Organophilic Layered Silicates Research Articles

Improved quantum yield of thermally activated delayed fluorescence by nanoconfinement in organophilic octosilicate

A hybrid of a thermally activated delayed fluorescent dye (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, designated as 4CzIPN) and an organophilic layered silicate (dioleyldimethylammonium-octosilicate) was synthesized to achieve high photoluminescence quantum yield (0.71) of the dye, which is the critical factor in device application. Absorption, photoexcitation, and luminescence spectra suggested that the molecular conformation of 4CzIPN in the organophilic silicate enabled the utilization of the S0 → S1 transition efficiently. Furthermore, thanks to the flexible assembly of the dioleyldimethylammonium moieties, 4CzIPN was dispersed in the hybrid to suppress concentration quenching. Emission spectra and photoluminescence lifetimes in ambient and N2 atmosphere revealed that the photoluminescence quantum yield increased by the utilization of transition to a lower vibrational state and protection of a triplet state of 4CzIPN from oxygen in air in the organophilic silicate.

Effect of organoclay reinforcement on the curing characteristics and technological properties of styrene-butadiene rubber

Rubber nanocomposites based on styrene–butadiene rubber (SBR) and organophilic layered silicate were prepared. Clay structures based on dodecyl benzene sulfonic acid (DBSA), nonyl phenol ethoxylate (NPE), and DBSA/NPE (50/50%) were prepared and characterized. The results indicate the intercalation of the used surfactants within the clay layers. Varying amount of organoclay, 2, 4, 6, 8, and 10 (phr), was added to the SBR matrix. X-ray diffraction revealed exfoliated structure for the modified clay–SBR composites. No new component in the rubber was found by fourier transform infrared measurements (FTIR). Scanning electron microscopy showed a uniform distribution of the modified clay with mixed DBSA/NPE (6 phr) in the matrix. The rheometric characteristics and physicomechanical properties of the SBR compounds were analyzed. The effect of DBSA/NPE clay loading on aging resistance of SBR nanocomposites at 90 ± 1°C for 4 and 7 days was also investigated. Rubber nanocomposites displayed an increase in the minimum and maximum torques, acceleration of the vulcanization process, and improved mechanical properties, with organoclay content up to 6 phr. This effect was more noticeable in the presence of the treated clay with DBSA/NPE. Also incorporation of DBSA/NPE-clay (6 phr) resulted in significant improvement of the degradation profile of the nanocomposites at 90 ± 1°C for 4 days. POLYM. COMPOS., 36:1293–1302, 2015. © 2014 Society of Plastics Engineers

Exfoliated/intercalated silicate/hot styrene butadiene rubber nanocomposites: Structure–properties relationship

AbstractRubber nanocomposites based on hot styrene‐butadiene rubber (SBR) and organophilic layered silicate were prepared via mechanical mixing followed by compression molding. Varying amount of organically modified nanosilicate, 2.5, 5, 10, and 15 parts per hundred of rubber (phr), was added to the SBR matrix to examine the influence of nanosilicate on morphology and structure–property relationships. The morphology of nanocomposites was studied by X‐ray diffraction and transmission electron microscopy which reveal that the nanocomposite contained a good dispersion of intercalated/exfoliated layers through the matrix. The interaction between SBR matrix and nanofiller was studied by infrared spectroscopy. No clear evidence for the formation of new components in the rubber was found but infrared spectroscopy denoted evidence for exfoliation. The reinforcing effect of the nanosilicate was determined by mechanical testing and dynamomechanical analysis. The results indicate that the tensile properties and the storage modulus increased with increasing nanofiller loading. This suggests a strong rubber–nanosilicate interaction which is attributed to the exfoliated/intercalated structure. Thermogravimetric analysis revealed that incorporation of organoclay enhances the thermal stability of the nanocomposites. The best thermal stability was observed for nanocomposites containing 5 phr nanosilicate. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of the polymer microstructure on the behavior of syndiotactic polypropylene/organophilic layered silicate composites

