Organo-modified Layered Double Hydroxide Research Articles

Elongational flow‐induced microstructure evolutions in polypropylene/layered double hydroxides nanocomposites

AbstractIn this work, the effect of the non‐isothermal elongational flow on the morphology and mechanical properties of polypropylene (PP)‐based nanocomposites containing Mg‐Al layered double hydroxides (LDHs) modified with stearate or oleate functional groups has been investigated. In particular, nanocomposites containing 5 and 10 wt% of LDHs prepared through melt compounding were subjected to uniaxial elongational flow at the exit of the extruder, leading to the formation of fibers characterized by different draw ratios (DRs). The mechanical characterization of the fibers demonstrated a progressive enhancement of the tensile strength as a function of the DR with increasing the content of nanofillers. Notably, for the fibers stretched at a DR of 200 and containing 10 wt% of LDHs modified with oleate groups, the tensile strength increased fourfold as compared to that of the unfilled matrix. These results have been attributed to a progressive enhancement of the extent of the dispersions of the embedded LDHs induced by the application of the elongational flow, as also confirmed by morphological analyses. In all, the obtained results demonstrated the beneficial effect of the elongational flow in promoting the achievement of superior mechanical properties in LDHs‐containing nanocomposites, hence widening the application field of these nanostructured materials.Highlights PP/organomodified LDH nanocomposites were obtained through melt compounding. Nonisothermal elongational flow was applied to the extrudates at the die exit. Anisotropic fibers showed progressively enhanced tensile strength values. Elongational flow promoted a gradual evolution of the material microstructure. A gradual improvement of the nanofiller dispersion was observed upon elongation.

Preparation and evaluation of thermoplastic vulcanizate / organo-modified layered double hydroxide nanocomposite: Statistical modelling and optimization

This study investigates the fabrication and optimization of a novel thermoplastic vulcanizate (TPV) nanocomposite consisting of organo-modified layered double hydroxide (O-LDH) and a polypropylene (PP)/polybutadiene rubber (PBR) base for the first time. O-LDH was prepared by condensation reaction between an aminosilane-modified LDH (Si-LDH) and both maleic-anhydride-grafted-liquid polybutadiene (LPBR-g-MA) and maleic-anhydride-grafted polypropylene (PP-g-MA). A two-component mixture consisting of LPBR-g-MA and PP-g-MA (weight ratio:60/40) (Comp-g-MA) was used as the compatibilizer agent, and bis-(triethoxysilylpropyl)-tetrasulfid (TESPT) was employed as the vulcanizing agent which was activated in the presence of MA. Response surface methodology (RSM) integrated by central composite design (CCD) was utilized to maximize the gel content and minimize the number-averaged rubber particle size (NARPS) of TPV-Nanocomposite by optimizing the amounts of Comp-g-MA, TESPT and O-LDH. The outcomes revealed that increasing the O-LDH and Comp-g-MA up to a certain amount, decreased the size of the vulcanizate PBR domains due to the formation of a strong interface, but it caused an increasing trend for the %gel up to a maximum value. The optimized TPV sample (OTPV) was obtained using 8.2 % Comp-g-MA, 5.8 % O-LDH and 2.5 % TESPT and exhibited 50.4 % of gel content and 135.6 μm of NARPS. OTPV showed superior properties in terms of morphological stabilization, thermal stability and oil-resistance due to the synergistic effect of Comp-g-MA and O-LDH components into the PP/PBR blends.

