Organo-modified Clay Research Articles

Nanosize and microsize clay effects on the kinetics of the thermal degradation of polylactides

Polylactide (PLA)–montmorillonite (MMT) micro- and nanocomposites based on semicrystalline and amorphous polymers and unmodified or organomodified clays at 5 wt% content were produced by melt mixing. Based on the three different test methods that were used to follow thermal degradation, different conclusions were obtained. During melt processing, thermomechanical degradation was more pronounced in the presence of all fillers, which apparently acted catalytically, but to different degrees. During isothermal degradation in air from 180 °C to 200 °C, degradation rate constants were calculated from novel equations incorporating changes in intrinsic viscosity (IV). Results show that the thermal degradation rate constants of the amorphous PLA and its composites are lower than those of the semicrystalline PLA and its composites. Due to better filler dispersion in the polymer matrix, the thermal degradation rate constants of the nanocomposites are significantly lower than those of the unfilled polymers and their microcomposites under air. As per dynamic TGA data and thermal kinetic analysis from weight losses and activation energy calculations, organomodified nanofillers have a complex effect on the polymer thermal stability; the unmodified fillers, however, reduce polymer thermal stability. These TGA data and kinetic analysis results also support the findings that the thermal stability of the amorphous PLA and its composites is higher than that of the semicrystalline polymer and its composites and the thermal stability of the nanocomposites is higher than that of the microcomposites. In general, mathematical modeling based on random thermal scission equations was satisfactory for fitting the TGA experimental data.

Long‐lived layered silicates‐immobilized 2,6‐bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modification

AbstractHeterogeneous‐layered silicate‐immobilized 2,6‐bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium‐ and organomodified‐layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified‐methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life‐time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548–564, 2009

Thermal Stability of Polypropylene/Organo-Clay Nanocomposites Produced in a Single-Step Mixing Procedure

Thermal stability of polymer nanocomposites prepared by melt mixing of polypropylene (PP) with organo-modified clay (Cloisite C93A) and maleic anhydride grafted polypropylene (PP-g-MA) used as compatibilizer, has been studied. Thermogravimetric analysis (TGA/DTG) results showed improved thermal stability of PP in the presence of organo-clay in oxygen atmosphere. Significant prolongation of oxidation induction time (measured at 200°C) for nanocomposite, in the presence of even 1% organo-modified clay has been found.

Comparative analysis of nanocomposites based on polypropylene and different montmorillonites

Nanocomposites of polypropylene (PP) were prepared by melt mixing using maleic anhydride modified polypropylene (PPg) and different organophilic montmorillonites (OMMT). The selected organo-modified clays differ in their initial particle size, amount and type of surfactant and/or their cation-exchange capacity. All composites have 80, 15 and 5 wt% of PP, PPg and OMMT, respectively. The materials were characterized using TGA, XRD, SEM and rotational rheometry. Cloisite 15A, Cloisite 93A, Nanomer I44 and a bentonite modified with octadecylammonium (B18) display intercalation and exfoliation after mixing and annealing and produce nanocomposites with different degrees of ‘solid-like’ rheological behavior. The composites based in Cloisite 15A and Nanomer I44, which use the same intercalant, show very similar phase structure and rheological response, regardless of the origin and initial characteristics of the clays. These nanocomposites are the most affected by the thermal history during rheological characterization in the molten state. On the other hand, Cloisite 10A and Cloisite 30B display collapse of the silicate layers after compounding with no evidence of exfoliation.

Study of Interlayer Spacing Collapse During Polymer/Clay Nanocomposite Melt Intercalation

