LDH Nanocomposites Research Articles

Degradability enhancement of poly(lactic acid) by stearate-Zn(3)Al LDH nanolayers.

Recent environmental problems and societal concerns associated with the disposal of petroleum based plastics throughout the world have triggered renewed efforts to develop new biodegradable products compatible with our environment. This article describes the preparation, characterization and biodegradation study of poly(lactic acid)/layered double hydroxide (PLA/LDH) nanocomposites from PLA and stearate-Zn3Al LDH. A solution casting method was used to prepare PLA/stearate-Zn3Al LDH nanocomposites. The anionic clay Zn3Al LDH was firstly prepared by co-precipitation method from a nitrate salt solution at pH 7.0 and then modified by stearate anions through an ion exchange reaction. This modification increased the basal spacing of the synthetic clay from 8.83 Å to 40.10 Å. The morphology and properties of the prepared PLA/stearate-Zn3Al LDH nanocomposites were studied by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), thermogravimetric analysis (TGA), tensile tests as well as biodegradation studies. From the XRD analysis and TEM observation, the stearate-Zn3Al LDH lost its ordered stacking-structure and was greatly exfoliated in the PLA matrix. Tensile test results of PLA/stearate-Zn3Al LDH nanocomposites showed that the presence of around 1.0–3.0 wt % of the stearate-Zn3Al LDH in the PLA drastically improved its elongation at break. The biodegradation studies demonstrated a significant biodegradation rate improvement of PLA in the presence of stearate-Zn3Al LDH nanolayers. This effect can be caused by the catalytic role of the stearate groups in the biodegradation mechanism leading to much faster disintegration of nanocomposites than pure PLA.

Effect of bilayered stearate ion‐modified MgAl layered double hydroxide on the thermal and mechanical properties of silicone rubber nanocomposites

AbstractThe homogeneous dispersion of nanofillers in polymer matrices to form polymer nanocomposites remains a challenge in the development of high‐performance polymer materials for various applications. In the work reported, a stearate ion‐modified MgAl layered double hydroxide (St‐LDH) as nanofiller was incorporated in a silicone rubber (SR) matrix by solution intercalation and subsequently characterized. X‐ray diffraction and transmission electron microscopy studies confirm the formation of a predominantly exfoliated dispersion of St‐LDH layers of 75–100 nm in width and about 1–2 nm in thickness in the SR. Thermogravimetric analysis shows that the thermal degradation temperature of the exfoliated SR/St‐LDH (1 wt%) nanocomposites is about 80 °C higher than that of pure SR. Differential scanning calorimetric studies indicate that the melting and crystallization temperatures are higher by 4 and 10 °C for 5 and 8 wt% St‐LDH‐loaded SR nanocomposites compared to neat SR. A significant improvement of 97% in tensile strength and 714% in storage modulus and a reduction of 82% in oxygen permeability have been achieved at 3 wt% St‐LDH loading in SR. Copyright © 2011 Society of Chemical Industry

Structural characterization and thermal properties of polyamide 6.6/Mg, Al/adipate-LDH nanocomposites obtained by solid state polymerization

A new nanocomposite was obtained by dispersing an adipate-modified layered double hydroxide (Ad-LDH) with adipic acid and hexamethylene diamine. These samples were polymerized in the solid phase under a nitrogen flow for 200 min at 190 °C. The structural and compositional details of the nanocomposite were determined by powder X-ray diffraction (PXRD), fourier transform infrared (FTIR) spectroscopy, focused ion beam (FIB), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The PXRD patterns and FIB images show a partially intercalated and partially exfoliated dispersion of layered crystalline materials in the polyamide 6.6 matrix. The best dispersion level is achieved in polyamide 6.6/LDH nanocomposites with low LDH loading. Some residual tactoids and particle agglomerates are also evident at high concentration. The best thermal stability of the nanocomposites is shown by the sample with 0.1% LDH content, for which it is higher than that of pure polyamide.

