packaged acerolas, which exhibited an increase in shelf life of 50% compared with control fruits. A lower loss of weight was observed for these samples by about 30-57% compared with control fruits, but minor modifications of pH, titratable acidity and soluble solid content occurred during storage. CONCLUSION This study demonstrated the potential of FVR flour for edible coating and film formulation. Practical application on acerolas constituted a motivating route to evaluate and optimize this process; however, microbiological and sensory analyses are necessary to assess the material acceptability and safety.

Eletrofiação de polímeros em solução: parte II: aplicações e perspectivas

In our previous review[1], the process of electrospinning was discussed on the basis of theoretical and experimental aspects toward preparation of different polymeric nanofibers. In this second review, we focus on the aspects related to the application of electrospun materials in various fields such as medicine, agriculture, sensors, and processing of other materials. We discuss the most often characterization techniques used for these materials and their potential. This review complements the previous one and uses the same terminology.

Interaction of levofloxacin with lung surfactant at the air-water interface

The molecular-level interaction of levofloxacin with lung surfactant was investigated using Langmuir monolayers and atomistic molecular dynamics (MD) simulations. In the simulation, the DPPC/POPC mixed monolayer was used as a lung surfactant model and the molecules of levofloxacin were placed at the air-lipid interface to mimic the adsorption process on the lung surfactant model. The simulation results indicate that amphoteric levofloxacin expands the lung surfactant, also stabilizing the film for levofloxacin fractions until 10% w/w at least. The Langmuir monolayers made with the lung surfactant Curosurf had expanded isotherms upon incorporation of levofloxacin, without changes in monolayer elasticity. In fact, levofloxacin induced film stability with increased collapse pressures in the Curosurf isotherms and delayed the phase transition, according to Brewster angle microscopy (BAM) imaging. Using polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS), we found that levofloxacin is preferentially located in the head group region, inducing an increased organization of the Curosurf film. This location of levofloxacin was confirmed with MD simulations. The stability inferred demonstrates that the lung surfactant can be used as a drug delivery system for the administration via inhalation or intratracheal instillation of levofloxacin to treat lung diseases such as pneumonia and respiratory distress syndrome.

Caracterização físico-mecânica de filmes de borracha natural epoxidada curáveis em temperatura ambiente

This paper presents the crosslinking study at room temperature of epoxidised natural rubber (ENR), of 25% of epoxidation level, with a curing agent containing thiol trimethylolpropane tris(2-mercaptoacetate) (TMP-SH). The compositions were made from solubilization of ENR, and subsequent reaction with TMP-SH. Compositions with 5, 10 and 20 phr of TMP-SH, NR and ENR controls were prepared. It was also prepared a composition with NR and 10 phr of TMP-SH to demonstrate the effect of epoxide group. The crosslinking formation of the films was determined by physical-mechanical properties as equilibrium swelling index, tensile strength and dynamic-mechanical properties. The results showed the efficiency of the cure agent and the influence of TMP-SH content incorporated, in the studied properties, and the ENR composition with 10 phr of curing agent presented the best physical-mechanical performance.

Molecular organization and doping in poly(2-methoxyaniline)/Ni(dmit)2 films obtained with the Langmuir–Blodgett technique

The control of the properties of materials at the molecular level is pursued for many applications, especially those associated with nanostructures. In this paper, we show that the coordination compound [Ni(dmit)2], where (dmit) is the 1,3-dithiole-2-thione-4,5-dithiolate ligand, can induce doping of poly(2-methoxyaniline) (POMA) in molecularly ordered Langmuir and Langmuir–Blodgett (LB) films. Doping was associated with interactions between the components and the compression of the Langmuir film at the air–water interface, according to polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data. Taking these results together with in situ UV-Vis absorption measurements, we could identify the molecular groups involved in the interaction, including the way they were reoriented upon film compression. The Langmuir films were sufficiently stable to be transferred as Y-type LB films, while the hybrid POMA/[Ni(dmit)2] films remain doped in the solid state. As expected, the molecular charges affected the film morphology, as observed from combined atomic and electric force microscopy measurements. In summary, with adequate spectroscopy and microscopy tools we characterized molecular-level interactions, which may allow one to design molecular electronic devices with controlled electrical properties.