Síntese e caracterização de nanocompósitos à base de poliuretano dispersos em água com argilas hidrofílica e organofílica

A área de pesquisa de materiais nanoestruturados tem recebido destacada atenção nos últimos anos por parte da comunidade científica, ressaltando-se os nanocompósitos à base de polímero e argila. Nesta Dissertação foram sintetizados nanocompósitos à base de poliuretano (NWPUs) com argilas do tipo montmorilonita (MMT), hidrofóbicas (organofílicas) e hidrofílica. Os monômeros empregados na síntese foram poli(glicol propilênico) (PPG); polibutadieno líquido hidroxilado (HTPB); ácido dimetilolpropiônico (DMPA), diisocianato de isoforona (IPDI) e hidrazina (HYD), como extensor de cadeia. Nas formulações, foram variadas as proporções de HTPB e o teor das argilas. As argilas organofílica Cloisite 30B e hidrofílica Cloisite Na+ foram incorporadas em 1, 3 e 5 %, enquanto que a organofílica Cloisite 15A foi incorporada no teor de 1%. As dispersões foram caracterizadas quanto ao teor de sólidos totais, tamanho médio de partículas e viscosidade. Os filmes vazados a partir das dispersões foram caracterizados por espectroscopia na região do infravermelho (FTIR), difração de raios-x (XDR), microscopia eletrônica de varredura (SEM) e microscopia de força atômica (AFM). A resistência térmica e a transição vítrea dos materiais foram determinadas por termogravimetria (TG) e calorimetria diferencial de varredura (DSC), respectivamente. O teor de absorção de água e o comportamento mecânico dos filmes foram avaliados. Foi verificada, por XRD, a ausência do pico de cristalinidade, característico das argilas puras e não-deslaminadas. As micrografias obtidas por SEM confirmam uma dispersão homogênea das argilas na matriz poliuretânica. Os filmes à base de nanocompósitos (NWPUs) apresentaram propriedades mecânicas superiores às apresentadas por aqueles obtidos a partir das dispersões sem a presença de argila (WPUs). A adesão dos revestimentos formados, pela aplicação das dispersões em diversos substratos, também foi verificada visualmente. Os resultados das análises mostraram que houve a formação de nanocompósitos à base de água, formados tanto a partir da argila hidrofílica quanto das organofílicas

The investigation of exfoliation process of organic modified montmorillonite in thermoplastic polyurethane with different molecular weights

Cloisite 30B (30B) was melt-mixed with two kinds of thermoplastic polyurethane (TPU) with different molecular weights to discern the roles of molecular diffusion and shear in the exfoliation process. The higher level of exfoliation was achieved in TPU matrix with higher molecular weight due to the appropriate viscosity. In order to have an insight into the mechanism of exfoliation, the degree of dispersion and exfoliation of 30B was characterized by wide angle X-ray diffraction and transmission electron microscopy. The layers of 30B were exfoliated via a slippage process, which was also observed in polyamide 12 nanocomposites recently.

Structure-Property Relationships in Biaxially Deformed Polypropylene Nanocomposites

Semi-solid forming processes such as thermoforming and injection blow moulding are used to make much of today’s packaging. As for most packaging there is a drive to reduce product weight and improve properties such as barrier performance. Polymer nanocomposites offer the possibility of increased modulus
(and hence potential product light weighting) as well as improved barrier properties and are the subject of much research attention. In this particular study, polypropylene–clay nanocomposite sheets produced via biaxial deformation are investigated and the structure of the nanocomposites is quantitatively determined in order to gain a better understanding of the influence of the composite structure on mechanical properties. Compression moulded sheets of polypropylene and polypropylene/Cloisite 15A nanocomposite (5 wt.%) were biaxially stretched to different stretching ratios, and then the structure of
the nanocomposite was examined using XRD and TEM techniques. Different stretching ratios produced different degrees of exfoliation and orientation of the clay tactoids. The sheet properties were then investigated using DSC, DMTA, and tensile tests .It was found that regardless of the degree of exfoliation or
orientation, the addition of clay has no effect on percentage crystallinity or melting temperature, but it has an effect on the crystallization temperature and on the crystal size distribution. DMTA and tensile tests show that both the degree of exfoliation and the degree of orientation positively correlate with the dynamic mechanical properties and the tensile properties of the sheet.

Optimization of the processing of HNBR/organoclay nanocomposite

In the current investigation, rubber/clay nanocomposites were prepared by two different methods using hydrogenated nitrile butadiene rubber (HNBR) and the organoclay namely Cloisite 15A (C15A). A new novel approach involving swelling of C15A by ulltrasonication in HNBR solution has been carried out for improving the exfoliation and compatibilization of organoclays with HNBR matrix. With the addition of 5phr of clay, the elongation at break and tear strength improved by 16% and 24% respectively. The effect of coupling agents namely amino functional silane and tetrasulfido silane on the nanocomposites have been investigated. The elongation at break and tear strength improved by 46% and 77% respectively with the use of silanes. The improvement in the mechanical properties attributes to improved interaction between the organoclays and HNBR matrix. This interaction has been studied by X-ray diffraction and transmission electron microscope. Pre-dispersion technique clearly suggests very good improvement in the dispersion and properties due to better filler-rubber compatibility. © 2010 American Institute of Physics.

