Nanoclay Platelets Research Articles

The mixed impact of nanoclays on the apparent diffusion coefficient of additives in biodegradable polymers in contact with food

In face of growing environmental concerns, biodegradable and bio-sourced plastic nanocomposites are emerging as a new class of materials, especially for the food packaging sector. However, their use in food contact raises new issues in term of consumer safety.The aim of this study was to determine the impact of nanoclays on the apparent diffusion coefficient (Dapp) of selected additives from biopolymers into fatty food simulants. For the most part, nanoclay addition has a non-conventional impact. To understand this, the following parameters were studied: (i) the exfoliation state of nanoclay platelets in the polymer matrix, (ii) the sorption of food simulant by the polymer matrix, and (iii) the crystallinity of the materials. At first glance, solvent uptake and crystallinity agree with the results of diffusivity, however these parameters cannot explain the extreme differences between Dapp values.

Weathering, salt spray corrosion and mar resistance mechanism of clay (nano-platelet) reinforced polyurethane nanocomposite coatings

Weathering, salt spray corrosion and mar resistance mechanism of clay (nano-platelet) reinforced polyurethane nanocomposite coatings

Rheological and mechanical properties of PMMA/organoclay nanocomposites prepared via ultrasound-assisted in-situ emulsion polymerization

This study investigated the rheological and mechanical properties of PMMA/organically modified Cloisite 30B nanocomposites (clay loading 1–5 wt%) synthesized via ultrasound-assisted in-situ emulsion polymerization. XRD patterns and TEM micrographs of the nanocomposites confirm complete exfoliation and uniform distribution of nanoclay platelets in host poly(methyl methacrylate) matrix. As a consequence, the nanocomposites synthesized with sonication were found to have superior properties as compared to the nanocomposites synthesized with mechanical stirring. Measurement of rheological properties using melt rheology revealed that magnitudes of storage modulus, loss modulus and complex viscosity increased with incorporation of clay platelets in polymer matrix due to the flow restriction of PMMA chains induced by nanofiller. Analysis of mechanical properties of nanocomposites showed maximum Young’s modulus of 1.8GPa with weight average molecular weight (Mw) of 581,130 g mol−1 for 2 wt% clay loading. The enhancements in rheological and mechanical properties of nanocomposites are attributed to the physical and chemical effect of ultrasound and cavitation, i.e. generation of intense microturbulence and free radicals in the emulsion polymerization reaction system.

Poly(acrylic acid-co-styrene)/clay nanocomposites: efficient adsorbent for methylene blue dye pollutant

In this contribution, polymer/clay (nano)composites, based on poly(acrylic acid) (PAA) and poly(acrylic acid-co-styrene) poly(AA-co-St), were synthesized by free radical polymerization, using 2,2′-azobis(isobutyronitrile) (AIBN), as initiator and organomodified clay (OMMT), as nanofillers. The structural and morphological characteristics of the obtained (nano)composites, PAA/OMMT (1, 3, 5 wt%), poly(AA75-co-St25)/OMMT (3 wt%) and poly(AA25-co-St75)/OMMT (3 wt%), were examined by X-ray diffraction and scanning electron microscopy, indicating the successful intercalation of polymer chains into the clay nanoplatelets. Thermal properties of obtained (nano)composites were evaluated according to thermogravimetric analysis and differential scanning calorimetry. Based on morphological and thermal results, poly(AA25-co-St75)/OMMT (3 wt%) (nano)composite was selected as an efficient adsorbent matrix for methylene blue dye, with about 74% of elimination obtained after only 80 min of swelling, under soft conditions.

