Rheological properties of poly(acrylonitrile‐co‐methyl acrylate)/clay nanocomposites prepared via emulsion polymerization

Poly(acrylonitrile‐co‐methyl acrylate)/clay nanocomposites were prepared by free radical polymerization in emulsion using 2‐acrylamido‐2‐methyl‐1‐propanesulphonic acid (AMPS) as a compatibilizer. The resultant nanocomposites were of partially exfoliated morphology despite the variations in clay content among the nanocomposites, as confirmed by transmission electron microscopy and small‐angle X‐ray scattering analysis. Rheological studies of these materials were carried out using parallel plate geometry. The storage modulus increased monotonically with increasing clay content throughout the frequency range studied. However, the neat copolymer, poly(acrylonitrile‐co‐methyl acrylate) and its nanocomposites, exhibited long relaxation behavior as the storage modulus (G′) was greater than the loss modulus (G″) throughout the angular frequency range studied. The complex viscosity of the nanocomposites increased with increasing clay content and they exhibited shear‐thinning behavior. Despite the enhanced rheological properties observed, the copolymer and its nanocomposites underwent structural changes during oscillatory measurements due to cyclization reactions. POLYM. COMPOS., 32:59–66, 2011. © 2010 Society of Plastics Engineers     

Polymer/silicate nanocomposites synthesized with potassium persulfate at room temperature: polymerization mechanism, characterization, and mechanical properties of the nanocomposites

Polymer/silicate nanocomposites were synthesized using potassium persulfate (KPS) in the presence of silicate and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) without exterior redox co-catalysts at a room temperature. A mechanism for the room temperature polymerization in the presence of silicate was suggested: AMPS attached on the surface of silicate layers would oxidize Fe⁺² in silicate lattice to become Fe⁺³ and the Fe⁺³ would decompose KPS to form radicals like redox co-catalysts. Poly (acrylonitrile) (PAN)/silicate nanocomposite showed an exfoliated structure, but poly (methyl methacrylate) (PMMA)/silicate nanocomposite showed an intercalated structure. Polymers recovered from the nanocomposites synthesized at a room temperature had high isotactic configurations compared to bulk polymers. The dipole–dipole interaction between monomers and silicate surface might make the lamella of monomers to form on the silicate layer surface and produced polymers with more isotactic configurations. PAN/silicate nanocomposite showed two glass transition temperatures at 113 and 151 °C. The lower temperature might be related to the molecules with low molecular weight. PMMA/silicate nanocomposite had a storage modulus of 4.47×10⁹ Pa at 40 °C.     

Effects of different kinds of clay and different vinyl acetate content on the morphology and properties of EVA/clay nanocomposites

A series of EVA/clay nanocomposites and microcomposites have been prepared via melt-blending. Using four kinds of EVA with different vinyl acetate (VA) contents: 28, 40, 50 and 80 wt%, and four kinds of clay: three are organophilic clay (OMMT) and one unfunctionalized clay (Na-MMT), the effects of different VA content of EVA and the kinds of the clay on the morphology and properties of EVA/clay nanocomposites were systematically investigated. In previous studies, there are only two distinct nanostructures to distinguish polymer/clay nanocomposites: the intercalated and the exfoliated. But in this paper, we proposed a new nanostructure—‘the wedged’ to describe the dispersion degree of clay in nanocomposites, it means the sheets of clay were partly wedged by the chains of polymer. The wedged, the intercalated and the partially exfoliated structures of EVA/clay nanocomposites were characterized by X-ray diffraction (XRD) and by high-resolution transmission electron microscopy (HRTEM). The enhanced storage modulus of EVA/clay nanocomposites was characterized by dynamic mechanical thermal analysis (DMTA). The enhanced degree in the storage modulus of the OMMT on EVA/clay nanocomposites with the partially exfoliated and intercalated structure is much higher than that with wedged structure, and that with the higher VA content is higher than that with the lower. The thermal stabilities of EVA/clay nanocomposites were also studied by thermal gravimetric analysis (TGA).     

