Nanocomposites based on polyethylene and Mg-Al layered double hydroxide. Part II. Rheological characterization

The rheological properties of Mg-Al based layered double hydroxide (LDH)/polyethylene nanocomposites have been presented in details. Both unmodified and maleic anhydride (MAH) grafted polyethylene based composites are characterised. The X-ray diffraction and electron microscopic investigations reveals the primary structures of the dispersed LDH particles exists as thin platelets. The rheological analysis carried out under different modes show behaviors typical of those reported extensively in literature for various cationic clay based polymer nanocomposites. The dispersed LDH particles show stronger interaction with maleic anhydride grafted matrix. The influence of LDH loading increases the shear thinning nature of the composite melt. The storage modulus vs. frequency plots of the composites show apparent plateau behaviors in low frequency region in a dynamic frequency sweep experiment. The appearance of stress overshoot peak in flow reversal experiment indicates that the dispersed LDH particles form structural aggregation, which are ruptured by shearing, but reform with time when shearing is stopped.     

Synthesis and characterization of ethylene vinyl acetate/Mg–Al layered double hydroxide nanocomposites

Mg–Al layered double hydroxide (LDH)/Ethylene vinyl acetate (EVA‐28) nanocomposites were prepared through solution intercalation method using organically modified layered double hydroxide (DS‐LDH). DS‐LDH was made by the intercalation of sodium dodecyl sulfate (SDS) ion. The structure of DS‐LDH and its nanocomposites with EVA‐28 was determined by X‐ray diffraction (XRD) and transmission electron microscope (TEM) analysis. XRD analysis shows that the original peak of DS‐LDH shifted to lower 2θ range and supports the formation of intercalated nanocomposites while, TEM micrograph shows the presence of partially exfoliated LDH nanolayers in addition to orderly stacked LDH crystallites in the polymer matrix. The presence of LDH in the nanocomposites has been confirmed by Fourier transform infrared (FTIR) analysis. The mechanical properties show significant improvement for the nanocomposite with respect to neat EVA‐28. Thermogravimetric (TGA) analysis shows that thermal stability of the nanocomposites is higher than that of EVA‐28. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1845–1851, 2007     

Dispersion characterization in layered double hydroxide/Nylon 66 nanocomposites using FIB imaging

Layered double hydroxides (LDHs), a newly emerging 2D host material, consist of cationic brucite-like layers and exchangeable interlayer anions. In this work, the morphology and dispersion of LDH particles in LDH/Nylon 66 (salt) nanocomposites has been investigated using focused ion beam (FIB) techniques, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The FIB images show that LDHs are present in the polymer phase dispersed to different degrees, with partial intercalation, exfoliation, and aggregation all being observed. The most even dispersion was achieved in nanocomposites with the lowest loading (0.5 wt % LDH). Residual tactoids and agglomerates were most common in the samples made with the highest concentration of LDHs studied here (5 wt %). The dispersion observed using FIB was consistent with TEM and XRD analysis, yet this technique had significant benefits in terms of time and simplicity over these “conventional” technologies. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and properties of exfoliated nanocomposites through intercalated a photoinitiator into LDH interlayer used for UV curing coatings

The exfoliated polymer/layered double hydroxide (LDH) nanocomposites based on MgAl were prepared through intercalating a photoinitiator into LDH interlayer, following by UV irradiation induced polymerization. The fragmental photoinitiator, 2-hydroxy-2-methyl-1-phenylpropane-1-one (1173) firstly reacted with isophorone diisocyanate (IPDI) to obtain the semiadduct, 1173-IPDI, and then reacted with the LDH modified by aminoundecanoic acid, obtaining LDH-1173 with an intercalated microstructure, which was characterized by FTIR, XRD, and TGA measurements. The obtained LDH-1173 was mixed with the multifunctional acrylate oligomer and monomer, and then exposed to a UV lamp to prepare a polymer/LDH nanocomposite. From the XRD, TEM and HR-TEM analysis, as well the photopolymerization kinetics investigation, it was found that the LDH-1173 effectively initiated the photopolymerization of acrylates, and formed exfoliated polymer/LDH nanocomposites. However, the mostly intercalated polymer/LDH nanocomposites were obtained for the systems with additional 1173 except for LDH-1173 addition. Compared with the pure polymer material, both the exfoliated and intercalated polymer/LDH nanocomposites exhibited the enhancements in mechanical and thermal properties, as well as hardness.     

