Propiedades reológicas del polipropileno en flujos elongacionales y de cizallamiento

Las deformaciones elongacionales y de cizallamiento tienen un papel muy importante en las operaciones de transformación de polímeros como extrusión, inyección, soplo y termoformado. El flujo del material a través de un canal que posee una contracción abrupta, ha sido usado para obtener medidas de viscosidad elongacional y de cizallamiento. En este trabajo fueron desarrollados procedimientos experimentales y teóricos para evaluar estas viscosidades con la ayuda del modelo de Cogswell, para dos tipos de polipropileno de propiedades reológicas diferentes. Los resultados en cizallamiento fueron comparados con medidas realizadas en un reómetro rotacional y mostraron una buena concordancia, y la viscosidad elongacional fue inferida a altas tasas de deformación

Effect of Prior Photodegradation on the Biodegradation of Polypropylene/Poly(3-hydroxybutyrate) Blends

In this work, the effect of blend composition and previous\ud photodegradation on the biodegradation of polypropylene/\ud poly(3-hydroxybutyrate) (PP/PHB) blends\ud was studied. The individual polymers and blends with\ud or without the addition of poly(ethylene-co-methyl acrylate-\ud co-glycidyl methacrylate) [P(E-MA-GMA)] as a\ud compatibilizer (in the case of 80/20 blend) were\ud exposed to UV light for 4 weeks and their biodegradation\ud was evaluated. The biodegradation of PHB phase\ud within the blends was hindered as PHB was the dispersed\ud phase and PP fibrous particles were observed\ud at the surface of the blend samples after biodegradation.\ud Previous photodegradation lessened PHB biodegradation\ud but enhanced the biodegradation of PP and\ud the blends within the biodegradation time studied.\ud Photodegradation resulted in cracks at the surface of\ud PP and the blends, which probably facilitated the biotic\ud reactions due to an easier access of the enzymes to\ud deeper polymer layers. It also resulted in a decrease of\ud molecular weight of PP phase and formation of carbonyl\ud and hydroxyl groups which were consumed during\ud biodegradation. Size exclusion chromatography\ud analysis revealed that only the short chains of PP were\ud consumed during biodegradation.Capes, FAPESP, CNPq for financial support and Kleber Vaccioli for performing the respirometry experiments

Oscilador LC monolítico comandado por tensão a 2,4GHz

Esta Comunicação tem como finalidade divulgar o projecto de um VCO monolítico a 2.4GHz para integrar uma Malha de Captura de Fase (PLL). O Oscilador projectado é baseado num par diferencial cruzado (parte activa). O circuito funciona com uma tensão de 2.8V e com uma tensão de comando entre 1.6V e 1.8V, produzindo uma variação de frequência entre 2.4GHz e 2.75GHz.info:eu-repo/semantics/publishedVersio

Influence of the type of polypropylene on the photodegradation of blends of polypropylene/high impact polystyrene

Este trabalho visa avaliar a influência do tipo de polipropileno no comportamento da blenda polipropileno/poliestireno de alto impacto (PP/HIPS) quando exposta à radiação UV. Foram usados uma resina virgem de PP (PPv) e outra reprocessada (PPrep). Inicialmente, avaliou-se o comportamento individual dos componentes da blenda, HIPS, PPv e PPrep, quando submetidos à radiação UV por até 15 semanas de exposição. As técnicas de caracterização utilizadas para monitorar o desempenho tanto das resinas individualmente quanto das blendas submetidas à radiação UV foram: propriedades mecânicas (tração e impacto), medidas de índice de fluidez (MFI), análise térmica (DSC), espectroscopia no infravermelho (FTIR) e microscopia eletrônica de varredura (MEV). A partir dos resultados com essas técnicas verificou-se que o PPv foi a resina mais afetada pela radiação e consequentemente as blendas preparadas com esse PP também foram mais sensíveis à fotodegradação do que as demais. Em termos de fotoestabilização este resultado mostra-se interessante, já que as blendas PP/HIPS preparadas com uma resina previamente degradada necessitariam de menores teores de aditivos do que esse mesmo tipo de blenda preparada com resina virgem

Plasma polymerized acetaldehyde thin films for retention of volatile organic compounds

The aim of this work is the production and characterization of plasma polymerized acetaldehyde thin films. These films show highly polar species, are hydrophilic, organophilic and easily adsorb organic reactants with CO radicals but only allow permeation of reactants with OH radicals. The good step coverage of films deposited on aluminum trenches is useful for sensor development. Films deposited on hydrophobic substrates may result in a discontinued layer, which allows the use of preconcentration in sample pretreatment. Deposition on microchannels showed the possibility of chromatographic columns and/or retention system production to selectively detect or remove organic compounds from gas flows.FAPESPCNPqUniversity of Puerto Rico - Advance it Progra

