Nanoclay dispersion in a miscible blend: an assessment through rheological analysis

In this study, miscible polymer blend nanocomposite of Poly(ethylene oxide)/Poly(methyl methacrylate), (PEO/PMMA), with sodium montmorillonite (Na⁺-MMT) clay were prepared at a constant concentration of nanoparticles via different solution intercalation methods. The resultant nanocomposites possess different structure and dispersion of Na⁺-MMT clays which are assessed through a combination of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The rheology of the neat blend and two different layered silicate nanocomposites were investigated using linear viscoelastic measurements with a parallel plate rheometry at small strain amplitudes. It was found that regardless of the extent of dispersion, the storage and loss modulus increased by incorporating the nanoparticles into the matrix of PEO/PMMA. Moreover, at low frequencies the rheological response of the nanocomposite in which layered silicates benefit from a better dispersion becomes relatively invariant with frequency and represents a mediocre solid-like behavior in comparison to the nanocomposite in which the nanoparticles are intercalated or agglomerated.     

Rheological behavior of polypropylene/layered silicate nanocomposites prepared by melt compounding in shear and elongational flows

Melt rheology and processability of exfoliated polypropylene (PP)/layered silicate nanocomposites were investigated. The nanocomposites were prepared by melt compounding process in the presence or absence of a PP‐based maleic anhydride compatibilizer. PP/layered silicate nanocomposites showed typical rheological properties of exfoliated nanocomposites such as nonterminal solid‐like plateau behavior at low frequency region in oscillatory shear flow, higher steady shear viscosity at low shear rate region, and outstanding strain hardening behavior in uniaxial elongational flow. The melt processability of exfoliated PP/layered silicate nanocomposites was significantly improved due to good dispersion of layered silicates and increased molecular interaction between the PP matrix and the layered silicate organoclay. Small‐angle X‐ray scattering and transmission electron microscopy results revealed that the layered silicate organoclay was exfoliated and good interaction between PP matrix and organoclay was achieved by using the PP‐g‐MAH compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3506–3515, 2007     

Mechanical and rheological properties of the maleated polypropylene–layered silicate nanocomposites with different morphology

Three types of maleated polypropylene–layered silicate nanocomposites with different dispersion states of layered silicate (deintercalated, intercalated, and exfoliated states) are prepared from two kinds of polypropylenes with different molecular weights, organically modified layered silicate and pristine montmorillonite to investigate the effect of the final morphology of the nanocomposite on the rheological and mechanical properties. Maleated polypropylene with high molecular weight intercalates slowly and the other with low molecular weight exfoliates fast into the organophilic layered silicates. Rheological properties such as oscillatory storage modulus, nonterminal behavior, and relative viscosity has close relationship with the dispersion state of layered silicates. The exfoliated nanocomposite shows the largest increase and the deintercalated nanocomposite shows almost no change in relative shear and complex viscosities with the clay content. The exfoliated nanocomposite shows the largest drop in complex viscosity due to shear alignment of clay layers in the shear flow. In addition, the final dispersion state of layered silicates intimately relates to the mechanical property. The dynamic storage moduli of nanocomposites show the same behavior as the relative shear and complex viscosities. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1526–1535, 2003     

Investigation of the influence of processing conditions on the thermal,rheological and mechanical behavior of polypropylene nanocomposites

The use of polypropylene (PP)‐layered silicate nanocomposite has attracted great interest in the polymer industry over the last years. On one hand, PP is widely used in many fields of applications because of good performance and cost. On the other hand, the major advantage of layered silicate nanofiller in the polymer matrix is the small amount of filler (<5 wt%) needed to enhance various properties such as Young's modulus. The most commonly used layered silicates are organomodified montmorillonite (MMT). In this study, a PP/organoclay nanocomposite, filled with layered silicate Nanofil SE3010 (1 and 5 wt%), provided by Rockwood Additives, USA, was used. The polymer nanocomposites were prepared via melt intercalation in a laboratory kneader. The compatibilizer (PP grafted with maleic acid anhydride) admixture content relative to the organoclay content (1 and 5 wt%) was chosen at a ratio of 1:1 (clay:compatibilizer). The influence of different processing conditions (rotation speed and residence time) on the thermal, rheological, and mechanical properties and the interlayer distance was investigated. It was the target to determine whether a short and intensive or a long and soft process performs better. Different properties prefer different states of dispersion of MMT in the polymer matrix. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Fabrication and characterization of new semiconducting nanomaterials composed of natural layered silicates (Na-MMT), natural rubber (NR), and polypyrrole (PPy)