The influence of the chemical structure of alkylammonium organo-modifying montmorillonite clays on the ability to form nanocomposites by melt blending, depending on the processing temperature and the organoclay thermal treatment, has been investigated. On one side chlorinated polyethylene/Cloisite 30B (nano)composite has been prepared by melt intercalation at 175 degrees C and its wide angle X-ray diffraction pattern revealed that the peak characteristic of the interlayer spacing of the organoclay was shifted to lower d-spacing, indicating a collapse of the organoclay structure. On the other side, (nano)composites based on ethylene-vinyl acetate copolymer/Cloisite 30B have been prepared by melt intercalation at 140 degrees C. At this temperature, exfoliation was observed with the as-received organoclay while the same organo-modified clay, simply dried at 180 degrees C for 2 hours, induced again the formation of a composite with a collapsed structure. The effect of the Cloisite 30B thermal treatment on the morphology and mechanical properties of ethylene-vinyl acetate-based (nano)composites was investigated using wide angle X-ray diffraction and tensile tests. In order to shed some light on the origin of this clay interlayer collapse, organoclay modified with various ammonium cations bearing long alkyl chains with different amounts of unsaturations were studied using wide angle X-ray diffraction and X-ray photoelectron spectroscopy before and after thermal treatment at 180 degrees C for 2 hours. Isothermal thermogravimetric analysis of all organoclays was also investigated. The layers collapse effect is discussed depending upon the level of unsatured hydrocarbon present in the organic surfactant.

New Approach to Elaborate Exfoliated Starch-Based Nanobiocomposites

The present paper reports the successful elaboration of exfoliated plasticized starch-based nanobiocomposites. This was made possible by using cationic starch as a new clay organomodifier to better match the polarity of the matrix and thus to facilitate the clay exfoliation process. To demonstrate the efficiency of this new approach, either natural (MMT-Na) or organomodified (OMMT-CS) montmorillonite were incorporated into the starch nanobiocomposites by a melt blending process. The morphological analyses (SAXD and TEM) showed that MMT-Na leads to the formation of intercalated nanobiocomposites. On the contrary, OMMT-CS allowed the elaboration of well-exfoliated nanobiocomposites. Tensile tests performed on the obtained nanobiocomposites showed that exfoliated nanobiocomposites display enhanced mechanical properties compared to those of the intercalated nanobiocomposites and neat matrix. These results clearly highlight the great interest in using OMMT-CS to obtain starch-based nanobiocomposites with improved properties.

Poly(m-xylene adipamide)-montmorillonite nanocomposites: effect of organo-modifier structure on free volume and oxygen barrier properties

It was shown that nanoparticle–polymer interactions that affect the free volume and oxygen barrier properties of poly(m-xylene adipamide)/clay nanocomposites can be tailored by the choice of organic modifier of montmorillonite clay. Three different organo-modified clay compounds based on montmorillonite (Cloisite 30B, 10A and 93A) were dispersed in the resin poly(m-xylene adipamide) at loading levels of 2 wt% clay. Samples were melt compounded and extruded using a laboratory scale twin screw micro compounder. Positron annihilation lifetime spectroscopy (PALS) was used to examine the free volume of the polymer nanocomposites. PALS results suggested that the Cloisite 10A additive should give the higher reduction in gas permeability as it results in the lowest free volume for the nylon resin when compared to all of the clay additives examined. Oxygen transmission rates (OTR) were measured on nanocomposite films and the Cloisite 10A additive was found to give the best oxygen barrier, showing a reduction of OTR of 66% compared to the neat resin. In all cases examined, PALS free volume data was found to have excellent correlation to the measured oxygen transmission rates. The addition of Cloisite 10A resulted in the highest crystallinity and an increase in glass transition temperature when compared to the neat resin. Results indicate that the improved barrier properties of the clay compounds is primarily due to an increase in the degree of crystallinity of the polymer, with the nanoparticles being more effective nucleating agents when favourable nanoparticle–polymer interactions are present.

Poly(ethylene terephthalate) clay nanocomposites: Improved dispersion based on an aqueous ionomer

Poly(ethylene terephthalate) (PET) clay nanocomposites were synthesized using two different types of organo-modified clay: Cloisite 10A (a montmorillonite) and Somasif MEE (a synthetic fluoromica). In addition to these organo-modified clays, a nanocomposite using the unmodified clay, Somasif ME100, was also prepared. The facile method of preparation involved the dispersion of the clays in water together with an aqueous dispersion of an ionomer having a high level of compatibility with PET. After the removal of water, nanocomposite samples were prepared by a melt compounding route. Ionic interactions of the ionomer with the clay facilitated a high degree of exfoliation of the clay platelets in the PET matrix. Samples were characterized by TEM, XRD, melt rheology and TGA-MS. TEM analysis showed differences in the degree of clay platelet orientation and exfoliation between Cloisite 10A and the Somasif clays, with the Somasif MEE and ME100 clay additives giving a more ordered and exfoliated morphology. Melt rheology results were consistent with TEM observations with the more exfoliated samples giving higher viscosities. TGA-MS revealed that the Somasif ME100 sample showed a high level of thermal stability, while the organo-modified clay additives exhibited some thermal degradation at the PET processing temperatures.