Organo-modified LDH fillers endowing multi-functionality to bio-based poly(butylene succinate): An extended study from the laboratory to possible market

Polybutylene succinate (PBS) were processed in melt extrusion by dispersion of organo-modified layered double hydroxide (LDH). Depending on the organic anion interleaved into LDH fillers (L-tyrosine (TYR), L-tryptophan (TRP), L-ascorbate (ASA) and 3-(4-hydroxyphenyl)propionate (HPP)), it was possible to control and tune the properties of the resulting PBS composites. Each LDH filler is found to act differently toward PBS, thus modifying its viscoelastic properties (as expressed by a chain extending effect), its rate of hydrolysis and photo-degradation or its antibacterial activity. The highest chain extending effect was observed in the case of LDH with L-tryptophan, the worst – with L-ascorbate anion. However, L-ascorbate anions interleaved into LDH present 100% activity in antibacterial properties. A better compromise may be achieved when PBS is mixed with different LDHs such as those combining HPP and ASA, making possible to target efficiently multi-properties such as small rate of hydrolysis, photo-stability, biocide activity as well as chain extension, thus turning to a multifunctional (bio)nanocomposites with new possible applications. Finally, a possible scale-up is demonstrated on thin films.

Corrosion Studies of 12-Aminododecanoate Modified Zn-Al LDH/Epoxy Coating

Addition of environmentally friendly layered double hydroxide (LDHs) to organic coatings can increase barrier properties within the coatings due to the platelet structure of the LDHs. A new approach combining silane coupling agents to enhance compatibility of the inorganic and organic matrix is used to form improved corrosion resistance coatings. For this work, Zn-Al-LDH are prepared via a co-precipitation method and modified by sodium 12-aminododecanoate through an anion exchange process. The organo-modified layered double hydroxide (LDH) is functionalized using 3-aminopropyltriethoxysilane (APTES) which is then incorporated into the epoxy matrix (EPON 828). The reaction between amine part of the amino dodecanoate as a strong nucleophilic group and epoxy ring part as an electrophilic group improves compatibility of LDHs layers and epoxy molecules in the composite. Differential scanning calorimetry is used to study this exothermic epoxy-amine ring opening reaction to determine the curing temperature of the coatings before and after modified LDH inclusion. The change in LDH structure, effect of incorporation of modified LDHs in the epoxy matrix, grafting of APTES on the LDH surface and elemental analysis are investigated respectively, by x-ray diffraction, thermogravimetric analysis, infrared spectroscopy and energy dispersive x-ray analysis. In the last step of preparation, Epikure 3571 as a curing agent, is added to the LDHs/epoxy system, then the coating is applied on steel substrates. After the thermal curing process, the anti-corrosion performance provided by this coating is assessed by multiple methods including, open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl aqueous solution. Further, scanning electron microscopy is used to study morphological changes on the coating before and after immersion test and to scan the localized corrosion spots. The results are compared with the coated steel samples with clear epoxy coating and none modified LDH/epoxy. Figure 1

Pulsed laser deposition of functionalized Mg–Al layered double hydroxide thin films

In this paper, magnesium–aluminium layered double hydroxide (LDH) has been functionalized with sodium dodecyl sulfate (DS) and deposited as thin film by pulsed laser deposition (PLD). Mg, Al-LDH powders were prepared by co-precipitation and used as reference material. Intercalation of DS as an anionic surfactant into the LDHs host layers has been prepared in two ways: co-precipitation (P) and reconstruction (R). DS intercalation occurred in LDH powder via both preparation methods. The films deposited via PLD, in particular at 532 and 1064 nm, preserve the organic intercalated layered structure of the targets prepared from these powders. The results reveal the ability of proposed deposition technique to produce functional composite organo-modified LDHs thin films.

An insight into the interaction between functionalized thermoplastic elastomer and layered double hydroxides through rheological investigations

Abstract Nanocomposites based on maleated poly(styrene-(ethylene-co-butylene)-styrene) copolymer (SEBSgMA) and organo-modified layered double hydroxide (OLDH) have been formulated with the aim to investigate the effects of interfacial interactions between the grafted maleic anhydride groups of the copolymer and the OLDH nanolayers on the rheological properties of nanocomposites. The spectroscopic analysis indicates the establishment of specific polymer/nanofiller interactions, whose extent has been highlighted through morphological and rheological investigations. Specifically, oscillatory melt rheology and shear relaxation tests have been considered in order to deeply investigate the interfacial bridging interactions. Obtained results highlight that SEBSgMA-based nanocomposites containing a high amount of OLDH show solid-like rheological behavior, quite similar to that of crosslinked polymers, attributable to the formation of a gel-like structure.

