Organically-modified Clay Research Articles

Valorization of post-consumer recycled polypropylene through their reinforcement with amine and amine/silane organically modified clays for potential use in food packaging

The deterioration of the properties of post-consumer recycled polyolefins is one of the challenges to address for their further use in new packaging systems. In this work, sheets based on nanocomposites of flexible post-consumer recycled polypropylene (PCPP) and amine (NI44P) and amine/silane (NI.31PS) organic-modified clays were developed in order to study the effect of these nanoclays in the improvement of the PCPP’s properties for food packaging applications. Clays tended to reduce the water vapor permeability of the sheets, and interestingly, this effect was more significant by the presence of aminopropyltriethoxysilane as a coupling agent in the clay due to its possible interactions with the oxidized groups of the recycled polymer. Conversely, oxygen permeability increased with NI.31PS clay, but was greatly reduced with the addition of NI.44P at 1 wt%. The nanocomposite with NI.31PS at 3 wt% presented the highest increase of tensile strength. The nanocomposites complied with the overall migration limit towards aqueous and fatty simulants. Migration values were lower in 10 % ethanol and 3 % acetic acid than in olive oil.

Crystal and morphology development in immiscible nonpolar polymer blend nanocomposite based on low‐density polyethylene and linear low‐density polyethylene in presence of clay and compatibilizer

AbstractIn this work, polyolefin‐blend/clay nanocomposites based on low‐density polyethylene (LDPE), linear low‐density polyethylene (LLDPE), and organically modified clay (OC) were prepared by melt extrusion. Various grades of maleic anhydride (MA) grafted polyethylene (PE‐g‐MA) were used and examined as compatibilizers in these nanocomposites. Differential scanning calorimetry analysis showed that OC and compatibilizer affect the crystallization behavior of LDPE/LLDPE with different mechanisms. Thermodynamic calculations of wetting coefficient based on interfacial energy between OC, LD, and LL, Morphological characterization based on field emission scanning electron microscopy, X‐ray diffraction, small angles X‐ray scattering, and dynamic rheology measurements revealed that the compatibilizer and OC were localized at the interface of LDPE and LLDPE phases with a preferred tendency toward one phase. Results demonstrated that at a specific amount of OC, there is an optimum compatibilizer concentration to achieve nanodispersed OC and beyond that the compatibilizer causes a structural change in the polymer crystalline morphology. It was also found that the tensile property enhancement of LDPE/LLDPE/OC nanocomposites is closely related to the crystalline structure development made by incorporation of both OC and compatibilizer.

Influence of organically modified clays on the barrier properties of bromo butyl rubber composites for tyre inner liner application

ABSTRACT The barrier and mechanical properties are the primary requirement of a rubber for tyre inner liner application that can be fulfilled by incorporation of organically modified clay (OMC) into rubber matrix. In this work, functional rubber composites with an improved gas barrier performance were prepared using bromobutyl rubber (BIIR) and natural rubber (NR) as the elastomer phases, and OMC and carbon black (CB) as the functional fillers by employing standard solid-state mixing and vulcanization methods. CB was partially replaced by OMC to achieve adequate barrier and mechanical properties. OMC modified composite showed ~35% improvement in the barrier properties as compared to the control compound (60 phr carbon black, 10 phr NR and 90 phr of BIIR loaded rubber compound). The dispersion of the nano clays were investigated by transmission electron microscopic (TEM), scanning electron microscopic (SEM) and X-ray diffraction (XRD) studies. The XRD study revealed that higher d- spacing and crystalinity of the nano clay composites ease the exfoliation tendency. The mechanical properties of the clay filled nano composites, such as hardness tensile strength, modulus and air barrier properties were superior to the control compound. The developed BIIR/nanoclay composites with improved barrier properties prepared by conventional mixing method in line with common industrial practice can be used in rubber products such as tire inner liner.

