Organo-modified Layered Silicates Research Articles

Characterization of Optimized Ternary PLA/PHB/Organoclay Composites Processed through Fused Filament Fabrication and Injection Molding.

The aim of this study was to investigate the structure–properties relationship of ternary blends of polylactide/polyhydroxybutyrate (PLA/PHB)/organo-modified layered silicate (OMLS). Morphological, thermal, rheological, and mechanical characterizations were performed to understand the influence of OMLS on PLA/PHB (70/30 wt%) formulations optimized through modifications with an epoxy-based chain extender, the use of a plasticizer, as well as the influence of the type of processing route: injection molding or fused filament fabrication. The addition of OMLS allowed the blend compatibility to be improved, with the appearance of a single melting peak on DSC thermograms at 146 °C, as well as the reduction in the size of the nodules for the injected molded specimens. Concerning the printed samples, AFM analysis revealed a coalescence of the PHB minor phase due to its degradation. This phenomenon was dramatically enhanced in the presence of OMLS and has been ascribed to the degradation of both the organo-modifier and the PHB minor phase in the blend. Rheological and mechanical tests (17% decrease in Young’s modulus and 13% decrease in elongation at break) confirmed this degradation that would have occurred during the manufacturing of the filaments and the printing of specimens due to additional thermal and cooling steps.

Use of Linear Viscoelastic Functions to Estimate the Aging Resistance and Internal Structure of Bituminous Binders

Rheology is the most widely used technique to evaluate the performance and aging of bituminous binders. Since there are many available rheological tests, there is also a wide range of aging indexes and it is not easy to choose the most appropriate one, because a single value may hardly be adequate for different properties or operating conditions. In order to generalize the usefulness of an index, a good starting point is deriving it from a set of data, such as the master curves of linear viscoelastic functions. Then, the problem is the quantification of aging in a single numerical value from continuous curves, covering a wide range of frequencies/temperatures. In this work, a summary of the aging indexes derived from the master curves is reported and discussed. The indexes are applied to a bituminous binder either with or without the addition of an organo-modified layered silicate. The apparent molecular weight distributions and relaxation spectra were also calculated from the master curves and used to characterize the effect of aging on the binder properties and structure. In this way, an interesting parallelism was observed between the SARA fractions and the populations derived from a deconvolution analysis of the apparent molecular weight distributions.

Nanoreinforcement mechanism of organomodified layered silicates in EPDM/CIIR blends: experimental analysis and theoretical perspectives of static mechanical and viscoelastic behavior

ABSTRACT Ethylene propylene diene (EPDM)–chlorobutyl rubber (CIIR) blends can withstand both radiation and hydrocarbon environments and are used for elastomeric components in nuclear plants. This work investigates the influence of organomodified layered silicates (OMLS) on the mechanical and viscoelastic properties of EPDM–CIIR blends. The morphology and physicochemical interactions are evaluated by X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy and correlated with the enhancement in mechanical properties. Mooney–Rivlin plots provided insight into the nonlinear mechanical behavior of EPDM–CIIR nanocomposites. From a dynamic mechanical analysis (DMA), it was found that blends with 5 phr OMLS content had the maximum storage modulus. Significant lowering as well as broadening of tanδ peak was observed for blends with well-dispersed OMLS (5 phr). The entanglement density and constrained volume near the interfaces, calculated from the DMA data, gave an insight to the reinforcing mechanism. Rheological characteristics of the nanoreinforced blends also revealed the stiffening effect of OMLS. Payne effect and stress relaxation studies confirmed good rubber–OMLS interactions. The applicability of various analytical models to predict the static and dynamic modulus as well as the Payne effect is explored.

XLPE – layered silicate nanocomposites for high voltage insulation applications: dielectric characteristics, treeing behaviour and mechanical properties

The study presented here investigates the performance of nano-reinforced cross-linked polyethylene (XLPE) for high-voltage insulation applications with particular focus on dielectric characteristics, treeing behaviour and mechanical properties. The nanocomposites with varying content of organo-modified layered silicate (nanoclay) were prepared by melt mixing of polyethylene, cross-linking agent and nanoclay. X-ray diffraction and atomic force microscopy studies showed that layered silicates were uniformly dispersed with exfoliation in XLPE matrix up to 5 wt% nanoclay content with formation of intercalated structures with slight agglomeration at higher nanofiller content. The dielectric loss, relative permittivity and dielectric strength of the nanocomposites increased with increasing nanoclay content, which was attributed to the inherent properties of XLPE and nanoclay, nanofiller dispersion and interfacial polarisation. The effect of frequency on the dielectric properties was also investigated. Incorporation of nanoclay in XLPE altered the electric field stress distribution in the material and consequently retarded water tree growth. The electric field distribution and the probability of water tree growth were studied by finite element method. Additionally, mechanical properties of the nanocomposite viz. tensile strength and modulus were also enhanced. The changes in the properties were correlated to the morphology of the nanocomposites, as well as polymer filler interactions.