Preparation of β-cyclodextrin-ester network and new organo-modified LDH as dual additives of PVA: Thermal, dynamic-mechanical and migration study

Abstract A new ternary nanocomposite based on poly(vinyl alcohol) (PVA) by using a β −cyclodextrin-ester network and organo-modified layered double hydroxides (MLDH) was prepared by water solution casting method. β-cyclodextrin-ester network (β-CDE) was synthesized by using the reaction of β-cyclodextrin with 3,3′,4,4′-benzophenone tetracarboxylic dianhydride in the basic media. The interlayer basal spacing of LDH was modified by using a bio based modifier containing three carboxylic groups (TA) through the regeneration method (MLDH). As a potential adjuvant, the MLDH, combined with and without β-CDE, was used in a PVA system. The morphology, thermal and thermo-mechanical properties of all the PVA systems as well as migration of modifier from PVA/MLDH and ternary PVA/CDE-MLDH nanocomposites were investigated. In the presence of the β-CDE, the MLDH showed a synergistic effect on improving all of the investigated properties of PVA. Based on TGA results, it can be concluded that adding both of the β-CDE network and MLDH into PVA matrix increased the char yields from 3.1 (in the neat PVA) to 6.1 (in the PVA/CDE-MLDH nanocomposite) in inert atmospheres. The temperature at 5 mass% loss (T5) increased from 188.1 °C to 197.7 °C in PVA/CDE-MLDH nanocomposite containing 4 mass% of each the β-CDE and MLDH in comparison to the neat PVA. Dynamic mechanical analysis revealed that the storage modulus and thermal stability were improved by incorporation of both MLDH and β-CDE into PVA. Migration results indicate that migration of TA from PVA matrix for PVA/CDE-MLDH is much lower than that for PVA/MLDH.

Enhanced adsorption capacity of dyes by surfactant-modified layered double hydroxides from aqueous solution

Abstract The utilization of organo-modified layered double hydroxides with anionic surfactants (organo-LDHs) as adsorbents were successfully carried out to remove various synthetic dyes from aqueous solution. Intercalation of anionic surfactants changed the surface properties of MgAl-LDH from hydrophilic to hydrophobic, and a charge inversion occurred with increasing the length of surfactant chains. Such changes in the surface properties of the organo-LDHs were important. Experimental data shown that the SNS-modified MgAl-LDH could be used as a broad-spectrum adsorbent to effectively remove anionic, non-ionic, and cationic dyes from aqueous solution.

Thermal and dynamic mechanical properties of PP/EVA nanocomposites containing organo-modified layered double hydroxides

Abstract In this study, organo-modified layered double hydroxides (LDH) as nanoparticleswere used to prepare hybrid nanocomposites based on polypropylene (PP), ethylene vinyl acetate copolymer (EVA) blend in presence of a maleated polypropylene (PP-g-MA) as compatibilizer via a one-step melt mixing process. Transmission electron microscope (TEM) was employed to determine localization of LDH nanoparticles in the blend nanocomposites. Microstructures of the nanocomposites were studied by means of scanning electron microscopy (SEM). Thermo-mechanical properties of nanocomposites were investigated by dynamic mechanical thermal analysis (DMTA). Differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were also used to investigate crystallization behavior and degradation process of the nanocomposites, respectively. The results showed that, LDH nanoparticles in the exfoliated and/or intercalated states were mainly localized in the EVA phase. The average particles size of EVA domains was reduced in presence of LDH and PP-g-MA. The storage modulus of nanocomposites was controlled by combination of LDH and PP-g-MA. The crystallization studies revealed that 5wt%LDH and PP-g-MA increased crystallization temperature to 133.4 °C while addition ofLDH in absence of the compatibilizer decreased the crystallization temperature to 122.7 °C.Investigation of thermal degradation behavior of samples indicated that presence of LDH and PP-g-MA in PP/EVA blendsimprovedinitial degradation temperature of nanocomposites by about 43% compared to the neat PP.