Functionalized polyvinyl chloride/layered double hydroxide nanocomposites and its thermal and mechanical properties

In this work, to inquire the impact of layered double hydroxide (LDH) nanoclay on functionalized poly(vinyl chloride) (PVC) through solution intercalation method, four kinds of nanocomposites were prepared. Mg-AL LDH and the obtained functionalize PVC composites were characterized through FT-IR, UV–Vis spectroscopy, TEM, XRD, contact angle, DSC, and UTM. Obtained results revealed that the functionalized PVC uniformly dispersed in the layer of LDH nanoclay. It is revealed that partially intercalated and disordered structure formed in PVC/LDH, PVC-TS (thiosulfate)/LDH, and PVC-S (sulfate)/LDH nanocomposites, whereas fully exfoliated structures formed in the PVC-TU (thiourea)/LDH nanocomposites. Further, it has been observed that the ultimate tensile strength for all the polymer nanocomposites enhanced with increased in the LDH content. These nanocomposites further exhibited higher thermal stability by at least by 51°C higher than the pristine PVC. Along with these, further it has been found that the functionalized PVC/LDH nanocomposites are proved to be effective as thermal stabilizer for PVC processing. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48894.     

Characterization of polyisoprene-clay nanocomposites prepared by solution blending

The effects of clay dispersion and the interactions between clays and polymer chains on the viscoelastic properties of polymer/clay nanocomposites are investigated using oscillatory shear rheology, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Four different montmorillonite silicates of natural clays, plasma-treated clays, and organically modified clays (OCs) have been used in this study. For the polyisoprene (PI)/clay nanocomposites, the exfoliation of the OC dispersed in the PI matrix is confirmed with XRD and SAXS although TEM images show both exfoliated and non-exfoliated nanoclay sheets. In contrast aggregation or intercalation is obtained for the other PI/clay composites studied here. Additionally, the effective maximum volume packing fraction of OC for the exfoliated nanocomposites is determined from the overlapping of dynamic viscosity at low frequency regime, in which the effective maximum volume packing fraction is larger than the percolation threshold determined from the storage modulus of the nanocomposites.     

Synergistic effects of exfoliated LDH with some halogen‐free flame retardants in LDPE/EVA/HFMH/LDH nanocomposites

The synergistic effects of exfoliated layered double hydroxides (LDH) with some halogen‐free flame retardant (HFFR) additives, such as hyperfine magnesium hydroxide (HFMH), microencapsulated red phosphorus (MRP), and expandable graphite (EG), in the low‐density polyethylene/ethylene vinyl acetate copolymer/LDH (LDPE/EVA/LDH) nanocomposites have been studied by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermal analysis (TGA and DTG), mechanical properties, limiting oxygen index (LOI), and UL‐94 tests. The XRD results show that EVA as an excellent compatilizer can promote the exfoliation of LDH and homogeneous dispersion of HFMH in the LDPE/EVA/HFMH/LDH nanocomposites prepared by melt‐intercalation method. The TEM images demonstrate that the exfoliated LDH layers can act as synergistic compatilizer and dispersant to make the HFMH particles dispersed homogeneously in the LDPE matrix. The results from the mechanical, LOI, and UL‐94 tests show that the exfoliated LDH layers can also act as the nano‐enhanced and flame retardant synergistic agents and thus increase the tensile strength, LOI values, and UL‐94 rating of the nanocomposites. The morphological structures of charred residues observed by SEM give the positive evidence that the compact charred layers formed from the LDPE/EVA/HFMH/LDH nanocomposites with the exfoliated LDH layers play an important role in the enhancement of flame retardant and mechanical properties. The TGA and DTG data show that the exfoliated LDH layers as excellent flame retardant synergist of MRP or EG can apparently increase the thermal degradation temperature and the charred residues after burning. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Morphology and thermal stabilization mechanism of LLDPE/MMT and LLDPE/LDH nanocomposites