AbstractSyndiotactic polypropylenes (sPPs) with several microstructures (i.e., syndiotacticities and molecular weights) and synthesized by means of two metallocenic catalysts were melt‐blended with 1 and 3 wt % organophilic layered silicates in the presence of a compatibilizer. X‐ray diffraction and transmission electron microscopy analysis showed that the clay was well dispersed in the composites, although the filler morphology depended on the polymer microstructure. Polypropylenes with low syndiotacticities and molecular weights presented the best clay dispersion. Nonisothermal differential scanning calorimetry analysis showed that the polymer microstructure and the clay content modified the thermal behavior of the composites. The compatibilizer and the clay acted as nucleant agents to increase the crystallization temperature of the matrix. Moreover, the double endothermic peak observed during heating scan and associated with the melt/recrystallization/remelt processes of the pure polymer matrix was reduced in the composites. With regard to the mechanical properties under tensile conditions, a synergic effect of the compatibilizer and the clay was observed. In particular, the addition of the compatibilizer alone was able to increase by about 20% the elastic modulus relative to the neat samples, whereas increases between 35 and 50% were measured when the clay was also added, depending on the polymer microstructure. Our results show that the microstructure of sPPs had strong effects on the behavior of its composites with clay in the presence of a compatibilizer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Study of matrix micro-cracking in nano clay and acrylic tri-block-copolymer modified epoxy/basalt fiber-reinforced pressure-retaining structures

In fiber-reinforced polymer pressure-retaining structures, such as pipes and vessels, micro-level failure com- monly causes fluid permeation due to matrix cracking. This study explores the effect of nano-reinforcements on matrix cracking in filament-wound basalt fiber/epoxy composite structures. The microstructure and mechanical properties of bulk epoxy nanocomposites and hybrid fiber-reinforced composite pipes modified with acrylic tri-block-copolymer and organophilic layered silicate clay were investigated. In cured epoxy, the tri-block-copolymer phase separated into disor- dered spherical micelle inclusions; an exfoliated and intercalated structure was observed for the nano-clay. Block-copoly- mer addition significantly enhanced epoxy fracture toughness by a mechanism of particle cavitation and matrix shear yielding, whereas toughness remained unchanged in nano-clay filled nanocomposites due to the occurrence of lower energy resistance phenomena such as crack deflection and branching.Tensile stiffness increased with nano-clay content, while it decreased slightly for block-copolymer modified epoxy. Composite pipes modified with either the organic and inorganic nanoparticles exhibited moderate improvements in leakage failure strain (i.e. matrix cracking strain); however, reductions in functional and structural failure strength were observed.

Nanostructure morphology and dynamic rheological properties of nanocomposites based on thermoplastic polyurethane and organically modified montmorillonite

Thermoplastic polyurethane (TPU) nanocomposites based on organophilic-layered silicates were prepared via melt blending. Wide angle X-ray diffraction (WAXD) and transmission electron microscope (TEM) were employed to investigate the state and mechanism of exfoliation of the layered silicate within TPU matrix. The TPU nanocomposites were found to have a partially exfoliated morphology at lower clay loading, whereas the morphology changed to an intercalated nanostructure at higher clay loadings. The effect of the state of dispersion of organoclay on rheological properties of the nanocomposites were carried out by rubber process analyzer (RPA), which exhibited more pronounced shear thinning behavior, and increased storage and loss modulus with the increase in organoclay content. The pseudo-plastic like behavior was observed due to change in liquid-like to solid-like behavior of nanoclay-filled systems.

Dry rolling and sliding friction and wear of organophilic layered silicate/hydrogenated nitrile rubber nanocomposite

Dry rolling and sliding tribological behaviors of hydrogenated nitrile rubber (HNBR) and its compound, containing 10 parts per hundred rubber (phr) organophilic layered silicates (OLS), were evaluated. As OLS modifier a quaternary amine with hydroxyl and double bonds was selected to support the intercalation/exfoliation by triggering possible interactions with HNBR. According to X-ray diffraction results the OLS was intercalated. Network-related parameters were deduced from dynamic-mechanical thermal analysis (DMTA). The tribological parameters, i.e., coefficient of friction (COF) and specific wear rate (Ws), were determined in various home-made test configurations. The OLS reinforcement of HNBR affected the COF and improved the resistance to rolling and sliding wear (except fretting) compared to the pure HNBR. The worn surfaces of the rubber compounds were inspected in scanning electron microscope (SEM) and the dominant wear mechanisms concluded.

Polymer-silica hybrids latexes dyed with Rhodamine B

AbstractSynthesis of latexes based on polystyrene (PSt) and polybutylacrylate (PBuA) dyed with Rhodamine B (RhB), by polymerization in ternary microemulsions, is discussed in this paper. Silica was generated through the solgel process of methacryloxypropyl-trimethoxysilane (MPTS) and glycidyloxypropyltrimethoxysilane (GMPS). MPTS copolymerizes, through its double bounds, with St or BuA. GMPS can form covalent bonds with RhB by opening of the oxyranic cycle. The smallest average diameter of the particles was obtained for latexes prepared with MPTS+GMPS couple. Latexes with RhB prepared in the presence of an organophilic layered silicate (Cloisite 20 A) were used for comparing the influence of the inorganic fillers on microemulsion properties. By St and BuA copolymerization with MPTS hybrids which can react by sol-gel process with GMPS, a coupling agent for RhB, were prepared. By using RhB as molecular sample, polarity modifications for polymer-inorganic latexes were put in evidence.