Effect of swelling agent on the physical properties of PET–clay nanocomposite materials prepared from melt intercalation approach

A series of poly(ethylene terephathalate) (PET)/organo-modified clay nanocomposites were successfully prepared by melt intercalation through the twin-roller mixer. Two kinds of swelling agents are used as organo-modifiers of the pristine clay. Wide-angle X-ray diffraction (WAXRD) and transmission electron microscopy (TEM) were employed to study the morphology of the PET–clay nanocomposites. The quaternary alkylphosphonium salt (4-carboxybutyl) triphenylphosphonium bromide ( Φ 3P +-C 4)-modified clay was found to show better dispersion capability than that of quaternary alkylammonium salt hexadecyltrimethyl ammonium bromide (Me 3N +-C 16)-modified clay that existed in the polymer matrix. The thermo-mechanical properties were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analyzer (DMA). The optical clarity was examined by UV–visible transmission spectra. The better dispersion of ( Φ 3P +-C 4)-modified clay in PET leads to excellent improvement of physical properties such as optical clarity, thermal stability and mechanical strength of the PET–polymers than that of using (Me 3N +-C 16)-modified clay.

Thermal, Morphological and Dynamic Mechanical Characterization of Melt Blended PC Nanocomposites

Polycarbonate (PC) nanocomposites were prepared by melt intercalation technique in an intermeshing co-rotating twin-screw extruder. Both unmodified (Na+MMT) and organo-modified (Cloisite 10A & OMMT) clays were used for the preparation of nanocomposites. The effect of addition of clays on the morphological and dynamic mechanical properties of PC matrix has been studied. The wide angle X-ray (WAXD) studies reveal a dominated exfoliated morphology of the nanocomposites at a clay content of 5%. The intercalated morphology is predominated upto clay content of 3%. Transmission electron microscopy (TEM) demonstrated the co-existance of intercalated/exfoliated morphology in all the composites. Dynamic mechanical analysis (DMA) shows an increase in storage modulus indicating higher stiffness in case of organomodified clay filled composites as compared to unmodified & virgin matrix.

Polymer nanocomposites with layered silicates

The topics of current research in the field of polymer nanocomposites with layered silicates are addressed. The factors influencing the efficiency of the clay exfoliation in a polymer during melt processing are summarized, namely type of a machine used, mixing conditions and molecular characteristics of polymers utilized, including that of polymeric compatibilizers. New methods leading to the clay exfoliation in a polymer matrix are described. Application of exfoliation promoter allows to eliminate the necessity to compatibilize organo-modified clay with hydrophobic polymer matrix. Shear induced crystallization of polyolefin based nanocomposites is also addressed; even weak shearing induces alignment of clay platelets, results in polymer chains orientation and enhances the nucleation of crystallization.

Fabrication of pre-exfoliated clay masterbatch via exfoliation-adsorption of polystyrene nanobeads

The approach studied in the present work produced an exfoliated state of clay layers via confinement of the charged nano-sized polystyrene (PS) beads within the gallery of swollen pristine clay. It was demonstrated that adsorption of the polymer nanobeads dramatically promotes expansion of the clay gallery. A comparative study of incorporation was conducted by employing organo-modified clay along with two different colloid polymer systems: electrostatically stabilized PS nanobeads and cationic monomer-grafted PS nanobeads. The mechanism of adsorption of the monomer-grafted polymer beads onto clay via cationic exchange between the alkyl ammonium group of the polymer nanobeads and the interlayer sodium cation of the layered silicate was verified by using several techniques. As distinct from the polymer nanobeads formed using conventional miniemulsion polymerization method, competitive adsorption of stabilizing surfactant molecules was be prevented by grafting the surface functional groups into the polymer chain, thereby supporting the observed effective adsorption of the polymer beads. The presence of surface functional groups that support the establishment of strong polymer-clay interactions was suggested to improve the compatibility of the clay with the polymer matrix and eventually play a crucial role in the performance of the final nanocomposites.