Analysis of dynamic oscillatory rheological properties of PP/EVA/organo-modified LDH ternary hybrids based on generalized Newtonian fluid and generalized linear viscoelastic approaches

A comprehensive investigation was performed on single-step melt processed polypropylene (PP)/(ethylene vinyl acetate copolymer (EVA)/organo-modified layered double hydroxide (LDH) counterpart ternary hybrids to explore the effect of LDH loading on small-amplitude oscillatory shear (SAOS) rheological properties and to correlate the properties with microstructure. The rheological results were analyzed in detail from qualitative and quantitative perspectives. Using qualitative interoperation of storage modulus and complex viscosity alteration against LDH loading, and also quantitative analysis by viscosity models based on both the generalized Newtonian fluid (GNF) and generalized linear viscoelastic (GLVE) approaches, detailed predictions were carried out on the microstructure of samples and also partitioning of the organo-modified LDH particles and their intercalation and exfoliation extent within hybrids. By comparing the elasticity and relaxation spectrum of PP-rich/LDH with those of EVA-rich/LDH hybrids, it was predicted that organo-modified LDH platelets, in the case of PP-rich samples, have been located at the interface or within the EVA dispersed particles, while in the case of EVA-rich samples, they mainly localized within the matrix. In addition, the crossover frequency and slope of G′ and G″ curve at terminal region were correlated with the extent of intercalated and exfoliated structures of filler. The validity of these predictions on microstructure of the developed hybrids was confirmed visually using transmission electron microscope (TEM) micrographs.

Bio-nanocomposite films reinforced with organo-modified layered double hydroxides: Preparation, morphology and properties

Bio-nanocomposite films based on organo-modified layered double hydroxides (OLDH)/poly(butylene adipate-co-terephtalate) (PBAT) were prepared with solution casting method. The morphology and structural characterizations on the OLDH and OLDH/PBAT bio-nanocomposite films were performed by Fourier transform infrared (FT-IR) spectrum, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The physical properties of the films were determined by thermal, mechanical and optical analysis, and contact angle testing and water vapor transmission (WVT) measurement. The XRD results show that the basal spacing of the layered double hydroxides (LDH) was increased from 0.88nm to 4.45nm after the modification by long-chain lauryl alcohol phosphoric acid ester potassium (MAPK). The exfoliated OLDH were well dispersed in the PBAT matrix. The crystallization temperature of the OLDH/PBAT bio-nanocomposite films was significantly higher than the base matrix. The hydrophilic, optical, tensile and water vapor barrier properties of the films were obviously improved by the addition of OLDH with low content (1%). The results of this study would be useful for investigating the potential to develop the eco-friendly packaging films.

Poly(butylene succinate) bionanocomposites: a novel bio-organo-modified layered double hydroxide for superior mechanical properties

Bionanocomposites based on poly(butylene succinate) and a novel organo-modified layered double hydroxide have been prepared by in situ polymerization.

Nanohybrids of organo-modified layered double hydroxides and polyurethanes with enhanced mechanical, damping and UV absorption properties

The construction of high-performance polymer–clay nanocomposites plays an important role in developing new types of organic–inorganic hybrids.