Organo-modified layered silicate nanocomposites of EPDM–chlorobutyl rubber blends for enhanced performance in γ radiation and hydrocarbon environment

In this work, blends of ethylene propylene diene monomer rubber and chlorobutyl rubber were reinforced with organo-modified layered silicate (nanoclay) to enhance their performance in radiation as well as hydrocarbons environments. The mechanical properties of the nanocomposites increased (up to 57%) and solvent transport coefficients decreased (by 30%) with increasing nanoclay content. The enhancement in properties was attributed to the dispersion of nanoclay platelets in the ethylene propylene diene monomer–chlorobutyl rubber blends and the chemical interaction between nanoclay and the polymer which were confirmed by morphological and spectroscopic analysis, respectively. The effect of nanofiller content on the mechanical properties, solvent uptake and thermal degradation of blends exposed to gamma radiation was investigated by irradiating the nanocomposites with gamma rays for cumulative doses of 0.5, 1 and 2 MGy. The ethylene propylene diene monomer–chlorobutyl rubber nanocomposites with 5 phr nanoclay had the best retention of mechanical properties and solvent sorption coefficients on exposure to radiation. Depending on the dose of cumulative radiation exposure, chain scission and/or crosslinking occurred in the nanocomposites, resulting in varying degrees of changes in properties.

Recent advances in production of poly(lactic acid) (PLA) nanocomposites: a versatile method to tune crystallization properties of PLA

A new approach leading to poly(lactic acid) (PLA) nanocomposites designed with improved nucleating/crystallization ability has been developed. As proof of concept, nanofillers of different morphology (organo-modified layered silicates, halloysite nanotubes and silica) were surface-treated with ethylene bis-stearamide (EBS), a selected fatty amide able to promote chain mobility during PLA crystallization from the melt and nucleation. The fine dispersion of the nucleating additive via nanoparticles (NPs) as ‘nano-template’ is leading to nanocomposites showing unexpected improvements in PLA crystallization rate. This was evidenced by differential scanning calorimetry (DSC) from the high values of the degree of crystallinity (20–40%) with respect to neat PLA (4.3%) and the sharp decrease in crystallization half-time under isothermal conditions (at 110°C), even below one minute. Furthermore, after injection molding the outstanding crystallization properties of PLA were again confirmed. Accordingly, the PLA-nanofiller/EBS nanocomposites revealed remarkable degree of crystallinity (in the range of 30–40%). Surprisingly, the presence of EBS can significantly increase the impact resistance of PLA and PLA based nanocomposites. By considering the remarkable increasing in crystallinity, a key parameter to allow PLA utilization in durable applications, the development of the new approach is expected to lead to significant improvements in the processing and performances of PLA products.

Incorporation of Organomodified Layered Silicates and Silica in Thermoplastic Elastomers in Order to Improve Tear Strength

Organomodified layered silicates and silicas have been incorporated in thermoplastic elastomers such as styrene-ethylene-butylene-styrene copolymers (SEBS) and polyurethanes (PU) in order to improve mechanical properties - especially tear strength. The organically modified layered silicates used were Cloisite® 30B, a montmorillonite modified with a ternary ammonium salt with hydroxyls as end groups and Nanofil®2 which is organically modified by long chains of hydrocarbon and benzyl groups. Sepiolite, a natural clay with fibrous morphology was also used. The silicas incorporated are Aerosil 300, hydrophilic fumed silica and Aerosil R202, hydrophobic fumed silica. nanoparticles are incorporated between 1 and 5 weight percent. A compatibilizer SEBS grafted with maleic anhydride has been incorporated in some of the formulations for a better dispersion of some of the nanoparticles. Different ways of incorporation have been investigated. For SEBS formulations, melt blends of SEBS pellets and clays have been prepared with an internal mixer and then films have been casted. For polyurethanes, solvent blending of polyols and clays were carried out in a vessel and then, compression molding of the blend with diisocyanates was made to synthesize polyurethanes. Materials have been compared on the basis of normalized tear test and sequenced tensile test. Mechanical parameters, as stabilization ratio (Mullins effect) and viscoelastic ratio, have been defined by integration of the stress-strain curves obtained. An interesting improvement of tear strength was observed for modified materials.