Probing the dielectric relaxation processes and their correlation with ions transportation in the complexes of plasticized nanocomposite solid polymer electrolyte

Plasticized nanocomposite solid polymer electrolyte (PNSPE) film consisted of poly(ethylene oxide) and poly(methyl methacrylate) blend as host matrix, lithium perchlorate salt as ions dopant, ethylene carbonate as plasticizer, and montmorillonite clay nanoplatelets as inorganic nanofiller has been prepared by solution cast followed by the melt pressing. X-ray diffraction study of the PNSPE film confirms its amorphous structure with the existence of exfoliated nanoplatelets of the nanofiller. Dielectric and electrical dispersion of the film has been characterized systematically by employing the dielectric relaxation spectroscopy in the frequency range 2 × 101 to 1 × 106 Hz, at different temperatures. The relaxation times attributed to the various processes of structural dynamics of the PNSPE film have been probed by considering the individual spectrum of all the dielectric and electrical functions which are further validated by their master plot representation. The relaxation times corresponding to the dynamics of the electric double layers, electrode polarization, and interfacial polarization-affected polymer chain segments, cations coordinated polymers chain segments, and also the ionic conductivity in the ion–dipolar–nanofiller coordinated structures of the film have been determined. A generalized behaviour of these relaxation processes for probing the dynamical structures in all the solid polymer electrolytes has been demonstrated. It is further explored that these relaxation times of the PNSPE film exhibit a correlation with the dc ionic conductivity, and their temperature-dependent variation obeys the Arrhenius behaviour of nearly the same relaxation activation energies which are also found in good agreement with the conductivity activation energy.

Vulcanization kinetics and mechanical properties of organically modified nanoclay incorporated natural and chlorobutyl rubber nanocomposites

The curing kinetics, vulcanizate properties, mechanical reinforcement and chemical interactions of organically modified nanoclay filled natural rubber (NR) and chlorobutyl (CIIR) rubbers have been studied. From the vulcanization studies, it is observed that nanoclays are more intercalated in NR matrix rather than CIIR matrix. To understand the exact mechanism operating in the vulcanization behavior of NR and CIIR, autocatalytic model was applied. The vulcanization kinetic studies revealed that the nanoclay distribution at high temperature (190 °C) in CIIR matrix is somewhat intercalated in nature. Highly pronounced reversion behavior was observed in NR matrix. The mechanical reinforcement of vulcanizates was examined using the change in modulus values at 100% and 300% elongation. The mechanical properties were modeled using different kind of models such as Guth-Smallwood, Halpin-Tsai, modified Halpin-Tsai and Mori-Tanaka models. Finally, the dispersion of nanoclay platelets in CIIR and NR matrix was confirmed by the phase images obtained from AFM technique.

Weathering, salt spray corrosion and mar resistance mechanism of clay (nano-platelet) reinforced polyurethane nanocomposite coatings

Performance properties like weathering and corrosion resistance are critical for automotive top coats. Using two types of clays Cloisite 30B(C30B) and Cloisite 20 A(C20 A), a 2 K polyurethane (PU) pack coating formulation was modified at nanoscale. These coatings show better resistance to salt spray (500 h) and accelerated weathering conditions (1000 h). When observed under atomic force microscopy (AFM) nanoscale morphology of these nanocomposite coatings show globular (C30B) and rod-like (C20 A) hard segment formation of size˜200 nm, which compared to pristine PU coatings are more uniformly formed and evenly distributed across the microscale surface (surface texturing). Visual, spectroscopic & chemical analysis confirmed better performance of nanocomposite coatings under ultraviolet/humidity and salt cycles. Dry film thickness & gloss; dft1000 (G[1000]) was reduced by 25% (32%) for pure PU, 14.03% (16.7%) for PU-3C30B and 20% (22.7%) for PU-3C20 A respectively. The overall colour difference in CIELab values ΔE* was 9.794, 7.623 and 8.450 for PU, PU-3C30B and PU-3C20 A. Salt spray (500 h) rusted about 35% area of mild steel (ms panels) for PU, while for PU-3C30B and PU-3C20 A it was only 5% and 10% respectively. Fourier transform infrared (FTIR) shows better retention of functional groups in aged and corroded nanocomposite coatings versus pristine coatings. This proves that two dimensional clay particles when duly exfoliated interact with hard segments and play a significant role in resisting weathering forces, salt spray corrosion and even mar.