Organophilic Layered Silicate Modified Vinylester-Urethane Hybrid Resins: Structure and Properties

A commercial vinylester-urethane (VEUH) hybrid resin was modified with organophilic layered silicates (OLS), incorporated in various amounts (0.1 to 5 wt.%). As organophilic intercalants of the layered silicate (synthetic fluorohectorite) trimethyl dodecylamine (TMDA) and octadecylamine - N,N-bis[allyl(2-hydroxypropyl)ether] (OAE) served. The latter quaternary amine was expected to support the intercalation/exfoliation of the silicate by participating in the crosslinking reactions. Both OLS types became intercalated based on X-ray diffractograms (XRD). Dynamic-mechanical thermal analysis (DMTA) displayed a slight increase in the stiffness by adding OLS up to 2.5 wt.%. However, at 5wt% OLS content the stiffness of the nanocomposites was below that of the unfilled hybrid resin. The glass transition temperature (Tg) did not change practically with the OLS type and content. Fracture mechanical tests were performed on compact tension (CT) specimens. The fracture toughness (Kc) increased slightly, while the fracture energy (Gc) markedly with increasing OLS content. Unexpectedly, TMDA proved to be a more suitable intercalant than OAE. The failure mode of the specimens was studied in a scanning electron microscope (SEM) and discussed. In addition, the water sorption behavior of the OLS modified VEUHs was determined and the diffusion coefficients (D) deduced.

Preparation of Recycled Polypropylene/ Organophilic Modified Layered Silicates Nanocomposites Part I: The Recycling Process of Polypropylene and the Mechanical Properties of Recycled Polypropylene/Organoclay Nanocomposites

The recycling process of polypropylene (PP) and the elaboration of recycled polypropylene/modified clay nanocomposite by melt intercalation method have been investigated. The purpose of this work is to characterize the influence of the recycle processing of an homopolypropylene on the mechanical, thermal, and rheological properties of the polymer, and then to obtain a predictive mechanism of polypropylene degradation in a twin-screw extruder in order to be able to reinforce its behavior for a new application. We can see that the mechanical properties decrease according to the recycling times at two chosen different temperature profiles. At the high temperature profile (195—230°C), the rheological behavior of homopolypropylene is more influenced than at the low temperature profile (175—190°C), the viscoelastic properties are highly modified, the viscosity increases, and the mechanical properties decrease as much as the polypropylene matrix appears to be less accurate. The thermal properties of the recycled polypropylene are investigated by differential scanning calorimetry (DSC) analysis: the crystallization temperature and crystallization time decrease as a function of the number of extrusion cycles. The incorporation of the organophilic layered silicates and maleic anhydride grafted polypropylene (MAPP) compatibilizer improves significantly the mechanical properties of the recycled polypropylene.

Mechanical and Fracture Toughness Behavior of TPNR Nanocomposites

Thermoplastic natural rubber (TPNR) nanocomposites containing organophilic layered silicates were prepared by melt blending method at 180°C using internal mixer (Haake 600P). The aim of this study is to determine the influence of the organoclay filler on the mechanical and fracture properties. In this study, two mixing methods were employed to incorporate filler into matrix, namely the direct (DM) and indirect (IDM) method. The mechanical properties of TPNR nanocomposites were studied using tensile, flexural, and impact tests. The tensile and flexural tests revealed that the optimum loading of organoclay was at 4 wt% using the indirect method of mixing. Plane stress fracture toughness of thermoplastic natural rubber (TPNR) nanocomposite was determined by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. The EWF measurements indicated that the specific essential work of fracture (we) decreased in the presence of nanoclay. Nevertheless, these TPNR nanocomposites met the basic requirement of the EWF concept of full ligament yielding, which was marked by a load drop in the force—displacement curves of the DDEN-T specimens.