Mechanism of gas permeation in processed HNBR/nanoclay composites

The influence of the layered silicate clay platelets on the nitrogen permeation properties of hydrogenated nitrile butadiene rubber (HNBR)/nanoclay nanocomposites has been investigated. Nanocomposites of HNBR modified with different percentages of the organoclay are processed through various routes. Commercially available organoclay (CLOISITE 15A) and various silane-coupling agents are used to improve the dispersion of the nanoclay in HNBR. A total of 10 different formulations of nanocomposites are manufactured. The addition of the organoclay has resulted in a significant enhancement of the nitrogen barrier properties of the manufactured nanocomposite. The mechanism of the reduction in the permeability is explained through the changes in the morphology and its bond to the filler. These changes are confirmed through examination of the morphology using x-ray diffraction, transmission electron microscope, and dynamic mechanical thermal analysis. There has been a drastic reduction up to 55.7% in nitrogen permeability. The reduction in gas permeation in HNBR is attributed to uniformly exfoliated clay platelets. Finally, three different permeability models, namely, the Nielsen model, modified Nielsen model, and Cussler model, have also been considered to predict the permeability behavior of nanocomposites with different volume filler fractions. The experimental values of gas permeability have been compared with theoretical models. It is observed that the modified Nielsen model closely matches with the measured permeation behavior. © 2011 Wiley Periodicals, Inc.

The ageing behaviour of hydrogenated nitrile butadiene rubber/nanoclay nanocomposites in various mediums

Hydrogenated nitrile butadiene rubber (HNBR) nanocomposites were prepared using commercially available organoclays (Cloisite 15A). The main focus of the current investigation is to study the influence of the organoclay reinforced in HNBR after subjecting it to long-term oxidative ageing and immersion studies. All the different nanoclay nanocomposites were air aged for a period of 168 h and at 150°C. The changes in the mechanical properties such as tensile strength and elongation at break have been compared with respect to the control sample. For immersion tests, three different liquid mediums were considered for this current investigation. All the samples were immersed in different mediums for a period of 168 h at 150°C. The changes in the swelling index and the mechanical properties have been reported with respect to the control sample. After reinforcing nanoclays into HNBR there was good resistance to swelling in all the three different liquid mediums in comparison to control sample. Tensile testing was performed on the immersed nanocomposites to evaluate the mechanical behaviour after immersion studies. A probable mechanism behind the improved performance has been suggested. © The Author(s) 2012.

Influence of nanoclays on mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber nanocomposites

In this research, two different methods have been investigated for optimising the preparation of hydrogenated acrylonitrile butadiene rubber/clay nanocomposites. Commercially available organoclay (Cloisite 20A) has been considered for the preparation of rubber nanocomposites. A detailed analysis has been made to investigate the morphological structure and mechanical behaviour at room temperature and at elevated temperature. Also the influence of organoclays on permeability has been studied. Structural analysis indicates very good dispersion for a low loading of 5 parts per hundred (phr) amount of nanoclays. Significant improvements in mechanical properties have been observed with the addition of organoclays at both room and elevated temperatures. Even with the low level of addition of nanoclays, there was a remarkable reduction in permeability. © Institute of Materials, Minerals and Mining 2011.

Efeito de argilas organofílicas na estrutura e propriedades de nanocompósitos de poli(metacrilato de metila)

Nacomposites of polymers and lamellar clayminerals, has generated high scientific and technological interest, for having mechanical properties and gas barriers differentiated of polymers and conventional composites. In this work, it was developed nanocomposites by single screw extruder and injection, utilizing commercial raw material, with the goal to investigate the quality of new developed materials. It was evaluated the influence of the content and the kind of clay in the structure and in the nanocomposites properties. It was used regular and elastomeric poly (methyl methacrylate) (Acrigel LEP 100 and Acrigel ECP800) and six montmorillonites (Cloisite 10A, 11B, 15A, 20A, 25A e 30B) at the concentration of 1% e 3% in weight. The nanocomposites were characterized by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), colorimetric, optical transparency, flexural and tensile tests, Rockwell hardness and esclerometry. It was founded that is possible to obtain intercalated and exfoliated nanocomposites PMMA/MMT, and the top results was obtained in the materials with 1%in clay weight organophilizated with 2M2HT (Cloisite 15A and 20A) presented intercalate and hybrid morphology (exfoliated and flocullated). The ones that was produced with organophilizated clay with 2MHTL8 (Cloisite 30B) had excellent visual quality, but the majority presented hybrid morphology. In the materials processed with organophilizated clay with MT2ETOH (Cloisite 30B), there were color change and loss of transparency. It occurs improvement in a few mechanical properties, mainly in the materials produced with PMMA elastomeric (Acrigel ECP800), being more significant, the increase in the resistance to stripping in those nanocomposites

Effect of modified clays on the structure and functional properties of biofilms produced with zein