Tensile mechanical response of polyethylene – clay nanocomposites

In this work we report on the microstructural and the mechanical characteristics of high density polyethylene (HDPE)-clay nanocomposites, with particular attention to the creep behaviour. The samples were prepared through melt compounding, using two high-density polyethylenes with different melt flow rate (MFR), two different organo-modified clays, and changing the relative amount of a polyethylene grafted with maleic anhydride (PEgMA) compatibilizer. The intercalation process is more effective as the matrix melt viscosity decreases (higher MFR), while the clay interlamellar spacing increases as the compatibilizer amount increases. The relative stiffness of the nanocomposites increases with the addition of clay, with a limited enhancement of the relative yield stress. The better intercalation obtained by the addition of the compatibilizer is not accompanied by a concurrent improvement of the tensile mechanical properties. The creep resist- ance is enhanced by the introduction of clay, with an appreciable dependence on both the polyethylene and the clay type.

Preparation and Properties of New in-situ Acrylic Copolymer/Terpolymer- Clay Hybrid Nanocomposites

Abstract Acrylic copolymer- and 5% acrylic acid (AA) modified terpolymer-hybrids with unmodified montomorilonite clay (Cloisite Na) and organo-modified clay (Cloisite 10A) were synthesized by in-situ free radical bulk polymerization. Hybrid nanocomposites were investigated by Atomic Force Microscopy (AFM), X-ray diffraction (XRD) technique, thermogravimetric analysis (TGA), dynamic mechanical and mechanical properties. XRD results suggested polymer intercalation in both unmodified and organo-modified clay in the copolymer and terpolymer hybrids. AFM analysis further confirmed these results. Cloisite 10A hybrids and the terpolymeric nanocomposites demonstrated superior mechanical and dynamic mechanical properties. Terpolymer-clay hybrids with 9 wt% Cloisite 10A also showed higher thermal stability. The possible reasons for improvement of mechanical properties and thermal stability were discussed with reference to the structure and interaction.

Essential work of fracture and failure mechanisms of polypropylene–clay nanocomposites

The fracture behavior of polymer nanocomposites (PNCs) based on a polypropylene with organo-modified clays (2 wt.%) and different coupling agents was studied by means of essential work of fracture (EWF). The PNC microstructure was characterized by clay particle dispersion at the micron scale (>1 μm) and sub-micron scale (200 nm to 1 μm), with good intercalation and partial exfoliation (<100 nm). Tensile testing showed significant improvements (+25–50%) corresponding to nanoparticle reinforcement effects. Fracture surfaces revealed that fracture occurred by void initiation at larger clay particles, followed by void growth and coalescence as the surrounding matrix stretched into ligaments. EWF improvements (+20%) were noted for PNCs that had fewer micron scale particles and showed higher tensile improvements. Toughness improvements were attributed to higher voiding stresses and improved matrix resistance attributed to finer, more oriented clay nanoparticles.

Tribological behaviour of clay – thermoset polyester nanocomposites

Clay – thermoset polyester nanocomposites and conventional clay filled composites are produced using organo-modified clay as the reinforcement and unmodified inorganic clay as filler, respectively. Composites are prepared with clay contents of 1 wt.%, 3 wt.% and 5 wt.%. Tribological property of the nanocomposite system is studied to assess the influence of nanoclay and compared with conventional clay filled composites. The wear test is carried out on a pin-on-disc tribometer with the composite pin sliding over a disc made of tool steel. The coefficient of friction and wear loss decreases significantly on addition of organoclay, whereas for conventional clay filled composites wear loss and coefficient of friction increases with increase in inorganic clay content. The nanocomposites exhibit a maximum of 85% improvement in wear resistance and 35% decrease in coefficient of friction. The highest wear resistant and least coefficient of friction is observed in the nanocomposite with a clay content of 3 wt.%.

