Exfoliation and dispersion enhancement in polypropylene nanocomposites by in‐situ melt phase ultrasonication

A novel process using ultrasonics to enhance the exfoliation and dispersion of clay platelets in polypropylene‐based nanocomposites has been proposed and investigated. The materials studied were isotactic polypropylene of various molecular weights reinforced with organophilic montmorillonite clay (nanoclay) at 4–6 wt% loadings. X‐ray diffraction (XRD) and rheological measurements, on a model system of nanoclay in mineral oil, were first used to determine ultrasonic energy requirements. The effectiveness of the proposed ultrasonic processing technique on polypropylene nanocomposites was evaluated by XRD and transmission electron microscopy (TEM). The effects of added maleic anhydride–grafted polypropylene compatibilizer, polypropylene molecular weight, and pretreatment of the nanoclays on the nanocomposite exfoliation were also investigated. Results indicate that ultrasonic processing of polymer nanocomposites in the melt state is an effective method for improving exfoliation and dispersion of nanoclays. Issues regarding molecular weight degradation, optimization, mechanical properties, and continuous processing are beyond the scope of the present study and are currently being investigated in our laboratory. Polym. Eng. Sci. 44:1773–1782, 2004. © 2004 Society of Plastics Engineers.     

The effect of clay dispersion on the properties of LLDPE/LLDPE‐g‐MAH/montmorillonite nanocomposites

In this work, three coupling agents presenting different grafting contents and molecular weights were used to prepare linear low density polyethylene (LLDPE)/linear low density polyethylene grafted with maleic anhydride (LLDPE‐g‐MAH)/montmorillonite nanocomposites with various morphologies. The clay dispersion was analyzed at the micrometric level by scanning electron microscopy and at the nanometric level by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that coupling agents having intermediate molecular weights led to the highest exfoliation extents, whereas the coupling agent presenting the highest molecular weight led to a poor delamination of the clay platelets. The properties of the nanocomposites produced and of their LLDPE/LLDPE‐g‐MAH reference blends were analyzed. It was shown that the best improvements in mechanical and barrier properties are not necessarily achieved for the nanocomposites, exhibiting the highest exfoliation extents. The length of the tactoids also plays a crucial role on the macroscopic properties. In addition, a high level of delamination could result in a loss of reinforcement effect, due to the inherent flexibility of the individual clay platelets. Finally, the strength of the clay/polymer interface, which was evaluated through surface tension measurements, seems to play a significant role on the properties of the nanocomposites. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.     

Effect of screw rotation speed on the properties of polystyrene/organoclay nanocomposites prepared by a twin‐screw extruder

We discuss the effect of screw rotation speed on the mechanical and rheological properties and clay dispersion state of polystyrene (PS)/organoclay (clay) nanocomposites prepared by melt compounding with a counterrotating‐type twin‐screw extruder. Poly(styrene‐co‐vinyloxazolin) (OPS) was used as an additional material. The Young's modulus of the PS/OPS/clay nanocomposites showed the maximum value at a screw rotation speed of 70 rpm in this study. This implied the existence of an optimized screw rotation speed for the melt compounding of the polymer/clay nanocomposites. For PS/clay systems without the addition of OPS, the peak intensity from clay increased and the distance between clay platelets in the nanocomposites decreased with the screw rotation speed. On the other hand, inverse results were obtained for PS/OPS/clay systems. According to the transmission electron microscopy photographs, the PS/OPS/clay nanocomposite at 70 and 100 rpm had fully exfoliated clay platelets. The dynamic rheological properties of the PS/clay nanocomposites were almost the same as those of neat PS. On the other hand, the storage and loss moduli of the PS/OPS/clay nanocomposites at the same frequency were larger than those of the PS/clay system. On the whole, the bonding between clay platelets and PS was important for increasing the viscosity and elasticity in the melts of the PS/clay system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1165–1173, 2006     

Study on effect of duration of the ultrasonication process on solvent‐free polyurethane/organoclay nanocomposite coatings: Structural characteristics and barrier performance analysis

