Abstract EVA systems, using an environmentally friendly organoclay modified with a non-ionic and free of ammonium ions modifier (BN-AM), were prepared in a single-screw laboratory extruder and characterized by rheological, morphological and thermal properties. WAXD analysis suggested that the nanocomposites with 1.5 wt% of BN-AM presented an exfoliated structure, while the rheological results showed that the nanocomposites with BN-AM organoclay tended to present a more pronounced shear thinning behavior when compared to EVA and the nanocomposites with the traditional organoclay. The SEM/EDS analysis by using elemental mappings showed good dispersion of the organoclays (BN-AM and BN-CT) in the EVA matrix. Thermogravimetry analysis showed an improvement in thermal stability of EVA when the non-ionic modifier was used instead of the traditional one. In general, it was concluded that the addition of low content of BN-AM organoclay in EVA matrices is a promising option for the production of nanocomposites.
In this study, composites based on polyurethane (PU) derived from castor oil and montmorillonite/polypyrrole doped with dodecylbenzenesulfonic acid (MMt-PPy.DBSA) were developed. In order to investigate the potential use of these materials for electromagnetic shielding applications, the electrical and mechanical properties of PU/MMt-PPy.DBSA composites were determined and compared with composites containing neat PPy.DBSA. The electrical conductivity of PU/MMt-PPy.DBSA composites was found to be higher than those for PU/PPy.DBSA with a similar filler content. Additionally, with a higher conductive additive content, significant increases in the tensile stress (σ) and elastic modulus (E) were observed, suggesting that MMt-PPy.DBSA acts as reinforcing agent for the PU matrix. The electromagnetic interference shielding effectiveness (EMI SE) of composites is mainly dependent on the morphology and filler content. The PU/MMt-PPy.DBSA composite containing 25 wt % of MMt-PPy.DBSA showed a maximum EMI SE of -21 dB, which is similar to the value required for commercial applications (-20 dB). The results revealed that PU/MMt-PPy.DBSA composites are promising materials for electromagnetic shielding applications.
Elastomer thermoplastics are a class of polymeric materials that received industry attention due to the possibility of joining the elastic of elastomers with the thermoplastics processability. The synergistic properties are linked to the appropriate processing. This study evaluated the effect of rotor speed during polymer mixing and the dynamic vulcanization process of polypropylene and nitrile rubber blends. Bismaleimide was employed as multipurpose agent (crosslinking coagent for peroxide and compatibilizer). Morphology, mechanical properties, compression set and oil resistance tests were evaluated for compositions containing 50 and 70 PHR of elastomer. The compatibilization of TPV was realized by infrared spectroscopy. It was shown a compatibilizer effect and better dispersion, achieving the inversion phase, only studying the effect of processing conditions (rotor speed, addition sequence, additives), without any extra interfacial agent. There is a tendency to obtain better performance with decrease speed at dynamic vulcanization or/and at torque stabilization, mainly for blends with 50 PHR of rubber.
Abstract This work evaluated the rheological, mechanical and electromagnetic shielding properties of nitrile rubber (NBR) and carboxylated nitrile rubber (XNBR) blends added with 30 phr of conductive carbon black. The NBR/XNBR ratios studied were 100/0, 80/20, 50/50, 20/80, 10/90 e 0/100. The results obtained showed that increasing the content of XNBR in the blends, reduced the vulcanization rate (CRI), but the mechanical properties have increased in relation to the samples with high NBR content. Through the analysis of scanning electron microscopy showed that the carbon black were dispersed best in compositions rich on XNBR elastomer, these samples also showed higher resistance to swelling. Result that corroborates with the values found for tensile strength. The greater attenuation on radar range was also observed to the sample containing only nitrile rubber, the attenuation value was 50% of the absorbed energy, approximately -3 dB.
Resumo Neste trabalho foram avaliadas as propriedades reológicas, mecânicas e de blindagem eletromagnética de misturas elastoméricas envolvendo borracha nitrílica (NBR) e borracha nitrílica carboxilada (XNBR) formuladas com 30 pcr de negro de fumo condutor. As proporções de NBR/XNBR estudadas foram 100/0, 80/20, 50/50, 20/80, 10/90 e 0/100. Os resultados obtidos demonstraram que o aumento no teor de XNBR reduziu a taxa de vulcanização (CRI), contudo as propriedades mecânicas aumentaram em relação às amostras com alto teor de NBR. Através da análise de microscopia eletrônica de varredura foi observada uma melhor dispersão do negro de fumo condutor nas composições ricas em XNBR, que também apresentaram maior resistência ao inchamento. Estes resultados corroboram com os valores encontrados para a resistência à tração. A maior atenuação na faixa do radar foi observada também para a amostra contendo somente a borracha nitrílica carboxilada, o valor de atenuação encontrado foi de 50% da energia emitida, aproximadamente -3 dB.
