Intercalation of 2,4-dihydroxybenzophenone-5-sulfonate anion into Zn/Al layered double hydroxides for UV absorption properties

Zn/Al-layered double hydroxides (LDHs) containing the organic anion of 2,4-dihydroxybenzophenone-5-sulfonate (DHBS) have been synthesized by co-precipitation method. Surface, structural, thermal and absorption properties of the ZnAl-DHBS-LDHs nanohybrids were characterized by BET analysis, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry and differential thermal analysis and UV–visible spectroscopy. The results revealed that organic UV absorbent-DHBS has been intercalated into the interlayer spaces of ZnAl-LDHs and the intercalation of DHBS in LDHs interlayer galleries resulted to higher thermal stability and better UV absorption ability; these show that the hybrid ZnAl-DHBS-LDHs phase has potential applications as a UV absorber.     

Preparation and properties of polymer/LDH nanocomposite used for UV curing coatings

The thermal and mechanical properties of UV curing coatings consisted of urethane acrylates as an oligomer and a diacrylate monomer were reinforced by using layered double hydroxide (LDH). The LDH was organically modified by an ion-exchange process, in which the nitrate anions were replaced by long alkyl sulfate anions. With organic modification, the d-spacing of inorganic LDH layers was greatly enlarged to 2.75 from 0.78 nm, leading the LDH to be organophilic. During in situ photopolymerization process, the d-spacing of LDH layers was further enlarged to 4.29 nm, indicating the intercalation of polymer chains. For comparison, polymer/LDH nanocomposite filled with un-modified LDH was also prepared, and showed less enhancement in thermal and mechanical properties.     

Second staging of tartrate and carbonate anions in Mg–Al layered double hydroxide

The intercalation of tartrate was performed through ion exchange using carbonate Mg–Al layered double hydroxide (LDH) as precursor. The intermediate crystalline phase (so-called second-staging phase) was observed during the intercalation process. The pure second-staging LDH, in which alternate interlayer regions are occupied by carbonate and tartrate anions, was obtained by the deintercalation of interlayer tartrate with carbonate. It was also found that the interlayer tartrates are so stable that they are difficult to exchange by carbonate at room temperature.     

Preparation and characterization of polymer/layered silicate pharmaceutical nanobiomaterials using high clay load exfoliation processes

The purpose of this study was to prepare and characterize lamellar silicate nanocomposites using exfoliation processes, high clay load and polyvinylpyrrolidone (PVP), ethylcellulose (EC) and polyquaternium-H (PQH). The clays (sodium montmorillonite, Viscogel S4™, S7™ and B8™) were pre-treated with ultrasonic energy in order to increase clay exfoliation yields. Polymeric nanocomposites were characterized by XRPD, DSC, TGA, DLS and NMR. The results revealed a new exfoliation method and new intercalated nanocomposites. High clay load was used to obtain the nanocomposites, which enables its application at an industrial scale. These nanocomposites could be broadly applied across the pharmaceutical, medical and food industries.     

3,4-Dichlorophenoxyacetate interleaved into anionic clay for controlled release formulation of a new environmentally friendly agrochemical

A new layered organic–inorganic nanohybrid material, zinc-aluminum-3,4-dicholorophenoxyacetate (N3,4-D) in which an agrochemical, 3,4-dichlorophenoxyacetic acid (3,4-D), is intercalated into zinc-aluminum-layered double hydroxide (ZAL), was synthesized by coprecipitation method. A well-ordered nanomaterial was formed with a percentage loading of 53.5% (w/w). Due to the inclusion of 3,4-D, basal spacing expanded from 8.9 Å in ZAL to 18.7 Å in N3,4-D. The Fourier transform infrared study shows that the absorption bands of the resulting nanohybrid composed of both the 3,4-D and ZAL further confirmed the intercalation episode. Thermal analysis shows that ZAL host enhances the thermal stability of 3,4-D. Controlled-release experiment shows that the release of 3,4-D in the aqueous media is in the order of phosphate > carbonate > sulfate > chloride. These studies demonstrate the successful intercalation of the 3,4-D and its controlled release property in various aqueous media.     

