Preparation of different dendritic‐layered silicate nanocomposites

Several dendrimer–clay nanocomposites have been prepared. Firstly, the dendrimer (DE₁)/clay nanocomposite was obtained via an in situ free radical polymerization of a double bond‐ended dendrimer (DE₁), derived from Behera's amine by using 2,2′‐azobisisobutyronitrile (AIBN), as initiator, and Cloisite 30 B, as nanofiller. Further free radical in situ copolymerization processes were conducted between DE₁, methyl methacrylate (MMA), and styrene (St). Two other dendrimer/clay nanocomposites were prepared by the reaction of second generation (G₂)–36‐acid dendrimer (DE₂) and N,N′,N′,N′‐tetrakis[2‐hydroxy‐1,1‐bis(hydroxylmethyl) ethyl]‐α,α,ω,ω‐alkane‐tetracarboxamide [6]‐10‐[6] Arborols (DE₃) with montmorillonite clay (MMT). POLYM. ENG. SCI., 53:2166–2174, 2013. © 2013 Society of Plastics Engineers     

Aliphatic polyamidoamine hyperbranched polymers/layered silicate nanocomposites

Polyamidoamine hyperbranched polymer (Hyp)/clay nanocomposites were synthesized by using both of montmorillonite and laponite clays. Poly amidoamine hyperbranched polymer (Hyp) was prepared by one‐pot polymerization via couple monomer methodology. Afterward, the amino ends of Hyp were modified with methyl methacrylate (MMA), styrene (St) and butyl methacrylate (n‐BuMA) polymers which were previously prepared via ATRP (atom transfer radical polymerization) to form the corresponding new hyperbranched polymers Hyp₁, Hyp₂ and Hyp₃. Those formed polymers were inserted into the modified clay, such as montmorillonite and laponite to form their nanocomposites. The formed polymer/clay nanocomposites were characterized via XRD, TEM, and thermal analyses. The formed hyperbranched polymers generally showed intercalation behavior more than the exfoliation one mostly because of the bulkiness of the hyperbranched skeleton. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High performance epoxy‐layered silicate nanocomposites

High performance epoxy‐layered silicate nanocomposites based on tetra‐glycidyl4,4'‐diamino‐dipheny1 methane (TGDDM) resin cured with 4,4'‐diaminodipheny1 sulfone (DDS) have been successfully synthesized. Fluorohectorites modified by means of interlayer cation exchange of sodium cations for protonated dihydro‐imidazolines and octadecylamine were used. Fluorohectorite exchanged with 1‐methy12‐norsteary1‐3‐stearinoacid‐amidoethy1‐dihydro‐imidazolinium ions was immiscible with the epoxy matrix. In contrast, fluorohectorites exchanged with hydroxyethy1‐dihydro‐imidazolinium (HEODI) and riciny1‐dihydro‐imidazolinium ions (RDI) favored the formation of a nanocomposite structure. This is most likely due to the presence of ‐OH groups in their molecular structure, which has a catalytic effect on the polymerization occurring between the silicate layers. The diffusion of epoxy and curing agent molecules between the silicate layers is also promoted. Microscopy observations revealed that the dispersion of the silicate aggregates on a microscale was proportional to the degree of separation of the silicate layers on a nanoscale. Decreased apparent glass transition temperature was observed in all the nanocomposites. Finally, mechanical property studies showed that epoxy‐layered silicate nanocomposite formation could simultaneously improve fracture toughness and Young's modulus, without adversely affecting tensile strength.     