Layered double hydroxide/NaSb(OH)6–poly(vinyl chloride) nanocomposites: Preparation, characterization, and thermal stability

AbstractA novel layered double hydroxide/NaSb(OH)6‐based nanocomposite (Sb‐LDH) has been prepared via intercalation of thio‐antimonite (SbS33−) and reconstruction of LDH using Mg‐Al LDH as precursors. It is composed of LDH nanolayers with thickness of 25 nm and NaSb(OH)6 nanoparticles with diameter of 3–25 nm. The presence of NaSb(OH)6 will decrease the decomposition intensity and hinder the decomposition of Mg‐Al LDH because of the potential synergetic effect. When applied to poly(vinyl chloride) (PVC) composites, both Mg‐Al LDH and Sb‐LDH can enhance the thermal stability and increase the decomposition temperature of PVC. Compared with Mg‐Al LDH, Sb‐LDH results in higher decomposition temperatures and whiteness and higher initial and long‐term stabilities due to the presence of NaSb(OH)6, which can react with HCl and coordinate with Cl in the PVC chains. Because Mg‐Al LDH will accelerate the dehydrochlorination of PVC driving by the Lewis acid such as AlCl3, the thermal stability of PVC decreases with increasing nanofiller loading. When 1 wt % Sb‐LDH was added, the color change time and Congo red time of PVC composites are 140 min and 154 min, respectively. With enhanced thermal stabilization, this novel LDH nanocomposite could gain promising application in thermal stabilizer for PVC resins. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation and properties of biodegradable starch-layered double hydroxide nanocomposites

Abstract Well-dispersed starch-layered double hydroxide (LDH) nanocomposites were prepared by a newly developed approach of directly synthesizing the LDH in the starch dispersion. The approach involved a fast LDH nuclei precipitation followed by a hydrothermal treatment that simultaneously leached starches from the granules and aged the LDH nuclei. X-ray diffraction and transmission electron microscopy analyses showed that the LDH crystallites homogeneously dispersed in the acid-modified corn starch (AMS) matrix, whereas they tended to aggregate in the native normal corn starch (NCS) matrix. The LDH did not significantly influence the crystalline structure of starch molecules in the nanocomposites. The addition of LDH resulted in a pronounced phase separation in NCS, but not in AMS. With 10.47 wt.% of LDH, the AMS–LDH nanocomposites displayed unchanged transparency and moisture sensitivity, and an increase in modulus by as much as 37%. Our study revealed that lower-viscous starches produced by a proper acid modification can facilitate the dispersion of LDH and improve the modulus of nanocomposites.

Alkaline-earth-doped mixed oxides obtained from LDH nanocomposites as highly basic catalysts

The anionic exchange of the nitrate compensating anions in host Mg/Al LDH by negatively charged [M(Edta)] 2− (M = Ca 2+, Sr 2+, Ba 2+) guest entities has been performed. The increase from 0.83 nm to 1.5 nm of the d 0 0 3 interlayer distance shows that intercalation has taken place leading to well ordered lamellar materials with 3–9 wt.% of alkaline-earth (AE) cations loading. The basic properties of the M/Mg(Al)O mixed oxides catalysts obtained by thermal decomposition of the [M(Edta)]–Mg/Al LDH precursors have been investigated by TPD of CO 2, FTIR spectroscopy of adsorbed CDCl 3 and catalytic test reaction of 2-methyl-3-butyn-2-ol (MBOH). The AE-containing mixed oxides exhibit higher basicity than Mg(Al)O with, particularly, a large increase of the densities of sites of medium and high strength. Remarkably, the nature of the AE cations allows to finely tune the basicity. All the AE-containing mixed oxides are able to perform the isomerization reaction of 2,3-dimethyl-1-butene (DB-1) into 2,3-dimethyl-2-butene (DB-2), the Ca-containing sample being the most active according to its larger content of strong basic sites.

Intercalation of Macrocyclic Crown Ether into Well-Crystallized LDH: Formation of Staging Structure and Secondary Host−Guest Reaction