Enhanced piezoelectric response in nanoclay induced electrospun PVDF nanofibers for energy harvesting

Templated nanofibers of poly(vinylidene fluoride) have been designed on top of two dimensional nanoclay platelets for energy harvesting application. Dimension of nanofiber has been varied using different nanoclay content prepared through optimized electrospinning. The alteration in structure (electroactive phase) and morphology has been worked out as a function of nanoclay concentration. Nearly 90% piezoelectric active phase has been stabilized in presence of minimum quantity of nanoclay. Hybrid nanofiber is found to be tougher (300%) and stiffer by design, which in turn suitable for device application. Unimorph using hybrid nanofiber exhibits power generation up to 100 ms against less than 50 ms tenure using pristine fiber. Device has been fabricated using various nanofibers and demonstrates very high output voltage (70 V) and power density (68 μW cm−2) from the device made of hybrid nanofiber. Various modes of body movements e.g. bending, twisting, walking, foot and finger tapping can generate considerable power using the hybrid device and are able to transform waste mechanical energy to useful electric power. Underlying mechanism of charge separation in template system has been revealed which explain the high conversion of energy using the hybrid device.

A Protein-Based, Water-Insoluble, and Bendable Polymer with Ionic Conductivity: A Roadmap for Flexible and Green Electronics.

Proteins present an ecofriendly alternative to many of the synthetic components currently used in electronics. They can therefore in combination with flexibility and electroactivity uncover a range of new opportunities in the field of flexible and green electronics. In this study, silk‐based ionic conductors are turned into stable thin films by embedding them with 2D nanoclay platelets. More specifically, this material is utilized to develop a flexible and ecofriendly motion‐sensitive touchscreen device. The display‐like sensor can readily transmit light, is easy to recycle and can monitor the motion of almost any part of the human body. It also displays a significantly lower sheet resistance during bending and stretching regimes than the values typically reported for conventional metallic‐based conductors, and remains fully operational after mechanical endurance testing. Moreover, it can operate at high frequencies in the kilohertz (kHz) range under both normal and bending modes. Notably, our new technology is available through a simple one‐step manufacturing technique and can therefore easily be extended to large‐scale fabrication of electronic devices.

Mechanically strong and electrically conductive multilayer MXene nanocomposites.

Polymer nanocomposites offer the opportunity to bridge properties of nanomaterials to the macroscale. In this work, layer-by-layer (LbL) assembly is used to demonstrate nanocomposites of 2D titanium carbide nanosheets (MXene) and clay nanoplatelets (montmorillonite) to fabricate freestanding thin films with unique multifunctional properties. These thin films can be tuned by adjusting the thickness to exhibit a tensile strength of 138 MPa-225 MPa, EMI specific shielding effectiveness normalized to thickness and density up to 24 550 dB cm2 g-1, and sheet resistance from 855 Ω sq-1-3.27 kΩ sq-1 (corresponding to a range of conductivity from 53 S m-1 to 125 S m-1). This composite is the strongest MXene-based LbL film prepared to date, in part due to the nacre-like brick-and-mortar structure. Ultra-strong, multifunctional films of this nature are desirable for many applications ranging from membranes, to structural and multifunctional composites, energy harvesting and storage, and materials for aerospace.

