Maria Inês Bruno Tavares

Polymer blends based on polyolefin elastomer and polypropylene

A new family of homogeneous polyolefin polymers that exhibit unique molecular and rheological properties designated polyolefin elastomers (POEs) are characterized by a narrow molecular weight and high degrees of comonomer distribution. Because these copolymers are often elastomeric in nature, one of the uses for these materials is as impact properties improver for brittle polymers such as polypropylene at low temperatures. In this work a study was carried out about the effectiveness of the polyethylene elastomer (POE) as an impact modifier for polypropylene in relation to the traditional modifier EPDM. In this study the flow properties of of the POE/PP and EPDM/PP blends were also evaluated. The blends were analyzed by solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The results showed that PEE/PP and EPDM/PP blends present a similar crystalline behavior, which resulted in a similar mechanical performance of the blends, on the composition analyzed. It was also verified that the POE/PP blend presents lower torque values than the EPDM/PP blend, which indicates a better processability when POE is used as an impact modifier.

Impact behavior of sugarcane bagasse waste–EVA composites

Abstract The impact performance of chopped bagasse–EVA matrix composites is evaluated and compared with the behavior of bagasse filled PP and PE matrix composites and wood-based materials. The volume fraction and size of the chopped bagasse used as filler was varied. The experimental results show that the incorporation of bagasse strongly reduces the deformation capacity of EVA polymer. The reduction of the deformation capacity of the composites was also inferred by solid-state NMR relaxation analysis. The impact strength was independent of the bagasse size, but varied with the volume fraction. As a function of the volume fraction it was shown that the mechanical performance of bagasse–EVA composites could be tailored to reproduce the behavior of wood-based particle boards.

Characterization of EPDM/atactic polypropylene blends by high‐resolution solid‐state NMR

The study of EPDM/atactic polypropylene blend compatibility was investigated by cross-polarization/magic angle spinning carbon-13 NMR spectra, variation contact time experiment analysis, proton spin-lattice relaxation time in the rotating frame, carbon-13 spin-lattice relaxation time, and a dipolar dephasing experiment. The data are discussed in terms of mobility and compatibility of polymeric blends.

NMR study of plasticized PVC

Samples PVC plasticized by di-isobutylphthalate and di-2-ethylhexylphthalate, with plasti- cizer content varying up to 180 parts per hundred, have been examined using solid-state tH- and t3C-NMR. Proton spin-lattice relaxation times in both the laboratory and the rotating frames were measured, with analysis into multi-exponential components where necessary. Cross-polarisation magic- angle spinning ~3C spectra have also been obtained, including variation with contact time. The data are discussed in terms of the domain structure of the samples at the microscopic level and of the role of the plasticizer.

Psychiatric hospital beds and prison populations in South America since 1990: does the Penrose hypothesis apply?

IMPORTANCE In 1939, English mathematician, geneticist, and psychiatrist Lionel Sharples Penrose hypothesized that the numbers of psychiatric hospital beds and the sizes of prison populations were inversely related; 75 years later, the question arises as to whether the hypothesis applies to recent developments in South America. OBJECTIVE To explore the possible association of changes in the numbers of psychiatric hospital beds with changes in the sizes of prison populations in South America since 1990. DESIGN, SETTING, AND PARTICIPANTS We searched primary sources for the numbers of psychiatric hospital beds in South American countries since 1990 (the year that the Latin American countries signed the Caracas Declaration) and compared these changes against the sizes of prison populations. The associations between the numbers of psychiatric beds and the sizes of prison populations were tested using fixed-effects regression of panel data. Economic variables were considered as covariates. Sufficiently reliable and complete data were obtained from 6 countries: Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. MAIN OUTCOMES AND MEASURES The numbers of psychiatric beds and the sizes of prison populations. RESULTS Since 1990, the numbers of psychiatric beds decreased in all 6 countries (ranging from -2.0% to -71.9%), while the sizes of prison populations increased substantially (ranging from 16.1% to 273.0%). Panel data regression analysis across the 6 countries showed a significant inverse relationship between numbers of psychiatric beds and sizes of prison populations. On average, the removal of 1 bed was associated with 5.18 more prisoners (95% CI, 3.10-7.26; P = .001), which was reduced to 2.78 prisoners (95% CI, 2.59-2.97; P < .001) when economic growth was considered as a covariate. The association between the numbers of psychiatric beds and the sizes of prison populations remained practically unchanged when income inequality was considered as a covariate (-4.28 [95% CI, -5.21 to -3.36]; P < .001). CONCLUSIONS AND RELEVANCE Since 1990, the numbers of psychiatric beds have substantially decreased in South America, while the sizes of the prison populations have increased against a background of strong economic growth. The changes appear to be associated because the numbers of beds decreased more extensively when and where the sizes of prison populations increased. These findings are consistent with and specify the assumption of an association between the numbers of psychiatric beds and the sizes of prison populations. More research is needed to understand the drivers of the capacities of psychiatric hospitals and prisons and to explore reasons for their association.