Detailed analysis of dynamic mechanical properties of TPU nanocomposite: The role of the interfaces

Organo-modified layered silicates (OMLSs) can largely improve mechanical properties of Thermoplastic polyurethanes (TPUs) as well as affect their microdomain morphology. Nanocomposite TPU containing OMLSs were prepared by melt blending at different concentrations. The addition of OMLS has both induced variation in enthalpy of melting of hard and soft phases, and influenced the glass transition temperature of soft domains, as result of the microdomain phase segregation measured by means of fourier transform infrared spectroscopy (FT-IR). Small angle X-ray scattering (SAXS) analysis has shown that the mean distance between hard domains was mostly unaffected by the filler. However, its distribution broadened with the increasing concentration of the OMLSs, resulting in increased extent of the hard domain interface. The storage modulus of TPU nanocomposites incremented with the silicate content, while the dynamic strain scan tests showed pronounced non linear viscoelastic behavior. The analysis of morphological data obtained by SAXS and FT-IR measurements were correlated to thermal and dynamic mechanical properties of TPU samples suggesting a crucial role of the soft domains interface. The storage modulus and loss tangent of TPU nanocomposites were found to increase with the increasing of the interface area of soft domains with both hard domains and OMLS stacks.

Effect of Organo-modified Layered Silicates on the Properties of Poly(Methyl Methacrylate) Nanocomposites

Poly(methyl methacrylate) (PMMA)/layered silicate nanocomposites were prepared using melt intercalation technique. Commercially modified nanoclays such as Cloisite 30B (C30B), Cloisite 20A (C20A), and Bentone 109 (B109) have been used as organoclays for the preparation of nanocomposites. PMMA matrix has been grafted with maleic anhydride to modify the interfacial region and improve the interfacial adhesion between organoclays and PMMA matrix. Mechanical tests revealed an increase in the tensile modulus of PMMA/C30B (5%) nanocomposite to about 35% as compared to virgin PMMA matrix. Thermal measurements employing differential scanning calorimetry and thermogravimetric analysis also showed improved thermal stability and marginal increase in Tg of PMMA matrix with the incorporation of nanoclays. Wide angle X-ray diffractograms revealed an increase in d-spacing of C30B nanoclay from 18.5 to 39.4 Å in PMMA/C30B nanocomposites, thus confirming intercalated structure. The dispersion characteristics of organoclay within PMMA matrix was also investigated using transmission electron microscopy. Furthermore, dynamic mechanical analysis shows a substantial increase in storage modulus of PMMA matrix with the incorporation of organoclays. Additionally, an improved fire retardancy of PMMA was also observed in PMMA/B109 (5 wt%) nanocomposites with an evidence of reduced horizontal rate of burning.

New trends in polylactide (PLA)-based materials: “Green” PLA–Calcium sulfate (nano)composites tailored with flame retardant properties

Starting from gypsum, a by-product of lactic acid fabrication process, novel “green” composites have been produced by melt-blending polylactide (PLA) and this filler after a previous specific dehydration to obtain anhydrite II (AII). Such a material is potentially interesting in biodegradable/rigid packaging and in technical applications requiring rigidity, heat resistance and dimensional stability. In order to obtain PLA–AII composites characterized by specific end-use flame retardant properties, the addition of selected organo-modified layered silicates (OMLS) was considered. Co-addition of AII and OMLS leads to PLA (nano)composites characterized by good (nano)filler dispersion, thermal stability and adequate mechanical resistance. The flame retardant properties as shown by cone calorimetry showed significant increase in the ignition time compared to neat PLA and a substantial decrease, i.e., ca. 40%, of the maximum rate of heat release, whereas the UL94 HB test was successfully passed revealing non-dripping effect and extensive char formation. The study represents a new approach in formulating novel PLA grades with improved characteristic features.

Characterization of PET Nanocomposites with Different Nanofillers

This study investigates the influence of various nanofillers of different shapes and sizes on the properties of PET nanocomposites. PET was reinforced with 0.3 wt.% of different nanoreinforcements, namely: (i) 1D platelet-like shape of organo-modified layered silicates (montmorillonite) (platelet size approx. 1 x 200 nm) with average agglomerate size of: (a) 30 μm and (b) 8 μm; (ii) 3D spherical shape particles of titanium oxide with an average size of 21 nm and (iii) 3D spherical shape silica with an average particle size of 12 nm. PET nanocomposites were prepared by melt blending in an asymmetric batch minimixer followed by compression moulding process. The effect of nanofillers upon thermal, mechanical and structural properties in comparison to the neat PET are discussed.