The morphology and thermal stabilization mechanism of polymeric nanocomposites prepared by solution intercalation of linear low density polyethylene (LLDPE) with montmorillonite (MMT), MgAl layered double hydroxide (LDH), and ZnAl LDH have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). Both LLDPE/MMT and LLDPE/MgAl LDH nanocomposites exhibit mixed intercalated-exfoliated structures, whereas the LLDPE/ZnAl LDH nanocomposites exhibit completely exfoliated structures because the ZnAl LDH layers can be easily broken during the refluxing process. All nanocomposites show significantly enhanced thermal stability compared with virgin LLDPE due to the increases of the effective activation energy (E_α) during degradation process. However, LDHs nanocomposites show much higher thermal degradation temperatures than MMT nanocomposites with the same filler content because they have much higher E_α than MMT nanocomposites at the early degradation stage. The data of real time FTIR spectroscopy and morphological evolution reveal a catalytic dehydrogenation effect presents in MMT nanocomposites, which may decrease the E_α of degradation and thermal stability of MMT nanocomposites.     

The Polymerization of Unsaturated Polyester and Silane-Functionalized Layered Double Hydroxides

The preparation of surface-modified layered double hydroxides/unsaturated polyester (LDH/UP) nanocomposites were performed. By in situ coprecipitation, LDHs, modified through grafting of vinyltriethoxysilane (VTS) carrying a double bond using the anionic surfactant sodium dodecyl sulfate (SDS), were used as nanofillers for unsaturated polyester (UP). The morphology of LDH and nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Moreover, the thermal properties were determined by thermogravimetric analysis (TGA) and thermal degradation mechanism was discussed.     

In situ synthesis,morphology, and thermal properties of polystyrene—MgAl layered double hydroxide nanocomposites

Polystyrene (PS)/layered double hydroxide (LDH) nanocomposites were synthesized by in situ free radical bulk polymerization. LDH formed by magnesium and aluminum (Mg:Al—molar ratio of 2:1) was prepared by coprecipitation method and intercalated with sodium dodecyl sulfate (DDS). The nanocomposites were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and flammability test. The XRD and TEM demonstrated that synthesized nanocomposites in all compositions studied showed a high global dispersion of LDH in PS, suggesting exfoliation. The results of TGAs (when 50% mass loss was selected as a comparison point) and flammability tests for synthesized nanocomposites, presented a significant improvement in thermal stability and flammability property when compared with pure PS. This behavior and properties indicate application of the surfactant intercalated LDH reinforced PS in fields where thermal stability is an important characteristic. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Thermoplastic polyurethane and nitrile butadiene rubber blends with layered double hydroxide nanocomposites by solution blending

Polymer blending coupled with nanofillers has been widely accepted as one of the cheaper methods to develop high‐performance polymeric materials for various applications. In the present work, dodecyl sulfate intercalated Mg? Al‐based layered double hydroxide (DS‐LDH) was used as nanofiller in the synthesis of polyurethane blended with nitrile butadiene rubber (PU/NBR; 1:1 w/w) nanocomposites, which were subsequently characterized. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the partial dispersion of Mg? Al layers in PU/NBR blends at lower filler content followed by aggregation at higher filler loading. In comparison to the neat PU/NBR blend, the tensile strength (156%) and elongation at break (21%) show maximum improvement for 1 wt% filler loading. The storage and loss moduli, thermal stability and limiting oxygen index of the nanocomposites are higher compared to the neat PU/NBR blend. Glass transition temperature and swelling measurements increase up to 3 wt% DS‐LDH loading in PU/NBR compared to either neat PU/NBR or its other corresponding nanocomposites. XRD and TEM analyses indicate the partial distribution of DS‐LDH in PU/NBR blends suggesting the formation of partially exfoliated nanocomposites. The improvements in mechanical, thermal and flame retardancy properties are much greater compared to the neat blend confirming the formation of high‐performance polymer nanocomposites. Copyright © 2009 Society of Chemical Industry     

Linear low density polyethylene (LLDPE)/clay nanocomposites. Part I: Structural characterization and quantifying clay dispersion by melt rheology

In this study, linear low density polyethylene (LLDPE)/clay nanocomposites with various clay content were prepared by melt processing using two different compatibilizers, maleic anhydride grafted polyethylene (PE-g-MA) and oxidized polyethylene (OxPE). Effects of structure and physical properties of the compatibilizers on the clay dispersion and clay amount on the microstructure and physical properties of the nanocomposites were investigated. The OxPE was shown to significantly create interfacial interactions between the polymer phase and clay layers. Rheological behavior of the samples was examined by a dynamic oscillatory rheometry in linear viscoelastic region. Percolation threshold (?_p) and corresponding aspect ratio (A_f) values were determined by analyzing the improvement in storage modulus at low frequency region depending on the clay loading. Lower percolation and higher aspect ratio values were obtained for the sample series prepared with the PE-g-MA than that prepared with the OxPE. Moreover, fractal size of the clay network above the percolation point was determined by the scaling law for physical gelation of colloidal flocks to quantify clay dispersion depending on the compatibilizer structure. It was found that the PE-g-MA yielded better clay dispersion and more exfoliated structure compared to the OxPE. Microstructural characterization of the samples was also characterized by XRD and TEM.     

