Addition Of Layered Silicates Research Articles

Morphology and thermal properties of clay based biocomposites

Abstract Carboxymethylcellulose/poly(ethylene glycol) (CMC/PEG) blend and CMC/PEG/montmorillonite (MMT) nanocomposites were produced by the solvent casting method. The clay, a sodium MMT, was incorporated in the polymer matrix at low weight loadings (from 1 wt% to 7 wt%). The MMT dispersion in the matrix was evaluated by X-ray diffraction, which revealed an intercalated structure of the nanocomposites. Different levels of intercalation have been detected. The changes in morphology caused by the addition of layered silicate on CMC/PEG blend were investigated by scanning electron microscopy (SEM). The SEM images of CMC/PEG blend containing 5% of MMT displayed more homogenous morphology than CMC/PEG blend. The compatibilizing performance of the filler was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy. The effect of the introduction of the clay on the crystallization temperature, melting temperature and crystallization degree of CMC/PEG revealed that clay behaved as a nucleating agent and enhanced the crystallization rate of PEG. Furthermore, it was demonstrated that the addition of a small percentage of montmorillonite (1%) was enough to improve the thermal stability of the nanocomposites.

Vibrational energy-harvesting performance of bio-sourced flexible polyamide 11/layered silicate nanocomposite films

ABSTRACTThe energy-harvesting efficiency of melt processed polyamide 11 (PA11) films and its nanocomposites have been investigated as a function of filler type and content. In the present work, nanoclays have been used as structural modifiers in a PA11 matrix. The nanocomposites were prepared using layered clays, Cloisite 20A, 10A, and Na+, by extrusion process through varying the filler content, 1, 2, 4, and 5 wt.%. The crystalline structure of these nanocomposites has been studied by X-ray diffractometer. It has been demonstrated that layered silicates are not significant for the structural quality of the obtained nanocomposites. Regarding the interlayer peak of different clays, it has also been revealed that Cloisite 20A is partially exfoliated, whereas 10A and Na+ are totally exfoliated in the PA11 matrix. From mechanical and dynamic mechanical analyses, it was found that the addition of layered silicates results in an increase in mechanical properties. The piezoelectric strain coefficient d33 and dielectric constant εR have been measured on polarized films at ambient temperature. Among all the prepared nanocomposites only Cloisite Na+-loaded PA11 nanocomposites showed the best piezoelectric constant. This observation showed that piezoelectric constant not only depends on the crystalline phases but also on the nature of the filler. Cloisite Na+ is more polar than other modified clays and high polarity leads to a better polarization response. A specific method for the quantification of energy vibration recovery has been developed for these nanocomposites. The capabilities of vibrational energy recovery were studied on PA11 loaded with Cloisite Na+.

Effect of layered silicates and reactive compatibilization on structure and properties of melt-drawn HDPE/PA6 microfibrillar composites

Microfibrillar composites (MFCs) of HDPE matrix with PA6 reinforcing fibrils formed in situ by melt drawing were modified by ethylene/glycidyl methacrylate copolymer (PEGMA) and addition of layered silicates using different mixing protocols. The goal was enhancement of adhesion between fibrils and matrix, their reinforcement by clay, and evaluation of the effect of clay on the MFC morphology, especially the fibril dimensions. Improved mechanical properties, including toughness, were found in the case of pre-blending Cloisite 15A (C15) with both polymeric components. Pre-blending of Cloisite C30B (C30) in PA6 is effective at low draw ratios only, whereas simultaneous addition of both clays leads to significant worsening of properties. In many cases, low stiffness increase indicates existence of clay-induced controversial effects which may eliminate reinforcement induced by fibrils and clay. The results indicate that these effects are significantly affected by the extent and course of clay migration between polymer phases during extrusion-mixing and melt drawing. Possible explanation of affecting the properties due to low-modulus interface supported by finite element analysis (FEA) is presented.