Abstract The rheological properties of acrylic paints and polyaniline (PAni) blends, with different contents of PAni doped by dodecyl benzene sulphonic acid (DBSA) and, dispersed by mechanical stirrer and ultrasonic, were investigated by controlled shear rate testing ramps. The results showed that the commercial acrylic paint had tended to deliver the required stability on the blends, in order to avoid sedimentation process. All samples exhibited non-Newtonian flow behavior (shear thinning), increasing PAni content the flow behavior index (n) decreased (0.41 to 0.11) and power law model were used to fitted the experimental curves. The results showed that the addition of PAni-DBSA affects the viscoelastic behavior of the mixtures due to the interactions between the components in the mixture. The best properties were obtained for samples 90/10 wt % dispersed by ultrasonic, indicating the feasibility of the usage as a conducting paint.
This work studied ternary catalyst systems composed of neodymium versatate, t-butyl chloride and diisobutylaluminium hydride used in the cis-1,4 polymerization of butadiene in hexane. The effect of Cl/Nd and Al/Nd molar ratios on the polymerization was investigated. The polymers were characterized by size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FT-IR) and viscosimetry in melted-state. The catalytic activity, molecular weight, molecular weight distribution and Mooney viscosity were strongly influenced by the Cl/Nd molar ratio. The highest cis contents were observed at Cl/Nd molar ratio > 3. The maximum of catalytic activity was obtained at Cl/Nd molar ratios between 3 and 5. The microstructure of polybutadiene was significantly influenced by the increase in the Al/Nd molar ratio. The maximum value, 99% of cis content, was observed for the Al/Nd molar ratio = 10. The conversion data versus reaction time showed that the rate of polymerization increases with the Al/Nd molar ratio reaching a maximum in Al/Nd = 23. The molecular weight distribution curves showed a significant chain transfer process for polymers produced at higher Al/Nd molar ratios.
O objetivo deste trabalho foi estudar sistemas catalíticos ternários constituídos por versatato de neodímio, cloreto de t-butila e hidreto de di-isobutil-alumínio para a polimerização de 1,4-cis de butadieno em hexano. Foram investigados os efeitos das razões molares Cl/Nd e Al/Nd sobre a reação de polimerização. Os polímeros foram caracterizados por cromatografia de exclusão por tamanho (SEC), espectroscopia na região do infravermelho (FT-IR) e viscosimetria no estado fundido. A atividade catalítica, massa molar, distribuição de massa molar e viscosidade Mooney foram fortemente influenciados pela variação da razão molar Cl/Nd. Os maiores teores de unidades cis foram observados em razões molares Cl/Nd > 3. O valor máximo de atividade catalítica foi obtido em razões molares Cl/Nd na faixa de 3 a 5. A microestrutura do polibutadieno foi significativamente influenciada pelo aumento da razão molar Al/Nd. Foi observado um valor máximo, 99% de unidades cis, na razão molar Al/Nd = 10. Os dados de conversão versus tempo de reação mostraram que a velocidade de polimerização aumenta com a razão molar Al/Nd alcançando um valor máximo na razão molar Al/Nd=23. As curvas de distribuição de massa molar evidenciaram um significativo processo de transferência de cadeia para os polímeros produzidos em razões Al/Nd mais altas.
This work studied ternary catalyst systems composed of neodymium versatate, t-butyl chloride and diisobutyl-aluminium hydride used in the cis-1,4 polymerization of butadiene in hexane. The effect of natural aging of the catalyst (1 to 60 days at 8.5°C) on the conversion, catalyst activity and on the micro and macrostructure characteristics of polybutadiene was investigated. The effect of forced aging by heating (40°C), of the different phases of the catalyst preparation on the polymerization characteristics and the synthesized polymer was also studied. The polymers were characterized by size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FT-IR) and viscosimetry in solution and melted-state. Accelerated aging of the different phases of the catalyst (F1, F2, F3 and F4) affected the conversion and the catalytic activity in distinct ways. The results of the conversion and catalytic activity showed that F1 was the most affected phase by accelerated aging at 40°C. In this step the neodymium versatate was added to the solution of diisobutyl-aluminium hydride (Catalyst 447). The microstructure did not change with the natural aging of the catalyst while the macrostructure showed dependence on this variable. When the catalyst aging time increased from 1 to 10 days a slight increase in the conversion and the catalytic activity was observed.
O objetivo deste trabalho foi estudar sistemas catalíticos ternários constituídos por versatato de neodímio, cloreto de t-butila e hidreto de di-isobutil-alumínio para a polimerização de 1,4-cis de butadieno em hexano. Foi investigado o efeito do envelhecimento natural do catalisador (1 a 60 dias a 8,5°C) sobre a conversão, a atividade catalítica e a micro- e macroestrutura do polibutadieno. Foi estudado também o efeito do envelhecimento forçado (40°C), das diferentes fases do preparo do catalisador sobre as características da polimerização e do polímero sintetizado. Os polímeros foram caracterizados por cromatografia de exclusão por tamanho (SEC), espectroscopia na região do infravermelho (FT-IR), viscosimetria em solução e no estado fundido. O envelhecimento forçado das diferentes fases do catalisador (F1, F2, F3 e F4) afetou a conversão e a atividade catalítica de maneiras distintas. Os resultados de conversão e atividade catalítica mostraram que a fase mais afetada pelo envelhecimento forçado a 40°C foi a F1, etapa em que o versatato de neodímio é adicionado à solução de hidreto de di-isobutil-alumínio (Catalisador 447). A microestrutura não se alterou com o envelhecimento natural do catalisador enquanto que a macroestrutura mostrou dependência desta variável. Foi observado um ligeiro aumento na conversão e na atividade catalítica à medida que o tempo de envelhecimento do catalisador aumentou de 1 para 10 dias.
