Yêda Medeiros Bastos de Almeida

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.

A biodegradabilidade da blenda de poli(β-Hidroxibutirato-co-Valerato)/amido anfótero na presença de microrganismos

The increasing consumption of plastics has generated environmental problems because it takes more than a hundred years for a discarded polymer to degrade. The ideal plastic should present desirable industrial properties and be degradable within a satisfactory time period. Researches is conducted to plastics with good properties for packaging, but that are biodegradable when discarded to the environment. In this work we evaluated the biodegradation of the blend of the copolymer poly(hydroxybutyrate-hydroxyvalerate, PHB-HV, which is a natural, biodegradable and biocompatible thermoplastic, and of the starch amphiprotic, in the proportion of 75 and 25% m/m, respectively. The results were obtained through the Sturm test, a methodology for the evaluation of biodegradation in the presence of a mixed culture of Phanerochaete chrysosporium and Talaromyces wortmannii fungi. The results pointed to biodegradation of the blend as a function of the time, with the appearance of terminal carboxylic groups. In addition, a new crystalline symmetry was observed in the polymeric structure.

Evaluation of the types of starch for preparation of LDPE/starch blends

Nesse trabalho foi realizado um estudo sobre diferentes tipos de amido quanto ao crescimento, e a atividade amilolitica de culturas mistas e isoladas dos fungos Phanerochaete chrysosporium e Talaromyces wortmannii. Avaliaram-se tambem as propriedades termicas e mecânicas das blendas de polietileno/amido anfotero (na proporcao 80/20 (m/m)) antes e apos a inoculacao das culturas mistas desses fungos.O amido regular Amidex 3 e o amido modificado Fox5901 foram os que se destacaram quanto ao crescimento celular e producao da enzima amilase. Apesar do pouco tempo de exposicao dos filmes com os fungos, pode-se concluir que os microrganismos promovem mudancas fisicas e quimicas na estrutura da blenda, modificando suas propriedades termicas e mecânicas. A alteracao do grau de cristalinidade e das propriedades mecânicas das blendas podem ser indicios da modificacao provocada pelo processo de biodegradacao.

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.

The Effect of Polystyrene on the Crystallization of Poly(3-hydroxybutyrate)

Mechanical properties, morphology and nonisothermal crystallization of poly(3-hydroxybutyrate) (PHB) and blends of PHB and polystyrene (PS) were studied by tensile tests, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). A two-phase structure composed by a PHB matrix and nearly spherical particles of PS was clearly noticed in SEM images. The presence of small amounts (0.5% to 3%) of amorphous PS affected the crystallinity of PHB, being more evident when high cooling rates were applied. The kinetics of nonisothermal crystallization was modeled according to Ozawa equation. The dependence of Ozawa parameters on temperature followed the same trend for PHB and PHB/PS blends; model parameters were found to be lower for the blends than for the neat PHB.

Effect of the radiolitic sterilization in polyethylene/starch blends

Samples of LDPE/modified starch blends 80/20 m/m before and after exposure to gamma rays were examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The effect of gamma radiation is clearly seen in the samples irradiated at a dose of 25 kGy. The main alteration in the polymeric material after exposure at the radiation range was a decrease in the mechanical properties, alterations in the chemical structure of the blend with an increase in the carbonyl and vinyl indices and the appearance of new crystalline symmetry generating a crystalline domain not existing before in the blend.

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.

Evaluation of photodegradation in LDPE/modified starch blends

Photodegradation of LDPE/modified starch blends 80/20 m/m has been examined by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X ray diffraction (DRX) before and after exposure to ultraviolet radiation (UV). Samples were exposed to UV in the laboratory for periods of 6, 24, 48 and 60 hours. The main alteration in the polymeric material after exposure to the radiation was a decrease in the mechanical properties, tensile strength and elongation. There were also changes in the chemical structure of the blend with an increase in the carbonyl and vinyl indices, 65.58 and 53.29%, respectively. The analysis of the blend crystallinity pointed to the formation of a new crystalline symmetry that did not exist before the irradiation.

Evaluation of a PVC sensing phase for determination of chlorinated hydrocarbons in water by mid-infrared spectroscopy

In this work, mid-infrared spectroscopy has been employed to investigate the effect of amount (25 or 40%) and type of plasticiser (di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl phthalate (DOP) and 2-nitrophenyl octyl ether (NPOE)) on the analytical response of a poly(vinylchloride) (PVC) sensing phase for the determination of the chlorinated hydrocarbons (chlorobenzene (ClB), trichloroethylene (TCE) and trichlorobenzene (TCB)) in water. It was observed that films with 40% of plasticiser provided higher sensitivity and lower limits of detection than those with 25%, although the later films are easier to handle. A similar behaviour was also observed for sensing phases prepared with the plasticisers NPOE and DOS. By employing a DOS-based PVC sensing phase and extraction time of 60 min, limits of detection of 0.3, 0.6, and 0.5 mg L-1 were obtained for chlorobenzene, trichloroethylene and trichlorobenzene, respectively.

Caracterização físico-química da superfície de filmes de poli(tereftalato de etileno)

The current work is concerned with some techniques which allow the characterization of PET film surface, i.e: refractometry, roughness, friction coefficients analysis and contact angle analysis. The samples analysed were homopolymer, corona-treated and a poly(ethylene terephthalate-co-1,4 ciclohexanedimethanol) films. The corona-treated PET film showed higher surface tension value due to the major contribution on the polar groups. The copolyester film structure showed to be much less crystalline than the others, which have been obtained by refractive index measurements. These amorphous structures and the higher tension level of the treated films should provide a better understanding of the adhesion phenomena.