Microstructure,crystallization and dynamic mechanical properties of polyamide/clay nanocomposites after melt‐state annealing

Polyamide 6/clay (PA/clay) nanocomposites produced by melt‐compounding were treated under various melt‐state annealing processes. The effect of melt‐state annealing on the microstructure, crystallization, and dynamic mechanical properties was characterized by transmission electron microscope (TEM), modulated differential scanning calorimetry (MDSC), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA). Clay layers were exfoliated in PA matrix. The crystalline transformation between α and γ‐crystalline phase was virtually dependent on the annealing process and clay loading. After melt‐state annealing between 230 and 250°C, clay induced the appearance of a new endothermic peak in PA/clay. PA/clay after melt‐state annealing exhibited a higher elastic modulus above T_g and a lower β relaxation below T_g as compared with the non‐annealed sample. FTIR analysis demonstrated that the melt‐state annealing caused strong hydrogen bonding interaction of amide groups with clay layers. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Thermal and mechanical properties of PA12/C30B nanocomposites in relationship with nanostructure

This work focuses on the effect of nanoclay mass fraction on the properties of polyamide 12 matrix. Relationships between mechanical, thermal, and structural properties of polyamide 12/Cloisite^® 30B nanocomposites were studied. The material structure, previously described from XRD and TEM experiments, was more thoroughly characterized in the present work using SEM and FTIR techniques. The FTIR results clearly showed that clay galleries are intercalated by PA chains, which leads to a partially exfoliated nanostructure, confirming the TEM observations and the XRD analysis. However, a few micrometric aggregates are evidenced by SEM analysis, particularly at high clay fractions. TGA and DTA measurements showed that the thermal stability of PA12 matrix is slightly modified by the Cloisite^® 30B content. Viscoelastic properties of the nanocomposites in solid‐state were analyzed as functions of strain, frequency, and temperature. The extent of the linear response regime of the material is shown to be sensitive to the amount of clay: nonlinearities appear at lower strain values as the clay mass fraction increases. Both relative dynamical moduli also increase with increasing clay mass fraction, with frequency dependence for the viscous modulus and without frequency dependence for the elastic modulus. Finally, similarities have been pointed out between viscoelastic properties of the nanocomposites in solid and melt states. For example, the percolation threshold is highlighted at the same clay mass fraction, ～2%, in both states. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41938.     

Melt rheology of polypropylene reinforced with polyaniline‐coated short glass fibers

This research deals with the melt rheology of isotactic polypropylene (iPP) reinforced with short glass fibers (SGF) coated with electrically conductive polyaniline (PAn). Composites containing 10, 20, and 30 wt % PAn‐SGF were studied. Moreover, a composite of 30 wt % PAn‐SGF was also prepared with a blend of iPP and PP‐grafted‐maleic anhydride (iPP/PP‐gMA). The composites showed linear viscoelastic regime at small strain amplitudes. The onset of nonlinearity decreased as the concentration of filler increased. The time‐temperature superposition principle applied to all composites. The filler increased the shear moduli (G′, G″) and the complex viscosity η*. Steady‐state shear experiments showed yield stress for the composites with 20 and 30 wt % PAn‐SGF. Strikingly, the 10 wt % composite showed higher steady state viscosity than the 20 wt %. Rheo‐optics showed that shear induced disorder of microfibers at a concentration of 10 wt %. However, at 20 wt % concentration shear aligned the microfibers along the flow axis, this would explain the anomalous steady state viscosity values. The viscosity exhibited a shear thinning behavior at high shear rates for all composites. Creep experiments showed that the filler induced greater strain recovery in the composites and that the amount of strain recovery increased as the PAn‐SGF concentration increased. However, the enhancement of strain recovery (as well as shear viscosity) was more significant when using the iPP/PP‐gMA blend, suggesting greater adhesion between this matrix and the filler PAn‐SGF. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Dynamic mechanical,rheological, and thermal properties of intercalated polystyrene/organomontmorillonite nanocomposites: Effect of clay modification on the mechanical and morphological behaviors