Effectively improved ionic conductivity of montmorillonite clay nanoplatelets incorporated nanocomposite solid polymer electrolytes for lithium ion-conducting devices

Synergistic effects of lithium salt concentration and inorganic nanofiller incorporation on the ionic conductivity of polymer blend matrix based nanocomposite solid polymer electrolytes (NSPEs) have been examined. The montmorillonite (MMT) clay nanoplatelets incorporated NSPE films based on poly(ethylene oxide) and poly(methyl methacrylate) blend matrix with lithium tetrafluoroborate (LiBF4) ionic salt have been prepared by the solution-cast method followed by melt-press technique. The 1, 3, and 5 wt% MMT amounts along with 13.3 wt% LiBF4 amount as compared to the weight of polymer blend have been used for the preparation of NSPE films. X-ray diffractometer (XRD) and the Fourier transform infrared (FTIR) spectrometer have been employed for structural characterization of these NSPE films. The complex permittivity and ac electrical conductivity spectra are investigated by using the dielectric relaxation spectroscopy, whereas the electrochemical performance of these materials has been characterized by the electrochemical analyzer. The XRD patterns reveal that the NSPEs are predominantly amorphous and have the intercalated and exfoliated MMT platelets, whereas the relative changes in their FTIR spectra confirm the ion–dipolar–nanofiller interactions between the functional groups of the blended polymers, lithium ions, and the MMT nanoplatelets. The permittivity and conductivity spectra of these materials are analyzed for exploring the dominant contribution of electrode polarization and dipolar polarization in the low and high frequency regions, respectively, and the presence of relaxation processes associated with structural dynamics of the solid-state ion–dipolar complexes. It has been found that the NSPE of relatively fast polymer chain segmental dynamics exhibits higher ionic conductivity. The room temperature ionic conductivity of the 13.3 wt% LiBF4 containing SPE is found more than two times higher as compared to that of the SPE film having 9.7 wt% LiBF4. When the MMT is incorporated, the ionic conductivity of 13.3 wt% LiBF4 containing NSPEs enhances by about one order of magnitude at room temperature. The dc ionic conductivity of the 13.3 wt% LiBF4 containing SPE film is found 1 × 10–5 S/cm at 55 °C, whereas it is 1.65 × 10–5 S/cm at 27 °C for the 5 wt% MMT incorporated NSPE film. The significantly enhanced ionic conductivity with ions transference number close to unity, high electrochemical stability voltage window and good reversibility of these NSPE materials confirm their potential applications as ion conductor/separator for the development of all-solid-state ion conducting devices and the lithium-ion batteries.

Influence of size, aspect ratio and shear stiffness of nanoclays on the fatigue crack propagation behavior of their epoxy nanocomposites

In this study, the fatigue crack propagation (FCP) of epoxy clay nanocomposites is investigated. Especially effect of size, aspect ratio and tactoid shear - stiffness of clay nanoplatelets are analyzed in detail. To achieve a systematical approach, two highly pure synthetic fluorohectorites having large lateral extension (averagely 3.8 μm) with different tactoid shear stiffness states were used and compared to natural Montmorillonite (MMT) with significantly smaller tactoid lateral size (400 nm). A novel nanocomposite preparation method combining solvent casting with 3-roll milling was applied to achieve excellent dispersion of nano-additives. The FCP behavior is improved by incorporation of all types of layered silicates, however highest FCP resistance was observed by shear stiff fluorohectorites with large lateral extension. Responsible toughening mechanisms are mainly depending on the lateral extention of nanoclays. This can be explained by SEM micrographs of fracture surfaces and relating the particle size with dynamic crack tip opening displacements.

Electrospun polyimide/organic montmorillonite composite nanofibrous membranes with enhanced mechanical properties and flame retardancy

Polyimide/organic montmorillonite nanofibrous membranes were fabricated through electrospinning of polyamic acid/organic montmorillonite precursors followed by a thermal imidization process. Scanning electron microscopy micrographs showed small amounts of organic montmorillonite addition (<3%) and increase in the diameter of polyimide nanofibers. However, higher organic montmorillonite fraction generated microspheres due to the aggregation of clay nanoplatelets. Transmission electron microscopy images indicated that both exfoliated and intercalated organic montmorillonites existed in polyimide nanofibers when low quantity of clay was loaded (<3%). As the clay amount increased, exfoliated structure disappeared and stacked clay layers were observed. The optimum concentration of organic montmorillonite is 3%. By incorporating 3% clay, the tensile strength and modulus of membrane increased by 92.1 and 48.6%, respectively. Moreover, the limiting oxygen index value arose from 29.2 to 30.4%. Higher thermal stability was also achieved because of the heat barrier effect of clay layers. The onset decomposition temperature increased by 17℃ by adding 5% clay. These results demonstrate that tiny organic montmorillonite incorporation is relatively effective for improving the mechanical properties as well as flame retardancy of polyimide nanofibrous membrane.