Interfacial tension in polymer blends : measurements and analysis

Interfacial tension is one of the most important parameters that influence the morphology of polymer blends. However, few data are available regarding interfacial tension between polymers due to experimental difficulties.Two devices, one based on the pendant drop method and another based on the spinning drop method, were constructed in this work to conduct an experimental study of interfacial tension between polymers. With both instruments, it was possible to view the drop in real time and to calculate the interfacial tension on-line. The following aspects were considered: special syringe design, the necking and capillary effects, in the pendant drop method, and sealing of the rotating tubes and density measurement in the spinning drop method. The two devices were shown to be reliable and complementary. A method to infer interfacial tension from transient measurements was suggested.Interfacial tension was measured for different polymer pairs. The effects of temperature, molecular weight, bimodal blending and molecular weight distribution were evaluated. The effect of adding compatibilizers was also studied. Surface analysis of the interfaces was performed using E.S.CA. to explain the experimental results.The experimental results were compared with the predictions of lattice theories and the square gradient theory. A strategy to evaluate the Flory-Huggins interaction parameter between polymers was developed. When this strategy was employed, theoretical predictions and experimental data showed good agreement for the influence of temperature and molecular weight on interfacial tension. However, the theory could not predict the effect of polydispersity on interfacial tension

Nonlinear viscoelastic properties of polystyrene solutions

In this work the nonlinear behavior of concentrated polystyrene solution was examined using sliding plate rheometer developed at McGill University. In this rheometer a novel transducer is used to measure the shear stress and an optical system is used to measure birefringence during flows involving high shear rates.The steady shear stress was found to be independent of shear rate at high shear rates. The Cox-Merz rule was found to be valid for concentrations less than 0.199 g.cm$sp{-3}$, but a deviation from the rule was observed for higher concentrations. Sigmoidal damping functions, based on both the shear stress measurements and the birefringence measurements, were determined. The exponential stress coefficient and the third normal stress difference were calculated from experimental data for different values of exponential rate constant and different strain scale factor. The exponential rate constant was shown to have a strong influence on both the exponential stress coefficient and the third normal stress difference

Polymer toughening using residue of recycled windshields: PVB film as impact modifier

In this work, poly(vinyl butyral) (PVB) film originated from the mechanical separation of windshields was tested as all impact modifier of Polyamide-6 (PA-6). The changes undergone by PVB film during the recycling process and the blend manufacturing were evaluated by thermal analyses, infrared spectroscopy and loss oil ignition. Blends of PA-6/original PVB film and PA-6/recovered PVB film were obtained in concentrations ranging from 90/10 to 60/40. The mechanical properties of the blends were investigated and explained in light of the blends morphologies, which in turns were correlated to the changes undergone by the PVB film during the recycling process. The original film presented a plasticizer content of 33 wt.%, which decreased to as low as 20 wt.%, after the recycling and blend preparation processes. The PA-6/PVB film blends presented lower values of tensile strength and Young`s modulus than Polyamide-6, but all blends presented a dramatic increase in their toughness, with a special feature for the 40 wt.%(, blend, which resulted in a super toughened material (impact strength exceeding 500 J/m). Similar results were obtained with recovered PVB film and super tough blends were also obtained. The use of recovered PVB resulted in a smaller improvement of the impact strength due to the loss of plasticizer undergone during the recycling process. The morphological observations showed that if the interparticle distance is smaller than around 0.2 mu m (critical value), the notched Izod impact strength values increase considerably and the fracture surface of blends exhibit characteristics of tough failure. (C) 2007 Elsevier Ltd. All rights reserved

Propiedades reológicas del polipropileno en flujos elongacionales y de cizallamiento.

Elongational and shear deformations have an important paper in polymer processing such as extrusion, injection molding, blow molding and thermoforming. The flow of material in a planar channel with an abrupt contraction has been used to obtain measurement of elongational and shear viscosities. In this work, experimental and theoretical procedures have been developed to evaluate elongational and shear viscosity from the data that are inferred during the flow of a polymer in a contraction die. Cogswell´s model was used for the calculation and two types of polypropylene with different rheology properties were tested experimentally. The shear viscosity measurements obtained using the contraction die were in good agreement with the ones obtained by rotational rheometry, and elongational viscosity was inferred for high rates of deformation.Las deformaciones elongacionales y de cizallamiento tienen un papel muy importante en las operaciones de transformación de polímeros como extrusión, inyección, soplo y termoformado. El flujo del material a través de un canal que posee una contracción abrupta, ha sido usado para obtener medidas de viscosidad elongacional y de cizallamiento. En este trabajo fueron desarrollados procedimientos experimentales y teóricos para evaluar estas viscosidades con la ayuda del modelo de Cogswell, para dos tipos de polipropileno de propiedades reológicas diferentes. Los resultados en cizallamiento fueron comparados con medidas realizadas en un reómetro rotacional y mostraron una buena concordancia, y la viscosidad elongacional fue inferida a altas tasas de deformación