Organically-modified Montmorillonite Clay Research Articles

Synthesis, characterization, and dynamic‐mechanical properties of styrene‐acrylate/nanoclay interpenetrating polymer network

AbstractWaterborne styrene/acrylate latex interpenetrating polymer network (LIPN) with core‐shell structure was synthesized via a three‐stage emulsion polymerization method. A natural montmorillonite (MMt) and an organically modified montmorillonite (OMMt) were used to see their effect on the morphology and damping properties of polymer‐clay nanocomposite LIPN. The samples were characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA), and X‐ray diffraction (XRD). The appearance of a single peak in the particle size distribution curve and nearly monodisperse latex particles observed in the SEM images indicated that all LIPN particles were of nanoscale size, without evidence for new nucleation occurrence. TEM images demonstrated that latex particles had clearly core‐shell structures. It also showed that most of the OMMt clay platelets were encapsulated in the polymer latex particles. According to the tan δ‐temperature curve, addition of 0.5 wt% OMMt to the core layer improved the damping properties of the LIPN, while MMt could not affect the damping curve significantly. The results indicated that the diffusion of polymer chains into the OMMt clay galleries has increased the internal friction and so improved the damping properties.

Enhancing the Thermal and Mechanical Properties of Organic-Inorganic Hybrid Nanocomposite Films Based on Poly Lactic Acid/OMMT Nano Clay

Organic (PLA) inorganic (OMMT nano clay) hybrid nanocomposite films were fabricated using poly lactic acid (PLA) with various weight percentages (1-3wt%) of organically modified montmorillonite (OMMT) nano clay by means of one step solvent casting method. The thermal, mechanical and water absorption properties were determined as per standard testing methods to determine the optimum percentage loading of OMMT nano clay within the PLA-OMMT nanocomposite was investigated. The surface morphology of the organic-inorganic hybrid nanocomposite films was analyzed through XRD, SEM, and TEM surface analytical techniques. The incorporation of OMMT clay in to PLA matrix is found to have enhanced the thermo-mechanical properties. The water absorption and solubility test results also support the data from thermo-mechanical tests. The 2 wt % OMMT clay loaded PLA films showed the best results among all. The obtained results showed that the thermal, mechanical and water absorption properties could be increased significantly with the optimum incorporation of OMMT nano clay in a PLA matrix, in comparision wih the neat PLA.

Properties of antimony oxide-coated clay/polypropylene composites

Brominated flame retardant polypropylene composites were prepared by melt blending polypropylene, tetrabromobisphenol A, antimony oxide and organically-modified montmorillonite clay. The synergy between antimony oxide, clay and the brominated fire retardant was studied by thermogravimetric analysis under oxygen and UL-94 testing. Thermal, structural and tensile properties were studied using differential scanning calorimetry, X-ray diffraction and a universal testing machine respectively. Tetrabromobisphenol A and/or antimony oxide with clay is more efficient than clay alone in improving the flame retardancy of the materials and promoting carbonization in the polypropylene matrix. Thermogravimetric analysis showed significant improvements in the degradation temperature for all composites compared with the neat one. This can be ascribed to the physico-chemical adsorption of the volatile degradation products on the silicates. In the presence of montmorillonite, the melting and cooling points and degree of crystallization shift to higher values. These observations are compatible with the assumption that montmorillonite and other additives behave as nucleating agents, as a result of their large relative surface area. Moreover, the structure of the composites was characterized by scanning electron microscopy, which revealed good dispersion of the fillers in the polymer matrix. The experimental results of tensile tests indicated that the incorporation of clay and other additives improved the Young’s modulus, but decreased the tensile strength.

Effect of polyethylene glycol-intercalated organoclay on vulcanization characteristics and reinforcement of natural rubber nanocomposites