Effect of nanofiller on the behavior of a melt‐drawn HDPE/PA6 microfibrillar composite

ABSTRACTMicrofibrillar composites (MFCs) with reinforcing fibrils formed in situ by melt drawing were modified by the addition of layered silicates using different mixing protocols, viz simultaneous addition of components, application of respective premade nanocomposites and their combinations. The objective was to combine reinforcement with changes in the final structure, especially the fibril dimensions. The presented results indicate good potential of the nanoclay to enhance the MFC based on the melt‐drawn HDPE/PA6 system. The best mechanical behavior was achieved with the simultaneous addition of all components. The majority of the nanofiller material was contained inside the PA6 fibrils. Both fibrils dimensions and mechanical behavior were significantly affected by the nanofiller migration to the PA6 phase in the course of mixing and melt drawing. Due to a complex effect of the clay, deterioration of mechanical properties was also found. As a result, numerous, in some cases contradictory, effects of nanofillers must be perfectly harmonized to improve the properties of MFCs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41868.

Low Velocity Impact and Creep-Strain Behaviour of Vinyl Ester Matrix Nanocomposites Based on Layered Silicate

The impact properties of neat vinyl ester and the nanocomposites were performed using a low velocity impact testing. The addition of layered silicate into the polymer matrix shows that an optimum range of nanoclay reinforcement in the vinyl ester matrix can produce enhanced load bearing and energy absorption capability compared to the neat matrix. In addition, the amount of microvoids in the nanocomposites structure influences the overall properties. Likewise, the influence of the clay addition into the neat polymer on the creep relaxation behaviour at 25°C and 60°C was studied. In both cases, the presence of the layered silicate remarkably improved the creep behaviour. The improvement of these properties can be assigned to the stiff fillers and the configurational linkage between the polymer and the layered silicate which are supported by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterisations by showing a distinct change in surface morphology associated with improved impact toughness and creep response.

Effect of an organoclay on the reaction-induced phase-separation in a dynamically asymmetric epoxy/PCL system

The addition of layered silicates can significantly affect the phase behaviour of both immiscible thermoplastic blends and partially miscible thermoset systems that undergo reaction-induced phase separation (RIPS) during curing. This study focuses on the phase behaviour of polycaprolactone (PCL)/epoxy in the presence of organically modified montmoril- lonite (oMMT). Due to the high dynamic asymmetry caused by the differences in the molecular weights and viscosities of the PCL and the uncured epoxy, the critical point is localised at low PCL concentrations, as indicated by the pseudophase diagram. The addition of oMMT to the system led to the marked shift of the critical point towards higher concentrations of PCL, with an increase in the oMMT content occurring as a consequence of the preferential localisation of the clay in the epoxy phase, making this phase more dynamically slow. Significant changes in morphology, including phase inversion of the PCL/epoxy systems caused by the presence of oMMT, were recorded for PCL concentrations ranging from 10 to 30%.

Experimental investigation on the influence of the composition on the morphology and the mechanical properties of short glass fiber-reinforced polypropylene nanocomposites

Polypropylene composites containing 0–5 wt% layered silicate and 0–30 wt% short glass fibers are prepared by melt compounding. To investigate the influence of different compositions on the mechanical properties of short glass fiber-reinforced polypropylene nanocomposites, materials with various filler contents are prepared. At a glass fiber content of 10 wt% Young's modulus of the layered silicate-containing composites decreases by around 30% compared to conventional glass fiber-reinforced polypropylene. But at higher glass fiber loadings, an increasing modulus of up to 10% is observed. However, the addition of layered silicate results in large decreases of the tensile and the notched impact strength. A maleic anhydride-grafted polypropylene enhances Young's modulus and the tensile strength. © 2012 Society of Plastics Engineers

Enhanced bacterial inhibition activity of layer-by-layer structured polysaccharide film-coated cellulose nanofibrous mats via addition of layered silicate

Organic rectorite (OREC) was used to prepare the intercalated composites with chitosan (CS). The negatively charged cellulose nanofibers hydrolyzed from electrospun cellulose acetate fibrous mats were modified with multilayers of the positively charged CS-OREC intercalated composite and the negatively charged sodium alginate (ALG) via layer-by-layer (LBL) technique. The morphology and antibacterial activity of the resultant samples were studied by regulating the number of deposition bilayers, the compositions of dipping solutions and outermost layer of films. Field emission scanning electron microscopy images indicated that the thickness of CS-OREC/ALG bilayer formed on fibers was estimated from 12 to 26 nm. Additionally, the energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy results indicated that CS and OREC were successfully deposited on cellulose fibers. The bacterial inhibition experiments demonstrated that LBL films modified fibrous cellulose mats with the addition of OREC can increase the degree of inhibition on Escherichia coli.