Montmorillonite/polypyrrole (MMT/PPy) nanocomposites were prepared by the in situ polymerization of pyrrole in the presence of clay, natural sodium bentonite, (MMT-Na+) in aqueous solutions with or without an anionic surfactant, sodium dodecyl sulfate (SDS), using Iron (III) chloride hexahydrate (FeCl3.6H2O) as oxidant. The structure and properties of the nanocomposites obtained by the in situ polymerization of pyrrole in the presence of SDS (MMT/PPy.SDS) and without surfactant (MMT/PPy) were compared and evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis and the four-point probe method. The XRD patterns of the MMT/PPy composites shows that the d001 spacing in MMT (1.42 nm) was changed to higher values, indicating the intercalation of PPy on MMT for both nanocomposites. The XRD pattern, SEM and TEM images of the MMT/PPy.SDS nanocomposites confirmed that the presence of SDS in the reaction medium promoted, beyond intercalation, the partial exfoliation of the clay. The MMT/PPy.SDS nanocomposites showed electrical conductivity (9.50 S/cm) higher than the MMT/PPy nanocomposites (4.44 S/cm). The presence of the clay significantly improved the thermal stability of PPy.
Nanocompósitos de montmorilonita/polipirrol (MMT/PPy) foram preparados a partir da polimerização in situ do pirrol na presença de argila, bentonita sódica natural, (MMT-Na+) em solução aquosa com ou sem surfactante aniônico, dodecil sulfato de sódio (SDS), utilizando-se o cloreto de ferro (III) hexahidratado (FeCl3.6H2O), como oxidante. A estrutura e propriedades dos nanocompósitos obtidos pela polimerização in situ do pirrol na presença de SDS (MMT/PPy.SDS) e sem surfactante (MMT/PPy) foram avaliadas e comparadas a partir da espectroscopia de infravermelho com transformada de Fourier (FTIR), difração de raios X (DRX), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), análise termogravimétrica (TG) e método padrão quatro pontas. Os difratogramas dos nanocompósitos revelaram que o espaçamento basal d001 da MMT (1,42 nm) foi alterado para valores maiores, indicando a intercalação do PPy na MMT para ambos os nanocompósitos obtidos. Os difratogramas e as imagens de MET e MEV dos nanocompósitos de MMT/PPy.SDS confirmaram que a presença do SDS na reação promoveu, além da intercalação, esfoliação parcial da argila. Os nanocompósitos MMT/PPy.SDS apresentaram condutividade elétrica (9,50 S/cm) maior do que o nanocompósito de MMT/PPy (4,44 S/cm). A presença da argila melhorou de forma significativa a estabilidade térmica do PPy.
In this study, epoxy nanocomposites containing different fractions of n-phenylaminopropyl (POSS) were prepared. The nanocomposites were studied by transmission electron microscopy (TEM), gel content, dynamic-mechanical analysis (DMA) and thermogravimetric analysis (TGA). The parameters for Avrami's equation were calculated from the degradation curves. The dispersions used to form the nanocomposites were effective above 5 wt % of POSS, and the gel content increased with the addition of POSS. The DMA analysis exhibited an increase in the storage modulus (E') and a shifting of Tg to higher temperatures upon POSS incorporation. The weight loss indicated that the POSS promoted an increase in thermal stability of the epoxy resin. The Avrami parameters demonstrated that the addition of POSS decreased the Avrami constant (k'), increased the half-life (t1/2) of degradation and promoted changes in the Avrami exponent (n). These results suggest that the increase in the glass transition temperature and thermal stability depend on the reactive groups in the POSS nanoparticles.
The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.
Poly(vinyl alcohol) (PVA) hydrogels were obtained by freezing (-22 °C) and thawing (+25 °C) process, resulting in a semi-interpenetrating polymer network (s-IPN) with a sulfonated polyester (PES). The cryo-gels samples were analysed in terms of its water uptake capacity (WU) as a function of pH, temperature and ionic strength. WU of all samples were relatively high, and they showed a reasonable sensitivity to both pH and ionic strength. The pH- and ionic strength dependence is attributed to the dissociation of ionizable groups of PES. The degrees of crystallinity of the cryo-gels, determined by using differential scanning calorimetry (DSC), are lower than pure PVA. Besides, decrease of glass transition temperature (Tg) of the samples when compared with pure PVA was observed. This results are due interactions between PVA and PES, which lead to an increase on the amorphous content of the hydrogels. Our results show that, despite of changes in the microstructure of the hydrogels due the presence of the polyelectrolyte, the cryo-gels reveal a long-term stability.