Polystyrene (PS)/organomontmorillonite nanocomposites were prepared by melt processing with a twin‐screw extruder. Sodium montmorillonite was organically modified with stearyl trimethyl ammonium chloride to evaluate the effect of clay modification on the performance of the nanocomposites. A comparative account of nanocomposites prepared with the commercial clay Cloisite 20A (C20A) is presented. X‐ray diffraction studies indicated that the clay layers were completely dispersed, and a delaminated structure was formed in the case of C20A/PS and organomontmorillonite/PS nanocomposites. The dispersion characteristics of the clays within the matrix polymer were further investigated through transmission electron microscopy analysis. Mechanical tests revealed increases in the tensile, flexural, and impact strengths of 83, 55, and 74%, respectively, for C20A/PS nanocomposites at a 5% clay loading. The viscoelastic response of the nanocomposites, studied with dynamic mechanical analysis, also showed a substantial increase in the storage modulus of the nanocomposites with the incorporation of organically modified nanoclays. Furthermore, the melt‐state rheology of the organically modified nanocomposites displayed three distinct regions—glassy, plateau, and terminal—from the high‐frequency region to the low‐frequency region, with a considerable increase in the storage modulus in the glassy and terminal regions. Differential scanning calorimetry and thermogravimetric analysis were also used to evaluate the effect of the addition of nanoclays on the glass‐transition temperature and thermal stability of the PS matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphology and melt rheology of nylon 11/clay nanocomposites

Nylon 11 (PA11)/clay nanocomposites have been prepared by melt‐blending, followed by melt‐extrusion through a capillary. Transmission electron microscopy shows that the exfoliated clay morphology is dominant for low nanofiller content, while the intercalated one is prevailing for high filler loading. Melt rheological properties of PA11 nanocomposites have been studied in both linear and nonlinear viscoelastic response regions. In the linear regime, the nanocomposites exhibit much higher storage modulus (G′) and loss modulus (G″) values than neat PA11. The values of G′ and G″ increase steadily with clay loading at low concentrations, while the G′ and G″ for the sample with 5 wt % clay show an inverse dependence and lie between the modulus values of the samples with 1 and 2 wt % of clay. This is attributed to the alignment/orientation of nanoclay platelets in the intercalated nanocomposite induced by capillary extrusion. In the nonlinear regime, the nanocomposites show increased shear viscosities when compared with the neat resin. The dependence of the shear viscosity on clay loading has analogous trend to that of G′ and G″. Finally, a comparison has been made between the complex and steady viscosities to verify the applicability of the empirical Cox‐Merz rule. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 542–549, 2006     

FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites

Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the α-phase, the addition of clay silicate layers favor the formation of the γ-crystalline phase in PA6CN.We focus on the reason why silicate layers favor the formation of γ-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the γ-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding.The silicate layers were indeed found to weaken the hydrogen bonding both in the α- and γ-phases. This was also confirmed by X-ray diffraction studies. The γ-phase is most likely concentrated in regions close to the silicate layers, whereas the α-phase is favored in the bulk matrix.     

Polyamide 6/clay nanocomposites using a cointercalation organophilic clay via melt compounding

Polyamide 6/clay nanocomposites (PA6CN) were prepared via the melt compounding method by using a new kind of organophilic clay, which was obtained through cointercalation of epoxy resin and quaternary ammonium into Na‐montmorillonite. The dispersion effect of this kind of organophilic clay in the matrix was studied by means of X‐ray diffraction (XRD) and transmission electron microscopy (TEM); the silicate layers were dispersed homogeneously and nearly exfoliated in the matrix. This was probably the result of the strong interaction between epoxy groups and amide end groups of PA6. The mechanical properties and heat distortion temperature (HDT) of PA6CN increased dramatically. The notched Izod impact strength of PA6CN was 80% higher than that of PA6 when the clay loading was 5 wt %. Even at 10 wt % clay content, the impact strength was still higher than that of PA6. The finely dispersed silicate layers and the strong interaction between silicate layers and matrix decreased the water absorption. At 10 wt % clay content, PA6CN only absorbs half the amount of water compared with PA6. The dynamic mechanical properties of PA6CN were also studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 953–958, 2003     

Influences of Functionalized Nanoclays on Morphology and Mechanical Properties of Polyvinyl Alcohol-Based Composites by Twin-Screw Extruder

Polyvinyl alcohol-based nanocomposites filled with different weight percentage of functionalized nanoclays were prepared by melt processing with a twin-screw extruder. The effective incorporation of amine-modified bentonite nanoclays in the PVA matrix leads to the increase in thermal stability, stress–strain properties. The effect of the addition of functionalized nanoclays in PVA matrix exhibits intercalated nanocomposite structure. The thermal decomposition (T_d) temperature of the composites increases up to 30°C, than pristine PVA. The morphology influences were studied by TEM. These clay nanocomposite films could be useful for wound dressing material and for enhancing the moisture absorbance properties.     