Understanding the effect of nano-modifier addition upon the properties of fibre reinforced laminates

This work presents a survey of the effect of three different commercially available nano-modifiers on the mechanical properties of an epoxy/anhydride unidirectional carbon fibre reinforced laminates. The nano-modifiers consisted of an organo-modified layered silicate, vapour grown carbon fibre (VGCF) and a triblock copolymer (SBM). The work has shown that tensile modulus exhibited little difference between the unmodified laminates while a modest decrease was observed for the tensile strength. Properties related to the toughness of the matrix, demonstrated improvements compared to the unmodified laminate such as the notch sensitivity under compression, ILSS and G IIC performance. The improvement of the G IIC for the VGCF modifier in particular was found to be over 100%. It was suggested that high aspect ratio of the nano-additive helped to constrain the growth of the micro-cracks which in turn delayed failure. Mode I G IC performance however, was found to decrease as a result of the fibre tows preventing optimum dispersion of the modifier. The effect of this was a very high “effective” clay concentration in the interlayer resin rich regions and a less than optimum fibre dispersion, results in promotion of the propagating crack rather than inhibition.

Nanoscale Rubber Reinforcement: A Route to Enhanced Intercalation in Rubber-Silicate Nanocomposites

Abstract Addition of organo-modified layered silicates (e.g., montmorillonite clay) to polymer matrices can produce effective polymer nanocomposites by intercalation of macromolecules into the interlayer galleries. Flexible rubber nanocomposites represent an untapped application of this technology that is still in an early stage of development. This research focuses on the enhancement of rubber matrices through the incorporation of different types of layered silicates along with a dispersion agent, hexamethoxymethylmelamine (HMMM). Styrene-co-butadiene rubber (SBR) and acrylonitrile-co-butadiene rubber (NBR) nanocomposites were prepared via a straightforward rubber compounding process and investigated through wide angle x-ray diffraction to determine the resulting clay morphology. The mechanical evaluation of the rubber nanocomposites was by tensile and tear testing. The dispersing agent affected both the morphology, registered as an increase in the gallery height, and mechanical properties, which showed significant additional reinforcement with the optimal combination of organoclay and rubber type. This work thus demonstrates the positive benefit of such a dispersion agent.

Ethylene/vinyl acetate copolymer/clay nanocomposites

AbstractThis article highlights the history, synthetic routes, material properties, and scope of ethylene/vinyl acetate copolymer (EVA)/clay nanocomposites. These nanocomposites of EVAs are achieved with either unmodified or organomodified layered silicates with different methods. The structures of the resulting polymer/inorganic nanocomposites have been characterized with X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The addition of a small amount of clay, typically less than 8 wt %, to the polymer matrix unusually promotes the material properties, such as the mechanical, thermal, and swelling properties, and increases the flame retardancy of these hybrids. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 471–480, 2006

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.

Synergistic effect of compatibilizer in organo-modified layered silicate reinforced butadiene rubber nanocomposites

We have prepared nanocomposites of intercalated and exfoliated organosilicates in butadiene rubber (BR) by using a two-stage melt blending process. We used X-ray diffraction and transmission electron microscopy to examine, respectively, the intergallery spacing of the organosilicates and their dispersion in the BR. Marked enhancements in the mechanical and thermal properties of BR occurred when it incorporated <10 parts of organosilicates and the loading ratio of the organosilicate to dicarboxylic acid-terminated butadiene oligomer was approximately three. In particular, the addition of 10 parts of organosilicate and 3 parts of compatibilizer in the BR led to a more than four-fold increase in the tensile strength, a 150% increase in modulus at 100% elongation (M100), and 232 and 410% enhancements in the tear strength and elongation at break, respectively, relative to those of neat BR. The degradation temperature for the BR nanocomposite containing only a 10-part loading of organosilicate was 51°C higher than that of neat BR; these increases reduced, however, to 9 –13°C upon the addition of the CTB compatibilizer. In addition, the relative water vapor permeabilities of the BR nanocomposites containing 10 parts of organosilicate— both in the presence and absence of the compatibilizer—reduced to 20% of that of the neat BR. POLYM. ENG. SCI., 46:80 – 88, 2006. © 2005 Society of Plastics Engineers