Reinforcing effect of organoclay in nitrile rubber - Effect of mill mixing and latex stage mixing

Abstract The urge for materials with diverse applications has paved the way to fabricate composites based on, one-dimensional filler like nanoclays. The main aim of the work was to study the effect of mill mixing and latex stage mixing on the reinforcing effect of organoclay in Nitrile Rubber. The non-ionic surfactant assisted latex stage mixing route proved to be more efficient and feasible when compared to mill mixing. Mechanical properties were measured and, about 150% increase in tensile strength and 79% increase in tensile modulus were obtained for the latex based composites at 3 phr clay loading when compared to neat rubber composites. Dynamic strain sweep tests revealed that, the low strain modulus for latex mixed composites was higher. Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) results indicated that the addition of organoclay hardly affected the thermal properties of the rubber matrix. Transmission Electron Micrographs revealed homogeneous dispersion of partially exfoliated and intercalated nanoclay platelets in the latex state substantiating the viability of latex mixing over mill mixing. The extent of reinforcement in the nanocomposites was also analyzed with the help of different micromechanical models.

Inherently Flame Retardant Nylon 6 Nanocomposite Fibers

In this study, inherently flame retardant nanocomposite nylon 6 fibers infused with nanoclay and intumescent additives were compounded and melt-spun. Two approaches were adopted to mitigate the loss of mechanical properties typically observed nanocomposite fiber systems: (a) additive particle size reduction; and (b) elastomer toughening of the nanocomposite system. As a result, the ductility of the FR nanocomposite formulations was improved significantly. Structural and morphological characterization of the melt-spun fibers using TEM and XRD demonstrated good dispersion of the additives and exfoliation of the nanoclay platelets. Microscale Combustion Calorimetry analysis demonstrated effective reduction of heat release capacity and thus significant enhancement of flame retardant performance of the compounded fibers.

Compatibility effects of modified montmorillonite on elastic and visco-elastic properties of nano-reinforced Poly(lactic acid): Experimental and modeling study

This paper aims to highlight the effects of the compatibility between nano-clay platelets and polymer matrix and capability of combined approaches (experimental and modeling) to capture the visco-elastic properties of the studied materials. In this context, a study, as complete as possible, is conducted through microstructural observation, mechanical characterization and micromechanical modeling. Nano-clay reinforced Poly(lactic acid) blends with different modified nano-clay platelets (Cloisite 30B and Cloisite 93A) were prepared. The linear elastic and visco-elastic behaviors of nano-reinforced samples were characterized. And a combination of lenght–scale–sensitive experimental techniques helped to describe the micro-structure through different microstructural parameters. These parameters were used as input into a viscoelastic micromechanical model. Comparison between experimental data (Complex, loss and storage moduli) and model predictions were in good agreement.

Flame Retardant Multilayered Coatings on Acrylic Fabrics Prepared by One-Step Deposition of Chitosan/Montmorillonite Complexes