Location of a nanoclay at the interface in an immiscible poly(ε-caprolactone)/poly(ethylene oxide) blend and its effect on the compatibility of the components

Nanocomposites based on 80/20 and 20/80 (w/w) poly(e-caprolactone) (PCL)/poly(ethylene oxide) (PEO) immiscible blends and organophilic layered silicates were prepared with melt extrusion. From transmission electron microscopy analysis, it was observed that the exfoliated silicate platelets were preferentially located at the interface between the two blend phases. When the blend-based nanocomposites were prepared via a two-step process in which the silicates were first premixed with the PEO component or with the PCL component, the silicate layers migrated from the PEO phase or PCL phase to the interface. The rheological behavior of the nanocomposites was also investigated. At low frequencies, the frequency dependence of the storage modulus changed from a liquidlike behavior for the unfilled blend to a solidlike behavior for the nanocomposites, indicating the formation of a network structure as a result of exfoliation. From the scanning electron micrographs, a monotonic decrease of the PEO domain size in the 80/20 PCL/PEO blend was observed as a function of the organophilic clay content. Therefore, a clear emulsifying effect was induced by the organophilic layered silicates in the immiscible PCL/PEO blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

DSC Study of Syndiotactic Polypropylene/Organoclay Nanocomposite Fibers: Crystallization and Melting Behavior

The effect of anisotropic particles of organophilic layered silicate on the crystallization and melting behavior of prepared nanocomposite systems was studied. The matrix was syndiotactic polypropylene (sPP). Organophilic layered silicate M-QDA filler was prepared by modification of hectorite SOMASIF ME 100 with octadecyl amine. The compatibilizer was isotactic polypropylene (iPP) grafted with maleic anhydride (iPP-g-MA). The silicate was exfoliated in situ within the sPP during the melting process to produce anisotropic nanoparticles. The sPP/M-ODA nanocomposite was spun at different drawing ratios. The resulting fibers were examined by differential scanning calorimetry. It was found that neither the spinning process nor the presence of nanofiller affected the crystallinity of the sPP matrix of the nanocomposite in comparison with the neat sPP. At a raised drawing ratio of the fibers slightly increased crystallinity of matrix was observed; however, it was still lower than the neat sPP fibers prepared at the same drawing ratio. The presence of M/ODA nanofiller in sPP matrix increased the melting temperature of the fibers.

Effect of the aspect ratio of silicate platelets on the mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber (HNBR)/layered silicate nanocomposites

The role of the aspect ratio of the layered silicate platelets on the mechanical and oxygen permeation properties of hydrogenated nitrile rubber (HNBR)/organophilic layered silicate nanocomposites was investigated. Montmorillonite (MMT) and fluorohectorite (FHT) bearing the same type of intercalant (i.e., octadecylamine; ODA), however, showing different aspect ratio was involved in this study. The dispersion of the layered silicates was assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Increasing aspect ratio (MMT < FHT) resulted in higher stiffness under uniaxial tensile loading. The dispersion state (“secondary structure”) of the organophilic layered silicates reduced dramatically the oxygen permeability of the rubber matrix based on the labyrinth principle. The lowest oxygen permeability was measured for the HNBR/FHT–ODA films in which the layered silicates had the highest aspect ratio. By varying the FHT–ODA volume fraction in the latter compound the mechanical and permeation properties were measured and modelled. It was found that the modified Guth’s and Nielsen’s equations predicted accurately the mechanical and permeation responses, respectively.

Rheological Properties of Polystyrene‐Organophilic Layered Silicate Nanocomposites

AbstractA series of nanocomposites based on polystyrene (PS) and organophilic layered silicates (OLS) were prepared by solution blending method using organophilically modified silicate with ammonium salt of poly(styrene‐ran‐(4‐vinylbenzyl chloride)). Two different types of base layered silicate were used for the preparation of the nanocomposites: sodium montmorillonite (Na‐MMT) and synthetic smectite (SWN). The morphology and thermal stability of the PS/OLS nanocomposites were characterized by TEM and TGA. The rheological properties of the nanocomposites were investigated using a stress‐controlled rotational rheometer under small amplitude oscillation and steady transient shear in their melt state. In addition, the effects of the contents and aspect ratio of OLS on the melt rheological properties were investigated.

Analysis of HNBR-Montmorillonite Nanocomposites

Morphologies and dynamic mechanical properties of hydrogenated acrylonitrile butadiene rubber (HNBR) filled with organophilic layered silicates (OLS) were investigated. The results from transmission electron microscopy (TEM), small angle X-ray scattering (SAXS, especially X-ray diffraction on larger structures) and dynamic mechanical analysis (DMA) favor the notion of local filler-filler network-like clusters consisting of exfoliated silicate layers. Especially, processing under high shear forces leads to an anisotropic structure of the network. Due to the orientation of the clusters the aspect ratio (at small deformations) increases. This is in accord with the large reinforcing effect observed for these materials. For example, the stress at 50% elongation from tensile test can be increased at 33% with 5 phr OLS compared to the unfilled reference. We estimate the activation energy of the immobilized polymer layer around the filler structures and show that the values depend on the spatial direction (the values are between 3.4 kJ/mol and 4 kJ/mol). As a result, the DMA–analysis could be used as a supporting method to evaluate orientation effects of the filler structures.

