Morphological and structural characterization of polypropylene based nanocomposites

Nanocomposites based on isotactic polypropylene and montmorillonite were studied, investigating the polymorphism of the polymer, and examining the interaction between polypropylene and silicate. Wide angle X-ray diffraction (WAXD) was used to study the crystallization of the matrix, particularly the influence of additives and processing. Small angle X-ray scattering (SAXS) was employed to assess the lamellar morphology, estimating how silicate dispersion could affect this factor. Interaction between polymer and clay was quantified from WAXD and SAXS profiles; by the position and shape of the clay basal peaks, two different degrees of interaction were identified, characterized by a different affinity between the constituents. Observation of the samples' morphology by transmission electron microscopy (TEM) confirmed the results of X-ray diffraction methods. A fitting procedure was applied to SAXS profiles and the dimensions of the clay stratifications were estimated. These results were successfully compared with those drawn by application of Scherrer equation on (001) WAXD peaks.     

Using an organically-modified montmorillonite to compatibilize a biodegradable blend

Glycerol-plasticized cornstarch and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) blends were prepared by melt-extrusion at a constant 70:30 (mass/mass) ratio in the presence of a commercial organoclay. The effect of increasing the organoclay content on the morphology and physical properties of the blends was investigated soon after processing and after aging for 12 months. After processing, the materials were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and dynamic mechanical analysis (DMA). The results indicated that increasing clay mineral contents promoted significant improvements in the compatibility between the components. After aging, the samples were characterized by SEM, XRD and small-angle X-ray scattering (SAXS). Unexpectedly, the reduced size of the PHBV dispersed phase and the decreased crystallinity of both phases in the hybrids were maintained. XRD and SAXS results unambiguously proved the presence of both exfoliated layers and a small volume fraction of organoclay aggregates in the aged clay polymer nanocomposites.     

聚氧化乙烯/改性层状粘土纳米复合材料

本文通过使用熔融挤出的方法制备聚氧化乙烯(PEO)/改性层状粘土纳米复合材料,采用小角度X射线衍射仪(SAXS)和透射电镜(TEM)对其微观形态特征进行表征,同时使用动态力学性能分析仪(DMA)对其动态力学性能进行研究。     

The quantitative analysis of nano-clay dispersion in polymer nanocomposites by small angle X-ray scattering combined with electron microscopy

The main objective of this work is to propose a new approach for the quantitative analysis of the degree of dispersion of clay particles in the polymer matrix by small angle X-ray scattering (SAXS) combined with electron microscopy. Due to the low temperature processibility and good thermal stability, poly[(butylene succinate)-co-adipate] (PBSA) was chosen as a model polymer matrix for this study. The nanocomposites of PBSA with four different weight percentages of organically modified montmorillonite (OMMT) loadings were prepared via melt-blending method. The dispersed structure of the clay particles in the PBSA matrix was studied by SAXS. Results show that the clay particles are nicely dispersed in the case of all nanocomposites. However, with a systematic increase in clay loading, the dispersed clay structure of the nanocomposites changes from a highly delaminated to a flocculated and then to a stacked intercalated one. The probability of finding neighboring clay particles in the PBSA matrix as well as their thickness was calculated using the Generalized Indirect Fourier Transformation technique developed by Glatter and the modified Caillé theory proposed by Zhang. The morphology of the nanocomposites was also extensively studied by scanning transmission electron microscopy (STEM). In the case of all nanocomposites, SAXS results were in good agreement with STEM observations. Finally, a correlation between the predicted morphology of nanocomposites and their melt-state rheological properties is reported.     

Polylactide/clay nanocomposites: A fresh look into the in situ polymerization process

Polylactide nanocomposites with organo‐modified montmorillonite presenting a high degree of clay exfoliation were prepared via in situ polymerization by using an improved methodology. The morphology of the nanocomposites was studied by WAXD and SAXS. The size distribution of clay aggregates in the polylactide matrices was quantitatively determined by SAXS applying the stacked‐disk model. The analyses show high degree of delamination of the silicate yielding exfoliated polylactide nanocomposites even at high concentration of clay (>10 wt %). L ‐lactide conversions measured by ATR‐FTIR were determined to be no less than 94% after 3 h of reaction in all polymerizations. DSC measurements were performed to study the influence of the clay content on the thermal behavior of the prepared nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Manipulating the microstructure and rheology in polymer‐organoclay composites