Mechanical response and rheological properties of polycarbonate layered‐silicate nanocomposites

The effect of clay loading on the mechanical behavior and melt state linear viscoelastic properties of intercalated polycarbonate (PC) nanocomposites was investigated. At low frequencies, the linear dynamic oscillatory moduli data revealed diminished frequency dependence with increasing nanoclay loading. The 3.5 and 5 wt% clay nanocomposites exhibited dramatically altered relaxation behavior, from liquid‐like to pseudo‐solid–like, compared to the pure PC and the 1.5 wt% clay nanocomposite. Thermal degradation of PC resulted from the melt compounding of organo‐modified nanoclays was evident from the reduction in the glass transition temperature and molecular weight of the PC nanocomposites. These nanocomposites also exhibited a significant decrease in the extent of tensile elongation and ductility with respect to the nanoclay incorporation. A concomitant decrease in the rheological properties at high frequencies was also observed, and was consistent with the lowering of the molecular weight of PC, particularly near or above the percolation threshold of nanoclay. These nanocomposites, nevertheless, exhibited elastic‐plastic deformation in compression, regardless of nanoclay content. Polym. Eng. Sci. 44:825–837, 2004. © 2004 Society of Plastics Engineers.     

毛细管动态挤出下聚合物熔体非线性流变行为的研究

采用毛细管动态流变仪,选用PELD、PP、PS和PA等典型物料,研究了毛细管动态挤出下各聚合物熔体的非线性流变行为。结果表明,不同物料的流变行为对振动力场的响应特性有较大差异,只有在一定的振幅和频率下振动力场才能有效降低熔体的黏度。实验首次发现,PP、PS和PA存在窄的振动参数区域,在此区域内,熔体的动态表观黏度值大于相应的稳态值,出现“加振变黏”现象。这一新的发现表明,并非“只要引入振动就一定有利于聚合物材料的成型加工”,必须考虑不同分子结构的聚合物材料对振动的不同响应规律。     

Structural,rheological, and mechanical properties of PA6/SAN/SEBS ternary blend/organoclay nanocomposites

The aim of this study was to investigate the effect of nanoclay addition on the morphological and mechanical properties of PA6/SAN/SEBS ternary blend. Two different nanoclays with different modifiers and two different mixing sequences were used to investigate the role of thermodynamic and kinetic, respectively, in the nanoclays localization. XRD, SEM, TEM, melt rheology, tensile and Izod impact tests were used to characterize the nanocomposites. Results of characterization of nanocomposites showed that clay localization is a very influential parameter to determine the type of morphology and, consequently, mechanical properties of ternary/clay nanocomposites. It was demonstrated that presence of nanoclay in the matrix results in the increase of stiffness, while localization of nanoclay at the interface improves the toughness and tensile strength. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41969.     

On the structure‐properties relationship in montmorillonite‐filled polyamide 6 nanocomposites

Polyamide 6/montmorillonite (MMT) nanocomposites were prepared by melt compounding method comprising 1–7.5 wt % of Nanomer I.24 TL or 5 and 10 wt % of Cloisite 15A organically modified nanoclays. The composite samples were characterized by synchrotron X‐ray, thermal and FT‐IR spectroscopy methods looking for changes in the micro‐ and nanostructure of both PA6 matrix and MMT reinforcement as a function of the clay content and type. These data were discussed in conjunction with the mechanical properties of the respective nanocomposites. Generally, the Young's modulus was found to increase proportionally to the clay content being the highest in samples with strong aggregation of MMT at micron length scale. The tensile strength passed through a maximum at 2.5 wt % clay load presenting a homogeneous microstructure with almost no agglomeration. Increasing the amount of MMT produced less crystalline PA6 matrices, richer in γ‐PA6 polymorph and resulted in larger long spacings of PA6 due to expansion of both crystalline and amorphous domains. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Effect of clay surfactant type and clay content on the rheology and morphology of uncured fluoroelastomer/clay nanocomposites prepared by melt‐mixing

Fluoroelastomer/clay composites were prepared by melt mixing in an internal mixer using Cloisite® Nanoclays: NA, 15A, 20A, 30B, and 93A at three different concentrations viz. 2.5, 5.0, and 10.0 phr. Rheology, X‐ray diffraction (XRD), and transmission electron microscopy (TEM) were used to characterize the composites prepared. Dynamic rheological measurements showed significant increase in storage moduli (G′) in the terminal frequency region for the uncured composites prepared from Cloisite® 15A and 20A. At higher frequencies, organically modified nanoclays plasticize the polymer matrix leading to lower modulus values. Using all three characterization techniques, Cloisite® 15A and 20A were shown to have intercalated structure in the fluoroelastomer matrix, whereas other nanoclays were shown to have inferior dispersion. The storage modulus increases proportionally with increase in the clay loading and no clay aggregation was observed at higher loadings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of nanoclay–polymer composites from soil clay with respect to their water‐holding capacities and nutrient‐release behavior