Multilayered coatings deposited using the layer-by-layer (LbL) assembly technique have attracted great interest in recent years as a sustainable and efficient solution for conferring flame retardant properties to fabrics. The unique structure and interaction established upon the coating assembly are the key factors for successful flame retardant properties. In this study we aimed at the deposition of multilayered coatings comprising chitosan and montmorillonite with a LbL-like structure and interactions by the simple processing of compacted chitosan/montmorillonite complexes obtained by the direct mixing of an oppositely charged solution/suspension. Upon drying, the prepared complex yielded a continuous coating characterized by a brick-and-mortar multi-layered structure, in which oriented clay nanoplatelets were held together by a continuous chitosan matrix. When deposited on acrylic fabrics these coatings were able to suppress the melt-dripping phenomenon, and at 10 and 20% add-ons achieved self-extinguishing behavior within a few seconds after ignition. Cone calorimetry testing revealed an increase in time to ignition (up to +46%) and considerable reductions of the rates at which heat is released (up to −62 and −49% for peak of heat release rate and total heat release, respectively). A reduction in the total smoke release (up to −49%) was also observed.

Influence of Nanoclay on the Properties and Morphology of Cement Mortar

This paper investigates the impact of partial substitution of cement with hydrophilic nanoclay platelets on the mechanical properties, workability, consistency, water absorption and morphology of cement mortar. Cement mortar mixtures with various replacement ratios, 0.5%, 1%, and 2% of nanoclay by weight of cement, were prepared and tested according to the standards. The results show that adding small quantities of nanoclay could improve the mechanical strengths of cement mortar. The best enhancements were reported for cement mortar reinforced with 2 wt.% nanoclay, where 11%, 5%, and 9% improvement in the compressive strength, flexural strength, and tensile strength, respectively, were observed. Adding nanoclay into cement mortar also leads to increase the amount of water needed to reach the normal consistency, elongate its setting time, increase its water absorption, but reduce its capillary water absorption coefficient and lower flowability of the pastes. SEM imaging showed a reasonable level of dispersion of nanoclay within the mortar.

Free-Radical Dispersion Polymerization of Ethylene with Laponite to Polyethylene–Clay Nanocomposite Particles

Composite clay/polymer nanoparticle dispersions have been studied for many different polymers but remained elusive for polyolefins even though polyolefins are an important class of polymers and are also industrially applied in the form of aqueous dispersions. Despite the hydrophobic and apolar nature of polyethylene, aqueous nanocomposite dispersions are formed via heterogeneous free-radical polymerization in the presence of the synthetic smectite clay Laponite-RD at relatively mild conditions (250 atm, 85 °C). The clay nanoplatelets effectively contribute to colloidal stability of the polyolefin particles formed and strongly enhance particle formation during the aqueous polymerization. Evolution of the polymer–clay interaction at an early stage of particle formation is instrumental, and initiator-derived polar end groups are decisively involved. The clay enhances polymerization yields and promotes the formation of smaller particles. Stable dispersions with polymer contents of up to 24% were obtained without the need of additional organic surfactants.

Organo-modified layered silicate nanocomposites of EPDM–chlorobutyl rubber blends for enhanced performance in γ radiation and hydrocarbon environment

In this work, blends of ethylene propylene diene monomer rubber and chlorobutyl rubber were reinforced with organo-modified layered silicate (nanoclay) to enhance their performance in radiation as well as hydrocarbons environments. The mechanical properties of the nanocomposites increased (up to 57%) and solvent transport coefficients decreased (by 30%) with increasing nanoclay content. The enhancement in properties was attributed to the dispersion of nanoclay platelets in the ethylene propylene diene monomer–chlorobutyl rubber blends and the chemical interaction between nanoclay and the polymer which were confirmed by morphological and spectroscopic analysis, respectively. The effect of nanofiller content on the mechanical properties, solvent uptake and thermal degradation of blends exposed to gamma radiation was investigated by irradiating the nanocomposites with gamma rays for cumulative doses of 0.5, 1 and 2 MGy. The ethylene propylene diene monomer–chlorobutyl rubber nanocomposites with 5 phr nanoclay had the best retention of mechanical properties and solvent sorption coefficients on exposure to radiation. Depending on the dose of cumulative radiation exposure, chain scission and/or crosslinking occurred in the nanocomposites, resulting in varying degrees of changes in properties.