A carboxyethyl substituted azacrown ether derivative (CSAE) was intercalated as a second host into a parent host of well-crystallized crystal of Mg−Al layered double hydroxide (MgAl-LDH) by a CSAE/NO3− ion-exchange reaction. The influence of intercalation temperature on the structures and compositions of CSAE−LDH nanocomposites was investigated. The composites obtained at the temperatures below 70 °C had almost the same CASE contents and layered structures with a basal spacing of about 1.6 nm, corresponding to the vertical orientation of CSAE plane to the LDH layer. The chemical analysis showed that a considerable amount of CO32− (with CO32−/CSAE molar ratio of 1.4) was incorporated in the interlayer of LDH. The CSAE content decreased while CO32− content increased with an increase of the intercalation temperature in the region above 70 °C. At 100 °C, a second staging phase of 2.33 nm appeared, attributed to the ordered stacking of the 1.6 nm phase and a 0.77 nm phase produced by the CO32−/CSAE exchange. At higher temperatures, a new phase with a basal spacing of 1.18 nm appeared, which corresponds to the tilt/twisted orientation of CSAE anions in the interlayer. The other second staging phase of 2.08 nm appeared obviously at 150 °C, due to the regular stacking of the 1.18 and 0.77 nm phases. The adsorptive properties for transition metal ions were studied using the 70 and 150 °C reacted composites. The 70 °C reacted one showed higher adsorptivity toward transition metal ions; the adsorptive capacity increased in the sequence of Cu2+ > Ni2+ > Co2+ > Zn2+, and distribution coefficient for Cu2+ was markedly higher than those for the other ions. However, the 150 °C reacted one showed little adsorptivity toward these ions. The adsorption for transition metal ions was accompanied by the intercalation of nearly equivalent amount of nitrate ions. This shows that the interlayer CSAE ions in the 1.6 nm phase act as a second host, but those in the 1.18 nm phase do not.

Ethylene vinyl acetate/ethylene propylene diene terpolymer‐blend‐layered double hydroxide nanocomposites

AbstractEthylene vinyl acetate (EVA‐45)/ethylene propylene diene terpolymer (EPDM) blend‐layered double hydroxide (LDH) nanocomposites have been prepared by solution blending of 1:1 weight ratio of EVA and EPDM with varying amounts of organo LDH (DS‐LDH). X‐ray diffraction and transmission electron microscopy analysis suggest the formation of partially exfoliated EVA/EPDM/DS‐LDH nanocomposites. Measurement of mechanical properties of the nanocomposites (3 wt% DS‐LDH content) show that the improvement in tensile strength and elongation at break are 35 and 12% higher than neat EVA/EPDM blends. Dynamic mechanical thermal analysis also shows that the storage modulus of the nanocomposites at glass transition temperature is higher compared to the pure blend. Such improvements in mechanical properties have been correlated in terms of fracture behavior of the nanocomposites using scanning electron microscopy analysis. Thermal stability of the prepared nanocomposites is substantially higher compared to neat EVA/EPDM blend, confirming the formation of high‐performance polymer nanocomposites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Rubber/LDH nanocomposites by solution blending

AbstractThe rubber nanocomposites containing ethylene vinyl acetate (EVA) having 60 wt % of vinyl acetate content and organomodified layered double hydroxide (DS‐LDH) as nanofiller have been prepared by solution intercalation method and characterized. The XRD and TEM analysis demonstrate the formation of completely exfoliated EVA/DS‐LDH nanocomposites for 1 wt % filler loading followed by partially exfoliated structure for 5–8 wt % of DS‐LDH content. EVA/DS‐LDH nanocomposites show improved mechanical properties such as tensile strength (TS) and elongation at break (EB) in comparison with neat EVA. The maximum value of TS (5.1 MPa) is noted for 3 wt % of DS‐LDH content with respect to TS value of pure EVA (2.6 MPa). The data from thermogravimetric analysis show the improvement in thermal stability of the nanocomposites by ≈15°C with respect to neat EVA. Limiting oxygen index measurements show that the nanocomposites act as good flame retardant materials. Swelling property analysis shows improved solvent resistance behavior of the nanocomposites (1, 3, and 5 wt % DS‐LDH content) compared with neat EVA‐60. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Preparation of LLDPE/MgAl‐LDH Exfoliation Nanocomposites with Enhanced Thermal Properties by Melt Intercalation

AbstractThe interlayer surface of MgAl layered double hydroxide (MgAl‐LDH) was modified by exchanging about half of the interlayer nitrate anions by dodecyl sulfate anions (DS) to get MgAl(H‐DS) LDH, and then the MgAl(H‐DS) was melt intercalated by LLDPE to get the LLDPE/MgAl‐LDH exfoliation nanocomposites. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), ion chromatography, transmission electron microscopy (TEM), and thermogravimetry analysis (TGA). The nanoscale dispersion of MgAl‐LDH layers in the LLDPE matrix was verified by the disappearance of (00l) XRD reflection of the modified MgAl‐LDH and by the TEM observation. The TGA profiles of LLDPE/MgAl‐LDH nanocomposites show a faster charring process between 210 and 370 °C and a higher thermal stability above 370 °C than LLDPE. The decomposition temperature of the nanocomposites with 10 wt% MgAl(H‐DS) can be 42 °C higher than that of LLDPE at 40% weight loss.