In this study, effect of duration of ultrasonication process on structural characteristics and barrier properties of solvent‐free castor oil‐based polyurethane (PU)/organically modified montmorillonite (OMMT) nanocomposites was investigated. A series of PU/OMMT composites were synthesized by in situ polymerization technique through an ultrasonication‐assisted process at various processing durations. Effect of ultrasonication duration on de‐agglomeration of clay stacks in castor oil dispersions was evaluated by optical microscopy, sedimentation test, and viscosity measurement. Wide angle X‐ray diffraction and Fourier‐transform infrared spectroscopy were employed to investigate the effect of processing time on degree of delamination of clay platelets and interfacial strength between clay layers and PU matrix. Also, surface morphology of the nanocomposites was analyzed by atomic force microscopy. The results showed that by increasing the ultrasonication time up to 60 min, the size of clay agglomerates decreased and the interlayer spacing of clay platelets increased. To evaluate the effect of ultrasonication duration on transport properties of the PU/OMMT composites, diffusion coefficient and permeability were determined through water uptake test. Electrochemical impedance spectroscopy was carried out to analyze the barrier properties and to evaluate the corrosion performance of these composite coatings on carbon steel panels. It was found that by increasing sonication time, the barrier property of nanocomposites against diffusion of water molecules improved, which is due to further separation of clay platelets, enhancement of the traveling pathways for water molecules and improvement of interactions between the two components. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Morphology,microhardness, and flammability of compatibilized polyethylene/clay nanocomposites

Morphology, thermal properties, and microhardness of ethylene‐glycidyl methacrylate copolymer (EGMA)/clay and ethylene‐acrylic ester‐glycidyl methacrylate terpolymer (EAGMA)/clay nanocomposites with different clay concentrations have been studied. The results have shown that EGMA and EAGMA are highly compatible with the organoclays Cloisite®20A (Cl20A) and Cloisite®30B (Cl30B). Intercalated structures are formed in the whole range of Cl20A loadings investigated, whereas partial degradation of the Cl30B organoclay was observed. The thermal characteristics and microhardness of EGMA/clay nanocomposites suggest that the filler dispersion deteriorates at high concentration. The concentrated EGMA/Cl20A nanocomposites have been used as masterbatches to prepare ternary high density polyethylene (HDPE)/Cl20A and low density polyethylene (LDPE)/Cl20A nanocomposites. Diffractometric characterization and scanning electron microscopy observations of these materials have shown that the intercalated structure of the starting EGMA/Cl20A masterbatches is preserved after dilution with the polyolefins. The results suggest that the silicate platelets remain localized within the EGMA droplets in the diluted nanocomposites. The latter display improved microhardness, whereas the mechanical properties, including elongation at break, are comparable with those of the neat polyolefins. Considerable enhancement of the flame retardant properties has been observed for the ternary nanocomposites. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Effects of extrusion conditions on the properties of recycled poly(ethylene terephthalate)/nanoclay nanocomposites prepared by a twin‐screw extruder

The effects of extrusion conditions on the mechanical properties of recycled poly(ethylene terephthalate) (rPET)/clay nanocomposites were studied. Nanocomposites of recycled PET containing 2.5 and 5.0 wt % of montmorillonite modified with organophilic quaternary ammonium salt (DELLITE 67G) were prepared by melt compounding using a corotating twin‐screw type extruder at two different screw rotation speeds: 250 and 150 rpm. The highest value of Young's modulus was found for low screw rotation speed (150 rpm). Morphological analysis using transmission electron microscopy (TEM) revealed the presence of fully exfoliated clay platelets in samples prepared at 150 rpm. It was concluded that the screw rotation speed should be optimized when preparing recycled PET/clay nanocomposites by melt compounding. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Continuous process for melt intercalation of PP–clay nanocomposites with aid of power ultrasound

A continuous ultrasound‐assisted process using a single screw extruder with an ultrasonic attachment was developed to prepare PP/clay nanocomposites of varying clay concentrations. The feed rate that controlled the residence time of the polymer in the ultrasonic treatment zone was varied. Die pressure and power consumption were measured. Rheological properties, morphology, and mechanical properties of the untreated and ultrasonically treated nanocomposites were studied. An intercalation of polymer molecules into clay galleries and a partial exfoliation, which occur at short residence times (of the order of seconds), were observed as evident from measurements by X‐ray diffraction and transmission electron microscopy. The obtained results indicate a possibility of the rapid intercalation and partial exfoliation of PP/clay nanocomposites without the matrix being chemically modified. J. VINYL. ADDIT. TECHNOL. 12:78–82, 2006. © 2006 Society of Plastics Engineers.     