Synthesis and characterization of resol‐layered silicate nanocomposites

Resol‐layered silicate nanocomposites were synthesized by intercalative polymerization of phenol and formaldehyde using layered clays such as an aminoacid‐modified montmorillonite (MMT) and a commercial modified MMT (Cloisite 30B). The composites were prepared by a sequential process in which one of the reactives of the phenolic resin was reacted with the organosilicate and subsequently cured with triethylamine. The nanocomposites were studied by means of X‐ray diffraction, atomic force microscopy, and thermogravimetric analysis. Results show a strong clay composition dependence on the intercalation state. The composite of resol with 2 wt % aminoacid‐modified MMT content has the best dispersion of clay layers. Thermal stability of nanocomposites was slightly increased in comparison with the neat resol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and combustion behaviour of polymer/layered silicate nanocomposites based upon PE and EVA

Polymer composites based on organically modified clay (organoclay) and polyethylene (PE) were prepared by melt processing to study their combustion behaviour. Formation of intercalated nanocomposites was observed only in presence of poly(ethylene-co-vinylacetate), added as a compatibilizer. The nanocomposite showed a reduced rate of combustion due to the accumulation of the silicate on the surface of the burning specimen which create a protective barrier to heat and mass transfer.     

Structure‐property relationships in copolyester elastomer‐layered silicate nanocomposites

While the field of polymer–clay nanocomposites is reaching maturity, some parts of the studied systems still present researchers with possibilities for the improvement of material properties. This study entails the understanding of the relationships in copolyester elastomer/organically modified layered silicate nanocomposite and the structure–property relationships within the system of the nanocomposite. A series of these nanocomposites was prepared via twin‐screw extrusion melt compounding. The experiments included the following three types of synthetic organosilicates: high aspect ratio Somasif (ME100) fluoromica and two lower aspect ratio Laponite synthetic hectorites, (WXFN) and (WXFP). These organosilicates were modified with quaternary octadecyltrimethylammonium bromide (ODTMA) and were used to prepare the nanocomposites. The nanocomposite structure on a micro‐ and nanometre scales was evaluated by two techniques, such as X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of the nanocomposites were examined to determine the impact aspect ratio of the nanofiller and wt % loading have on performance. The addition of the 2 wt % high aspect ratio of ME100‐ODTMA, in particular, showed statistically improved tensile strength, tear resistance, creep resistance, and water vapor permeation barrier enhancement. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41742.     

Preparation, characterization and antimicrobial activity of chitosan/layered silicate nanocomposites

Chitosan/layered silicate nanocomposites with different ratios were successfully prepared via solution-mixing processing technique. Unmodified Ca²⁺-rectorite and organic rectorite modified by cetyltrimethyl ammonium bromide were used. Their structures were characterized by XRD, TEM and FT-IR techniques. The results showed that chitosan chains were inserted into silicate layers to form the intercalated nanocomposites. The interlayer distance of the layered silicates in the nanocomposites enlarged as its amount increased. When the weight ratio between chitosan and organic rectorite was 12:1, the largest interlayer distance of 8.24 nm was obtained. However, with further increase of its amount, the interlayer distance of the layered silicates in the nanocomposites reduced. In vitro antimicrobial assay showed that pristine rectorite could not inhibit the growth of bacteria, but chitosan/layered silicate nanocomposites had stronger antimicrobial activity than pure chitosan, particularly against Gram-positive bacteria. With the increase of the amount and the interlayer distance of the layered silicates in the nanocomposites, the nanocomposites showed a stronger antibacterial effect on Gram-positive bacteria, while the nanocomposites showed a weaker antibacterial effect on Gram-negative bacteria. The lowest minimum inhibition concentration (MIC) value of the nanocomposites against Staphylococcus aureus and Bacillus subtilis was 0.00313% (w/v), and the relative inhibition time (RIT) against B. subtilis with concentration of 0.00313% (w/v) was >120 h.     

Flame retardancy and char microstructure of nylon‐6/layered silicate nanocomposites

We investigated the effect of organically modified clay alone and in combination with zinc borate on the thermal/flammability behavior of nylon‐6 nanocomposites. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increase in clay concentration. Nanocomposite films of approximately 0.5 mm thickness with 2.5 and 5 wt % clay burned for almost the same duration as neat nylon‐6 but with reduced dripping in horizontal flame test. The 10 wt % clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25–30%. Zinc borate/clay containing nanocomposite developed into a very good intumescent system in cone calorimeter test, swelling about 10–13 mm height prior to ignition forming a cellular char structure. This was found to be an effective composition in reducing the heat release and mass loss rate of nylon‐6 by about 65% and at par with 10 wt % clay nanocomposite. Flame retardant behavior could be attributed to distinct char morphologies observed through scanning electron microscopy. Fourier transform infrared spectroscopy of the 10 wt % clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1540–1550, 2007     