In-Situ Polymerization of Poly (Methyl Methacrylate)/MgAl Layer Double Hydroxides Nanocomposites with High Dispersion and Enhanced Physics Properties

ABSTRACTPoly(methyl methacrylate)/MgAl layer double hydroxides (PMMA/MgAl LDH) nanocomposites were prepared by in situ free radical polymerization with the organic modified MgAl-K2 LDH in the methyl methacrylate monomer and initiator of benzoyl peroxide. The morphology of MgAl-K2 LDH and PMMA/MgAl-K2 LDH nanocomposites were investigated by transmission electron microscopy (TEM) and powder X-ray diffraction, indicated that the MgAl-K2 LDH were dispersed in PMMA matrix to form PMMA/MgAl-K2 LDH nanocomposites with heterogeneous morphology comprising both exfoliated and intercalated PMMA/MgAl-K2 LDH nanocomposites . The thermal and mechanical characterization were carried out by thermogravimetric analysis (TGA) ¡Bdifferential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The properties of PMMA/MgAl-K2 LDH nanocomposites exhibit the better thermal and mechanical properties.

Structural characterisation and thermal properties of exfoliated polystyrene/ZnAl layered double hydroxide nanocomposites prepared via solution intercalation

Exfoliated polystyrene/ZnAl layered double hydroxide (PS/ZnAl LDH) nanocomposites were synthesised by a solution intercalation method and characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). It has been found that the exfoliated LDH layers with a thickness of less than 1 nm disorderedly disperse in the PS matrix. The XRD and TEM results show that the exfoliation of LDH can be divided into solvent swelling and layer breaking processes and is affected by several reaction parameters. Completely exfoliated LDH layers can be achieved by decreasing the content of LDH, elongating the refluxing time, and rapid precipitation. The TGA data show that the PS/ZnAl LDH nanocomposites have significantly enhanced thermal stability. When 50% weight loss was selected as a point of comparison, the thermal decomposition temperature of exfoliated PS/ZnAl LDH nanocomposites with 10 wt% ZnAl LDH is 39 °C higher than that of pure PS. The thermal stability of the exfoliated nanocomposites is usually better than that of intercalated composites.

LLDPE/ZnAl LDH-exfoliated nanocomposites: effects of nanolayers on thermal and mechanical properties

The exfoliated nanocomposites (LLDPE/ZnAl LDH) were synthesized by refluxing dodecyl sulfate-intercalated ZnAl-layered double hydroxide [Zn3Al(DS)] in a non-polar xylene solution of linear low density polyethylene (LLDPE). Their thermal and mechanical properties were studied via X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and tensile tests. The molecular dispersion of Zn3Al(DS) nanolayers within the LLDPE matrix has been verified by the disappearance of the d003 XRD diffraction peak of Zn3Al(DS) and observation of the TEM image. TGA profiles of the LLDPE/ZnAl LDH nanocomposites show a faster charring process in the temperature range from 200 to 400 °C and better thermal stability above 370 °C than that of pure LLDPE. When 30% weight loss was selected as a point of comparison, the thermal decomposition temperature of LLDPE/ZnAl LDH nanocomposites with 5 wt% content of Zn3Al(DS) is 56 °C higher than that of pure LLDPE. The apparent activation energy values of LLDPE, and the LLDPE/ZnAl LDH nanocomposites with 5 and 10 wt% content of Zn3Al(DS) are determined as 94, 215, and 150 kJ mol−1, respectively, by the Flynn–Wall method in the kinetic analysis of the thermo-oxidation degradation process. The Young's modulus of the LLDPE/ZnAl LDH nanocomposite with 20 wt% Zn3Al(DS) has a 59% increase over that of pure LLDPE although its strength and elongation at break show some decrease due to the decrease of the crystallinity of the LLDPE matrix and/or some aggregations of exfoliated nanolayers of Zn3Al(DS) in the LLDPE matrix.

Preparation of poly (methyl methacrylate)/LDH nanocomposite by exfoliation-adsorption process

Exfoliated nanocomposite based on Mg, Al layered double hydroxide (Mg,Al-LDH) and poly(methyl methacrylate) (PMMA) has been prepared by exfoliation/adsorption process with acetone as co-solvent. The product was characterized by X-ray diffraction (XRD), thermal analysis and High Resolution Transmission Electronic Microscope (HREM). The results suggest that the brucite-like sheets of LDH disperse individually in the polymer matrix, and the thermal stability of the nanocomposite increases highly.