Mechanical properties and rheological behavior of poly(butylene terephthalate)/clay nanocomposites with different organoclays

Poly(butylene terephthalate)–clay nanocomposites with three different organically modified clays were prepared via melt blending in a twin‐screw extruder. Decyl triphenylphosphonium bromide, hexadecyl triphenylphosphonium bromide, and cetyl pyridinium chloride were used to modify the naturally occurring montmorillonite clay. The organically modified clays were characterized with X‐ray diffraction for the d₀₀₁‐spacing and with thermogravimetric analysis to determine the thermal stability. The prepared nanocomposites were injection‐molded and examined for the dispersion quality of the clay, the mechanical properties, and the rheological behavior. The tensile strength of the nanocomposites increased with a 1% addition of clay; however, more clay decreased the tensile strength. Nanocomposites with finely dispersed clay platelets and nanocomposites with poorly dispersed clay platelets showed very different rheological behaviors. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and mechanical properties of heterophasic PP–EP/EVA/organoclay nanocomposites

The effect of vinyl acetat (VA) on the morphological, thermal stability, and mechanical properties of heterophasic polypropylene–(ethylene‐propylene) copolymer (PP–EP)/poly(ethylene vinyl acetate) (EVA)/organoclay nanocomposites was studied. Tailored organoclay C20A was selected to enhance the exfoliation of the clay platelets. Depending on the VA content, there were two morphological organoclay populations in the systems. Both populations were directly observed by scanning transmission electron microscopy and measured by wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The content of VA in EVA originated spherical and elongated morphologies in the resultant nanocomposites. High‐VA content led to a better intercalation of the organoclay platelets. Measurement of thermal properties suggested that higher VA decreases thermal stability in samples both with and without organoclay, although nanocomposites had higher thermal stability than samples without clay. The storage modulus increased both with nanoclay and VA content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The effect of organic modifier‐12‐aminolauric acid on morphology and thermal properties of polylactide nanocomposites

A novel organically modified montmorillonite (OMMT) based on a bifunctional organic modifier‐12‐aminolauric acid (ALA) was synthesized. Polylactide (PLA) nanocomposites with this new and traditional OMMT were prepared by solution casting method. The effects of the organic modifiers on structure, morphology and thermal properties of PLA nanocomposites have been investigated using Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results indicate that ALA has distinct effects on the dispersion of MMT platelets into the PLA matrix, where partial exfoliated as well as intercalated structures have been obtained, when compared with ordinary modifier, cetyltrimethyl ammonium bromide (CTAB). TGA data verifies that PLA nanocomposites with ALA‐MMT organoclay display enhanced thermal stability. The optimal clay loading of ALA‐MMT occurs at 3%wt, leading to the best compromise between clay dispersion and thermal properties. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Polypropylene nanocomposite using maleated PP and diamine

The insertion of the aliphatic diamine inside the organoclay will help the dispersion of the clay platelets in the PP/clay nanocomposite due to the reaction between the maleated PP and the diamine. Cloisite®20A was just simply mixed with hexamethylene diamine (HMDA) under shearing condition in Brabender mixer. HMDA group was successfully penetrated into silicate layers. As a result of penetration, d‐spacing of organoclay was increased. Polypropylene/clay nanocomposites were prepared by compounding with maleated PP and amine‐treated clay. From the FTIR spectra, reaction between amine group and maleic‐anhydride group was confirmed. The effect of the organoclay on the properties of the nanocomposite such as the morphology, dynamic mechanical properties, crystal structure and crystallization behavior, glass transition temperature, thermal stability, and tensile properties were investigated and analyzed. Nanocomposites with amine‐treated clays show enhanced properties compared with those with non–amine‐treated clay (Cloisite®20A). From the TEM analysis, nanocomposites with amine‐treated clays shows better dispersibility compared with those with Cloisite®20A alone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Estimation of reinforcement in compatibilized polypropylene nanocomposites by extensional rheology

Structural characterization in polymer nanocomposites is usually performed using X‐ray scattering and microscopic techniques, whereas the improvements in processing and mechanical properties are commonly investigated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X‐ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene‐nanoclay system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of organoclay modification on microstructure and properties of polypropylene–organoclay nanocomposites