Ibuprofen-loaded poly(ε-caprolactone) layered silicate nanocomposites prepared by hot melt extrusion

Ibuprofen loaded poly(epsilon-caprolactone) (PCL) layered silicate nanocomposites were prepared by hot-melt extrusion. The morphology and extent of dispersion of ibuprofen and layered silicate was studied using a combination of wide-angle X-ray diffraction (WAXD), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Exhaustive examination across the length scales revealed the composite to have both an intercalated and exfoliated morphology. The ibuprofen was well dispersed and distributed throughout the PCL matrix. Most significantly, the static tensile and dynamic mechanical properties of PCL can be manipulated as a function of nanoclay loading and is dependent on the aspect ratio of clay platelets. The glass transition of PCL increased by up to 16 degrees C on addition of nanoclay, as determined from dynamic mechanical thermal analysis (DMTA). This behaviour was attributed to the constrained mobility of PCL chains intercalated between clay platelets and to the tethering of PCL chains by hydrogen bonding with platelet edges. As a consequence, PCL crystallisation was inhibited and confirmed from non-isothermal crystallisation experiments using differential scanning calorimetry (DSC). The fraction of PCL that was crystalline (X(c)) decreased by 15% on addition of ibuprofen and nanoclay, although the temperature of crystallisation (T(c)) did not change significantly. The dissolution of ibuprofen from PCL can be retarded by addition of layered silicates (nanoclays) to the polymer matrix.

Effect of montmorillonite modification on the behaviour of polyamide/polystyrene blends

AbstractBACKGROUND: In nanocomposites with multiphase matrices, the addition of layered silicate not only has a reinforcing effect, but also changes significantly the morphology, namely the size and the structure of the dispersed phase. In this paper, we focus on systems with polyamide 6 (PA6)/polystyrene (PS) matrices. The effect of clay was studied over the whole composition range together with the simultaneous variation of basic parameters influencing the structure and mechanical behaviour, i.e. the clay treatment type and mixing protocol.RESULTS: At all compositions, remarkable refinements of both particulate and co‐continuous structures by clay were found. This effect and a significant shift of the glass transition temperature of blend components were more pronounced for clay with less polar treatment as a result of distinct localization of clay in the interfacial area (due to its lower affinity for PA6 phase). An increase in modulus was found at all compositions, whereas strength and toughness were enhanced at low PS contents only, as a consequence of small particle size and enhanced interfacial bonding.CONCLUSIONS: The results presented indicate that nanosilicates can effectively influence the structure and properties of PA6/PS blends. Copyright © 2008 Society of Chemical Industry

Enzymatic degradation kinetics of poly(butylene succinate) nanocomposites

In this work, poly(butylene succinates) (PBS)/organically modified layered silicates (OMLS) composites were prepared by solution blending. The degradability of PBS, PBS/layered silicates and PBS/OMLS nanocomposites have been investigated using enzymatic degradation method. Effects of layered silicates and OMLS contents on the degradation behavior of PBS were explored. The results reveal that the degradability of the composites was both enhanced by the addition of layered silicates or OMLS as compared to the pristine PBS sample. The calculated data based on the autocatalytic model show that the degradation kinetics of PBS/layered silicates composites is the chain scission process with the following autocatalytic reactions, which is very similar to that of pure PBS matrix. On the other hand, the surface-catalyzed reaction model may be more suitable to describe the degradation behavior of the PBS/OMLS nanocomposite. Moreover, the results show that rate-controlling step of the degradation reaction for PBS/OMLS nanocomposite is more probable to be the desorption step.