Short alkyl chain length ionic liquid as organic modifier in polypropylene/clay nanocomposite: a thermal comparative study

The most common polymeric nanocomposites are constituted of organically-modified clays. Generally, these organic modifiers are based on quaternary ammonium salts. These systems have as disadvantage the low thermal resistance of its modifiers under processing. Ionic liquids (IL) with different molecular structures can be used as organic modifier in lamellar clays-based polymeric nanocomposites, being promising not only to increase interactions between the nanoclay and the matrix, but also to increase the thermal resistance. In this study, polypropylene-based/montmorillonite nanocomposites were compared from two different organic modifiers. The use of short alkyl chain length imidazolium-based IL as montmorillonite modifier was investigated in terms of the thermal stability when compared to the usual quaternary ammonium salt surfactant. Integral procedure decomposition temperature was employed to determine the effect of these two different organoclay modifiers in PP-nanocomposites. The activation energy for these samples was calculated using Flynn–Wall–Ozawa (FWO) method. It was also used the multiple linear regression analysis to calculate the activation energy in order to evaluate the accuracy of this method when applied to nanocomposites.Article HighlightsShort length alkyl group in ionic liquid was able to improve the thermal stability of PP-based nanocomposite.IPDT methodology is more realistic to evaluate the thermal stability of ionic liquid-based nanocomposite.MLR methodology was efficient to assess the entropic contribution associated to polymer-clay interactions, inter-lamellae spaces and interface morphology.

Structural observation of cement paste modified with hydrophobic organoclay

This study investigates the impact of different hydrophobic organically modified clay (OC), grouped according d001 and functional group of modifier, on hydration, microstructure, mechanical and water absorption properties of cement formulations. SEM, TGA, XRD and N2 sorption techniques employed for microstructural characterization. Pore and pore neck size distribution of cementitious materials was derived from QSDFT method applied on sorption isotherms. Results revealed that in OC-cement formulations the volume and the width of small capillary pores varies depending on the modifier type and d001 of OC, meanwhile the distribution of pore neck size is almost the same for all compositions. According to results, cement compositions with the addition of OC possessing aromatic substitute group and of larger d001 showed higher mechanical strength and substantially lower sorptivity.

Dynamically vulcanized thermoplastic elastomer nanocomposites based on linear low-density polyethylene/styrene-butadiene rubber/nanoclay/bitumen: morphology and rheological behavior

Dynamically crosslinked thermoplastic elastomer nanocomposites were synthesized as modifier for the bitumen binder-based asphalts. Linear low-density polyethylene (LLDPE) and styrene-butadiene rubber (SBR), with the ratio of 80/20, bitumen, and organically modified clay (OC) were all melt mixed in the presence of the sulfur curing system. The proposed mixing was carried out in an internal mixer at 160 °C with a rotor speed of 120 rpm. To enhance the molecular interactions between the polymer phases and the clay silicate layers, maleic anhydride-grafted LLDPE (PE-g-MA) with the maleiation degree of 50% was also incorporated into the mixture. Observation of the composite samples, using the scanning electron microscopy (SEM), revealed the matrix dispersed type of morphology for all dynamically vulcanized samples. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the exfoliation of the clay silicate layers with good dispersion. Rheomechanical spectrometry (RMS) was performed on the prepared nanocomposites. All dynamically vulcanized nanocomposites comprising 2.5% of OC exhibited shear-thinning behavior and non-terminal characteristics with a low frequency range. These indicate the formation of three-dimensional physical networks by the clay nanolayers throughout the LLDPE matrix. The presence of the bitumen in the composition of the prepared nanocomposites improved the flowability of the samples. This is a promising feature of the prepared nanocomposites to be used as an elastic and resistant modifier in the composition of the bitumen-based asphalts.

Comparison of Competitive and Synergistic Adsorption of Tetrabromobisphenol-A and Its Metabolites on Two Different Organic-Modified Clays

Experimental data of the adsorption of tetrabromobisphenol-A (TBBPA) and its metabolites [bisphenol-A (BPA) and 2,6-dibromophenols (2,6-DBP)] on two different organic-modified clays were determined...