Organo-layered double hydroxides composite thin films deposited by laser techniques

We used laser techniques to create hydrophobic thin films of layered double hydroxides (LDHs) and organo-modified LDHs. A LDH based on Zn-Al with Zn2+/Al3+ ratio of 2.5 was used as host material, while dodecyl sulfate (DS), which is an organic surfactant, acted as guest material. Pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) were employed for the growth of the films. The organic anions were intercalated in co-precipitation step. The powders were subsequently used either as materials for MAPLE, or they were pressed and used as targets for PLD. The surface topography of the thin films was investigated by atomic force microscopy (AFM), the crystallographic structure of the powders and films was checked by X-ray diffraction. FTIR spectroscopy was used to evidence DS interlayer intercalation, both for powders and the derived films. Contact angle measurements were performed in order to establish the wettability properties of the as-prepared thin films, in view of functionalization applications as hydrophobic surfaces, owing to the effect of DS intercalation.

Exfoliation and dispersion of nano-sized modified-LDH particles in poly(amide-imide)s containing N-trimellitylimido-l-methionine and 3,5-diamino-N-(pyridin-3-yl)benzamide linkages

The present study describes the synthesis and characterization of nanocomposite materials built from the assembly of organic polymer and two-dimensional host materials of organo-modified layered double hydroxide (LDH). Organo-modified LDH was synthesized in one step from the co-precipitation reaction of the Al(NO3)3.9H2O, Mg(NO3)2.6H2O and bioactive N-trimellitylimido-l-methionine under ultrasonic irradiation. The X-ray diffraction (XRD) results of the organo-modified LDH show that the dianion is intercalated in the interlayer region of Mg–Al LDH and enlarges the interlayer distance. An optically active and organo-soluble poly(amide-imide) (PAI) was prepared by the direct step-growth polymerization reaction of l-methionine based diacid with 3,5-diamino-N-(pyridin-3-yl) benzamide in the presence of molten tetrabutylammonium bromide as a green solvent. Different nanocomposites of organo-modified LDH and chiral PAI were synthesized via solution intercalation method. The microstructures and thermal stabilities of the obtained LDH and nanocomposite materials were investigated by XRD, field emission scanning electron microscope (FE-SEM), Fourier transform infrared spectra, transmission electron microscopy (TEM) and thermogravimetry (TGA) techniques. The FE-SEM, TEM and XRD results revealed a coexistence of exfoliated and intercalated modified LDH in polymer matrix. TGA results showed improved thermal properties in comparison with the neat PAI.

Production of NiAl-layered double hydroxide intercalated with bio-safe amino acid containing organic dianion and its utilization in formation of LDH/poly(amide-imide) nanocomposites

Novel Ni-Al layered double hydroxide (LDH) intercalated with bio-active amino acid containing dicarboxylate was synthesized via co-precipitation reaction of Ni(NO3)2. 6H2O, Al(NO3)3. 9H2O and N,N′-(pyromellitoyl)-bis-L-phenylalanine under ultrasonic irradiation. The X-ray diffraction (XRD) results of the organo-modified LDH show that the dianion are intercalated in the interlayer region of LDH and expanded the interlayer distance. An optically active and organo-soluble poly(amide-imide) was prepared by the direct step-growth polymerization of L-phenylalanine based diacid and 3,5-diamino-N-(4-hydroxyphenyl)benzamide in the presence of molten tetra-butylammonium bromide as a green solvent. Then nanocomposite materials built from the assembly of L-phenylalanine amino acid containing polymer and two-dimensional organo-modified LDH were synthesized by solution intercalation method. The structures and morphology of the synthesized materials were investigated by XRD, Fourier transform infrared spectra, field emission scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM) techniques. The thermal properties of the modified LDH and the resulting nanocomposites were studied by thermogravimetry analysis techniques and the results showed improved in the thermal properties of the nanocomposites in comparison with the neat polymer. The FE-SEM, TEM and XRD results revealed a coexistence of exfoliated and intercalated modified LDH in polymer matrix.