Reinforcing Effect of Organo-modified Layered Silicates in High-Density Polyethylene

This study focuses on the understanding of the reinforcing effect given by organo-modified layered silicates to a high-density polyethylene and the influence on the crystallization properties of this polymer. The addition of organo-modified clay to high-density polyethylene resulted in an evident increase in the tensile and flexural Young's modulus of the material with respect to unfilled polymer. The morphology, crystallinity, and thermo-oxidative stability of such nanocomposites were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and oxidation induction time test. The materials obtained show tactoid as well as intercalated and exfoliated structures with different dominant states depending on the loading level and process conditions. It was observed that organic ions not only change mixing behavior but also influence material properties, including the degree of crystallinity and the stability to the thermo-oxidative phenomena.

Clay intercalation and influence on crystallinity of EVA-based clay nanocomposites

Various polymer clay nanocomposites (PCNs) were prepared from ethylene vinyl acetate copolymer (EVA) with 9, 18 and 28% vinyl acetate (VA) content filled with different wt.% (2.5, 5 and 7.5) of a Montmorillonite-based organo-modified clay (Cloisite ® C15A and C30B). The PCNs were prepared using melt blending techniques. Morphological information regarding intercalation and exfoliation were determined by using wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). WAXS and TEM confirmed that increasing the VA content was necessary to achieve greater clay–polymer interaction as seen from the comparatively higher intercalation of clay platelets with 28% VA. The effect of addition of clay on the development and the modification of crystalline morphology in EVA matrix was also studied using WAXS and temperature-modulated differential scanning calorimetry (MDSC). Results are presented showing that the addition of clay platelets does not increase the matrix crystallinity but the morphology was significantly modified such that there was an increase in the ‘rigid’ amorphous phase. Mechanical properties were also evaluated against the respective morphological information for each specimen and there are indications that the level of clay–polymer interaction plays a significant role in such morphological modification, and in such a way that affects the final PCN mechanical properties which has wide and significant applications in the packaging industries.

Morphology, thermal, and viscoelastic properties of poly(glycidyl methacrylate- co-methyl methacrylate)-based nanocomposites with various organo-modified clays

New nanocomposites of poly(glycidyl methacrylate- co-methyl methacrylate) (PGM) cured with cyclohexanedicarboxylic anhydride (CDCA) and layered silicates of inorganic content 3 and 5 wt% were prepared by casting the solution of the mixture and subsequent cross-linking at finally 200 °C. Non-modified montmorillonite (MMT) and organo-MMTs (ODA-M, ALA-M, LEA-M, and HBP-M) modified with octadecylamine, 12-aminolauric acid, N-lauryldiethanolamine, and hexadecyltributylphosphonium bromide, respectively, were used as layered silicates. X-ray diffraction and morphological studies using transmission electron microscopy revealed that the highly intercalated nanocomposites with the interlayer spacing more than 5.5 nm are formed for the PGM–CDCA/ODA-M, LEA-M, and HBP-M composites with inorganic content 3 wt%. When the inorganic content was increased from 3 to 5 wt%, the degree of intercalation of all the PGM–CDCA/organoclay composites was lowered. Dynamic viscoelastic measurement revealed that the organoclay nanocomposites have significantly higher storage modulus than the PGM–CDCA neat resin. The thermogravimetric analysis revealed that the HBP-M composite with inorganic content 5 wt% has the highest thermal decomposition temperature.

Novel Thermosetting Resins Based on 4-(N-Maleimido)phenylglycidylether, 4

Summary: A series of polymer-clay nanocomposites were prepared by the simultaneous in situ curing of 4-(N-maleimido)phenylglycidylether/4,4-diaminodiphenylmethane (MPGE/DDM) with the intercalation/exfoliation of various organo-modified clays. The dispersion of the clays in the polymer matrix was produced by partial exfoliation and intercalation, as observed with X-ray diffraction and transmission electronic microscopy. Clay modified with a carboxylic acid-containing modifier showed enhancements with repesect to clay delamination in nanocomposite preparation. In comparison with the pristine resin, MPGE/DDM-clay nanocomposites showed improved glass transition temperatures, thermal stability and flame retardance. Preparation and characterization of polymer-clay nanocomposites based on a new maleimide-epoxy hybrid monomer.