The role of nanodispersion on the fire performance of organoclay–polyamide nanocomposites

This work has investigated the importance of nanoscale dispersion upon the fire performance of Nylon-6 nanocomposites by characterising the role of the char layer and its formation in reducing peak heat release rate during combustion. To do this, a series of layered silicate nanocomposites systems using Nylon-6 were prepared using twin screw extrusion techniques at different levels of clay addition and different processing temperatures. This work has shown that the addition of layered silicates improves the peak heat release rate in a synergistic manner, by forming a tough char layer that prevents or hinders the transfer of combustible products into the gaseous phase. Differences in nanoscale dispersion of the clay as measured using transmission electron microscopy (TEM) correlated strongly with changes in fire performance according to cone calorimetry measurements. Corresponding changes in the thermal decomposition behaviour (thermogravimetric analysis) and microstructure and elemental composition of the char layer (SEM) were used to further understand the fire retardation mechanism in the condensed phase. Comparison of the rate of mass loss with the heat release rates and XRD of the char were further used to investigate the role of the char layer in improving fire performance.

Reinforced Thermoplastic Acetylated Starch with Layered Silicates

Montmorillonite (MMT) and organically modified montmorillonite (OMMT) were utilized to reinforce the thermoplastic acetylated starch (TPAS) composite prepared with glycerol as a plasticizer. After the addition of layered silicates, the restriction of the motion of the intercalated acetylated starch molecular chains by the clay layer sheets led to an increase in melt viscosity and equilibrium torque. As expected, the tensile strength and storage modulus of the TPAS composite were remarkably enhanced due to the interaction of layered silicates with the TPAS matrix, but the thermal stability of the TPAS composite was not obviously improved. The greater reinforcing effect of OMMT than that of MMT could be attributed to the better dispersion of OMMT in the TPAS matrix, resulting from the larger distance between OMMT layers after the modification by organic ammonium cations with long alkyl chains.

A DSC study of the order–disorder transition of SEPS block copolymers in the block copolymer/paraffin oil/layered silicate nanocomposite gels

The effect of addition of layered silicate on the order–disorder transition of poly[styrene-b-(ethylene-propylene)-b-styrene] (SEPS) block copolymer in the block copolymer/paraffin oil/layered silicate nanocomposite gels was investigated by means of differential scanning calorimetry (DSC) and modulated DSC (MDSC). The addition of layered silicate has significant influences on the order–disorder transition and the phase structure of the block copolymer. With increasing layered silicate, the order–disorder transition temperature of the block copolymer decreased. The addition of layered silicate reduced the ordering level of the block copolymer. MDSC results revealed that the order–disorder transition is a glass transition-like process. A thermal event related to the ordering process, which took place in the preparation of the sample and hid in the specimen, has been revealed by MDSC first time.

Poly(ethylene 2,6-naphthalate)/layered silicate nanocomposites: fabrication, crystallization behavior and properties

In this study, poly(ethylene 2,6-naphthalate) (PEN)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PEN polymer into organically-modified layered montmorillonite through the melt blending process. Both X-ray diffraction data and transmission electron microscopy images of PEN/layered silicate nanocomposites indicate most of the swellable silicate layers were exfoliated and randomly dispersed into the PEN matrix. Mechanical and barrier properties of the fabricated nanocomposites performed by dynamic mechanical analysis and permeability analysis show significant improvements in the storage modulus and water permeability when compared to neat PEN. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization behavior and melting behavior of PLSNs. DSC isothermal results revealed that the crystal growth process of PEN and PLSNs are a three-dimensional spherulitic growth. The activation energy of PEN increases with increasing content of layered silicates. The result indicates that the addition of layered silicate into PEN reduces the transportation ability of polymer chains during crystallization processes.

Morphology and properties of thermoplastic polyurethane composites incorporating hydrophobic layered silicates

AbstractPolyurethane (PU) composites incorporating Cloisite 15A (15A) were prepared via melt compounding and solvent casting. The melt‐compounded composites had better dispersion and a smaller silicate stack size as a result of the higher shear forces associated with twin‐screw extrusion. The PU microphase separation and hard domain order were greater in the melt‐processed materials. At the concentrations of 15A employed in this study (≤7 wt %), the filler did not have an observable effect on the microphase texture of either the solvent‐ or melt‐processed PU. The tensile properties of the melt‐compounded materials were lower than those of their solvent‐cast counterparts because of thermal degradation. The solvent‐cast composite containing a 3 wt % loading of 15A displayed improved tensile strength and elongation, primarily because of plasticization by the silicate organic treatment. The addition of layered silicates with high aspect ratios increased the hysteresis and permanent set of this PU elastomer. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 300–309, 2005