A series of nanocomposites prepared by melt‐blending of cloisite‐based organoclays with poly(ethylene‐vinylacetate) (EVA) and neutralized poly (ethylene‐methacrylic acid) (EMA) copolymers were investigated via DSC, small‐angle X‐ray scattering (SAXS), and rheological techniques. SAXS results indicated partial clay exfoliation in all samples. In both EMA and EVA systems, the nominal melting temperature T_m and bulk crystallinity are not significantly affected by the presence of organoclays, suggesting that clay particles are predominantly confined in the amorphous phase. In rheological measurements (above T_m), the EVA‐clay system demonstrated a solid‐like rheological behavior under the small‐strain oscillatory shear, yet it was able to yield and flow under a steady shear, which is the characteristic of physical crosslinking. In contrast, the EMA‐clay system exhibited a melt‐like rheological behavior, where the influence of organoclay on the thermorheological behavior of the EMA composite was quite minimal. We propose that the carbonyl groups of vinylacetate in EVA interact with the clay surface, resulting in a strong physically crosslinking like interaction in the melt. On the other hand, the interaction between EMA and clay is weak because of repulsion between carboxyl anions and negatively charged clay surface.     

Characterization of nanoclay orientation in polymer nanocomposite film by small-angle X-ray scattering

The orientation distribution of layer-shaped nanoclays (e.g. organoclays and pristine clays) dispersed in a polymer matrix is an important parameter to control the properties of polymer nanocomposites. In this study, we demonstrate that the use of multi-directional 2-D small-angle X-ray scattering (SAXS) can quantitatively describe the orientation distribution of organoclays (e.g. Cloisite C20A) in melt-pressed nanocomposite films, containing ethylene-vinyl acetate (EVA) copolymers as polymer matrices. Different weight fractions of organoclays were used to alter the orientation profile of nanocomposite films, in which the dispersion and morphology of organoclays were also characterized by complementary 2-D and 3-D transmission electron microscopy (TEM). All nanocomposites exhibited mixed intercalation/exfoliation clay morphology, where the intercalated structure possessed partial orientation parallel to the in-plane direction of the film. The higher content of the clay loading showed a higher clay orientation. A simple analytical scheme for SAXS data analysis to determine the orientation parameter (P₂) was demonstrated, the results of which are in agreement with the gas permeation properties of the nanocomposite films.     

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.     

Novel clay treatment and preparation of Poly(ethylene terephthalate)/clay nanocomposite by In-situ polymerization

Summary Novel clay treatment was proposed for poly(ethylene terephthalate) (PET)/clay nanocomposite and the clay dispersed trimellitate ester oligomers were prepared by esterification with 1, 2, 4-Benzenetricarboxylic anhydride (TMA, trimellitic anhydride) and montmorillonite (MMT) dispersed ethylene glycol (EG). The structure, interlayer distance and thermal stability of the clay dispersed trimellitate ester oligomers were investigated by NMR, WAXD, SAXS and TGA techniques.     

Melt-compounded salt-containing poly(ethylene oxide)/clay nanocomposites for polymer electrolyte membranes

The present study demonstrates the use of a simple and versatile melt-compounding route to prepare NaClO₄-containing poly(ethylene oxide) PEO/clay nanocomposites combining excellent mechanical properties with a competitive level of the ionic conductivity. The nanostructure and the resulting thermal, mechanical and conductive properties of the salt-containing PEO/clay nanocomposites were found to be highly sensitive to the clay type, i.e. aspect ratio of the clay, to the presence of an organic modifier in the intergallery spacing, and to the salt concentration. The highest increase of the shear storage modulus is obtained in the presence of single silicate layers, thus an exfoliated nanostructure, having a high aspect ratio. These structures are only obtained with an (polar) organically modified clay (Cloisite 30B), regardless of the presence of salt. The use of non-organically modified clays (Cloisite Na⁺ and Laponite) resulted in intercalated nanocomposites, with only a minor improvement in stiffness. A strong interaction between the Na⁺ from NaClO₄ and the Cloisite 30B silicate layers might be responsible for an increased PEO crystallinity and resultant additional increase in stiffness. A mechanism is proposed whereby the Na⁺ ions are drawn away from the PEO phase, to be complexed by the silicate layers, or even ion-exchanged with modifier cations. The addition of clay did not greatly affect the ion conductivity below the melt temperature of PEO. At higher temperatures, the nanocomposites displayed only slightly lower conductivities compared to the PEO/NaClO₄ complex, due to the presence of the clay platelets.     