Water and nutrients are two important inputs to agriculture that need to be used judiciously with higher efficiency to save these limited resources. For these purposes, a series of nanoclay–polymer composite (NCPC) superabsorbent nutrient carriers were prepared. These NCPCs were based on the reactions of different types of nanoclays (10 wt %) with partially neutralized acrylic acid and acryl amide by a free‐radical aqueous solution copolymerization reaction with N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator. The nanoclays isolated from three different types of soils were dominant in kaolinite (clay I ), mica (clay II ), and montmorillonite (clay III ), and a portion of each was freed from amorphous aluminosilicate. Thus, there were six different types of nanoclays used, namely, those dominated by kaolinite, mica, and smectite with and without amorphous aluminosilicate. Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) investigations showed evidence of interaction between the clays and polymer. XRD investigation also showed that the reaction between the polymer and clays I and II occurred on the surface of various clay particles without intercalating into the stacked silicate galleries, whereas in the case of clay III (the smectite‐dominated clay), evidence indicated the intercalation of polymer into the stacked silicate galleries of the clay and the exfoliation of the clay. The water absorbency decreased in the NCPCs compared to that of the pure polymeric hydrogel. In case of the pure polymer, the entire amount of nutrient loading released within 15 h of incubation; this was higher than that of the NCPCs. In the initial stage (up to 15 h), no significant differences in nutrient release were observed among the different polymer/clay composites, but there were differences in later stages. Among the different NCPCs, the percentage release of nutrients at 48 h ranged from around 70% in the polymer/clay III composite to 90% in the polymer/clay I composite. The presence of amorphous aluminosilicates in clay did not make any difference in the nutrient‐release rate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39951.     

Morphology,thermal and mechanical properties of nylon 12/organoclay nanocomposites prepared by melt compounding

Nylon 12 (PA12) nanocomposites with different organoclay loadings were successfully prepared by melt compounding. X‐ray diffraction indicated the dominance of the exfoliated clay morphology throughout the matrix after mixing in a Brabender twin‐screw extruder, in accordance with transmission electron microscopy observations. Thermogravimetric analysis showed that the thermal stability of the PA12 matrix was improved by about 20 °C on incorporation of only 5 wt% clay. Tensile and nanoindentation tests indicated that the elastic modulus and the hardness steadily increased by about 52 % and 67 %, respectively, with a clay concentration up to 5 wt%, while improvements in tensile strength were limited. Impact strength decreased linearly by about 25 % as the clay loading increased (up to 5 wt%), indicating an embrittlement due to clay addition, as evidenced by SEM observation on the fracture surfaces. The embrittling effect may be due to the weak interfacial adhesion between the clay platelets and the polymer matrix. Copyright © 2004 Society of Chemical Industry     

Mechanical,Thermal and Viscoelastic Behavior of Nylon 6/Clay Nanocomposites with Cotreated Montmorillonites

Nylon 6 nanocomposites were prepared using melt intercalation technique. Sodium montmorillonite (Na-MMT) was modified with octadecyl ammonium salt to evaluate the effect of clay modification on the performance of the nanocomposites. A comparative account with the nanocomposites prepared, using commercial clay cloisite 30B has been presented. X-ray diffraction (XRD) studies indicated an increase in the basal spacing of organically modified clays. Further, X-ray diffractograms of the nanocomposites displayed the absence of basal reflections suggesting the formation of an exfoliated structure. Transmission electron microscopy (TEM) investigations also confirmed exfoliation of clay galleries in the nanocomposites. Differential scanning calorimetry (DSC) measurements revealed both γ and α transitions in the matrix polymer as well as the nanocomposites. The crystallization temperature (T_c) exhibited a marginal increase in the C30B/Nylon 6 nanocomposites. Thermal stability of virgin Nylon 6 and the nanocomposites has been investigated using thermogravimetric analysis. Mechanical test revealed an increase in the tensile and flexural properties of Nylon 6 with the incorporation of nanoclays. Storage and loss modulus of virgin matrix increased with the incorporation of nanoclays. C30B/Nylon 6 nanocomposites exhibited optimum performance at 5% clay loading. Further, water absorption studies also confirmed comparatively lesser tendency of water uptake in these nanocomposites.     