Polymer layered silicate nanocomposites

Polymers filled with low amounts of layered silicate dispersed at nanoscale level are most promising materials characterized by a combination of chemical, physical and mechanical properties that cannot be obtained with macro‐ or microscopic dispersions of inorganic fillers. Polymer layered silicate nanocomposites can be obtained by insertion of polymer molecules in the galleries between the layers of phyllosilicate. Here, hydrated alkaline or alkaline earth metal cations are hosted which neutralize the negative charge resulting from isomorphous substitutions of Mg or Al cations within the silicate. Insertion of polymer molecules to prepare “intercalation hybrids” can be carried out by replacing the water hydration molecules in the galleries by polymers containing polar functional groups, using the so called ion‐dipole method. A more general technique involves compatibilization of the silicate by intercalation of an organic molecule, typically an organic alkylammonium salt, that replaces the cations in the interlayer galleries to form an organically modified layered silicate (OLS). The aliphatic chain of the OLS favors the intercalation of any type of polymer. Intercalated or delaminated polymer‐silicate hybrids are obtained depending on whether the stack organization of the silicate layers is preserved or is lost, with single sheets being distributed in the polymer matrix. The methods currently used for preparing polymer layered silicate (PLS) nanocomposites are: in situ polymerization, from polymer solution, or from polymer melt. Although PLS nanocomposites have been known for a long time, it is the possibility of preparing them by melt intercalation of OLS in processing that is boosting the present interest in these materials and their properties. So far PLS nanocomposites have been characterized by X‐ray diffractometry, transmission electron microscopy, differential scanning calorimetry, and NMR. Published results on PLS nanocomposites are reviewed concerning their characterization and properties with particular reference to fire retardant behavior.     

Preparation and characterization of polypropylene/layered silicate nanocomposites using an antioxidant

Polypropylene (PP)/layered silicate nanocomposites were prepared via simple melt mixing of three components, PP, layered silicates modified with octadecylamine (C18-MMT) and antioxidant, to investigate the role of antioxidant. TEM and X-ray scattering results confirmed the intercalated state of silicates in PP/layered silicate nanocomposites with antioxidant. In rheological and mechanical study, the nanocomposites with antioxidant showed higher properties than those of the unfilled PP. The nanocomposite with 5 wt% C18-MMT and 0.5 phr antioxidant exhibited about 1.4 times higher tensile modulus and 1.3 times higher storage modulus than the unfilled PP. However, PP/C18-MMT without antioxidant showed lower rheological values owing to the thermal decomposition of PP and the poor compatibility between PP and C18-MMT. It could be concluded that antioxidants played an important role in enhancing the compatibility between PP and C18-MMT. According to the real time X-ray diffraction, the nanocomposite showed the weak ordering of PP crystals than the unfilled PP in the load-extension plateau region of elongation.     

High temperature ablation of highly filled polymer‐layered silicate nanocomposites

At instantaneous thermal shocks and high temperature conditions, using the charring ablative heat shields is more effective than the other heat protection methods. In recent years, low‐filled layered silicate polymeric nanocomposites were introduced as new class of ablative materials. In this work, highly filled ablative polymeric nanocomposite is prepared and its thermal stability and ablation mechanism is studied under high external heat flux. The thermal degradation kinetics during pyrolysis, the variation of thermophysical properties as a result of ablation process and mathematical modeling of ablation process are performed for highly filled ablative polymeric nanocomposite samples compared with those of their composite counterparts under oxyacetylene flame test. The results show that the ablation performance of highly filled polymeric nanocomposite is higher than that of the composite, and the mathematical model is adequately confirmed by the experimental data of the thermophysical and ablation properties of highly filled nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and some properties of stereocomplex‐type poly(lactic acid)/layered silicate nanocomposites