Improving the physical properties of PEA/PMMA blends by the uniform dispersion of clay platelets

Poly(ethyl acrylate) (PEA)/poly(methyl methacrylate) (PMMA) emulsion blends that were combined with unmodified montmorillionite (MMT) to improve the physical properties via nanocomposite formation. We prepared a cationic PEA/PMMA latex and used a heterocoagulation process to create a homogeneous dispersion of the clay platelets in the matrix. The cationic PEA/PMMA emulsion blends were prepared using a cationic initiator in the presence of free surfactant, cetyl trimethylammonium bromide (CTABr), followed by mixing with an aqueous slurry of MMT. The PEA/PMMA-MMT nanocomposites could be processed at low temperatures. Low temperature processing prevented the commonly observed discoloration associated with many thermoplastic nanocomposites. DSC, SAXS, TEM and AFM were used to study the dispersion of MMT and morphology of PEA/PMMA-MMT nanocomposites. Tensile stress, elongation at break and Young's modulus demonstrated a significant reinforcing effect of clay.     

Reaction kinetics and characteristics of polyurethane/clay nanocomposites

The reaction behavior and physical properties of polyurethane (PU)/clay nanocomposite systems were investigated. Organically modified clay was used as nanofillers to formulate the nanocomposites. Differential scanning calorimetry was used to study the reaction behavior of the PU/clay nanocomposite systems. The reaction rate of the nanocomposite systems increased with increasing clay content. The reaction kinetic parameters of proposed kinetic equations were determined by numerical methods. The glass transition temperatures of the PU/clay nanocomposite systems increased with increasing clay content. The thermal decomposition behavior of the PU/clay nanocomposites was measured by using thermogravimetric analysis. X‐ray diffractometer and transmission electronic microscope data showed the intercalation of PU resin between the silicate layers of the clay in the PU/clay nanocomposites. A universal testing machine was used to investigate the tensile properties of the PU/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1641–1647, 2005     

Effect of molecular structures on static and dynamic compression properties of clay and amphiphilic clay/carbon nanofibers used as fillers in UHMWPE/composites for high-energy-impact loading

Three different ultrahigh-molecular-weight polyethylene (UHMWPE)–clay nanocomposites (Muscovite, Cloisite 30B and amphiphilic clay/carbon nanofibers) were investigated with the nanocomposite nanomorphology studied before and after dynamic mechanical compressive tests at high strain rates. Their material structure and thermal properties were investigated using techniques such as step-scan differential scanning calorimetry, split Hopkinson pressure bar, synchrotron small angle X-ray scattering (SAXS), and dynamic mechanical analysis. Results were associated with morphological changes observed after deformation. chemical vapor deposition (CVD)-modified nanocomposite, due to the molecular bonding and the extra functional groups, is designed with crystalline structures with fewer defects and higher stability. The increase in particulate/polymer interactions observed for the CVD-modified material decreased the elongation in the quasi-static test. However, the dynamic mechanical behavior contradicted the quasi-static behavior because at very high strain rates there was not sufficient time for the interlamellar and intralamellar defect facilitated plastic flow and the material transitioned through the glassy state. The SAXS results show that deformation strongly induced changes in the UHMWPE and UHMWPE–clay nanocomposite morphology. SAXS indicates that CVD-modified samples became more compact and dense, thus corroborating the formation of additional secondary bonds between structures and/or the carbon nanofibers alignment. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47094.     

Investigation of the morphology of polypropylene − nanoclay nanocomposites

The morphology development in polypropylene ? nanoclay composites with different weight percentages of nanoclay additives was studied using a combination of wide‐angle X‐ray diffraction, small‐angle X‐ray scattering (SAXS), polarized optical microscopy and transmission electron microscopy. SAXS studies showed an increase in long period with increase in additive weight percentage. Thermal analysis showed that even if the clay platelets are not completely exfoliated they can act as effective nucleating agents. Studies indicated that the ultimate morphology formation is influenced by both the thermodynamics of mixing and crystallization and spherulite formation. During spherulite growth, unenclosed clay platelets were excluded at the spherulite boundaries. From the observed results, a schematic model of morphology formation in polypropylene ? nanoclay composites is proposed. © 2013 Society of Chemical Industry     