Development of one-step synthesized LDH reinforced multifunctional poly(amide–imide) matrix containing xanthene rings: study on thermal stability and flame retardancy

New exfoliated poly(amide–imide)/Zn–Al layered double hydroxide (LDH) nanocomposites were synthesized by solution intercalation using synthesized organo-modified LDH (OLDH) as nanofiller obtained by one-step method.

Novel nanocomposites consisting of a semi-crystalline polyamide and Mg–Al LDH: Morphology, thermal properties and flame retardancy

New long aliphatic chain polyamide/Mg–Al layered double hydroxide (LDH) nanocomposites were successfully prepared via a solution intercalation technique under ambient condition in N,N-dimethylacetamide as solvent. The polyamide was synthesized using direct polycondensation reaction from an oleic acid based monomer which was characterized by proton nuclear magnetic resonance and size exclusion chromatography. The polyamide showed a semi-crystalline structure with melting temperature of 223°C. Organo-modified Mg–Al LDH was produced by one-step method and used to improve properties of the polyamide. Thermal properties and flame retardancy of the nanocomposites were studied by thermogravimetric analysis, differential scanning calorimetry and microscale combustion calorimeter. The thermal degradation results in both air and nitrogen atmospheres showed that the addition of organo-modified LDH resulted in a substantial increase in the thermal stability and char yields of the nanocomposites as compared to the neat polyamide. The flammability tests revealed that incorporation of the organo-modified LDH in the polyamide resulted in a reduction of the heat release rate, heat release capacity and total heat release.

A New Approach to Reducing the Flammability of Layered Double Hydroxide (LDH)-Based Polymer Composites: Preparation and Characterization of Dye Structure-Intercalated LDH and Its Effect on the Flammability of Polypropylene-Grafted Maleic Anhydride/d-LDH Composites

Dye structure-intercalated layered double hydroxide (d-LDH) was synthesized using a one-step method, and its intercalated behaviors have been characterized by Fourier transform infrared spectroscopy (FTIR), wide angle X-ray scattering (WAXS), scanning electron microscopy, thermogravimetric analysis (TGA), etc. As a novel functional potential fire-retarding nanofiller, it was used to prepare a polypropylene-grafted maleic anhydride (PP-g-MA)/d-LDH composite by refluxing the mixture of d-LDH and PP-g-MA in xylene, aiming to investigate its effect on the flammability of the PP-g-MA composite. The morphological properties, thermal stability, and flame retardant properties of the PP-g-MA/d-LDH composite were determined by FTIR, WAXS, transmission electron microscopy, TGA, and microscale combustion calorimetry. Compared with NO3-LDH (unmodified LDH) and LDH intercalated by sodium dodecylbenzenesulfonate (conventional organo-modified LDH), d-LDH can significantly decrease the heat release rate and the total heat release of the PP-g-MA composite, offering a new approach to imparting low flammability to LDH-based polymer composites.

Quantum dots in organo-modified layered double hydroxide framework-improved peroxynitrous acid chemiluminescence for nitrite sensing

In this study, the directional luminescent quantum dot (QD)-layered double hydroxide (LDH) assembly was fabricated by embedding the trace QDs onto the exterior surface of the organo-modified LDHs. It was found that this novel nanomaterial was able to extraordinarily improve an ultra-weak chemiluminescence (CL) emission from peroxynitrous acid (ONOOH). The enhanced CL emission was attributed to the electrostatic concentration of peroxynitrite (ONOO−) onto the orderly surface of the QD-organo-modified LDHs as well as the hydrophobic microenvironment of the organo-LDHs, facilitating the production of superoxide radical (O2−) and hydroxyl radical (OH). In addition, the CL intensity increased with increasing the concentration of nitrite in a wide range of 1.0–1000μM with a detection limit of 0.3μM (S/N=3). Therefore, the proposed method was applied for the selective and sensitive detection of nitrite in sausage samples. Recoveries from spiked real samples were in the range of 96–103%. The results of the proposed method for sensing nitrite in real samples were agreed with those obtained by the standard spectrophotometric method.