Nanostructured zinc oxide (ZnO) prepared by combustion in solution was used to obtain nanocomposites. The ZnO particles were characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), and scanning electron microscopy (SEM), showing crystallite size of 32 nm and a superficial area of 32.6 m2 g-1. Nanocomposites with 1, 3, and 5 wt.% of ZnO in the polymeric matrix were obtained using the in situ polymerization of ethylene with catalytic activities between 1500-1700 kg (molZr h PE)-1. The high-density polyethylene nanocomposites (PEZnO) were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), SEM, and transmission electron microscopy (TEM). The nanocomposites with 1 wt.% ZnO gave excellent mechanical properties, and all were active against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria.

Abstract The use of epoxidized rubber as compatibilizer in silica-filled rubber compounds has been proposed in literature. However, the investigation of the reaction kinetics between the epoxy groups and the hydroxyl groups at the silica surface is not yet described. It is a difficult task, mainly because of the high dilution of the system due the difficulty of incorporating high levels of silica in a matrix containing epoxidized rubbers of high molecular weight. In this work, a mixture of precipitated silica and an epoxidized liquid rubber (EpLHPB) was prepared and the reaction between silanols and epoxy groups was followed by DSC under isothermal conditions, at 150, 160 and 170 °C. An autocatalytic data treatment was applied to determine the kinetic parameters of the reaction. Furthermore, it was possible to estimate the amount of epoxy groups required for the saturation of the external surface of the silica, resulting in 5.4 epoxy groups/nm2.

Atualmente, cargas nanométricas são utilizadas para desenvolver novos materiais poliméricos com melhor desempenho mecânico. Neste trabalho, foi empregada uma mistura de borracha termoplástica de poli(estireno-b-butadieno-b-estireno) (SBS) e de argila Montmorilonita (Cloisite 10A) via intercalação por fusão. Uma suspensão de Cloisite 10A em ciclohexano foi adicionada a SBS em solução. Para maior compatibilidade entre a argila e a borracha termoplástica utilizou-se uma borracha termoplástica epoxidada como agente compatibilizante. Neste estudo, a proporção argila compatibilizante foi de 0,6 até 3,0 para verificar a influência desta proporção nas propriedades mecânicas dos nanocompósitos. As propriedades morfológicas e mecânicas dos nanocompósitos foram avaliadas através da difração de raios X, microscopia eletrônica de transmissão, ensaio de tração, análise dinâmico-mecânica (DMA) e avaliação do torque final da mistura. A combinação de argila/conpatibilizante favoreceu a formação de estruturas mais alongadas de argila que promoveram o ganho de módulo e tensão com pequena redução de alongamento.

Nanoscale fillers have been used to develop new polymeric materials with better mechanical performance. In this study, a mixture of thermoplastic rubber, poly (styrene-b-butadiene-b-styrene) (SBS), and Montmorillonite (Cloisite 10A) was obtained via the melt intercalation. A suspension of Cloisite 10A in cyclohexane was added to SBS in solution. To increase the compatibility between the clay and the thermoplastic rubber an epoxidized rubber was used as coupling agent. The proportion of clay and compatibilizer was changed from 0.6 to 3.0 to probe the influence of this ratio on the mechanical properties of the nanocomposites. The morphological and mechanical properties were evaluated using X-ray diffraction, transmission electron microscopy, tensile testing, dynamic mechanical analysis (DMA) and evaluation of the final torque of the mixture. The combination of clay /compatibilizer favored the formation of elongated structures, leading to an increased modulus and strength with a small reduction in elongation.

O comportamento da borracha natural na forma látex frente à reação de epoxidação foi avaliado visando estabelecer as melhores condições reacionais sem a ocorrência de reações laterais, que promovem a coagulação do látex e o desenvolvimento de um aglomerado de borracha. Grupos epóxidos foram gerados através da reação de epoxidação a partir da formação in situ do ácido perfórmico. As amostras foram caracterizadas qualitativamente por espectroscopia de infravermelho (FTIR) e o grau de modificação determinado por ressonância magnética nuclear de hidrogênio (1H-RMN). Análises de calorimetria exploratória diferencial (DSC) demonstraram que a mobilidade da cadeia polimérica foi influenciada pela presença de grupos epóxidos, com aumento linear na temperatura de transição vítrea (Tg). Os resultados indicaram que a epoxidação do látex de borracha natural, sem a ocorrência de reações laterais, é possível e dependente das condições reacionais.