Organoclay localization in polyamide 6/ethylene-butene copolymer grafted maleic anhydride blends: the effect of different types of organoclay

Localization of organoclays between two phases of polyamide 6 (PA6)/maleic anhydride grafted ethylene-butene copolymer (EB-g-MAH) blends, prepared via melt mixing, was investigated as a function of organoclay type. Cloisite 30B, Cloisite 20A and Cloisite 15A were used as different types of organoclay. The influence of different blend compositions and clay contents were also studied. Contact angle measurements have been applied to determine surface tension of components and then to calculate the wetting coefficient which is a useful parameter for prediction of the organoclay location. In general, all organoclays were found to locate in the more hydrophilic polyamide 6 phase. However, for Cloisite 20A and Cloisite 15A transmission electron microscopy (TEM) observations revealed some organoclay layers in the EB-g-MAH phase. Phase structure and nanocomposite morphology were evaluated using scanning and transmission electron microscopy and small angle X-ray scattering (SAXS). Results indicated the formation of an exfoliated or an intercalated morphology in different samples. Dynamic-mechanical thermal analysis and thermal gravimetric analysis were used as an experimental probe to confirm the location of nanoclays predicted via wetting coefficient. The shifting of glass transition temperature for PA6 phase confirmed that nanoclays are more distributed in this phase.     

The TiO2–Clay-LDPE Nanocomposite Packaging Films: Investigation on the Structure and Physicomechanical Properties

The role of nanoclays and TiO₂ nanoparticle loadings were investigated on low density polyethylene crystalline structure, in addition to studying packaging film properties such as barrier, thermal and mechanical properties. The polymer crystal study indicated for the orthorhombic crystal phase and about 20% lower degree of crystallinity for nanocomposites containing more than 2 wt.% TiO₂ nanoparticles. Based on the X-ray diffraction technique, the dispersion of nanoclays was improved to almost good degree of clay exfoliation with the company of 4 wt.% TiO₂ nanoparticles. In agreement with XRD results, the TEM morphological studies mainly suggest that TiO₂ has a helpful effect on nanoclay exfoliation. The increase in degradation temperature of nanocomposites may be attributed to the formation of inorganic char on polymer melt. The barrier properties of TiO₂/clay nanocomposite packaging films depend mainly on nanoclay loading with an unclear trend from TiO₂ nanoparticles. The increase in elastic modulus and the yield stress of nanocomposite films showed great effects on film mechanical properties by nanoclays.     

Preparation and properties of polyethylene-octene elastomer (POE)/organoclay nanocomposites

Polyethylene-octene elastomer/organoclay nanocomposites were prepared by a melt blending process. It was found that the addition of a small amount of glycidyl methacrylate and a peroxide during the melt mixing induced facile intercalation of the polymer chains into the organoclay and dispersion of the clay particles on the nanometer scale, which was confirmed by X-ray diffraction and transmission electron microscopy. Enhanced mechanical properties of the nanocomposites were observed from tensile, dynamic mechanical, and tear testing. Oscillatory shear-controlled rheology in the molten state of the nanocomposites revealed a pseudo solid-like behavior as well as an enhanced shear thinning behavior.     

Structure and rheology of twin liquid crystalline polymers

Addition of short mesogenic segments at the ends of flexible chains alters the mechanical properties by orders of magnitude. Twin liquid crystalline polymers (TLCPs) were synthesized from 4-[(4′-alkoxybenzoyl)oxy]-benzoyl chloride and ,ω-dihydroxy-telechelic polytetrahydrofuran (PTHF) of different molecular weights. With increasing temperature, four equilibrium states of these TLCPs, i.e. crystalline state, phase separated state with mesogenic domains in isotropic PTHF matrix, phase separated amorphous state, and single phase isotropic state, have been observed by dynamic mechanical measurements, differential scanning calorimetry and polarizing microscopy. In the phase separated state, mesogenic domains function as physical crosslinks which give rise to unusually high viscoelastic properties at small strains. Disturbing this state by large amplitude shear resulted in very pronounced shear thinning and slow recovery of structure. At increased temperature, the mesogenic domains become isotropic and their effect as physical crosslinks was significantly reduced, as shown by lower viscoelasticity and weak shear thinning. In the single phase isotropic state above the coexistence temperature T_s, the TLCPs behaved like a common homopolymer of low molecular weight. T_s decreased as the weight ratio of PTHF spacer increased in the experimental range (50–82% PTHF).