Structure and conductive properties of poly(ethylene oxide)/layered double hydroxide nanocomposite polymer electrolytes

The oligo(ethylene oxide) modified layered double hydroxide (LDH) prepared by template method was added as a nanoscale nucleating agent into poly(ethylene oxide) (PEO) to form PEO/OLDH nanocomposite electrolytes. The effects of OLDH addition on morphology and conductivities of nanocomposite electrolytes were studied using wide-angle X-ray diffractometer, polarized optical microscopy, differential scanning calorimetry and ionic conductivity measurement. The results show that the exfoliated morphology of nanocomposites is formed due to the surface modification of LDH layers with PEO matrix compatible oligo(ethylene oxide)s. The nanoscale dispersed OLDH layers inhibit the crystal growth of PEO crystallites and result in a plenty amount of intercrystalline grain boundary within PEO/OLDH nanocomposites. The ionic conductivities of nanocomposite electrolytes are enhanced by three orders of magnitude compared to the pure PEO polymer electrolytes at ambient temperature. It can be attributed to the ease transport of Li⁺ along intercrystalline amorphous phase. This novel nanocomposite electrolytes system with high conductivities will be benefited to fabricate the thin-film type of Li-polymer secondary battery.     

In situ exfoliation of graphite oxide nanosheets in polymer nanocomposites using miniemulsion polymerization

Poly(styrene-co-butyl acrylate) (poly(St-co-BA)) nanocomposite latices based on graphene oxide (GO) were synthesized by miniemulsion polymerization. The polymerization procedure involved dispersing an aqueous solution of graphite oxide in a monomer phase, followed by emulsification in the presence of a hydrophobe and a surfactant into miniemulsions. The focus was to investigate the suitability of miniemulsion for the synthesis of polymer nanocomposites based on a graphene derivative (i.e., GO) with exfoliated structure in a one-step nano-incorporation technique. Poly(St-co-BA) nanocomposites containing the exfoliated GO nanoplatelets, which have improved mechanical and thermal properties were successfully synthesized by the miniemulsion process. The nanostructure of the nanocomposites was investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM and XRD indicated that the nanocomposites mainly showed exfoliated morphologies, except at relatively high GO content. TEM also revealed that the nanocomposite latices had the so-called ‘‘armored’’ structure, where the nanosized GO sheets are distributed around the edges of the copolymer particles.     

Intercalation and exfoliation behaviour of clay layers in branched polyol and polyurethane/clay nanocomposites

The exfoliation of clay layers was realized in a tri‐hydroxyl branched polyether polyol by direct mixing and the corresponding exfoliated polyurethane/clay nanocomposite was prepared by further in situ curing. The effects of various surface‐modified organoclays and various polyol types on the intercalation and exfoliation behaviour of clay layers were investigated. The interaction between the polyol and clay and the mixing temperature plays an important role in the occurrence of exfoliation and intercalation. The relationship between rheological data of polyol/clay dispersion and the intercalation or exfoliation state of the clay was established. This provides a convenient and efficient way to evaluate the dispersion state of the clay. Based on the experimental results, a possible layer‐by‐layer exfoliation mechanism is proposed. Copyright © 2006 Society of Chemical Industry     

The disorderly exfoliated LDHs/PMMA nanocomposite synthesized by in situ bulk polymerization

A new nanocomposite—disorderly exfoliated layered double hydroxides/poly(methyl methacrylate) (LDHs/PMMA)—was prepared by a two-stage process with an in situ bulk polymerization of methyl methacrylate (MMA) in the presence of 10-undecenoate intercalated LDH (LDH-U). The LDH-U was prepared using the co-precipitation method. The structural and compositional details of the LDH-U were determined by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), ²⁷Al and ¹³C magic-angle spinning nuclear magnetic resonance (²⁷Al and ¹³C MAS NMR), elemental analysis (EA), inductively coupled plasma-mass (ICP) and transmission electron microscopy (TEM). During the preparation of LDHs/PMMA nanocomposite, XRD and TEM were also employed to monitor the formation of the exfoliated LDHs/PMMA nanocomposite and the dispersion behavior of the LDH layers, respectively. The pre-polymerization process exfoliates LDH layers within pre-polymer, according to the XRD and TEM results. Additionally, the LDHs/PMMA nanocomposite contained 5 wt% LDH-U, indicating that the LDH layers were well exfoliated and dispersed in the PMMA matrix in a disordered fashion.     