Mechanical behaviour and fracture toughness evaluation of rubber toughened polypropylene nanocomposites

Rubber toughened polypropylene (PP) nanocomposites (RTPPNC) containing organophilic layered silicates were prepared by means of melt extrusion at 230°C using a co-rotating twin-screw extruder in order to examine the influence of the organoclay and polyethylene octene (POE) as filler and impact modifier, respectively, on mechanical and fracture properties. The mechanical properties of RTPPNC were studied through tensile, flexural and impact tests. The strength and stiffness of RTPPNC were improved significantly with an increase in the clay content, in the presence of maleic anhydride modified PP (PPgMAH). From the tensile and flexural tests, the optimum loading of organoclay in impact modified PP was found to be 6 wt-%. Conversely, the stiffness and strength of the blends decreased with respect to pure PP as the concentration of POE in the blends was increased. The essential work of fracture (EWF) method was also used to evaluate the fracture toughness of the RTPPNC. EWF measurements indicated that the specific essential work of fracture (we) decreased with an increase in the organoclay content. However, additions of POE elastomer are beneficial in enhancing the we of the PP blends. we appeared to increase with increasing POE content up to 20 wt-%.

Morphology, thermal and mechanical behavior of polypropylene nanocomposites toughened with poly(ethylene‐co‐octene)

AbstractRubber‐toughened polypropylene (PP) nanocomposites containing organophilic layered silicates were prepared by means of melt extrusion at 230 °C using a co‐rotating twin‐screw extruder in order to examine the influence of the organoclay and the addition of PP grafted with maleic anhydride (PPgMAH) as a compatibilizer on the morphological, mechanical and thermal properties. The mechanical properties of rubber‐toughened polypropylene nanocomposites (RTPPNCs) were studied through tensile, flexural and impact tests. Scanning electron microscopy (SEM) was used for investigation of the phase morphology and rubber particles size. X‐ray diffraction (XRD) was employed to characterize the formation of nanocomposites. The thermal properties were investigated by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The dynamic mechanical properties were examined by using dynamic mechanical analysis (DMA). From the tensile and flexural tests, the optimum loading of organoclay in RTPP was found to be 6 wt%. The optimum loading of PPgMAH, based on the tensile and flexural properties, was also 6 wt%. The increase in the organoclay and PPgMAH content resulted in a severe embrittlement, manifested by a drop in the impact strength and tensile elongation at break. XRD studies revealed that intercalated RTPPNCs had been successfully prepared where the macromolecular PP segments were intercalated into the interlayer space of the organoclay. In addition, the organoclay was dispersed more evenly in the RTPPNC as the PPgMAH content increased. TGA results revealed that the thermal stability of the RTPPNC improved significantly with the addition of a small amount of organoclay. Copyright © 2006 Society of Chemical Industry

Crystallisation behaviour of Polyamide-6 and Polyamide-66 nanocomposites

The crystallisation properties of injection moulded Polyamide-6 and Polyamide-66 nanocomposites based on organophilic layered silicates were investigated by differential scanning calorimetry and X-ray diffraction to better understand the influence of the nanoplatelets on these two matrices. It was found, that the thin clay platelets effect the crystal structure of Polyamide-6 and the crystallisation rate of both types of polyamides. Differences in thermal properties are ascribed to changes of the crystal modification and crystallite size of the polymer matrix.

Chlorosulfonated polypropylene: preparation and its application as a coupling agent in polypropylene–clay nanocomposites

Polypropylene nanocomposites containing organophilic layered silicate were prepared by melt mixing. In order to increase polypropylene polarity, Cl and SO 2Cl groups were introduced by reaction with sulfuryl chloride under UV irradiation. Chlorosulfonated polypropylene was subsequently melt-compounded with organophilized montmorillonite clay to produce a masterbatch. The masterbatch was then blended with commercial isotactic polypropylene. An organophilized silicate (Cloisite 15A) and three chlorosulfonated polypropylenes with different degrees of functionalization were used in this study. The effect of various processing procedures was examined as well. The morphology of nanocomposites obtained was examined using TEM and X-ray diffraction. It has been shown that the presence of polar groups leads to an increased gallery distance and partial exfoliation. Nevertheless, full exfoliation of clay platelets has not been achieved. The observed morphologies affected the resulting tensile mechanical behaviour: both stiffness and strength significantly increased.