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     

Interfacially compatibilized LDPE/POE blends reinforced with nanoclay: investigation of morphology,rheology and dynamic mechanical properties

Morphological, melt rheological and dynamic mechanical properties of low-density polyethylene (LDPE)/ethylene–octene copolymer (POE)/organo-montmorillonite (OMMT) nanocomposites, prepared via melt compounding were studied. The XRD traces indicated different levels of intercalated structures for the nanocomposites. Addition of a compatibilizer (PE-g-MA) improved the intercalation process. TEM results revealed existence of clay layers in both phases but they were mainly localized in the elastomeric POE phase. Addition of 5 wt% OMMT to the LDPE/POE blend led to reduction in the size of the elastomer particles confirmed by AFM. The complex viscosity and storage modulus showed little effect of the presence of the clay when no compatibilizer was added. As the extent of exfoliation increased with addition of compatibilizer, the linear viscoelastic behavior of the composites gradually changed specially at low-frequency regions. The interfacially compatibilized nanocomposites with 5 wt% OMMT had the highest melt viscosity and modulus among all the studied nanocomposites and blends. Also, this particular composition showed the best improvement in dynamic storage modulus. The results indicated that clay dispersion and interfacial adhesion, and consequently different properties of LDPE/POE/clay nanocomposites, are greatly affected by addition of compatibilizer.     

Microstructure‐properties correlations in dynamically vulcanized nanocomposite thermoplastic elastomers based on PP/EPDM

Thermoplastic vulcanized (TPV) nanocomposites were prepared in a laboratory mixer using EPDM, polypropylene of different viscosities, maleic anhydride modified polypropylene, an organo‐clay, and a sulfur‐based curing system. Based on the obtained results from X‐ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy (SEM), differential scanning calorimeter, and mechanical properties, the microstructure of the prepared nanocomposites was found to be sensitive to the viscosity difference between the two phases and the clay content. X‐ray diffraction and TEM images of the TPV nanocomposites showed that clay was nearly exfoliated and randomly distributed into the polypropylene phase. The SEM photomicrographs of the dynamically vulcanized thermoplastic elastomer samples showed that the rubber particles were dispersed through the polypropylene in form of aggregates and their size increased with the introduction of clay. The nanoscale dimensions of the dispersed clay resulted in a significant improvement of the tensile modulus of the TPV nanocomposite samples, from 20 to 90% depending on clay content and the viscosity ratio of PP/EPDM. In the PP nanocomposites, the clay layers act as nucleating agents, resulting in higher crystallization temperature and reduced degree of crystallinity. Moreover, the oxygen permeability in the TPV nanocomposites was found to be lower than in unfilled but otherwise similar materials. POLYM. ENG. SCI., 47:207–217, 2007. © 2007 Society of Plastics Engineers.     

Novel biobased nanocomposites from functionalized vegetable oil and organically-modified layered silicate clay

The new biobased nanocomposites are processed from anhydride-cured epoxidized linseed oil (ELO)/ or octyl epoxide linseedate (OEL)/diglycidyl ether of bisphenol F (DGEBF) epoxy matrix and organomontmorillonite clay. The selection of anhydride curing agent and biobased epoxy resulted in an excellent combination to provide an epoxy matrix having high elastic modulus, high glass transition temperature, and high heat distortion temperature (HDT), with higher amounts of functionalized vegetable oil (FVO), compared with amine-cured biobased epoxy. The sonication technique was utilized to process the organically-modified clay nanoplatelets in the glassy biobased epoxy network resulting in nanocomposites where the clay nanoplatelets are almost completely exfoliated and homogeneously dispersed in the epoxy network. The processed exfoliated clay nanocomposites showed higher storage modulus compared with the neat epoxy containing the same amount of FVO. Therefore, the lost storage modulus with larger amount of FVO can be regained with exfoliated clay nanoreinforcement.     

Synthesis and characterization of polypropylene/clay nanocomposites

Polypropylene/clay (PP/clay) nanocomposites were synthesized via intercalative polymerization. The nanostructure of the composites was investigated by wide‐angle X‐ray diffractometry (WAXD) and transmission electron microscopy (TEM). The WAXD patterns of the PP/clay nanocomposites indicated that the characteristic diffraction peak of the clay disappeared. The TEM image showed the clay was exfoliated into nanometer size and dispersed uniformly in the PP matrix. The composites exhibited much higher storage modulus compared to that of pure PP. At temperatures higher than T_g, the storage modulus of the PP/clay nanocomposites with 8.1 wt % clay content increased three times that of the pure PP. Additionally, the thermal stability of the nanocomposites significantly increased. The maximum decomposition temperature was increased by 44°C with the introduction of about 10 wt % clay. The heat‐distortion temperatures (HDTs) of the nanocomposites also increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3611–3617, 2001     

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.     