Synthesis and solution properties of a new pH-responsive polymer containing amino acid residues

The amine salt, N,N-diallyl-N-carboethoxymethylammonium chloride was cyclopolymerized in water using ammonium persulfate as an initiator to afford a cationic polyelectrolyte which on acidic hydrolysis of the pendant ester groups gave the corresponding cationic acid salt (CAS). The CAS was converted into an anionic polyelectrolyte (APE) and polybetaine (PB). The solution properties of the APE having two basic functionalities were investigated in detail by potentiometric and viscometric techniques. Basicity constants of the amine as well as the carboxylate groups in APE are ‘apparent’ and as such follow the modified Henderson-Hasselbalch equation; as the degree of protonation (α) of the whole macromolecule increases, the protonation of the amine nitrogens and carboxylate groups becomes increasingly more difficult and easier, respectively. While the APE, PB and CAS were found to be soluble in salt-free water, the corresponding PB and CAS of the SO₂ copolymers of the amine salt 1 were found to be insoluble in water.     

Effect of interlayer anions on chromium removal using Mg–Al layered double hydroxides:Kinetic,equilibrium and thermodynamic studies

The influence of interlayer anions such as NO3-, SO42-and Cl-on Mg–Al hydrotalcites for Cr(VI) removal from aqueous solution was studied. The structure of the prepared LDHs was characterized by XRD, SEM, FTIR, TGA, BET surface area and p Hzpc. The sorbent ability and sorption mechanisms were also investigated. The LDHs exhibit high removal for Cr(VI), and the sorbed amount depends on the nature of interlayer anion, which decreased in the following order: NO3-N Cl-N SO42-. Nitrate-containing LDH reached a Cr(VI) sorption equilibrium within only 30 min. The effects of operating conditions, including initial concentration, solution p H, agitation time and sorbent amount have been studied in batch mode. The optimum conditions were observed at an initial concentration of 100 mg·L-1, p H = 6, agitation time of 60 min and a sorbent dose of 2 g·L-1. The equilibrium data were fitted to the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models. The Langmuir model was found to sufficiently describe the sorption process, offering a maximum sorption capacity of 71.91 mg·g-1. The sorption kinetic follows pseudo-second-order reaction with high accuracy. Thermodynamic parameters suggested that the sorption process is spontaneous and endothermic in nature.     

Effect of photofunctional organo anion-intercalated layered double hydroxide nanoparticles on poly(ethylene terephthalate) nonisothermal crystallization kinetics

Very recently, we report a facile preparation and strong UV-shielding function of poly(ethylene terephthalate) (PET) nanocomposites using 4,4′-diaminostilbene-2,2′-disulfonic acid anion-intercalated layered double hydroxide (LDH_DDA). Herein, the effect of the photofunctional organo anion-intercalated LDH nanoparticles on nonisothermal crystallization kinetics of PET is reported by differential scanning calorimetry technique. First, the nonisothermal crystallization behaviour is discussed by several basic parameters including crystallization peak temperature, relative degree of crystallinity with temperature or time, and half-time of crystallization. Then, Avrami and Jeziorny method, as well as Mo model were applied for the PET/LDH_DDA nanocomposites. Finally, the crystallization activation energy was investigated by Kissinger method and Flynn conversion. The results reveal that the incorporation of LDH_DDA nanoparticles acted as nucleating agent and significantly accelerated the PET nonisothermal crystallization process, whereas had little effect on the three-dimensional growth pattern of spherulites.     