An electrolytic admicellar polymerization was chosen for synthesizing new semiconducting nanomaterials composed of sodium montmorillonite (Na⁺-MMT), polypyrrole (PPy), and natural rubber (NR). The contents of the pyrrole monomer and the Na⁺-MMT were varied from 100 to 800 mM and 1-7 parts per hundred of rubber (phr), respectively. Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to confirm the success of the synthesis. The morphological studies carried out by X-ray diffraction (XRD) and TEM pointed out the different states of dispersion of the layered silicates, whereas the study done by scanning electron microscopy (SEM) showed a great dependence of the nanocomposite morphology on the inclusion of the layered silicates. Thermal stability studies demonstrated the thermo-protecting and thermo-oxidative behaviors imparted by the layered silicates. The mechanical and DC electrical conductivity properties were significantly improved with the inclusion of the layered silicates, especially at a 7 phr loading.     

Using maleic anhydride grafted poly(lactic acid) as a compatibilizer in poly(lactic acid)/layered‐silicate nanocomposites

The goal of this work was to prepare exfoliated poly(lactic acid) (PLA)/layered‐silicate nanocomposites with maleic anhydride grafted poly(lactic acid) (PLA–MA) as a compatibilizer. Two different layered silicates were used in the study: bentonite and hectorite. The nanocomposites were prepared by the incorporation of each layered silicate (5 wt %) into PLA via solution casting. X‐ray diffraction of the prepared nanocomposites indicated exfoliation of the silicates. However, micrographs from transmission electron microscopy showed the presence of intercalated and partially exfoliated areas. Tensile testing showed improvements in both the tensile modulus and yield strength for all the prepared nanocomposites. The results from the dynamic mechanical thermal analysis showed an improvement in the storage modulus over the entire temperature range for both layered silicates together with a shift in the tan δ peak to higher temperatures. The effect of using PLA–MA differed between the two layered silicates because of a difference in the organic treatment. The bentonite layered silicate showed a more distinct improvement in exfoliation and an increase in the mechanical properties because of the addition of PLA–MA in comparison with the hectorite layered silicate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1852–1862, 2006     

Location of a nanoclay at the interface in an immiscible poly(ε‐caprolactone)/poly(ethylene oxide) blend and its effect on the compatibility of the components

Nanocomposites based on 80/20 and 20/80 (w/w) poly(ε‐caprolactone) (PCL)/poly(ethylene oxide) (PEO) immiscible blends and organophilic layered silicates were prepared with melt extrusion. From transmission electron microscopy analysis, it was observed that the exfoliated silicate platelets were preferentially located at the interface between the two blend phases. When the blend‐based nanocomposites were prepared via a two‐step process in which the silicates were first premixed with the PEO component or with the PCL component, the silicate layers migrated from the PEO phase or PCL phase to the interface. The rheological behavior of the nanocomposites was also investigated. At low frequencies, the frequency dependence of the storage modulus changed from a liquidlike behavior for the unfilled blend to a solidlike behavior for the nanocomposites, indicating the formation of a network structure as a result of exfoliation. From the scanning electron micrographs, a monotonic decrease of the PEO domain size in the 80/20 PCL/PEO blend was observed as a function of the organophilic clay content. Therefore, a clear emulsifying effect was induced by the organophilic layered silicates in the immiscible PCL/PEO blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Styrene butadiene rubber/clay nanocomposites for tire tread application