Characterization of polyisoprene-clay nanocomposites prepared by solution blending

The effects of clay dispersion and the interactions between clays and polymer chains on the viscoelastic properties of polymer/clay nanocomposites are investigated using oscillatory shear rheology, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). Four different montmorillonite silicates of natural clays, plasma-treated clays, and organically modified clays (OCs) have been used in this study. For the polyisoprene (PI)/clay nanocomposites, the exfoliation of the OC dispersed in the PI matrix is confirmed with XRD and SAXS although TEM images show both exfoliated and non-exfoliated nanoclay sheets. In contrast aggregation or intercalation is obtained for the other PI/clay composites studied here. Additionally, the effective maximum volume packing fraction of OC for the exfoliated nanocomposites is determined from the overlapping of dynamic viscosity at low frequency regime, in which the effective maximum volume packing fraction is larger than the percolation threshold determined from the storage modulus of the nanocomposites.     

Morphology,thermal, and mechanical properties of polyamide 66/clay nanocomposites with epoxy‐modified organoclay

A new kind of organophilic clay, cotreated by methyl tallow bis‐2‐hydroxyethyl quaternary ammonium and epoxy resin into sodium montmorillonite (to form a strong interaction with polyamide 66 matrix), was prepared and used in preparing PA66/clay nanocomposites (PA66CN) via melt‐compounding method. Three different types of organic clays, CL30B–E00, CL30B–E12, and CL30B–E23, were used to study the effect of epoxy resin in PA66CN. The morphological, mechanical, and thermal properties have been studied using X‐ray diffraction, transmission electron microscopy (TEM), mechanical, and thermal analysis, respectively. TEM analysis of the nanocomposites shows that most of the silicate layers were exfoliated to individual layers and to some thin stacks containing a few layers. PA66CX–E00 and PA66CX–E12 had nearly exfoliated structures in agreement with the SAXS results, while PA66CX–E23 shows a coexistence of intercalated and exfoliated structures. The storage modulus of PA66 nanocomposites was higher than that of the neat PA66 in the whole range of tested temperature. On the other hand, the magnitude of the loss tangent peak in α‐ or β‐transition region decreased gradually with the increase in the clay loading. Multiple melting behavior in PA66 was also observed. Thermal stability more or less decreased with an increasing inorganic content. Young's modulus and tensile strength were enhanced by introducing organoclay. Among the three types of nanocomposites prepared, PA66CX–E12 showed the highest improvement in properties, while PA66CX–E23 showed properties inferior to that of PA66CX–E00 without epoxy resin. In conclusion, an optimum amount of epoxy resin is required to form the strong interaction with the amide group of PA66. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1711–1722, 2006     

Subsurface mechanical properties of polyurethane/organoclay nanocomposite thin films studied by nanoindentation

A series of the exfoliated or intercalated PU/organoclay nanocomposite thin films were prepared by in situ polymerization of polyol/organoclay mixture, chain extender and diisocyanate. The surface mechanical properties of the PU/organoclay nanocomposite films were investigated by means of nanoindentation. The results show that the hardness, elastic modulus and scratch resistant of the nanocomposites dramatically improved with the incorporation of organoclay. This improvement was dependent on the clay content as well as the formation structure of clay in the PU matrix. At 3% clay content, the hardness and elastic modulus of intercalated nanocomposites increased by approximately 16% and 44%, respectively, compare to pure PU. For exfoliated nanocomposite, the improvements in these properties were about 3.5 and 1.6 times higher than the intercalated ones. The exfoliated PU nanocomposites also had greater hardness and showed better scratch resistance compared to the intercalated ones.     

Polypropylene nanocomposite film: A critical evaluation on the effect of nanoclay on the mechanical,thermal, and morphological behavior

Polypropylene (PP)/clay nanocomposites prepared by melt blending technique using different percentages of clay with and without maleic anhydride grafted PP (MA‐PP) were studied. The intercalated and exfoliated structure of nanocomposites was characterized by X‐Ray Diffraction (XRD) and transmission electron microscopy (TEM). Because of the typical intercalated and exfoliated structure, the tensile modulus of the nanocomposites were improved significantly as compared to virgin PP. The viscoelastic behavior of the nanocomposites was studied by dynamical mechanical analysis (DMA) and the results showed that with the addition of treated clay to PP there was substantial improvement in storage modulus increases. The thermal stability and crystallization of the PP nanocomposites as studied by differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA) were also improved significantly compared to PP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characteristics of nitrile rubber (NBR) nanocomposites based on organophilic layered clay