Stereocomplex‐type poly(lactic acid)‐ [PLA]‐ based blends were prepared by solution casting of equimolar PLLA/PDLA with different amounts of organo‐modified montmorillonite. The homocrystallization and stereocomplexation of PLAs were enhanced by annealing of the blends. The stereocomplexation of PLAs, intercalation of the polymer chains between the silicates layers, and morphological structure of the filled PLAs were analyzed by wide‐angle X‐ray diffraction and transmission electron microscope. Thermogravimetric analyses (TGA), differential scanning calorimetry (DSC), and tensile test were performed to study the thermal and mechanical properties of the blends. The homo‐ and stereocomplex crystallization of neat PLLA/PDLA were enhanced by annealing. The effect of annealing on the crystallization was emphasized by the addition of clay. With this structural change, thermal stabilities properties were also improved by the addition of clay. The silicate layers of the clay were slightly stacked but intercalated and distributed in the PLA‐matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Chemorheology and properties of epoxy/layered silicate nanocomposites

The effect of the organoclay nanoparticles on the rheology and development of the morphology and properties for epoxy/organoclay nanocomposites has been studied. The interlayer spacing increases with the temperature of cure resulting in intercalated morphologies with varying degrees of interlayer expansion, depending on the cure temperature used. Rheological studies of the curing process indicate that intergallery diffusion before curing is essential for exfoliation, before the morphology is frozen in by gelation and vitrification. The maximum increase in modulus was observed for the 2 wt% clay loading. Viscoelastic behavior and mechanical properties of the cured samples were correlated with the morphological and rheological study.     

Chemorheology of cyanate ester—organically layered silicate nanocomposites

The effect of nanoparticle addition on the flow and curing behavior of a phenolic triazine cyanate ester resin system has been studied using chemorheological, thermal and spectroscopic techniques. While the neat system exhibited Newtonian flow, the nanodispersed prepolymer exhibited pseudoplastic flow behavior, typical of polymeric fluids such as gels and pastes. Evolution of the morphology during curing has been found to be dependent on the rate of intergallery diffusion of the prepolymer and subsequent gelation and vitrification, as well as the intra and extragallery cure kinetics. Curing reactions of the cyanate ester nanocomposite system consisting of a di-functional phenol, a halogen cyanate and organically layered silicates were studied. Gel times were measured as a function of temperature by time sweeps on a controlled stress rheometer. Gelation and vitrification times and activation energies for the nanocomposite systems were lower than that of the neat resins, indicating a catalytic effect of the clays on the curing reaction. Curing kinetics experiments performed on DSC and FTIR confirmed this phenomenon. Based on above experiments, time-temperature-transformation diagrams for the different systems were constructed.     

Effect of ionomer on clay dispersions in polypropylene‐layered silicate nanocomposites

In this study, polypropylene (PP)/clay nanocomposites containing different concentrations of ethylene‐methacrylic acid ionomer (i.e. Surlyn®) were prepared, and the effect of ionomer on clay dispersion was studied via WAXD, rheology, SEM, and TEM. The role of the ionomer in the nanocomposites was compared with that of maleic anhydride grafted PP (PP‐g‐MA), which has been widely used as a compatibilizer in making PP/clay nanocomposites. With an increase in the concentration of compatibilizer, the position of d₀₀₁ peak of OMMT shifted toward a lower angle for PP‐g‐MA system, while the position remained almost unchanged for Surlyn system, in which a larger interlayer spacing (d₀₀₁) was found with respect to the former. In rheology, the addition of the ionomer led to a gradual increase in both moduli and complex viscosity, and the nonterminal behavior at low frequency was observed in both systems. In addition, the ternary hybrid containing 20 wt % Surlyn achieved the largest enhancement in relative viscosity, which was more than that of the nanocomposite prepared from pure Surlyn or pure PP, presumably indicative of the existence of strong interaction between the components. Finally, SEM and TEM micrographs demonstrated that exfoliated structure was preferred for PP/Surlyn/OMMT hybrids, while intercalated morphology for PP/PP‐g‐MA/OMMT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4024–4034, 2007     

Intumescent flame retardant–montmorillonite synergism in polypropylene‐layered silicate nanocomposites