Homogeneous and stable dispersion of layered silicates in their rubber nanocomposite is a matter of interest as it can significantly affect the material properties. Herein we propose a facile and easily industrialised approach for preparing highly dispersed montmorillonite (MMT)/rubber nanocomposites by the latex compounding method. Furthermore, an efficient way of enhancing the interlayer spaces of organically modified MMT (f-MMT) with alkyl-ammonium chains while mixing the styrene butadiene rubber (SBR) is reported. The f-MMT embedded SBR matrix shows a remarkable improvement of the modulus and tensile strength even in the low loading rate, which is ascribed to the well dispersion of the f-MMT enhancing interfacial interaction with the rubber matrix. Furthermore, we manufactured the practical pneumatic tire using f-MMT/SBR nanocomposite with outstanding wear resistance, grip performance and low-rolling resistance for the green tire application, opening up enormous opportunities to prepare high-performance rubber composites for future engineering applications.     

Preparation, characterization and antimicrobial activity of chitosan/layered silicate nanocomposites

Chitosan/layered silicate nanocomposites with different ratios were successfully prepared via solution-mixing processing technique. Unmodified Ca²⁺-rectorite and organic rectorite modified by cetyltrimethyl ammonium bromide were used. Their structures were characterized by XRD, TEM and FT-IR techniques. The results showed that chitosan chains were inserted into silicate layers to form the intercalated nanocomposites. The interlayer distance of the layered silicates in the nanocomposites enlarged as its amount increased. When the weight ratio between chitosan and organic rectorite was 12:1, the largest interlayer distance of 8.24 nm was obtained. However, with further increase of its amount, the interlayer distance of the layered silicates in the nanocomposites reduced. In vitro antimicrobial assay showed that pristine rectorite could not inhibit the growth of bacteria, but chitosan/layered silicate nanocomposites had stronger antimicrobial activity than pure chitosan, particularly against Gram-positive bacteria. With the increase of the amount and the interlayer distance of the layered silicates in the nanocomposites, the nanocomposites showed a stronger antibacterial effect on Gram-positive bacteria, while the nanocomposites showed a weaker antibacterial effect on Gram-negative bacteria. The lowest minimum inhibition concentration (MIC) value of the nanocomposites against Staphylococcus aureus and Bacillus subtilis was 0.00313% (w/v), and the relative inhibition time (RIT) against B. subtilis with concentration of 0.00313% (w/v) was >120 h.     

Effect of polymer matrix/montmorillonite compatibility on morphology and melt rheology of polypropylene nanocomposites

In this study, Ca²⁺‐montmorillonite (Ca²⁺‐MMT) and organo‐montmorillonite (OMMT) were modified by three compatibilizers with different degrees of polarity [poly(ethylene glycol) (PEG), alkyl‐PEG, and polypropylene (PP)‐g‐PEG]. PP/MMT nanocomposites were prepared by melt blending and characterized using X‐ray diffraction and transmission electron microscopy. The results showed the degree of dispersion of OMMT in the PP/PP‐g‐PEG/OMMT (PMOM) nanocomposite was considerably higher than those in the PP/PEG/OMMT and PP/alkyl‐PEG/OMMT nanocomposites, which indicated that the dispersion was relative to the compatibility between modified OMMT and PP matrix. Linear viscoelasticity of PP/MMT nanocomposites in melt states was investigated by small amplitude dynamic rheology measurements. With the addition of the modified MMT, the shear viscosities and storage modulus of all the PP/MMT nanocomposites decreased. It can be attributed to the plasticization effect of PEG segments in the three modifiers. This rheological behavior was different from most surfactant modified MMT nanocomposites which typically showed an increase in dynamic modulus and viscosity relative to the polymer matrix. The unusual rheological observations were explained in terms of the compatibility between the polymer matrix and MMT. In addition, the mechanical properties of PP/MMT nanocomposites were improved. A simultaneous increase in the tensile strength and toughness was observed in PP/PMOM nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the clay size on the dispersion morphology and emulsion stability of ABS/layered silicate nanocomposites