Morphological studies of polypropylene–nanoclay composites

Polypropylene–clay nanocomposites were prepared by a solution technique and a subsequent melt‐mixing process. A titanate coupling agent was used to improve the compatibility of the nanoclay particles with the polypropylene. The dispersion of the nanoclay particles in polypropylene was studied with X‐ray diffraction (XRD) and transmission electron microscopy (TEM). An increased d‐spacing value of the clay particles in the nanocomposites was observed, and it was compared with the values of as‐mined (pristine) and as‐received (organophilic) clay particles. The number of intercalated layers in a single clay crystallite was determined to be 4, and the number was confirmed with XRD data and TEM images. On the basis of the Daumas–Herold model (which is widely used for graphite intercalation compounds), the stage 2 and stage 3 structures of montmorillonite particles in polypropylene were recommended. A study on the stage structure suggested a way of determining the presence of polymer molecules in the clay galleries. The results confirmed the existence of single‐layered platelets with improved dispersion in polypropylene. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 218–226, 2005     

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     

Synergistic effect of dipentaerythritol and montmorillonite in EVOH‐based nanocomposites

To solve problems of stiffness of EVOH in film preparation, new formulations are investigated. First, dipentaerythritol (DPE) is blended with EVOH: it acts as plasticizer, decreases the EVOH crystallization temperature and allows the preparation of articles featuring enhanced flexibility and stretchability. However, beyond a certain loading (above 10 wt %) DPE can crystallize and segregate during cooling, causing further problems in EVOH processability due to material embrittlement. Then, a small amount of montmorillonite (MMT) is mixed in the EVOH/DPE system: it results that for specific compositions MMT inhibits the DPE crystallization. At the same time, DPE, thanks to its high polarity and affinity with both clay and polymeric matrix, improves the intercalation of the nanoclays, promoting the penetration of the polymer chains within the layers of the clay. The synergistic effects of DPE and MMT in EVOH matrix is confirmed by DSC, WAXD, SAXS and TEM analyses. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42265.     

Morphology, structure and properties of a poly(1-butene)/montmorillonite nanocomposite

A specifically formulated nanocomposite based on isotactic poly(1-butene) (PB) and montmorillonite was studied, by wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and polarized light optical microscopy, investigating the polymorphism of the polymer, and examining the interaction between PB and the silicate. Montmorillonite was found to disrupt the ordered morphology of the polymer, determining a dramatic increase in the rate of the II→I phase transition. Interaction between polymer and clay was studied by TEM and SAXS also under a quantitative point of view. A significant enhancement of physical-mechanical properties was observed, even though exfoliation did not occur, but just a slight intercalation and a reduction in the size of tactoids.     

Nonisothermal crystallization behavior of highly exfoliated polypropylene/clay nanocomposites prepared by in situ polymerization

Polypropylene/clay nanocomposites (PPCNs) were prepared via an in situ polymerization method with a Ziegler–Natta/clay compound catalyst in which the MgCl₂/TiCl₄ catalyst was embedded in the clay galleries. The wide‐angle X‐ray diffraction and transmission electron microscopy results showed that the clay particles were highly exfoliated in the polypropylene (PP) matrix. The nonisothermal crystallization kinetics of these PPCNs were investigated by differential scanning calorimetry at various cooling rates. The nucleation activity were calculated by Dobreva's method to demonstrate that the highly dispersed silicate layers acted as effective nucleating agents. The Avrami, Jeziorny, Ozawa, and Mo methods were used to describe the nonisothermal crystallization behavior of the PP and PPCNs. Various parameters of nonisothermal crystallization, such as the crystallization half‐time, crystallization rate constant, and the kinetic parameter F(t), reflected that the highly exfoliated silicate layers significantly accelerated the crystallization process because of its outstanding nucleation effect. The activation energy values of the PP and PPCNs determined by the Kissinger method increased with the addition of the nanosilicate layers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Isothermal crystallization of poly(ethylene‐co‐glycidyl methacrylate)/clay nanocomposites

Poly(ethylene‐co‐glycidyl methacrylate) (PEGMA)/clay nanocomposites with clay concentrations of 1, 3, or 5 wt % were prepared via y melt blending in a twin‐screw extruder. Wide‐angle X‐ray diffraction showed that the clay layers were intercalated by PEGMA. Differential scanning calorimetry was used to analyze the isothermal crystallization, and the equilibrium melting temperature was determined with the Hoffman–Weeks method. The Avrami, Tobin, Malkin, and Urbanovici–Segal models were applied to describe the kinetics of crystallization from the melt state under isothermal conditions. The crystallization kinetics showed that the addition of clay facilitated the crystallization of PEGMA, with the clay functioning as a heterophase nucleating agent; at higher concentrations, however, the physical hindrance of the clay layers to the motion of PEGMA chains retarded the crystallization process. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1051–1064, 2005