Inorganic layered double hydroxides as a drug delivery system—intercalation and in vitro release of fenbufen

Layered double hydroxides (LDHs), or so-called anionic clays, consist of cationic brucite-like layers and exchangeable interlayer anions. Because of their biocompatibility, some LDHs, such as Mg/Al, Zn/Al, Fe/Al and Li/Al-LDH, can be used as host materials for drug-LDH host–guest supramolecular structures. The anti-inflammatory drug fenbufen has been intercalated into layered double hydroxides for the first time by co-precipitation under a nitrogen atmosphere. The product has been characterized by powder X-ray diffraction (XRD), FT-IR spectroscopy, elemental analysis and thermogravimetry (TG) and shows an expanded LDH structure, indicating that the drug has been successfully intercalated into LDH. In addition, the dependence of the nature of the fenbufen intercalation process on conditions such as pH value and chemical composition of the host has been systematically investigated. The interlayer distance in the intercalated materials increases with increasing pH value, resulting from a change in the arrangement of interlayer anions from monolayer to interdigitated bilayer. Drug release characteristics of the pillared LDH materials were investigated by a dissolution test in a simulated intestinal fluid (buffer at pH 7.8). The results show that the drug release of supramolecular LDH materials was a slow process, especially in the case of Mg/Al intercalated materials, suggesting that these drug-inorganic hybrid materials can be used as an effective drug delivery system.     

Morphology and properties of PVC/clay nanocomposites via in situ emulsion polymerization

PVC/Na⁺–montmorillonite (MMT) nanocomposites were prepared via a simple technique of emulsion polymerization at several different MMT clay concentrations. X‐ray diffraction and transmission electron microscopy studies revealed the formation of a mixture of intercalated and exfoliated nanostructure. Tensile testing results showed that the tensile modulus of the nanocomposites increased with the addition of clay, while the tensile strength decreased little. The notched impact strength of the nanocomposites was also improved. For systems containing clay in the range of 2.1 to 3.5 wt %, the impact strength was almost two times as large as that of pure PVC. However, those mechanical properties began to decrease with the continuously increasing amount of clay. The fracture surface of pure PVC and the nanocomposites was observed by scanning electron microscope. Thermal properties of the nanocomposites were found to increase as a result of clay incorporation. The glass transition temperatures of the PVC/clay nanocomposites were nearly identical to that of pure PVC. The Vicat softening points exhibited a progressively increasing trend with the clay content added. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 277–286, 2004     

Synergistic flame retardant effects of Fe-OMMT with LDH in EVA/LDH composites

Abstract

The synergistic effects of Fe organic modified montmorillonite (Fe-OMMT) with layered double hydroxides (LDHs) in ethylene vinyl acetate copolymer/LDH (EVA/LDH) composites have been studied using thermal analysis [thermogravimetric analysis (TGA)], limiting oxygen index (LOI), UL-94 test and cone calorimeter test (CCT). The results showed that the addition of a given amount of Fe-OMMT apparently increased the LOI value and the rating in the UL-94 test. The results from the LOI and UL-94 tests show that Fe-OMMT can act as flame retardant synergistic agents in EVA/LDH composites. The CCT data indicated that the addition of Fe-OMMT in the EVA/LDH system can greatly reduce the heat release rate. The TGA data show that Fe-OMMT, as an excellent flame retardant synergist of LDH, cannot increase the thermal degradation temperature and the charred residues.     

SEM study of a polystyrene/clay nanocomposite

We carried out a scanning electron microscopy study to investigate the morphology of a polystyrene (PS)/montmorillonite nanocomposite. Monodispersed spherical particles, about 200 nm in diameter, were observed when PS/montmorillonite powder was dispersed in water, whereas planar silicate sheets were found for cetyltrimethylammonium bromide‐exchange montmorillonite. The fracture surface of a PS/clay nanocomposite pellet sample showed a lot of fibrils rather than the smooth surface of a pure PS pellet. After the PS/clay nanocomposite pellet was chemically etched, flaky montmorillonite particles were homogeneously dispersed in the PS matrix. A film sample, prepared by the pressing of the PS/clay nanocomposite melt, revealed that the montmorillonite primary particles oriented parallel to the surface, and the corresponding X‐ray diffraction distribution map of silicon atoms confirmed that the dispersed particles were montmorillonite primary particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 66–69, 2002     

Poly(ethylene-oxide)/clay/silica nanocomposites: Morphology and thermomechanical properties