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis, structure, and thermal stability of poly(methyl methacrylate)-co- poly(3-tri(methoxysilyil)propyl methacrylate)/ montmorillonite nanocomposites

The structure and the thermodegradation behavior of both poly(methyl methacrylate)-co-poly(3-tri(methoxysilyil)propyl methacrylate) polymer modified with silyl groups and of intercalated poly(methyl methacrylate)-co-poly(3- tri(methoxysilyil)propyl methacrylate)/Cloisite 15A™ nanocomposite have been in situ probed. The structural feature were comparatively studied by Fourier transform infrared spectroscopy (FTIR), 13C and 29Si nuclear magnetic resonance (NMR), and small angle X-ray scattering (SAXS) measurements. The intercalation of polymer in the interlayer galleries was evidenced by the increment of the basal distance from 31 to 45 Å. The variation of this interlayer distance as function of temperature was followed by in situ SAXS. Pristine polymer decomposition pathway depends on the atmosphere, presenting two steps under air and three under N2. The nanocomposites are more stable than polymer, and this thermal improvement is proportional to the clay loading. The experimental results indicate that clay nanoparticles play several different roles in polymer stabilization, among them, diffusion barrier, charring, and suppression of degradation steps by chemical reactions between polymer and clay. Charring is atmosphere dependent, occurring more pronounced under air. © 2012 Society of Plastics Engineers.

PLA and Organoclays Nanocomposites: Degradation Process and Evaluation of ecotoxicity Using Allium cepa as Test Organism

In this study, nanocomposites of PLA and organoclays Cloisite 20A and Cloisite 30B were prepared by the melt intercalation method and the obtained samples were characterized by transmission electron microscopy (TEM). Since composting is an important proposal to the final disposal of biopolymers, the influence of clays on the hydrolytic degradation process of PLA was evaluated by visual analysis and monitoring of molecular weight after periods of 15 and 30 days of degradation in compost. After degradation of the materials in composting environment, the evaluation of cytotoxic, genotoxic and mutagenic effects of compost aqueous extract was carried out using a bioassay with Allium cepa as test organism. The TEM micrographs permitted the observation of different levels of dispersion, including exfoliated regions. In the evaluation of hydrolytic degradation it was noted that the presence of organoclays can decrease the rate of degradation possibly due to the barrier effect of clay layers and/or the higher degree of crystallinity in the nanocomposite samples. Nevertheless, even in the case of nanocomposites, the molecular weight reduction was significant, indicating that the composting process is favorable to the chain scission of PLA in studied materials. In the analysis performed by the bioassay using A. cepa as test organism, it was found that after degradation of the PLA and its nanocomposites the aqueous extract of compost samples induced a decreasing in the mitotic index and an increasing in the induction of chromosomal abnormalities. These results were statistically significant in relation to the negative control (distilled water). By comparing the results obtained for the nanocomposites in relative to pure polymer, there were no statistically significant differences. The types of the observed chromosomal aberrations indicated a possible genotoxic effect of the materials, which may be related to an aneugenic action of PLA degradation products. © 2013 Springer Science+Business Media New York.

Enhanced bulk and superficial hydrophobicities of starch-based bionanocomposites by addition of clay

In this work, thermoplastic starch (TPS)-clay bionanocomposites were obtained by an innovative methodology using a combination of methodologies commonly used in the composites and nanocomposites preparations. The main objectives or novelties were to confirm efficiency of the processing methodology by field emission gun scanning electron microscopy and investigate the effect of clay content on the spectroscopic, bulk and surface hydrophilic/hydrophobic properties of these bionanocomposites. Raman and FTIR spectroscopies confirmed the changes in the spectroscopic properties of the TPS bionanocomposites with the addition of the clay materials. Water absorption and contact angle measurements were also used to analyze the effect of the clay content on the hydrophilic properties of the TPS bionanocomposites. The results also showed that the addition of the cloisite-Na+ clay increased the bulk and surface hydrophobicities of the TPS matrix, which may increase its industrial application, particularly in manufacturing of food containers. © 2013 Elsevier B.V.

Efeito da adição de argilas modificadas na estrutura e propriedades funcionais de biofilmes produzidos a base de zeína

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

O papel da argila na estabilização térmica de nanocompósitos: um estudo da ordem local e a média distância

Pós-graduação em Química - IQ

Estudo da influência de argilas organofílicas no processo de biodegradação do PLA

In this study nanocomposites of PLA and organoclays Cloisite 20A and Cloisite 30B were prepared by melt intercalation. The influence from the organoclays on the biodegradation of PLA was evaluated based on the respirometry method. The incorporation of clay Cloisite 20A did not change the mineralization curve of PLA. The nanocomposite with Cloisite 30B, on the other hand, presented a different behavior, indicating a delay in the polymer biodegradation. The materials were characterized by X-ray Diffraction, Thermogravimetric Analysis and Differential Scanning Calorimetry. The materials characterization indicated nanocomposites with an intercalated structure as well as reduced thermal stability and a slight increase in the degree of crystallinity compared to the pure polymer.