Synthesis and structural characterization of betaine- and imidazoline-based organoclays

The samples of organic-modified clays based on a Wyoming SWy-2 sodium montmorillonite (Na+-Mt) with the cationic surfactant hydroxyethylalkyl imidazoline (HEAI) and the amphoteric surfactant oleylamidopropyl betaine (OAPB) were synthesized via a cation exchange process. The obtained materials were characterized using XRD analysis, ATR-FTIR spectroscopy, SEM, BET and Water contact angle measurements. The potential sites of binding of OAPB and HEAI to the mineral surface were determined by the DFT calculations. For the variants of the structure of the complex, DFT calculations is performed and the interaction energy of the surfactant and clay mineral is estimated.

Clay/carbon nanotube hybrid mixture to reduce the electrical percolation threshold of polymer nanocomposites

Creating electrically conductive polymer composites with extremely low nanofiller concentration by melt compounding is a major research challenge. At low nanofiller concentration, the valuable properties of polymers are preserved and the feasibility of the composite is promoted. In this work, an organically modified clay (OMC) was utilized to alter the structure and consequently the electrical resistivity of carbon nanotubes (CNT)/polypropylene (PP) composite. As a result of OMC incorporation, the electrical percolation threshold concentration (EPTC) was reduced from 1.0 wt% CNT for the CNT/PP composite to 0.5 wt% CNT for the CNT:OMC/PP composite, corresponding to 50% reduction in the amount of CNT. The macro-dispersion analysis did not reveal any significant difference between the dispersion of CNT in the CNT/PP and CNT:OMC/PP composites. However, the processing behavior analysis showed a significant decrease in mixing torque and consequently mixing energy due to the addition of OMC. The decrease in mixing torque and/or mixing energy decreases the destruction of CNT aspect ratio. In addition, the DSC analysis showed a decrease in composite crystallinity due to OMC addition. This finding reveals a thinner insulating crystalline layer at the surface of CNT particles and consequently higher electrical conductivity. Based on these experimental findings, it can be speculated that the addition of OMC promoted the conductivity of the composite by decreasing the mixing shear stress and/or polymer crystallinity.

Reduction of filler networking in silica based elastomeric nanocomposites with exfoliated organo-montmorillonite

Montmorillonite with dimethyl di(hydrogenatedtalloyl) ammonium as the compensating cation was added to a silica based elastomeric composite and the hybrid filler system led to reduction of filler networking phenomenon, better stability of elastic modulus with temperature, enhancement of stresses at all elongations, improvement of ultimate properties. This composite was based on a blend of natural rubber, poly(1,4-cis-isoprene) and poly(styrene-co-butadiene) from anionic polymerization and contained 70 parts per hundred rubber (phr) of silica. The organically modified clay (OC) was below the threshold required to establish an hybrid OC-silica filler network. Such threshold (about 7phr) was estimated by preparing silica based nanocomposites containing various amounts of OC and determining shear storage and loss moduli as a function of strain amplitude. This work demonstrates that exfoliated OC favour lower dissipation of energy of silica based elastomeric composites under dynamic mechanical stresses and paves the way for further large scale applications.

Effect of Clay Addition on the Properties of Carbon Nanotubes-Filled Immiscible Polyethylene/Polypropylene Blends

The effects of organically modified clay (OMC) incorporation on the microstructure and the electrical and mechanical properties of polypropylene (PP)/polyethylene (PE) blends filled with carbon nanotubes (CNT) were investigated. All blends were prepared by melt mixing in a batch mixer. The microstructures were characterized by scanning electron microscopy. In the OMC:CNT filled blends, the CNT were found to selectively localize within the PE phase, while the clay particles were observed in the PP phase. The electrical resistivity of OMC:CNT filled blends did not show any significant change as a result of the clay addition since it was localized in the CNT-free phase. On the other hand, the addition of clay degraded the blends' mechanical properties due to the poor adhesion between the OMC and the PP matrix.