Organically modified montmorillonite (OMMT) clay was intercalated with low-molecular weight polyethylene glycol (PEG) oligomer at melt stage. The intercalation behaviour of PEG into the OMMT clay galleries and its interaction with clay platelets were characterized with X-ray diffraction (XRD) and differential scanning calorimetric techniques. A natural rubber (NR)–organoclay nanocomposite (NROCN) was prepared by melt-compounding of NR with PEG-treated organoclay (P-OMMT) and other compounding chemicals using a laboratory-scale internal mixer. XRD analysis of the nanocomposites revealed the intercalation of NR molecules into the P-OMMT clay galleries and subsequent exfoliation during the melt-compounding process. Vulcanization characteristics of the NROCN, especially processing safety and optimum curing time, have been interpreted with reference to the organic modifier of the montmorillonite clay, PEG modification and the degree of exfoliation. Solid-state mechanical properties of P-OMMT clay-filled NROCN vulcanizates have shown a significant enhancement in stiffness and strength characteristics whilst without scarifying the elasticity of the nanocomposites. Results have been explained in terms of the degree of exfoliation, dispersibility of the organoclay and strain-induced crystallization of the natural rubber.

In vivo bone formation by and inflammatory response to resorbable polymer-nanoclay constructs

The development of synthetic bone grafts with requisite mechanical and morphological properties remains a key challenge in orthopaedics. Supercritical carbon dioxide (scCO2)-processed nanocomposites consisting of organically-modified montmorillonite clay dispersed in poly-d-lactide (PDLA) have shown structural and mechanical properties similar to corticocancellous bone. Using quantitative undecalcified histology and micro-computed tomography (μCT), time and material-dependent influences on in vivo bone formation, and inflammatory response were characterized. This represents the first in vivo evidence of the ability of scCO2-processed PDLA-nanoclay constructs to support osteogenesis, while eliciting an inflammatory response comparable to PDLA-hydroxyapatite materials. Histologic analyses demonstrated that the in vivo performance of nanoclay-containing PDLA constructs was similar to pure PDLA constructs, though nanocomposites demonstrated more radiodense bone at all time points (μCT analysis), and higher bone volume at 6 weeks. Taken with previous structural and mechanical studies, these in vivo analyses suggest that scCO2-processed, polymer-clay nanocomposites may be suitable structural bone graft materials. From the Clinical EditorWith advances in science, orthopedic researchers have devoted significant amount of time in developing synthetic bone graft materials. Many of which are indeed currently in clinical use. In their previous studies, the authors described and studied supercritical carbon dioxide (scCO2)-processed nanocomposites consisting of organically modified montmorillonite clay dispersed in poly-D-lactide (PDLA) in in-vitro experiments. Here, in-vivo experiments were performed to investigate if this new material had improved mechanical properties, as well as the induction of inflammatory response. The overall positive findings may mean that this material could be used for future bone graft substitute applications.

The Use of Nanoclays to Modify the Morphology and Photoluminescence of Electrospun Poly(9-vinylcarbazole)/Poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] Blend Fibers

The morphology and photoluminescence properties of electrospun poly(9-vinylcarbazole) (PVK)/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) blend fibers, which were loaded with either halloysite clay nanotubes (HNTs) or an organically modified montmorillonite (OMMT) clay, were studied by scanning electron microscopy, transmission electron microscopy, and fluorescence spectroscopy. A concentration range of 0–30 wt.% was used for the clays, while the MEH-PPV concentration was fixed at 0.5 wt.%. Both clays, especially the OMMT clay, increased the phase separation of the components in the electrospun PVK/MEH-PPV blend fibers. This was attributed to their selective localization on the polymer phases. The HNTs and OMMT clay also increased energy transfer to the lowest energy states of MEH-PPV generated during electrospinning, and modified the amount of the partially overlapping conformation of carbazole groups (p-PVK) that constrained the aggregation of the PVK chains. These changes resulted in an increased emission from p-PVK, which varied depending on the type and concentration of the clay.

Small punch test on the analysis of fracture behaviour of PLA-nanocomposite films

The analysis of the fracture behaviour of polymeric films involves the determination of the specific essential work of fracture, which requires preparation, testing and evaluation of a large number of notched specimens. All these tasks demand significant time and costs; therefore, the use of alternative testing procedures that offer savings of both materials and time are becoming increasingly attractive options. Recently, the Small Punch Test (SPT) has experienced significant development as an alternative to conventional testing procedures in the field of steels and some metallic alloys. This work considers the applicability of SPT to the fracture characterisation of polylactide acid reinforced with organic-modified montmorillonite clay, using several weight percentages of nanoclay. The applicability of the experimental methodology is evaluated through comparison of the results obtained by SPT and conventional testing (tensile and essential work of fracture).