ABS/layered silicate nanocomposites were synthesized through an emulsion polymerization with different sizes of silicates. The particle sizes of Laponite, Cloisite‐Na and Kunipia‐F are about 20–30, 70–150, and 300–500 nm, respectively. When ABS was synthesized by the emulsion polymerization in the presence of Laponite and Cloisite‐Na, ABS/layered silicate nanocomposite emulsion showed a stable suspension without the precipitation of solid particle. On the other hand, ABS/layered silicate nanocomposite synthesized with Kunipia‐F showed the precipitation of large aggregated particles and the phase separation. Smaller sizes of silicates like Laponite and Cloisite‐Na than polymerized particle worked as resided barrier preventing the emulsion particle from coagulation. Larger size of silicate like Kunipia‐F than emulsion particle was not able to enclose the emulsion particle delicately because of its stiffness and large aspect ratio. The monomers inserted into the intercalated Kunipia‐F connected the ABS particles and clay particles. The Kunipia‐F particles anchored ABS particles around them inducing the aggregation and precipitation of ABS particles. ABS copolymer emulsion and aqueous silicate dispersion were mixed to compare with synthesized ABS/layered silicate nanocomposites and showed a stable suspension. With small amount of Laponite or Cloisite‐Na, nanocomposite emulsion of Kunipia‐F was also stabilized. Laponite and Cloisite‐Na worked as a steric stabilizer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of ethylene‐1‐butene copolymer on tensile properties and toughness of polypropylene/mica/organoclay hybrid nanocomposites

In this study, polypropylene (PP) was reinforced using 1 wt% organically modified‐grafted mica (OMGM) and various levels of Cloisite15A (C15A), 0–3 wt%. For OMGM preparation, polypropylene graft maleic anhydride (PP‐g‐MAH) was grafted onto diacetone acryl amid modified mica. The results showed the highest impact strength enhancement of 68% and Young's modulus of 12% for hybrid nanocomposite containing 1 wt% OMGM and 0.5 wt% C15A when compared to neat PP. In order to considerably improve the impact strength of PP with advantage of elastic modulus enhancement, PP was melt blended with above‐mentioned amounts of OMGM and C15A and different contents of ethylene‐1‐butene copolymer (EBR), 0–10 wt%. The dispersion of low‐ and high‐aspect ratio layered silicate tactoids and EBR nanoparticles in the polymer matrix was studied using transmission electron microscopy. The effect of EBR level on the crystallization behavior, tensile properties, impact strength, and fracture toughness of the resultant toughened hybrid nanocomposite was investigated. The presence of EBR nanoparticles did not show any sufficient effect on the melting and crystallization temperatures of the toughened PP and hybrid nanocomposites. However, the impact results indicated that the addition of EBR to neat PP remarkably increased the toughness while sharply decreased its Young's modulus. The incorporation of 7 wt% EBR in the hybrid nanocomposite containing 1 wt% OMGM and 0.5 wt% C15A considerably enhanced impact strength 119% and 30% in comparison to neat PP and its hybrid nanocomposite, respectively. Additionally, the incorporation of EBR nanoparticle in the presence of the silicate layered nanoparticles prevented significant decreasing in Young's modulus of the matrix. J. VINYL ADDIT. TECHNOL., 25:117–126, 2019. © 2018 Society of Plastics Engineers     

Nanostructure morphology and dynamic rheological properties of nanocomposites based on thermoplastic polyurethane and organically modified montmorillonite

Thermoplastic polyurethane (TPU) nanocomposites based on organophilic-layered silicates were prepared via melt blending. Wide angle X-ray diffraction (WAXD) and transmission electron microscope (TEM) were employed to investigate the state and mechanism of exfoliation of the layered silicate within TPU matrix. The TPU nanocomposites were found to have a partially exfoliated morphology at lower clay loading, whereas the morphology changed to an intercalated nanostructure at higher clay loadings. The effect of the state of dispersion of organoclay on rheological properties of the nanocomposites were carried out by rubber process analyzer (RPA), which exhibited more pronounced shear thinning behavior, and increased storage and loss modulus with the increase in organoclay content. The pseudo-plastic like behavior was observed due to change in liquid-like to solid-like behavior of nanoclay-filled systems.     