The effect of clay modification on organo‐montmorillonite/NBR nanocomposites has been studied. Organo‐montmorillonite/NBR nanocomposites were prepared through a melt intercalation process. NBR nanocomposites were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA) and a universal testing machine (UTM). XRD showed that the basal spacing in the clay increased, which means that the NBR matrix was intercalated in the clay layer galleries. On TEM images, organo‐montmorillonite (MMT) particles were clearly observed, having been exfoliated into nanoscale layers of about 10–20 nm thickness from their original 40 µm particle size. These layers were uniformly dispersed in the NBR matrix. The DMTA test showed that for these nanocomposites the plateau modulus and glass transition temperature (T_g) increased with respect to the corresponding values of pure NBR (without clay). UTM test showed that the nanocomposites had superior mechanical properties, ie strength and modulus. These improved properties are due to the nanoscale effects and strong interactions between the NBR matrix and the clay interface. Copyright © 2003 Society of Chemical Industry     

Thermal and mechanical behavior of unsaturated polyester [derived from poly(ethylene terephthalate) waste] and montmorillonite‐filled nanocomposites synthesized by in situ polymerization

Postconsumer poly(ethylene terephthalate) waste bottles were glycolyzed as precursors of unsaturated polyester resin (UPR) and their montmorillonite (MMT)‐filled nanocomposites. The glycolysis product (hydroxyl‐terminated oligomers) was converted into UPR with various acid contents. These resins were miscible with styrene and could be cured with peroxide initiators to produce thermosetting unsaturated polyester (UP). Nanocomposites composed of UP matrix and organically modified clay were prepared by in situ polymerization. These were characterized for thermal and dynamic mechanical properties. Transmission electron microscopy was also used to study the morphology at different length scales and showed the nanocomposites to be compromised of a random dispersion of intercalated/exfoliated aggregates throughout the matrix. With an increase in unsaturated acid content (for a fixed content of clay), the value of storage modulus varied from 2737 to 4423 MPa. The glass‐transition temperatures of these nanocomposites ranged from 54 to 78°C, and the crosslink density varied from 3.70 × 10⁵ to 5.72 × 10⁵ mol/m³. The X‐ray diffraction (XRD) of modified MMT exhibited a peak that vanished completely in the polymer nanocomposites. Thus, the XRD results apparently indicated a distortion of the platy layers of nanofiller in the UP nanocomposites. The nanocomposites showed higher modulus values (2737–4423 MPa) compared to the pristine polymer (2693 MPa). From thermogravimetric analysis, all of the nanocomposites were stable up to 200°C and showed a two‐stage degradation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of modifiers on morphology and thermal properties of novel thermoplastic polyurethane‐peptized laponite nanocomposite

Laponite RDS (Laponite containing pyrophosphate based peptizer) was modified with cetyl trimethyl ammonium bromide (cLS) and dodecylamine hydrochloride (dLS), respectively. Thermoplastic polyurethane (TPU)‐modified Laponite RDS nanocomposites were prepared by solution mixing technique. Morphologies of these two modified clay‐nanocomposites are found to be markedly different. cLS based TPU nanocomposites exhibit partly exfoliated, intercalated, and aggregated structure at lower clay content but a network type of structure is observed at higher clay content. However, dLS based TPU nanocomposites demonstrate spherical cluster type of structure at all clay contents. Nearly two fold increase in storage modulus is observed in both glassy and rubbery state with merely 1% cLS content which gradually decreases with an increase in the clay content. However, in case of dLS filled nanocomposite, gradual increase in storage modulus is observed with an increase in the clay content. Thermogravimetric analysis (TGA) studies indicate that the temperature corresponding to 5 wt % degradation of TPU is enhanced by 19.1 and 12.5°C with the addition of merely 1% cLS and dLS, respectively. However, the activation energy of degradation of neat TPU, as determined by isothermal TGA analysis, is found to be higher than that of the nanocomposites containing 1% of cLS and dLS, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