Effect of clay silylation on curing and mechanical and thermal properties of unsaturated polyester/montmorillonite nanocomposites

This work focuses on the chemical modification of montmorillonite (MMT) (Cloisite® Na) with compatible silanes, vinyltriethoxysilane (CVTES) and γ-methacryloxypropyltrimethoxysilane (CMPS) in order to prevent agglomeration and to improve montmorillonite interaction with an unsaturated polyester resin matrix seeking to achieve a multifunctional composite. Clays were dispersed in the resin by mechanical stirring and sonication and the nanocomposites were prepared by resin transfer into a mold. The mechanical, morphological, thermal and flammability properties of the obtained composites were compared with those prepared using commercial Cloisite® 30B (C30B) and Cloisite® 15A (C15A) clays. Advantages of using silane-modified clays (CVTES and CMPS) as compared with organic-modified clays (C30B and C15A) can be summarized as similar flexural strength and linear burning rate but higher storage modulus and improved adhesion to the polyester resin with consequent higher thermal deflection temperature and reinforcement effectiveness at higher temperatures. However, organic modified clays showed better dispersion (tendency to exfoliate) and consequently delayed thermal volatilization due to the clay barrier effect.

Enhanced morphology and mechanical characteristics of clay/styrene butadiene rubber nanocomposites

Achieving complete exfoliation of clay in their polymer nanocomposite is a matter of interest as it can significantly affect the material properties. Herein, an efficient way of enhancing the interlayer spaces of organically modified clays (OC) containing two types of surfactants, benzyl methyl hydrogenated tallow (Cloisite 10A) and dimethyl dihydrogenated tallow (Cloisite 20A) while mixing with the styrene butadiene rubber (SBR) is reported. The prolonged swelling of the OC in toluene helped the rubber chains to disentangle in the interlayer spaces identifiable from the morphology and the change of the d-value. The small angle X-ray scattering traces for all the Cloisite 20A/SBR composites indicated a very extensive dispersion of the OC and using the Guinier equation from SAXS, radius of gyration was calculated. An optimal size of 6–7nm for the dispersed clay particles was found for maximizing resistance to abrasion as well as mechanical properties. Finally the enhanced tensile properties were correlated with the vulcanization behavior as well as the filler/polymer interfacial interaction from rheology through the completely exfoliated morphology observed for the swollen clay filled samples. Moreover an exclusive mechanism for curing of the composites was also derived.

Cement substitution by organoclay – The role of organoclay type

In this paper three organically modified clays (OC) with different functional group of modifier and basal spacing (d001) but approximately the same alkyl chain length were considered in order to identify which parameter of OC is the most characteristic for the selection of appropriate OC for cement substitution. Compressive strength and water absorption changes in hardened cement paste due to partial cement substitution by OC at various dosages (0.5 up to 6wt%) and at water-to-solid ratios (0.27, 0.31 and 0.36) were examined. Microstructural changes evaluated by nitrogen sorption indicated that pore size distribution and especially micro and mesopores representing C–S–H structure have been much more affected by the type of modifier than the d001 of OC. Results showed that application of OC of the same d001, but having different functional group of modifier may result in either significant increment or reduction of the strength.