Microstructural evolution of electrically activated polypropylene/layered silicate nanocomposites investigated by in situ synchrotron wide-angle X-ray scattering and dielectric relaxation analysis

Electric field was found to facilitate the destruction of layer stacking and separation of silicate layers in polypropylene (PP)/layered silicate nanocomposites, resulting in the penetration of polymer chains into silicate galleries. In this study, we describe the real-time microstructural evolution of PP/clay nanocomposites under electric field investigated by in situ synchrotron wide-angle X-ray scattering (WAXS) analysis. We were able to identify two distinctive mechanisms for the formation of nanocomposites depending on the type of electric field. We observed that the exfoliation process prevails in the AC field, while the alignment of silicates parallel to the electric field predominates in the DC field. Dielectric relaxation analysis showed that the different mechanisms originate from different charge distributions of bound ions attached to the clay surfaces due to the applied electric field.     

Organically modified layered-silicates facilitate the formation of interconnected structure in the reaction-induced phase separation of epoxy/thermoplastic hybrid nanocomposite

We incorporated organic modified layered silicates (OLS) into the mixture of epoxy and poly(ether imide) (PEI) to obtain a ternary hybrid nanocomposite and investigated its reaction-induced phase separation behavior. We found that OLS had dramatic impact to the phase separation process and the final phase morphology. The onset of phase separation and the gelation or vitrification time were greatly brought forward and the periodic distance of phase-separated structure was reduced when OLS was incorporated. Phase separation of the unfilled specimens was greatly suppressed at temperatures higher than 190 °C, and no etch hole of PEI-rich phase could be observed in the SEM images. An interconnected, or bicontinuous morphology could only be observed at cure temperatures lower than 140 °C. On the contrary, the OLS-filled hybrid nanocomposites carried out obvious phase separation at cure temperatures ranging from 120 to 220 °C. Even at cure temperatures higher than 190 °C, the hybrid nanocomposites had an interconnected phase-separated microstructure. These phenomena were related to the preferential wettability, chemical reaction of OLS with epoxy oligomer and the enhanced viscosity of the mixture.     

Effect of organoclay on the properties of maleic‐anhydride grafted polypropylene and poly(methyl methacrylate) blend

Poly(methyl methacrylate)/polypropylene (PMMA/PP) and PMMA/maleic‐anhydride grafted PP (MAPP) blends and their blend nanocomposites containing 2 wt% organoclay (Cloisite 15A, denoted C15A), prepared by a melt mixer were studied. Both X‐ray diffraction (XRD) and transmission electron microscopy (TEM) revealed exfoliated polymer blend nanocomposites. Scanning electron microscopy (SEM) studies indicated a droplet dispersion morphology for all the blends while addition of C15A into PMMA/MAPP blend resulted to a co‐continuous morphology. In fact, rheological data and thermal properties indicated that the PMMA/MAPP/C15A nanocomposite showed a better homogeneous dispersion of silicate layers than PMMA/PP/C15A nanocomposite. A Cole–Cole plot and relaxation modulus indicated a solid‐like character for PMMA/MAPP and PMMA/MAPP/C15A, while a liquid‐like behavior was noticed for PMMA/PP and PMMA/PP/C15A. The effect of an organoclay on the dynamic mechanical properties of samples was investigated using dynamic mechanical analysis (DMA) which showed a significant enhancement on the storage modulus of the PMMA/MAPP/C15A as compared to PMMA/PP/C15A . POLYM. COMPOS., 38:431–440, 2017. © 2015 Society of Plastics Engineers     