A molecular dynamic study of the starch obtained from the Mangifera indica Cv. Bourbon and Espada seeds by 13C solid state NMR

Abstract The molecular mobility of the starch obtained from Mangifera indica Cv. Bourboun and Espada , has been characterised by 13 C solid state nuclear magnetic resonance, using techniques, such as magic angle spinning (MAS) and cross polarisation magic angle spinning (CPMAS) NMR and by proton spin-lattice relaxation time in the rotating frame ( T 1 H ρ ). The CPMAS 13 C NMR spectra of these seeds showed three signals for Bourboun and two very broad signals for Espada . The seeds of the Mangifera indica Cv. Bourboun and Espada are heterogeneous amorphous polysaccharides that present, at least, two domains with distinct molecular mobility. These domains differ in size and chain packing. The variable contact time decay confirms that these starches are amorphous and present one predominant rigid domain. Mango fruits were also analysed by delayed contact time experiments, and the 13 C decays showed that the polysaccharides are heterogeneous and contain one rigid domain that controls the relaxation parameter.

Tensile behavior of irradiated recycled polyolefin plastics

Solid wastes represent a potential source for raw materials in the world. In Brazil, municipal solid waste (MSW; 2-%) is expected to grow at a rate per year higher than the worldwide rate (1%). On the other hand, the consumption of polymer blends increases at a rate more than twice that of all plastics. Therefore, the recycling of polymeric blends has gained increasing attention in the world due to economic and environmental considerations. A two-step process, developed at the Institute (IMA/ UFRJ), allows one to recover plastic residues and permits the production of materials with controllable composition and homogeneous characteristics. The compression behavior of polyblends, composed of typical polymers that appear in domestic wastes-low and high polyethylenes-can be improved by gamma irradiation. In the present work, the tensile behavior of recycled 75/25 blends of low-density polyethylene (LDPE) and high-density polyethylene (HDPE), after exposure to gamma rays in the air, was investigated. Tensile testing, scanning electron microscopy, infrared and solid-state 13 C-nuclear magnetic resonance spectroscopy, as well as gel content were used to study the effect of gamma irradiation on the polymer blends. The tensile strength was found to increase with radiation dose while the elongation at break decreased. Our experimental results indicate that the gamma irradiation degradation process involves crosslinking at lower doses and chain scission at higher doses.

NMR studies of PVC molecular mobility

Abstract The molecular mobility of a polymer in the solid state can be determined by NMR relaxation measurements. The analysis of proton spin-lattice relaxation time (T 1 H) and proton spin-lattice relaxation time in the rotating frame (T 1 H ϱ ), allow information to be obtained about the behaviour of homogeneous samples. The response of this behaviour can be extracted by NMR solid state techniques such as: magic-angle spinning (MAS), variable contact time, inversion-recovery, spin-locking, delayed contact time and cross polarization-MAS.

A solid state NMR carbon-13 high resolution study of natural fiber from sugar cane and their composites with EVA

Abstract Natural fibers obtained from sugar cane have been analysed by carbon-13 high resolution solid state nuclear magnetic resonance (NMR) employing different techniques such as: cross-polarisation magic angle spinning (CP/MAS); variable contact time experiment and proton spin-lattice relaxation time in the rotating frame. Molecular mobility information for distinct types of sugar cane fibers, as well as two different mixtures (one of the mixtures contains equal amounts of waste fibers and the other has a random distribution of these waste fibers) and their composites with poly(ethylene-co-vinyl acetate) (EVA) were obtained from those techniques. Mechanical measurements (stress–strain) were also recorded for all samples. Both NMR and mechanical measurements responses showed that the mixtures of natural fiber can be used as a matrix in the composites.

Carbon-13 high resolution solid state NMR study of natural fibres obtained from sugar cane without treatment and their composites with EVA

Abstract Natural fibres from three distinct type of sugar cane without any specific treatment to remove the sugar, lignin and impurities and their composites with EVA, have been analysed by carbon-13 high-resolution solid state nuclear magnetic resonance (NMR). The NMR techniques used were cross-polarization magic angle spinning (CP/MAS); variable contact-time and proton spin-lattice relaxation time in the rotating frame (T1Hρ). From those measurements it was observed that the molecular mobility of chains along the fibres has a particular behaviour.