Estudo da estabilidade térmica e propriedades mecânicas de nanocompósitos de poliamida 6,6 com nanofibras de celulose

Neste estudo, a estabilidade térmica e as propriedades mecânicas da poliamida 6,6 (PA) e de seus nanocompósitos com nanofibras de celulose (NFC) foram investigadas. Objetivando a dispersão uniforme da NFC na PA e o processamento a altas temperaturas, os materiais foram inicialmente pré-misturados em solução e posteriormente processados por extrusão e moldagem por injeção. Os resultados obtidos por análise termogravimétrica confirmaram a maior estabilidade térmica das amostras sem NFC em relação as amostras com NFC. A pré-mistura e o processamento influenciaram na estabilidade térmica das amostras. Os resultados obtidos por ensaio de tração revelaram que a adição de 1% de NFC levou a um aumento médio de 16% no módulo elástico em relação a PA pura. A pré-mistura e a incorporação das NFC´s não prejudicaram o módulo elástico e a resistência máxima à tração, podendo indicar uma alternativa de uso para poliamida 6,6, dependendo da aplicação final do material.Palavras-chave: Nanofibras de celulose, poliamida 6,6, nanocompósitos estabilidade térmica, propriedades mecânicas

Correlação entre orientação molecular, cristalinidade e permeabilidade de filmes biaxialmente orientados de polietileno linear de baixa densidade

  Embora diferentes segmentos do mercado de filmes poliméricos possuam diferentes exigências de desempe-nho, as propriedades dos filmes dependem da arquitetura molecular, microestrutura, orientação molecular e cristalinidade, desenvolvidas em função do tipo de maquinário utilizado e das condições do processamento. Portanto, o conhecimento das microestruturas desenvolvidas é de grande interesse científico e tecnológico. Neste trabalho foi estudada a correlação entre orientação molecular, cristalinidade e propriedades de permea-bilidade, ao vapor de água e ao oxigênio, de filmes biaxialmente orientados de polietileno linear de baixa densidade (PELBD), obtidos pelo processo de extrusão plana e estirados com diferentes razões de estiramen-to. O estudo da orientação molecular revelou a mudança da estrutura morfológica das cadeias da fração cris-talina dos filmes submetidos a maiores graus de estiramento. Resultados do grau de cristalinidade dos filmes de PELBD evidenciaram uma tendência de aumento da cristalinidade com o aumento da orientação das ca-deias poliméricas, devido ao estiramento. Resultados de propriedades de barreira mostraram que o aumento do grau de estiramento possui efeito moderado na diminuição da permeabilidade ao oxigênio e ao vapor de água dos filmes PELBD, e que esse comportamento está relacionado ao grau de estiramento e cristalinidade dos filmes.Palavras-chave: Polietileno linear de baixa densidade, Orientação molecular, Permeabilidade, Cristalinidade

Morfologia de blendas de copolimero tribloco do tipo ABC e homopolimeros

Orientador: Maria do Carmo GonçalvesDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de QuimicaMestrad

A X-ray study of β-phase and molecular orientation in nucleated and non-nucleated injection molded polypropylene resins

The development of α and β-phases and the molecular orientation of injection molded disks of two isotactic polypropylene (i-PP) resins were studied by wide angle X-ray diffraction (WAXD) and pole figures. A nucleated (NPP) and non-nucleated (HPP) polymers were analyzed. The main proposal of this article was the comprehensive study of the interrelations between the processing conditions, phase contents and PP α-phase molecular orientation of injection molded PP resins. In both resins, it was observed that the α-phase was present in all regions along the thickness while the β-phase was present mainly in the external layers, decreasing from the surface to the core; however this last phase was present in a very small amount in the NPP resin. For both polymers, the orientation of the macromolecules c-axis was higher along the flow direction (RD) than along the transverse direction (TD). The b-axis of the PP α-phase molecules was oriented to the thickness direction (ND). The orientation of the c-axis along RD and b-axis along ND of the NPP samples was considerably higher than of the HPP samples, due to the NPP faster crystallization kinetics. For both polymers, the most influential processing parameters on the molecular orientation were the mold temperature and flow rate. The results indicate that, as the mold temperature increased, the characteristic molecular orientation of PP α-phase, with c-axis along RD and b-axis along ND, decreased. With increase in the flow rate an increase of the c-axis molecular orientation of the samples along RD was observed

Degradation of Polypropylene and Jute Fiber-Reinforced Composites Exposed to Natural and Accelerated Aging: Mechanical Properties and Wettability