Properties of polypropylene/layered-silicate nanocomposites and melt-spun fibers

Polypropylene (PP)/layered-silicate organoclay nanocomposites and their fibers were prepared by melt compounding and melt spinning, respectively, in the presence or absence of compatibilizer (PP-based maleic anhydride compatibilizer) to examine the effects of the organoclay dispersion and rheological behavior on the internal structure and tensile properties of the nanocomposite fibers. The compatibilized nanocomposites showed solidlike plateau behavior and strain hardening due to a three-dimensional network structure in the shear and uniaxial elongational flows. The tensile properties of the nanocomposite fibers were reduced compared with those of the pure PP fibers because some of the layered silicates were present as partially aggregated forms and the molecular weight of the compatibilizer was lower than that of the pure PP matrix. It was also found that the tenacity of the nanocomposite fiber increased and then decreased as the compatibilizer content increased because the compatibilizer affected the internal structure of the nanocomposite fibers. The positive effect of the compatibilizer was to generate a more effective exfoliated structure of organoclay in the polymer matrix. The negative effect was that the melt-spun nanocomposite fiber had a lower molecular weight than the pure PP fiber because the compatibilizer had a lower molecular weight. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal properties and flammability of acrylic nanocomposites based upon organophilic layered silicates

Summary Thermal and mechanical properties of poly(methylmethacrylate-co-dodecylmethacrylate) nanocomposites based upon exfoliated organophilic layered silicates, were investigated as a function of the silicate and comonomer content. Layered silicates such as sodium bentonite were rendered organophilic by means of ion-exchanging sodium cations for N,N,N,N-dioctadecyl-dimethyl-ammonium cations. Silicate exfoliation was enhanced by means of 5 and 10 wt.-% dodecyl-methacrylate (LMA) addition to afford translucent reinforced acrylic nanocomposites. In contrast to conventional filled acrylic polymers, only 10 wt.-% organophilic silicate was sufficient to increase Young's modulus from 2200 to 4030 MPa, glass temperature from 72 to 80 °C and degradation temperature from 220 to 256 °C with respect to the neat MMA/LMA (90 wt.-%/10 wt.-%) copolymer. Flammability studies, performed on a cone calorimeter, revealed that the maximum heat release rate of MMA/LMA copolymer nanocomposite decreased from 837 kW/m² to 566 kW/m². The nanocomposite morphology was examined by means of transmission electron microscopy (TEM). Received: 28 May 1999/Revised version: 24 September 1999/Accepted: 24 September 1999     

Preparation and mechanical properties of nitrile butadiene rubber/silicate nanocomposites

Elastomer nanocomposites consisting of nitrile butadiene rubber (NBR) latex and layered silicates are prepared by a modified latex shear blending process aided with ball milling. The mode of dispersion of layered silicates in NBR is partially exfoliated and intercalated when the concentration of layered silicates is below 7.5 wt%, as evidenced by transmission electron microscopy and X-ray diffraction results. The tensile and tear mechanical properties are much higher than that of neat NBR. Specifically, the tensile and tear mechanical properties of the NBR/layered silicates increase by 200 and 60%, respectively. The decomposition temperature of the nanocomposites increases slightly.     

Improved environmental stability in poly(p-phenylene vinylene)/layered silicate nanocomposite

Polymer-rich/clay-rich phase-separated, polymer-layered silicate nanocomposites are prepared through a solution blending of poly(xylylidene tetrahydrothiophenium chloride) with two kinds of layered silicates. By spin-coating, thin films of each phase were obtained, followed by thermal elimination of tetrahydrothiophene and HCl to final poly(p-phenylenevinylene) (PPV)/layered silicate nanocomposite. At ambient conditions, the PPV films are easily photodegraded due to the oxygen diffused in. Poly(p-phenylenevinylene)/layered silicate nanocomposite showed improved environmental stability against photodegradation under an air ambient condition. Additionally, optical absorption and photoluminescence measurements demonstrate that the thin films of clay-rich phase are much less photodegraded than those of polymer-rich and PPV reference.