Rosa Maria Souto-Maior

Time‐resolved picosecond optical nonlinearity and all‐optical Kerr gate in poly (3‐hexadecylthiophene)

A time‐resolved anisotropic configuration exploiting the Z‐scan technique in a one color pump‐and‐probe arrangement was implemented to measure the time response and the value of the nondiagonal component of the third‐order nonlinear susceptibility of a chloroform solution of poly (3‐hexadecylthiophene). In addition, an all‐optical Kerr gate with picosecond response using the polymeric solution was implemented.

Saturation effects in the nonlinear-optical susceptibility of poly(3-hexadecylthiophene)

We performed Z-scan measurements to investigate the optical nonlinearity of poly(3-hexadecylthiophene) in a chloroform solution. Values for the real and the imaginary parts of the nonlinear susceptibility were obtained for solutions with various polymer concentrations. The nonlinear-optical properties were studied as a function of polymer concentration and light intensity from which saturation of nonlinear refraction and saturated absorption were observed. The saturation intensity was determined, and the corresponding values are presented for all concentrations studied. Time-resolved measurements of the nondiagonal part of nonlinear susceptibility are also presented.

Degradation studies on plasticized PVC films submited to gamma radiation

Poly (vinyl chloride), PVC, is a rigid polymer and for several of its applications must be compounded with plasticizing agents. The plasticizers minimize the dipolar interactions, which exist between the polymers chains, promoting their mobility. In this work we studied the properties of PVC/plasticizer systems submitted to different doses of gamma radiation. We have used four commercial plasticizers amongt them di(2-ethylhexyl) phthalate, DEHP, which is present in a great number of commercial applications. The PVC/plasticizer systems have been studied as films made by the solvent evaporation technique. Irradiated and non-irradiated films have been characterized by viscosimetric analysis, mechanical essays and infrared spectroscopy. The results have shown that the rigid, non plasticized, PVC film presented the greatest degradation index, while among the plasticized films the one which presented the larger degradation index due to chain scission was the DEHP plasticized PVC.

Synthesis Of 3-Aryl-5-[Thien-3-Yl Methyl]-1,2, 4-Oxadiazoles

Abstract A convenient and efficient synthesis of eight new compounds 5a-h is described. The intermediates 4a-h have also been isolated and characterized the with help of spectroscopic data.

Estudo de propriedades de PVC modificado com grupos alquila e benzila

Poly(vinyl chloride) (PVC) ranks second among the most consumed thermoplastics in the world, and is considered the most versatile plastic. This versatility arises from its properties and suitability to a variety of transformation processes. The resin is non toxic and inert, therefore the choice of additives having these properties allows for the fabrication of films for food packaging and medical products. On the other hand, the PVC properties can be altered by sterilization processes, in particular through gamma radiation. In this paper we present a study of the flexibility and stability to gamma radiation of chemically-modified PVC. PVC was modified through substitution of chlorine by alkyl and benzyl groups using Grignard reagents. Modified PVC samples were characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy, infrared spectroscopy and differential scanning calorimetric analyses. Degradation of the polymers when submitted to gamma irradiation was evaluated by their viscometric parameters. The modified PVCs generally presented higher stability to gamma radiation than the original polymer. The benzyl substituted polymer exhibited the highest stability when submitted to the sterilization dosage of 25 kGy. The modified PVCs presented glass transition temperatures slightly lower than the original polymer pointing to an increase in flexibility due to the presence of alkyl and benzyl groups as substituents in the main chain.

Solvent-fractionated sugar cane bagasse lignin: structural characteristics and electro-spinnability

Abstract Lignin is one of the most abundant macromolecules on Earth. Lignins are obtained as by-products from the paper industry and used mostly as fuel. Their diverse composition has limited the development of high added-value applications: however, because of their abundance and sustainable origin, there is a growing interest in using lignins as a raw material and as a replacement for oil derivatives. In order to use lignins in bio-refineries, several processes must be studied and standardized. Lignin fractionation using solvents is a promising process. In this study, lignin from sugar cane bagasse (L1) was fractionated with solvents, and the fractions were characterized to evaluate structural aspects relevant for the production of fibers. L1 was extracted into four fractions with toluene (E1), ethanol (E2), methanol (E3), and dimethyl sulfoxide (DMSO, E4). Fractions E2, E3, and E4, showed only slightly different molar masses and molar mass distribution, but have relevant differences in their structural characteristics and processability. The ethanol extract (E2) provided lignins with a more flexible structure, and electro-spinning resulted in the production of nanofibers with diameters between 60 and 120 nm; the methanol fraction (E3) produced nanospheres with diameters between 90 and 350 nm; the DMSO fraction (E4) covered only a surface with electro-spray. These results show the possibility of developing high added-value applications using fractions of lignin from distinct biomasses or from their combination.

Desenvolvimento e caracterização de filmes à base de Poli(3-hidroxibutirato) aditivado com ZnOnano

Industrial Poly(hydroxybutyrate) PHB films were produced with the addition of nanostructured zinc oxide (ZnOnano) in different proportions (1, 3, 5% w/w). The films were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and infrared spectroscopy (FTIR). The antimicrobial activity against the bacteria E. coli was also evaluated. Homogeneous films with good dispersion of the nanoparticles in the polymer matrix were obtained. The stability of the polymer was not compromised by the nanoparticles, which functioned as nucleating agents to increase the crystallinity of the polymer. The principal component analysis (PCA) showed that the nanoclay modified the vibrations of the functional groups, indicating the existence of interactions between the polymer and ZnOnano. The nanocomposite film containing 5% of ZnOnano inhibited the growth of pathogenic E. coli., thus showing promise for applications in the food packaging industry.