We prepared polypropylene nanocomposites based on a modified organoclay with isobutyl trimethoxysilane to investigate the effects of such modifications of organoclay on the microstructure and properties of the nanocomposite. The organoclay was preliminarily intercalated with distearyldimethylammonium bromide via an ion exchange before being grafted with silane. The morphology of the polypropylene–organoclay nanocomposites was characterized by wide‐angle X‐ray diffraction analyses and transmission electron microscopy. The modification of the edges of clay platelets with organic silane resulted in a more uniform dispersion of nonagglomerated tactoids, which consisted of several intercalated clay platelets. However, the unmodified organoclay led to a mixed morphology with both agglomerated and nonagglomerated tactoids. The grafting of the clay edges with organic silane also affected the linear viscoelastic properties of the nanocomposites in the melt state, which was shown to be sensitive to the interaction between the edges of clay platelets as well as to the interaction of the polymer with the platelet edges. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1752–1759, 2006     

Synthesis and characterization of crosslinked polyurethane/clay nanocomposites

A series of glycerin‐crosslinked polyurethane (XPU)‐clay nanocomposites were prepared by in situ polymerization followed by solution casting and thermal treatment. The weight percent (wt %) of clay in the nanocomposites was varied between 0.25 and 10. The structural, rheological and dynamic mechanical properties of the nanocomposites were investigated. X‐ray diffraction (XRD) analysis showed that well dispersed clay platelets were formed in nanocomposites containing up to 1 wt % of clay. Scanning electron microscopy (SEM) showed that poorly dispersed and non‐exfoliated clays were present in composites containing >2 wt % of clay and resulted in phase‐separated disparities within the matrix. Rheological studies demonstrated that processability of polyurethane was significantly improved after clay addition such that solution viscosity decreased by between 76 and 90%. Furthermore, the presence of chemical and physical crosslink networks within the matrix resulted in a remarkable enhancement in the rubbery plateau storage modulus. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43346.     

Preparation of polystyrene–clay nanocomposites via dispersion polymerization using oligomeric styrene‐montmorillonite as stabilizer

This study describes the preparation of polystyrene–clay nanocomposite (PS‐nanocomposite) colloidal particles via free‐radical polymerization in dispersion. Montmorillonite clay (MMT) was pre‐modified using different concentrations of cationic styrene oligomeric (‘PS‐cationic’), and the subsequent modified PS‐MMT was used as stabilizer in the dispersion polymerization of styrene. The main objective of this study was to use the clay platelets as fillers to improve the thermal and mechanical properties of the final PS‐nanocomposites and as steric stabilizers in dispersion polymerization after modification with PS‐cationic. The correlation between the degree of clay modification and the morphology of the colloidal PS particles was investigated. The clay platelets were found to be encapsulated inside PS latex only when the clay surface was rendered highly hydrophobic, and stable polymer latex was obtained. The morphology of PS‐nanocomposite material (after film formation) was found to range from partially exfoliated to intercalated structure depending on the percentage of PS‐MMT loading. The impact of the modified clay loading on the monomer conversion, the polymer molecular weight, the thermal stability and the thermomechanical properties of the final PS‐nanocomposites was determined. Copyright © 2012 Society of Chemical Industry     

New aramid‐based nanocomposites: Synthesis and characterization

New type of nanocomposites containing various proportions of montmorillonite in aromatic polyamide was prepared via solution intercalation method. Aramid chains were synthesized by reacting 4,4′‐oxydianiline with isophthaloyl chloride in N,N′‐dimethyl acetamide. Dodecylamine was used as swelling agent to change the hydrophilic nature of montmorillonite into organophilic. Appropriate amounts of organoclay were mixed in the polymer solution using high‐speed mixer for complete dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterized by XRD, TEM, mechanical, thermal, and water absorption measurements. The structure and morphology of the nanocomposites determined by XRD and TEM revealed the formation of exfoliated and intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus of the nanocomposites with clay loading up to 6 wt%. The glass transition temperature increased up to 12 wt% clay content and thermal stability amplified with increasing clay loading. The water absorption reduced gradually as a function of organoclay and approached to zero with 20 wt% organoclay in the aramid. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Structure and properties of poly(ethylene oxide)‐organo clay nanocomposite prepared via melt mixing