SYNTHESIS OF POLY(METHYL METHACRYLATE)—CLAY NANOCOMPOSITES

Poly(methyl methacrylate)/clay nanocomposites were synthesized via in situ free radical polymerization of methyl methacrylate (MMA) in the presence of functionalized clay. Montmoril-lonite (MMT), a smectic type of clay, was treated with a commercial cationic surfactant, benzalkonium chloride (BAC), and a synthesized zwitterionic surfactant, octadecyldimethyl betaine (CI8DMB) Functionalized MMT was prepared via an ion exchange between Na,ions in the clay and the surfactant cations in aqueous medium. The intercalation of the surfactant in the clay galleries was determined using X-ray diffraction (XRD). The interlayer spacing for C18DMB was 2.03nm, higher than 1.86nm observed for BAC. This is due to longer chain length of C18DMB. Both organophilic clays formed a viscous gel when dispersed in the monomer, MMA. Poly(methyl methacrylate) (PMMA) nanocomposites were obtained by polymerizing the dispersions. XRD and transmission electron microscopy (TEM) indicate predominant exfoliation of the silicate layers in the polymer matrix for MMT treated with C18DMB, and partial exfoliation for MMT treated with BAC     

Twin‐screw compounding of poly(methyl methacrylate)/clay nanocomposites: effects of compounding temperature and matrix molecular weight

Poly(methyl methacrylate) (PMMA)/organoclay nanocomposites prepared by melt‐compounding using a co‐rotating twin‐screw extruder were intercalated nanocomposites. Commercially available PMMA resins of various molecular weights were used for comparison. The results showed an optimum compounding temperature for maximum intercalation with balanced shear and diffusion. Higher operating temperature reduced the shear mixing effect, and might have induced early degradation of the organoclay. Lower operating temperature, in contrast, reduced the mobility of the polymer molecules, which not only hampered the intercalation attempts, but also generated high torque in the extrusion. The mechanical behavior of the nanocomposites was studied. The tensile modulus, storage modulus and glass transition temperature of the nanocomposites increased with increasing clay content; however, an associated decrease in strength and strain at break was also observed. The notched impact strength also showed a slight decrease with clay content. Nanocomposites based on the lower molecular weight PMMA yielded more significant improvement in mechanical and thermal properties at the same clay content. Copyright © 2007 Society of Chemical Industry     

Nanocomposites based on layered silicate and miscible PVDF/PMMA blends: melt preparation, nanophase morphology and rheological behaviour

Polyvinylidene fluoride (PVDF)–organoclay nanocomposites were prepared by melt-extrusion using polymethylmethacrylate (PMMA) as an interfacial agent. These nanocomposite materials were analysed with respect to their morphological and rheological properties. The nanophase morphology development and nanophase dispersion were studied using TEM. A fine dispersion of partially to nearly fully exfoliated silicate layers in miscible PVDF/PMMA blend matrices was observed when organophilic montmorillonite was used. Increasing the amount of PMMA in the PVDF/PMMA blend leads to high degree of exfoliation.

The rheological behaviour of intercalated/exfoliated PVDF/PMMA nanocomposites containing various concentrations of organophilic silicate was also investigated. At low frequencies, the storage modulus is increasing with increasing PMMA content and the frequency dependence of the storage modulus gradually changes from liquid-like to solid-like for nanocomposites when 10 wt% of PMMA is added, indicating formation of a network structure.

Dynamic mechanical investigations show a dramatic increase of the storage modulus in the rubbery plateau compared to conventional mineral fillers, as a result of the network structure. Due to the ‘nano’-sized dispersion, property efficiency is already realized at low loading levels (3–5 wt%).     

Crystal structures and their effects on the properties of polyamide 12/clay and polyamide 6–polyamide 66/clay nanocomposites

Both polyamide 12 (PA 12)/clay and polyamide 6–polyamide 66 copolymer (PA 6/6,6)/clay nanocomposites were prepared by melt intercalation. The incorporation of 4–5 wt % modified clay largely increased the strength, modulus, heat distortion temperature (HDT), and permeation resistance to methanol of the polyamides but decreased the notched impact strength. Incorporation of the clay decreased the melt viscosities of both the PA 12 and PA 6/6,6 nanocomposites. Incorporation of the clay increased the crystallinity of PA 6/6,6 but had little effect on that of PA 12, which explained why the clay obviously increased the glass‐transition temperature of PA 6/6,6 but hardly had any effect on that of PA 12. The dispersion and orientation of both the clay and the polyamide crystals were studied with transmission electron microscopy, scanning electronic microscopy, and X‐ray diffraction. The clay was exfoliated into single layers in the nanocomposites, and the exfoliated clay layers had a preferred orientation parallel to the melt flow direction. Lamellar crystals but not spherulites were initiated on the exfoliated clay surfaces, which were much more compact and orderly than spherulites, and had the same orientation with that of the clay layers. The increase in the mechanical properties, HDT, and permeation resistance was attributed to the orientated exfoliated clay layers and the lamellar crystals. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4782–4794, 2006