Poly(ethylene-oxide) PEO/clay/silica nanocomposites were prepared via solution intercalation by exploiting phase separation based on the bridging of particles by polymer chains. The intercalated morphology of nanocomposites was confirmed by XRD. Vibrational modes of the ether oxygen of PEO in the hybrids are shifted due to the coordination of the ether oxygen with the sodium cations of clay and the H-bonding interactions of the ether oxygen with the surface silanols of hydrophilic fumed silica. Based on SEM, the overall density of nanoparticle aggregates in the interspherulitic region was observed to be higher compared to that inside spherulites. PEO/clay/silica hybrids show significant property improvements compared to PEO/clay hybrids and pure PEO. The system containing 10 wt.% clay and 5 wt.% silica has substantially higher modulus and much lower crystallinity compared to the 15 wt.% clay system. The physics behind the reinforcement effect and the reduction of crystallinity as a function of fumed silica loading is discussed based on the morphological characterization of the hybrids. Lastly, PEO/clay/silica hybrids display good thermal stability and are much stiffer compared to pure PEO and PEO/clay nanocomposites.     

Nonisothermal crystallization behavior of highly exfoliated polypropylene/clay nanocomposites prepared by in situ polymerization

Polypropylene/clay nanocomposites (PPCNs) were prepared via an in situ polymerization method with a Ziegler–Natta/clay compound catalyst in which the MgCl₂/TiCl₄ catalyst was embedded in the clay galleries. The wide‐angle X‐ray diffraction and transmission electron microscopy results showed that the clay particles were highly exfoliated in the polypropylene (PP) matrix. The nonisothermal crystallization kinetics of these PPCNs were investigated by differential scanning calorimetry at various cooling rates. The nucleation activity were calculated by Dobreva's method to demonstrate that the highly dispersed silicate layers acted as effective nucleating agents. The Avrami, Jeziorny, Ozawa, and Mo methods were used to describe the nonisothermal crystallization behavior of the PP and PPCNs. Various parameters of nonisothermal crystallization, such as the crystallization half‐time, crystallization rate constant, and the kinetic parameter F(t), reflected that the highly exfoliated silicate layers significantly accelerated the crystallization process because of its outstanding nucleation effect. The activation energy values of the PP and PPCNs determined by the Kissinger method increased with the addition of the nanosilicate layers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermoplastic olefin/clay nanocomposites: Morphology and mechanical properties

Thermoplastic olefin (TPO)/clay nanocomposites were made with clay loadings of 0.6–6.7 wt %. The morphology of these TPO/clay nanocomposites was investigated with atomic force microscopy, transmission electron microscopy (TEM), and X‐ray diffraction. The ethylene–propylene rubber (EPR) particle morphology in the TPO underwent progressive particle breakup and decreased in particle size as the clay loading increased from 0.6 to 5.6 wt %. TEM micrographs showed that the clay platelets preferentially segregated to the rubber–particle interface. The breakup of the EPR particles was suspected to be due to the increasing melt viscosity observed as the clay loading increased or to the accompanying chemical modifiers of the clay, acting as interfacial agents and reducing the interfacial tension with a concomitant reduction in the particle size. The flexural modulus of the injection moldings increased monotonically as the clay loading increased. The unnotched (Izod) impact strength was substantially increased or maintained, whereas the notched (Izod) impact strength decreased modestly as the clay loading increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 928–936, 2004     

Effect of clay on the morphology of blends of poly(propylene) and polyamide 6/clay nanocomposites

PP/NPA6 blends composed of poly(propylene) (PP) and polyamide 6/clay nanocomposites (NPA6) were prepared by twin‐screw extrusion and melt‐drawn into ribbons by a ribbon extrusion process. The influence of clay on the morphology of PP/NPA6 ribbons was investigated by means of field‐emission scanning electron microscopy and optical microscopy. The results show that at low clay content (3, 5 wt%), NPA6 exhibited continuous lamellar structure in PP as pristine PA6 did in a PP/PA6 blend, but at a higher clay content (10 wt%) only ellipsoids or elongated ellipsoids were observed. In order to explain the morphological difference, two factors, ie the compatibilization effect and melt rheology, have been taken into consideration. It has been found that both factors, and probably mainly the variation in melt rheology, were responsible for the morphological difference in the PP/NPA6 blends with different clay contents under the extensional flow field. Copyright © 2004 Society of Chemical Industry