Poly(ethylene oxide) (PEO)/organo clay nanocomposites were prepared by melt‐mixing using a laboratory kneader followed by compression molding. The nanocomposites were characterized by X‐ray diffraction, atomic force microscopy, and scanning electron microscopy. Their crystallization behavior in hot stage was investigated by polarized optical microscopy (POM). A decrease in size and regularity were observed as a result of incorporation of clay into the PEO matrix. The dynamic viscoelastic behavior of PEO/organo clay nanocomposites was assessed using a strain‐controlled parallel plate rheometer. The effects of clay concentration and the processing temperature on the rheological properties of the nanocomposites were extensively studied. A significant increase in the viscosity and storage modulus of the nanocomposites was found with the increasing clay content. The flow activation energy decreased with the incorporation of clay. The reinforcing effect of the organoclay was determined in dynamic mechanical analysis and tensile testing. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Synthesis and characterization of nylon 6/clay nanocomposites prepared by ultrasonication and in situ polymerization

Nylon 6 nanocomposites were prepared by the in situ polymerization of ε‐caprolactam with ultrasonically dispersed organically modified montmorillonite clay (Cloisite 30B®). Dispersions of the clay platelets with concentrations in the range 1–5 wt % in the monomer were characterized using rheological measurements. All mixtures exhibited shear‐thinning, signifying that the clay particles were dispersed as platelets and forming a “house of cards” structure. Samples with Cloisite concentrations above 2 wt % showed a drop in viscosity between the initial shearing and repeated shearing, indicative of shearing breaking down the initial “house of cards” structures formed on sonication. DMTA measurements of the samples showed an increase in the β‐relaxation temperature with increasing clay concentration. The bending modulus, at temperatures below T_g, showed an increase with increasing clay concentration up to 4 wt %. X‐ray diffraction measurements showed that all nylon 6/Cloisite 30B samples were exfoliated apart from the 5 wt %, which showed that some intercalated material was present. The nylon crystallized into the α‐crystalline phase, which is the most thermodynamically stable form. Preference for this form may be a consequence of the long time associated with the postcondensation step in the synthesis or the influence of the platelets on the nucleation step of the crystal growth. DSC measurements showed a retardation of the crystallization rate of nanocomposite samples when compared with that of pure nylon 6, due to the exfoliated clay platelets hindering chain movement. This behavior is different from that observed for the melt‐mixed nylon 6/clay nanocomposites, which show an enhancement in the crystallization rate. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optically transparent polycarbonate/clay nanocomposites with improved performance using phosphonium modified organoclay: Preparation and characterizations

The present work focuses on the morphology and properties of polycarbonate (PC)/clay nanocomposites prepared through melt blending and solution blending at two different loadings of organoclay (0.5 and 1 phr). The oraganoclay was prepared by incorporating thermally 2‐oxopropyl triphenyl phosphonium ion (OTPP) into the clay gallery with an intention to preserve the optical transparency of PC in the PC/clay nanocomposites. An increase in gallery height from 1.24 to 1.86 nm along with the extraordinary thermal stability (∼1.34% wt loss at 280°C, after 20 min) of the OTPP modified montmorillonite (OTPP‐MMT) made it suitable for retention of optical transparency of PC and delamination of the clay platelets in the nanocomposites. The morphological analysis revealed that the clay platelets were randomly dispersed into the PC matrix. An increase in glass transition temperature (T_g) as well as thermal stability of the PC in the nanocomposites was evident from thermal analysis. The strength and modulus of PC increased extensively with increase in OTPP‐MMT loading in the nanocomposites. The nanocomposites were found to retain optical transparency of PC without generation of any color in both the blending technique. POLYM. COMPOS., 199–212, 2016. © 2014 Society of Plastics Engineers     

Dynamic rheological study of paraffin wax and its organoclay nanocomposites

Dynamic rheological data for paraffin wax and its organoclay nanocomposites are reported. Dynamic mechanical analysis of paraffin wax for temperatures ranging from ?40 to 55°C showed a decrease of several orders of magnitude in the dynamic moduli and a significant shift toward viscous behavior, which resulted from the occurrence of two solid–solid phase transitions. In both the crystalline and mesophase regions, the dispersion of organoclay platelets in paraffin wax via ultrasonication increased the storage modulus, whereas the effect on the loss modulus was temperature‐dependent. The melt rheology data of the wax–clay nanocomposites at 70°C showed that the complex viscosities increased monotonically with clay addition and demonstrated shear‐thinning behavior for frequencies between 0.1 and 100 rad/s. The complex viscosity versus angular frequency data were well fit by a power‐law function for which the shear‐thinning exponent provides a gauge for the extent of clay exfoliation. The nanocomposites exhibited low‐frequency solid behavior, which indicated good exfoliation of the organoclay in the wax matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008