Effect of blend composition and organoclay loading on the nanocomposite structure and properties of miscible poly(methyl methacrylate)/poly(styrene-co -acrylonitrile) blends

Organically-modified montmorillonite clay nanocomposites of poly(styrene-co-acrylonitrile) (SAN), poly(methyl methacrylate) (PMMA) and SAN/PMMA miscible blend are investigated. Structure characteristics at the nanoscale and microscale and thermal and tensile properties are studied as a function of polymer blend composition and filler loading fraction. Blend miscibility and Tg are unaffected by up to 10% by wt. organoclay. Thermal degradation stability increases with SAN content and exhibits an optimum value of clay loading. Stiffness shows significant improvement. Tensile strength and elongation-at-break suffer as a result of nanocomposite formation. Modulus shows a maximum enhancement of 57% (5 ± 0.06 GPa at 10 wt% filler, 20/80 SAN/PMMA) and varies linearly with clay fraction for all compositions of matrix phase. Predictions of Halpin–Tsai composite model are in excellent agreement with the experimental behavior over full range of polymer blend composition. Fundamental aspects of a polymer blend–clay nanocomposite are clarified, such as lack of additional synergy between clay platelets and matrix, and tensile ductility reduction, compared with polymer–clay system. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Study of organically-modified montmorillonite clay for the removal of copper(II)

2-Oxyhydrazino-N-(2-methylen-yl-hydroxyphenyl)pyridinium (OMHP) ion was immobilized onto Na-montmorillonite clay (MMT). The modified clay (OMHP-MMT) was used for the removal of Cu(II). Experiments were carried out as a function of solution pH, stirring time, effect of some common ions and eluent type, concentration and volume. MMT, OMHP-MMT, and OMHP-MMT-loaded Cu(II) were characterized by X-ray diffractometry, electronic and infrared spectra, and elemental and thermogravimetric analyses. OMHP is suggested to be intercalated into MMT parallel to the aluminosilicate layers, with a capacity of 56.4mEq/100g. OMHP-MMT shows good stability in 0.1–1molL−1 hydrochloric or nitric acids, ammonia hydroxide, concentrated Na+, K+, NH4+, Cl− or SO42−. It shows good removal efficiency and selectivity towards Cu(II) at pH 3.0–8.0 and stirring time 10min with an removal capacity of 119mEq/100g. Most common ions do not interfere with the removal process except Fe3+. Extracted Cu(II) could be quantitatively recovered by 10mL 1% thiourea in 0.1molL−1 HCl with 100-fold preconcentration factor. OMHP-MMT was successfully applied to recover Cu(II) from different samples.

Preparation and characterization of low density polyethylene nanocomposites with modified montmorillonite clay

Organically modified montmorillonite clay (OMC) and its iron complex (OMC-Fe) were prepared using 1-acetylpyridinium chloride salicylhydrazone. Low density polyethylene (PE-LD) was compounded with either OMC or OMC-Fe (in amount of 3 or 7 wt. %) using ultrasonic radiation. The morphology of polyethylene composites was characterized by atomic force microscopy (AFM). The thermal stability and flammability properties of polyethylene composites were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The resultant composites exhibited improved flammability relative to the pure polyethylene.

Supercritical CO 2 intercalation of polycaprolactone in layered silicates

Supercritical carbon dioxide (scCO 2) intercalation of polycaprolactone (PCL) in layered silicates (clay) is studied. Wide angle X-ray diffraction patterns find that PCL is slightly intercalated in unmodified montmorillonite clay (NaMMT) but considerably intercalated in organic-modified montmorillonite clay (OMMT). The interlayer spacing in OMMT increases considerably from 1.94 nm in OMMT to 3.58 nm in the OMMT/PCL 10/90 sample. PCL8 having molecular weight of 80,000 is harder to intercalate into OMMT than PCL1 having molecular weight of 10,000. Higher scCO 2 pressures at a temperature allow larger intercalations of PCL in OMMT to exhibit larger interlayer spacings in OMMT. The interlayer spacings in OMMT, however, are not clearly found to relate with the CO 2 temperature at a given pressure. TGA data show that OMMT enhances the thermal stability of PCL1, with a higher content of OMMT giving a higher amount of PCL1 residue. DSC data find that the PCL1-intercalated OMMT expedites the melt-crystallization rate of PCL1 from the melt but suppresses the crystallinity of PCL1. Study of Avrami's rate constants k and exponent n finds that the PCL1-intercalated OMMT enhances the isothermal crystallization rate of PCL1 and that the crystal growth dimension is 3 for pure PCL1 but decreases with increasing OMMT content in the blends. Modulus data find that the PCL1-intercalated OMMT is an effective reinforcement for PCL8.