Synthesis and characterization of polystyrene/layered double‐hydroxide nanocomposites via in situ emulsion and suspension polymerization

Polystyrene (PS)/ZnAl layered double‐hydroxide (LDH) nanocomposites were synthesized via in situ emulsion and suspension polymerization in the presence of N‐lauroyl‐glutamate surfactant and long‐chain spacer and characterized with elemental analysis, Fourier transform infrared spectrum, X‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis. The XRD and TEM results demonstrate that the exfoliated ZnAl–LDH layers were well dispersed at molecular level in the PS matrix. The completely exfoliated PS/LDH nanocomposites were obtained even at the 20 and 10 wt % LDH loadings prepared by emulsion polymerization and suspension polymerization, respectively. The PS/LDH nanocomposites with a suitable amount of LDH showed apparently enhanced thermal stability. When the 50% weight loss was selected as a comparison point, the decomposition temperature of the exfoliated PS/LDH sample prepared by emulsion polymerization with a 5 wt % LDH loading was about 28°C higher than that of pure PS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3758–3766, 2006     

A comparative study of poly(methyl methacrylate) and polystyrene/clay nanocomposites prepared in supercritical carbon dioxide

Poly(methyl methacrylate) and polystyrene/clay nanocomposites have been prepared via pseudo-dispersion polymerizations in the presence of a poly(dimethylsiloxane) surfactant-modified clay (PDMS-clay) in supercritical carbon dioxide. The effects of the PDMS-clay concentration on polymer conversion, molecular weight, and morphology have been investigated. The insoluble dispersion of PDMS-clay is shown to be an effective stabilizer for both MMA and styrene polymerization in scCO₂. The nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). While XRD shows featureless patterns for both nanocomposites, the actual distributions of clay are found to be quite different between PMMA and PS nanocomposites, presumably due to the different interaction mechanisms between the polymers and clay. Consequently, the different states of clay in the two nanocomposites play an important role in the mechanical properties of the nanocomposites, and a to a lesser degree in the thermal properties.     

Influence of EMAA compatibilizer on the structure and properties of HDPE/hydrotalcite nanocomposites prepared by melt mixing

High‐density polyethylene (HDPE)/hydrotalcite nanocomposites were prepared and characterized with a partially neutralized sodium ionomer of poly(ethylene‐co‐methacrylic acid) (EMAA) as a compatibilizer. Moreover, nanocomposites based on this ionomer were characterized as patterns to analyze the interactions between the hydrotalcite sheets and the methacrylic groups on the ionomer. Hydrotalcite particles were organically modified with sodium dodecyl sulfate ions. Their presence in the interlayer space was confirmed by means of Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD). Morphological analysis carried out with XRD and transmission electron microscopy (TEM) revealed the partially exfoliated/intercalated structure achieved in the nanocomposites. The mechanical properties of the HDPE nanocomposites mainly depended on the nature of the polymer matrix. Higher values of the tensile strength and Young's modulus were found in the EMAA nanocomposites. Thermogravimetric analysis (TGA) showed that hydrotalcite particles improved the thermal stability and delayed the onset decomposition temperature of both HDPE and EMAA nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological,mechanical, and thermal features of PMMA nanocomposites containing two‐dimensional Co–Al layered double hydroxide

The focus of the current study is to investigate the influence of Co–Al layered double hydroxide (LDH) on the morphological, thermal, and mechanical features of poly(methyl methacrylate) (PMMA)‐based nanocomposites. Sodium dodecyl sulfate modified Co–Al LDH was synthesized by single step coagulation method. The PMMA nanocomposites containing different loadings of nanofiller (1–7 wt %) and polystyrene‐grafted maleic anhydride compatibilizer (5 wt %) were melt intercalated via twin screw extruder and later subjected to injection molding to prepare mechanical testing samples. The different properties of PMMA nanocomposites were studied by using XRD, TEM, FTIR, DSC, TGA, tensile, flexural, impact, and flammability analysis. The result of XRD analysis suggested the exfoliated morphology of the nanocomposite while the TEM demonstrated the intercalated structure at higher loading of LDH. The thermal characterization results revealed that thermal properties were improved by the addition of Co–Al LDH, whereas the flammability test exposed that dripping was minimum at 7 wt % loading. The mechanical properties exhibited that optimum results were obtained at 1 wt % loading of Co–Al LDH. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45774.     