A comparison of the temperature dependence of the modulus, yield stress and ductility of nanocomposites based on high and low MW PA6 and PA66

Nanocomposites with both organically modified and unmodified silicate have been prepared by an extrusion process using low and high molecular weight grades of PA6 and a low MW grade of PA66. Mechanical properties have been tested at temperatures ranging from 20 to 120 °C. The modulus increase in all nanocomposites with organically modified nanocomposites is similar: at room temperature an increase in the modulus of approximately 10% for each wt% of silicate is found. PA66 nanocomposites display an identical normalized modulus increase as PA6 nanocomposites, while unmodified silicate nanocomposites show a smaller increase in the modulus. The yield stress also increases with the addition of layered silicate. Low MW PA6 and PA66 nanocomposites show brittle fracture behaviour at room temperature, while high MW PA6 nanocomposites are ductile. With increasing temperature all nanocomposites become ductile at a certain temperature.

Thermal Properties and Flammability of Ethylene-Vinyl Acetate Copolymer/Montmorillonite/Polyethylene Nanocomposites with Flame Retardants

Ethylene-vinyl acetate copolymer (EVA)/montmorillonite (MMT) composite was blended with a linear low density polyethylene (LLDPE). X-ray diffraction and transmission electron microscopy (TEM) image of the EVA/MMT composite are in support of an intercalated with partially delaminated nanocomposite. The tensile strength of the nanocomposite is about 20% higher than that without layered silicates, MMT. Furthermore, the incorporation of MMT into polymer blend delays the main thermo-oxidative degradation. Cone calorimeter test points out that the addition of layered silicates into the pristine EVA/LLDPE blend or the blend with a low smoke non-halogen (LSNH) fire retardants, aluminum trihydroxide, and antimony trioxide, can reduce the maximum heat release rate by 30–40%. The smoke suppressing effect of layered silicates is only observed in the nanocomposite containing flame retardants. According to the limiting oxygen index (LOI) data and cone calorimeter test, the addition of the nanodispersed layered silicate and LSNH flame retardants to the EVA/LLDPE exhibits a synergistic effect on the flame retardancy and smoke suppression.

Morphology, thermal and mechanical behavior of polyamide 6/layered-silicate nanocomposites

The microstructure, morphology, thermal and mechanical properties of polyamide 6/layered-silicate nanocomposites (PLSN) have been studied using X-ray diffraction (XRD), tapping-mode atomic force microscopy (AFM), differential scanning calorimetry (DSC) and tensile tests. The XRD and AFM results indicate that the organically-modified layered silicates are intercalated in the polyamide 6 (PA6) matrix. Also, the crystallization and thermal behavior of PA6 are influenced by the addition of layered silicates into polymer matrix. A silicate-induced crystal transformation from the α-form to the γ-form of PA6 is confirmed by XRD and DSC, i.e., the formation of γ crystal is enhanced by the presence of silicates. In comparison to PA6, the thermal property of PLSN has been investigated using DSC. The possible origins of a new silicate-induced endothermic peak are discussed. Tensile tests show that the tensile modulus and yield strength increase while the strain-at-yield decreases with increasing clay loading.

Templating of cylindrical and spherical block copolymer microdomains by layered silicates

The influence of a highly anisotropic layered silicate (organically modified montmorillonite) in directing the mesoscopic self-assembly of a block copolymer blend is studied as a model for the development and tailoring of templated inorganic–organic hybrid materials. The potential for nanometer thick layers to induce large-scale mesoscopic ordering of cylindrical and spherical microdomains in asymmetric block copolymers is studied using a combination of rheology, electron microscopy, and small angle neutron scattering. Spherical microdomains arranged on a bcc lattice are templated by the anisotropic layered silicate and the kinetics of their growth are dramatically accelerated by the presence of even 0.1 wt.% (0.04 vol.%) of the filler. However, for cylindrical microdomain ordering, the kinetics are essentially unaffected by the addition of layered silicates and the development of three-dimensional mesoscopic order is possibly even disrupted. These results suggest that for the development of three-dimensional well-ordered nanostructures, the surface defining the pattern has to be significantly larger than the leading dimension of the structure being templated.