Study of Rheological Properties of Polypropylene/Organoclay Hybrid Materials

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.

Synthesis and rheological properties of oligoimide/montmorillonite nanocomposites

We report a facile strategy for preparing polyimides (PI)/montmorillonite (MMT) nanocomposites at moderate temperatures that avoids thermal degradation of organically-modified MMT (organo-MMT) that is commonly observed during conventional melt-blending of organo-MMT with commercial high molecular weight PI at elevated temperatures. Novel polyimides of low molecular weight (oligoimides) based on 1,3-bis(3′,4,-dicarboxyphenoxy)benzene and 4,4′ bis(4″-aminophenoxy)diphenylsulfone were synthesized and subsequently melt-blended at temperatures ranging from 150 to 250 °C with special organically-modified montmorillonite clay nanoparticles to form new polyimide/organo-MMT nanocomposites with special combination of physical and chemical properties for diverse applications such as microelectronic components where chemical inertness, high temperature stability, low dielectric constant, mechanical toughness and processability are primary requirements. It was found that application of a strong shearing flow near the glass transition temperature of the oligoimide to the oligoimide/organo-MMT nanocomposite melt blend containing 6±2 vol% of the organo-MMT resulted in three orders of magnitude increase in the viscosity. Partial exfoliation of the organo-MMT together with constrained deformation of the polymer between the rigid nanoparticle layers (as evidenced by formation of the network structure or fractal gel) are thought to be responsible for this observed viscosity behavior. The viscosity behavior is typical for model xylene/MMT system where the MMT particles were dispersed in xylene solvent homogeneously via ultrasonic mixing. This study suggests that the rheological methods used here may provide a valuable analytical tool to accelerate efforts to develop useful polyimide nanocomposites from synthetic oligoimides containing ceramic nanoparticles having different shapes and sizes. Further, because of their facile synthesis and desirable characteristics these polyimide/MMT clay nanocomposites are expected to be excellent model systems for exploring feasibility of new routes for driving organic polymers to self-assemble into useful nanocomposites.

Poly(ethylene terephthalate) ionomer based clay nanocomposites produced via melt extrusion

Poly(ethylene terephthalate) ionomer (PETI)/organically-modified montmorillonite clay (OMC) nanocomposites were prepared via melt extrusion. Sulfonated PET containing various incorporations of ionic comonomer and clay modifications were investigated. The random incorporation of ionic functionalities along the PET backbone enhances interactions between the matrix polymer and montmorillonite clay resulting in the creation of polymer-clay nanocomposites exhibiting a predominately exfoliated morphology. The morphology is correlated with mechanical properties and crystallization behavior. It is found that incorporation of clay into the random ionomers leads to increased mechanical properties and slower crystallization rates.

Morphological, mechanical and gas-transport characteristics of crosslinked poly(propylene glycol): homopolymers, nanocomposites and blends

Linear polyethers possess unusually high CO 2 solubility and, hence, selectivity due to the presence of accessible ether linkages that can interact with the quadrupolar moment of CO 2 molecules. In this work, membranes derived from crosslinked poly(propylene glycol) diacrylate (PPGda) oligomers differing in molecular weight ( M), as well as PPGda nanocomposites containing either an organically-modified montmorillonite clay or a methacrylate-terminated fumed silica are investigated and compared with highly CO 2-selective poly(ethylene glycol) diacrylate (PEGda) homopolymer and nanocomposite membranes previously reported. The rheological and permeation properties of PPGda depend sensitively on M, with the elastic modulus decreasing, but CO 2 permeability and CO 2/H 2 selectivity increasing, with increasing M. Incorporation of either nanofiller into PPGda enhances the elastic modulus and reduces the gas permeability in the resultant nanocomposites without strongly affecting CO 2/H 2 selectivity. Blending PPGda and PEGda prior to chemical crosslinking yields binary membranes that exhibit intermediate gas-transport properties accurately described by a linear rule of mixtures.