Polypropylene/clay nanocomposites have been prepared starting from pristine mont morillonite (MMT) and reactive compatibilizer hexadecyltrimethylammonium bromide (C16). The nanocomposite structure is evidenced by the X‐ray diffraction and high resolution electronic microscopy. Intumescent flame retardant has been added to polypropylene/clay hybrids. Their flammability behaviours have been evaluated using cone calorimetry. Synergy was observed between the nanocomposites and intumescent flame retardant. Copyright © 2003 Society of Chemical Industry     

Study on thermal stability and flame retardancy of polymer/layered silicate nanocomposites based on POE and POE‐g‐MAH

Ethylene‐octene elastomer (POE)/organo‐montmorillonite (OMT) and maleic anhydride‐grafted POE (POE‐g‐MAH)/OMT composites were prepared through melt mixing and influence of clay dispersion on thermal, dynamic mechanical, and flammability properties were investigated. The results showed that OMT forms intercalated/exfoliated structures in POE‐g‐MAH/OMT and agglomerated structure in POE/OMT microcomposites, resulting in more significant improvements of storage modulus and glass transition temperature in the POE‐g‐MAH/OMT rather than the POE/OMT composites. The POE‐g‐MAH/OMT nanocomposites have better thermal stability and significantly reduced flammability than the POE/OMT microcomposites, which was discussed on the basis of cone colorimeter test of the composites and energy dispersive X‐ray spectrum analysis of the combustion chars. POLYM. ENG. SCI., 54:2911–2917, 2014. © 2014 Society of Plastics Engineers     

Water uptake behavior of layered silicate/starch–polycaprolactone blend nanocomposites

The water uptake behavior of biodegradable layered silicate/starch–polycaprolactone blend nanocomposites was evaluated. Three different commercial layered silicates (Cloisite Na⁺, Cloisite 30B and Cloisite 10A) were used as reinforcement nanofillers. Tests were carried out in two different environments: 60 and 90% relative humidity using glycerol solutions. The clay/starch–polycaprolactone blend nanocomposites were obtained by melt intercalation and characterized by gravimetric measurements and tensile tests. The intercalated structure (determined by wide‐angle X‐ray diffraction) showed a decrease in water absorption as a function of clay content probably due to the decrease of the mean free path of water molecules. The diffusion coefficient decreased with clay incorporation but a further increase in the clay content did not show an important effect on this parameter. Elongation at break increased with exposure showing matrix plasticization. Mechanical properties of the nanocomposites deteriorated after exposure whereas they remained almost constant in the case of the neat matrix. Copyright © 2007 Society of Chemical Industry     

Biodegradable polyester layered silicate nanocomposites based on poly(ϵ‐caprolactone)

Nanocomposites based on biodegradable poly(?‐caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt interaction with PCL or by in situ ring‐opening polymerization of ?‐caprolactone as promoted by the so‐called coordination‐insertion mechanism. Both non‐modified clays (Na⁺ ‐MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL‐layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL‐based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of ?‐caprolactone was carried out in the presence of MMT organo‐modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites were characterized by a covalent bonding between the polyester chains and the clay organo‐surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts.     

Mechanical properties of layered silicate/starch polycaprolactone blend nanocomposites

The mechanical behavior of layered silicate/starch polycaprolactone blend nanocomposites was evaluated. Three different clays (Cloisite Na⁺, Cloisite 30B and Cloisite 10A) were used as reinforcement. Nanocomposites were prepared by melt intercalation followed by compression molding. These nanocomposites were characterized using X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis and tensile testing. X‐ray diffraction results showed that most of the clays were intercalated within the polymeric chains. In all cases, mechanical properties were improved with clay incorporation and the improvement was better as the clay content was increased. The best properties were achieved with Cloisite 10A due to their greatest compatibility with the matrix. A mechanical model, which takes into account the effective parameters of the clay, was used in order to estimate the dispersion of clay within the polymer. The highest dispersion was obtained for Cloisite 10A, which is in accordance with the experimental mechanical properties. Although dynamical‐mechanical properties improved with clay incorporation, the glass transition temperature was not affected. Copyright © 2006 Society of Chemical Industry