Natural rubber latex was submitted to epoxidation reaction to establish the best reaction conditions without the occurrence of side reactions, which promote coagulation of the latex and development of an agglomerate of rubber. Epoxy groups were produced by in situ epoxidation with formic acid and hydrogen peroxide. The samples were characterized qualitatively by Fourier Transform Infrared (FTIR) analysis and the degree of modification determined by Hydrogen Nuclear Magnetic Resonance Spectroscopy (1H-NMR) analysis. A linear increase in the glass transition temperature (Tg) was observed. The results show that the epoxidation of natural rubber latex is possible and depends on the reaction conditions.

Elastômeros termoplásticos vulcanizados, TPVs, à base de co-poliamida (PA6,6-6) e borracha nitrílica (NBR), foram preparados por vulcanização dinâmica em câmara de mistura a partir de um sistemas de vulcanização tendo como componente principal o peróxido de dicumila e os coagentes bismaleimida e enxofre. Variando-se a proporção dos componentes, estudou-se a influência do enxofre sobre as propriedades mecânicas e deformação permanente à compressão. A morfologia foi determinada por análise de microscopia eletrônica de varredura. Todos os TPVs apresentam propriedades mecânicas superiores à blenda PA/NBR correspondente. TPVs com domínios elastoméricos da ordem de 5 µm foram obtidos com o sistema de reticulação constituído de peróxido de dicumila/bismaleimida/enxofre (DCP/BMI/S) na proporção de 2,4/0,4/0,7 php, independentemente da forma de apresentação da NBR (compacta ou pó). Estes materiais apresentaram excelente desempenho mecânico alcançando-se tensões de ruptura da ordem de 20 MPa. A presença do enxofre conferiu propriedades mecânicas particulares aos TPVs. Para todos os sistemas de reticulação, os TPVs apresentaram boa resistência química em solventes apolares (iso-octano e óleo 20W50), atribuída à natureza química do par PA/NBR, e valores similares para a deformação permanente à compressão.

Thermoplastic vulcanizates (TPVs) based on polyamide (PA6,6-6) and nitrile rubber (NBR) were prepared by dynamic vulcanization in an internal mixer based on a mixed curing system having dicumyl peroxide as the main component and bismaleimide and sulfur as coagents. The proportion of the components as well as the influence of the sulfur content on the mechanical properties and compression set were studied. The morphologies were determined by scanning electronic microscopy. All the TPVs exhibit better properties than the blend. Elastomeric domains of ca. 5 µm were obtained for the curing system dicumyl peroxide/bismaleimide/sulfur (DCP/BMI/S) in a proportion of 2.4/0.4/0.7 php, independently of the form of the NBR (crumb or powder). These materials showed excellent mechanical properties, reaching a tension of rupture of about 20 MPa. The use of sulfur as curing co-agent gives the material unique properties. All the TPVs exhibited good resistance to non polar solvents (isooctane and oil 20W50) and similar values for the compression set.

The introduction of epoxy groups into the main chain of elastomers has emerged as a promising alternative, considering the monitoring of polymer-filler interaction leading to changes in the properties of vulcanizates. The epoxidation reaction (in situ) was chosen to modify elastomers, such as polybutadiene (BR) and copolymer of styrene-butadiene-rubber (SBR), because it is a simple, easily controlled reaction, even considering the small epoxidation degree. The modification degree of the polymeric chain was studied with FT-IR and ¹H-NMR. The shift of the Tg to high temperatures with the increase of the epoxy group in the polymer chain was monitored through differential scanning calorimetry (DSC). An analysis of the dynamic modulus of the material in relation to its dependence on the amplitude and temperature was carried out. The interaction between epoxidized elastomeric matrix and silica as filler was extremely improved, even in the presence of very low content of epoxy groups into the polymer chain.

A utilização de modificações químicas de polidienos comerciais tem sido estudada como um meio alternativo à síntese de novos polímeros, para otimização das propriedades finais destes materiais através da introdução de diferentes grupamentos reativos na cadeia polimérica. A modificação química pode ser feita através de diferentes métodos, os quais podem ser realizados tanto em solução como em massa, onde podem ser destacadas as reações de epoxidação, sulfonação, maleinização, carboxilação, etc. Neste trabalho foi estudado o método de epoxidação de borrachas do tipo SBR e BR. Foi possível observar que mesmo pequenos graus de modificação química causam mudanças marcantes nas propriedades finais dos polímeros, como determinado para a temperatura de transição vítrea.

Chemical modification of polydiene has been studied as an alternative route to obtain modified polymers with improved final properties. This improvement is due to the introduction of different kinds of reactive groups into a polymer chain, and it can be done in solution as well as in bulk. The chemical modification can be carried out by different methods such as epoxidation, maleination, carboxylation, sulfonation etc. In this work we show that in the epoxidation of SBR and BR even a small degree of modification can change the final properties of the polymer, as it occurred for the glass transition temperature.