Effect of organically modified clay on mechanical properties, cytotoxicity and bactericidal properties of poly(ϵ-caprolactone) nanocomposites

The objective of this study was to evaluate the use of organically-modified clay nanoparticles in poly(ϵ-caprolactone) (PCL) for developing biodegradable composites. PCL nanocomposites reinforced with two different types of organically-modified clay (Cloisite 30B, C30B and Cloisite 93A, C93A) were prepared by melt-mixing. Morphology of PCL/clay nanocomposites characterized by scanning electron microscopy indicated good dispersion of nanoclay in the PCL matrix. Reinforcement of nanoclay in PCL enhanced mechanical properties without affecting thermal and degradation properties of PCL. Cytocompatibility of PCL/clay nanocomposites was studied using both osteoblasts and endothelial cells in vitro. Both composites (PCL/C30B and PCL/C93A) were cytotoxic with high toxicity observed for C30B even at low content of 1 wt %. The cytotoxicity was found to arise due to leachables from PCL/clay composites. Electrical conductivity measurements of aqueous media confirmed leaching of cationic surfactant from the PCL/clay composites PCL matrix. Both composites were found to be bactericidal but C30B was more effective than C93A. Taken together, it was observed that organically-modified nanoclay as fillers in PCL improves mechanical properties and imparts bactericidal properties but with increased risk of toxicity. These PCL/clay composites may be useful as stronger packaging material with antibacterial properties but are not suited as biomedical implants or for food packaging applications.

Influence of Solvent Washing and Soxhlet Extraction on the Thermal Stability of Organically Modified Layered Silicates

Abstract An efficacious process for removing excess surfactant and sodium halide from an organically-modified clay is described in this paper. Improved thermal stability of the organoclay is observed using both washing with ethanol or Soxhlet extraction with methanol. The selection of the solvent to be used plays a vital role in removing the excess organic modifier from the organoclay. Approximately a 60 °C increment in onset thermal stability (T5%) is observed by solvent washing while a further 20 °C improvement is seen using Soxhlet extraction. Washing with hot deionized water followed by an ethanol washing will remove the excess modifier more effectively than does hot DI water and THF.

Organoclays with hexagonal rotator order for the paraffinic chains of the compensating cation. Implications on the structure of clay polymer nanocomposites

Organically modified clays (OC) were prepared by reacting montmorillonite (Mt) and dimethyl ditallow ammonium chloride (2HTCl), optionally adding either stearic acid (SA) or 2-stearamidoethyl stearate (SAES). Reactions were performed either at the solid state, in the absence of any other chemical substance, or with the help of solvents such as water and alcohol, or in poly(1,4-cis-isoprene) as the reaction medium. Characterization was performed by means of TGA, XRD, DSC, IR analyses. Two types of OC were identified, with 3.6–4.0nm and about 6nm as d001 basal spacing, independently of the synthetic route. The 3.6–4nm value could be explained with the bilayer placement of the tilted paraffinic chains of the ammonium cation. The 6nm value could arise from the perpendicular placement of the paraffinic chains, associated with the presence in the interlayer space of either the acid or the amide. For the first time, it is documented the occurrence of hexagonal rotator order in the packing of the long hydrocarbon tails of the 2HT compensating cation. SA and, in particular, SAES were found to enhance this type of order. A third type of OC, with 2.5nm as d001 basal spacing was obtained through solvent extraction of the above mentioned OC. Results reported in this work show that the crystalline structure of an OC depends on type and amount of low molecular mass substances present in the interlayer space: compensating cations and guests such as an acid and/or an amide. For a given compensating cation, the interlayer distance can be varied by changing the amount of the cation and by adding a guest. The Mt/2HT organoclay studied in this work reveals 2.5, 3.6–4.0 and 6.0nm as the interlayer distances of the minima of energy. Polymer chains are not involved in the OC crystalline structure, even if the OC synthesis is performed in the polymer matrix. This work strongly suggests that the best explanation for most interlayer spacing variation observed for clays in polymer nanocomposites is the different placement of intercalated low molecular mass substances, rather than the generally assumed polymer chain intercalation. Moreover, it presents the synthesis of OC at the solid state as a versatile method for preparing a large variety of clay polymer nanocomposites.