Use of purified and modified bentonites in linear low‐density polyethylene/organoclay/compatibilizer nanocomposites

Polyethylene‐based ternary nanocomposites were prepared with different clay structures, obtained by the modification of purified Resadiye bentonite as the reinforcement, a random terpolymer of ethylene, butyl acrylate, and maleic anhydride with the trade name Lotader3210 as the compatibilizer, and linear low‐density polyethylene (LLDPE) as the polymer matrix in an intensive batch mixer. The quaternary ammonium/phosphonium salts used for the modification of bentonite were dimethyldioctadecyl ammonium (DMDA) chloride (Cl), tetrakisdecyl ammonium (TKA) bromide (Br), and tributylhexadecyl phosphonium (TBHP) Br. The effects of the physical properties and structure of the organoclay on the clay dispersion were studied at different clay contents (2 and 5 wt %) and at a compatibilizer/organoclay ratio of 2.5. The extent of organoclay dispersion was determined by X‐ray diffraction (XRD) and was verified by transmission electron microscopy (TEM), mechanical testing, and rheological analysis. XRD analysis showed that the nanocomposite with the organoclay DMDA contained intercalated silicate layers, as also verified by TEM. The TEM analysis of the nanocomposites with TBHP exhibited intercalated/partially exfoliated clay dispersion. TKA, with a crowded alkyl environment, sheltered and hindered the intercalation of polymer chains through the silicate layers. In comparison to pure LLDPE, nanocomposites with a 33–41% higher Young's modulus, 16–9% higher tensile strength, and 75–144% higher elongation at break were produced with DMDA and TBHP, respectively (at 5 wt % organoclay). The storage modulus increased by 807–1393%, and the dynamic viscosity increased by 196–339% with respect to pure LLDPE at low frequencies for the samples with DMDA and TBHP (at 5 wt % organoclay). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A solution blending route to ethylene propylene diene terpolymer/layered double hydroxide nanocomposites

Ethylene propylene diene terpolymer (EPDM)/MgAl layered double hydroxide (LDH) nanocomposites have been synthesized by solution intercalation using organically modified LDH (DS-LDH). The molecular level dispersion of LDH nanolayers has been verified by the disappearance of basal XRD peak of DS-LDH in the composites. The internal structures, of the nanocomposite with the dispersion nature of LDH particles in EPDM matrix have been studied by TEM and AFM. Thermogravimetric analysis (TGA) shows thermal stability of nanocomposites improved by ≈40 °C when 10% weight loss was selected as point of comparison. The degradation for pure EPDM is faster above 380 °C while in case of its nanocomposites, it is much slower.     

Rubber/LDH nanocomposites by solution blending

The 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     

Synthesis of exfoliated PP/LDH nanocomposites via melt‐intercalation: Structure,thermal properties,and photo‐oxidative behavior in comparison with PP/MMT nanocomposites

Exfoliated polypropylene (PP)/layered double hydroxide (LDH) nanocomposites have been successfully synthesized via melt‐intercalation. Their structure, thermal properties, and photo‐oxidative behavior have been characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMA), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectrum. TGA and DMA data show that the PP/LDH nanocomposites have enhanced thermal stability compared with virgin PP and corresponding PP/montmorillonites (MMT) nanocomposites, especially in high temperature range during the thermal decomposition of the samples. XPS and FTIR results give positive evidence that the photo‐oxidation mechanism of PP in the PP/LDH materials is not modified compared with that of virgin PP. However, photo‐oxidation rate of PP/LDH materials is much lower than that of PP and PP/MMT samples, indicating that the PP/LDH nanocomposites have better UV‐stability. POLYM. ENG. SCI. 46:1153–1159, 2006. © 2006 Society of Plastics Engineers