Population growth and the way resources are being exploited are directly affecting the environment. The natural fiber market, for example, is worth billions of dollars and a huge amount of the fibers becomes waste. This considerable amount of waste motivates the study of the fibers as a reinforcement in polymeric matrix, which benefits both the environmental sustainability and technical-commercial development of new materials with good properties and reduced cost. In this study, jute fiber-reinforced composites previously manufactured from an industrial waste (W), polypropylene, compatibilizer, and nano-calcium carbonate (N), were exposed to natural and accelerated aging. The composites were tested by infrared spectroscopy, contact angle (CA) measurement, and tensile test. Infrared analysis showed greater oxidative degradation after accelerated aging. All CA values continued above 90° after natural aging. Among all compositions, the ones with the presence of N had the highest CA values, showing that N acted as a waterproofing agent. After accelerated aging, a significant decrease in all CA values was observed. The composites did not show significant variation in the elastic modulus after either aging. Deformation at break decreased significantly for compositions with no jute fiber in both aging programs. No remarkable reduction was observed in the compositions with jute fibers

Nanocomposites of polyamide 6/residual monomer with organic-modified montmorillonite and their nanofibers produced by electrospinning

Nanocomposites of an organic-modified montmorillonite (MMT) and polyamide 6 (PA6) with a residual monomer were produced by melt mixing in a torque rheometer. By wide angle X-rays diffraction (WAXD), intercalated/exfoliated structures were observed in the PA6/MMT nanocomposites with 3 and 5 wt. (%) of MMT; on the other hand, when 7 wt. (%) of MMT was added, a nanocomposite with exfoliated structures was obtained due to the predominant linking reactions between the residual monomer and the "nanoclays" organic surfactant. Solutions of these PA6/MMT nanocomposites at 15, 17 and 20 wt. (%) in formic acid were prepared. The 3 and 5 wt. (%) nanocomposites were successfully electrospun; however, electrospinning of the 7 wt. (%) nanocomposite was not possible. WAXD, scanning and transmission electron microscopy results showed that the 3 and 5 wt. (%) nanofibers with average diameter between 80-250 nm had exfoliated structures. These results indicate that the high elongational forces developed during the electrospinning process changed the initial intercalated/exfoliated structure of the nanocomposites to an exfoliated one

Nanocomposites of recycled and of virgin polyamide 6.6 with cellulose nanofibers

The inherent properties of cellulose nanofibers (CNFs) make them an interesting and sustainable choice for reinforcing polymeric matrices intended for the automotive, electronic, construction, and packaging sectors. Effective recycling and reuse of polyamide 6.6 significantly reduce the environmental impact of automotive components throughout its entire life cycle. Nanocomposites of recycled polyamide 6.6 and CNF and of virgin polyamide 6.6 and CNF were processed through dissolution in a formic acid/water mixture followed by melt extrusion and injection molding. The results show that pure recycled polyamide exhibited a thermal degradation onset temperature 10 °C lower and a 9 % lower crystallinity compared to pure virgin polyamide. The method used for processing the nanocomposites resulted in homogeneous dispersion and good anchoring of CNF in both polymer matrices. The processing method and the presence of CNF reduce the thermal stability by up to 15 °C for recycled polyamide nanocomposites and up to 26 °C for virgin polyamide nanocomposites. The processing method did not significantly impair the elastic modulus and tensile strength of both recycled and virgin polyamides, showing a 3 % and 1 % reduction in tensile strength for recycled and virgin polyamides, respectively. The incorporation of 1 wt% and 2 wt% of CNF in virgin polyamide showed an increase in the elastic modulus of 16 % and 5 %, respectively, and a reduction in ductility. In summary, this work offers an alternative processing pathway for nanocomposites of recycled or virgin polyamide 6.6 with CNF; however, some improvements are still necessary to achieve the reinforcing effect of CNF on the mechanical strength of the matrices

Poly(acid lactic)-montmorillonite clay bionanocomposites loaded with tea tree oil for application in antibacterial wound healing

This study evaluated the ability of tea tree essential oil (TT) incorporated into polymer-clay bionanocomposites to in vitro eliminate resistant microorganisms towards applications in antibacterial wound healing. Antimicrobial bionanocomposites were prepared in two steps, namely sonication and melt intercalation, and montmorillonite clay and poly(acid lactic) (PLA) were chosen because they constitute a polymer-clay bionanocomposite to be applied in wound dressing. X-ray diffraction (XRD) results indicated good incorporation of the organic compounds, TT oil, and glycerol (G) (the latter used as a plasticizer) into the clay galleries. Dynamic-mechanical analysis (DMA) results showed a 2–30 % increase in storage modulus and up to 10 °C decrease in glass transition temperature, proving the influence of both TT oil and G on the stress transfer of the reinforcement clay phase. Thermogravitmetric analyses (TGA) revealed TT oil and G addition worsened the thermal stability of the bionanocomposites, which show a mass loss onset decrease up to 90 °C and a clay content between 1.5 and 3 wt%. In vitro antimicrobial activity tests revealed only the combinations of TT oil and G reduced Escherichia coli and Staphylococcus aureus satisfactorily and showed the antimicrobial activity of the bionanocomposites