Effect of resin composition on curing kinetic of nanoclay-reinforced unsaturated polyester resins

Curing behavior of two resins of different unsaturated polyesters [FARAPOL 101 (UF) and Bushpol 81715 (UB)] containing 3 wt % organically modified clay (OMC), catalyzed with methyl ethyl ketone peroxide as initiator and promoted by cobalt naphtenate accelerator was investigated by dynamic differential scanning calorimetry (DSC) and gel time test methods. Chemical structures of UF and UB resins were characterized by 1H NMR, XRD and TEM techniques were used for morphology characterization of nanocomposites. DSC results showed that after adding OMC, the redox reaction rate of UF increased less than that of UB resin. Measurements of cloud-point temperature (T c) indicated that the miscibility of styrene/UB alkyd chains was more than that of styrene/UF alkyd chains. Therefore, the alkyd/styrene ratio inside the platelets in UB would be more than that in the platelets in UF nanocomposite. Among the three factors in redox reaction rate of UB/OMC and UF/OMC systems namely: (1) decreasing alkyd-styrene copolymerization share among platelets of OMC, (2) decreasing the activation energy, (3) decreasing the number of collisions, the first one was more effective in UF/OMC system than in UB/OMC system. Consequently, the difference between redox reaction rates of UF/OMC and neat UF was negligible compared with the corresponding difference for UB/OMC and neat UB system.

Modeling Sorption and Diffusion of Organic Sorbate in Hexadecyltrimethylammonium-Modified Clay Nanopores – A Molecular Dynamics Simulation Study

Organoclays are highly sorptive engineered materials that can be used as amendments in barrier systems or geosynthetic liners. The performance of confining and isolating the nonpolar organic contaminants by those barrier/lining systems is essentially controlled by the process of organic contaminant mass transport in nanopores of organoclays. In this article, we use molecular dynamics (MD) simulations to study the sorption and diffusion of organic sorbates in interlayers of sodium montmorillonite and hexadecyltrimethylammonium (HDTMA(+))-modified montmorillonite clays. Simulated system consisted of the clay framework, interlayer organic cation, water, and organic sorbate. Their interactions were addressed by the combined force field of ClayFF, constant-valence force field, and SPC water model. Simulation results indicated that in HDTMA coated clay nanopores, diffusion of nonpolar species benzene was slowed because they were subjected to influence of both the pore wall and the HDTMA surfactant. This suggested the nonpolar organic compound diffusion in organophilic clays can be affected by molecular size of diffusive species, clay pore size, and organic surfactant loading. Additionally, a model that connected the diffusion rate of organic compounds in the bulk organoclay matrix with macropores and nanopores was established. The impact of intercalated organic cations on the diffusion dominated mass transport of organic compounds yielded insight into the prediction of the apparent diffusion behavior of organic compounds in organic-modified clays.

Insight on the striking influence of the chain architecture on promoting the exfoliation of clay in a polylactide matrix during the annealing process

The influence of the topological structure of polylactide (PLA) chains on the microstructure of PLA–organically modified clay (OMC) nanocomposites was studied. Here, an OMC with a hydroxyl group-containing modifier (I.34TCN) was used as the nanofiller. According to the results from the XRD and TEM measurements, the change in the dispersed states of the OMC with star-shaped PLA (PLA3-x) was totally different from that with linear PLA (PLA1-1) during annealing at high temperature. A transition from the intercalated to the exfoliated structure appeared in the simple PLA3-x/OMC mixture during the annealing process, but the intercalated structure was retained in the PLA1-1/OMC system. The enhanced exfoliation of the OMC in the PLA3-x matrix was attributed to the spatial limitation of the star-shaped PLA3-x, which made the intercalated interlayer swell. As a result, the concentration of PLA3-x chains within the layers of the OMC was lower than that of the outside bulk, and so, more PLA3-x chains diffused into the interlayers of the clay until the clay sheets separated (exfoliation state). Furthermore, the exfoliation extent of the OMC in the star-shaped PLA3-x/OMC composites strongly influenced the glass transition temperature (Tg) of star-shaped PLA3-x.