Fibrillar Silicate Research Articles

Largely enhanced water responsive sensitivity of ENR composites by simultaneously introducing cellulose nanocrystals and fibrillar silicate

In this study, water-responsive elastomer nanocomposites were designed and prepared by simultaneously introducing cellulose nanocrystals (CNCs) and fibrillar silicate (FS) into epoxidized natural rubber (ENR) via latex compounding followed by in-situ drying and filming. The simultaneous presence of CNCs and FS reduces the dense packing of both FS and CNCs because the initial dispersion of FS and CNCs in the latex is homogeneous and mutually separated, and the interaction between FS and CNCs is weaker than that between CNCs. More importantly, the longer FS forms network framework, and some of the shorter CNCs are assembled with FS through hydrogen bonding interaction, forming the much stronger network in CNC/FS/ENR composites. As a result, CNCs and FS show a synergistic effect on the water-responsive sensitivity. Among various ENR composites with the same volume fraction of fillers, 2CNC/4FS/ENR composite exhibits the strongest network, and its storage modulus and reversible water responsive sensitivity are approximately 11.5 times and 3 times that of 6CNC/ENR composite, respectively.

Interfacial nanomechanical properties and chain segment dynamics of fibrillar silicate/elastomer nanocomposites

For fiber reinforced rubber composites, the interface is the most critical factor affecting the stress transfer efficiency and the ultimate reinforcing effect. In this study, we investigated the interfacial interaction of three kinds of fibrillar silicate (FS) filled natural rubber (NR) composites via a combination of quantitative nanomechanical technique of atomic force microscopy (AFM-QNM) and broadband dielectric spectroscopy (BDS) measurements. The force-deformation curves at nanoscale of these composites was revealed to quantitatively obtain the interfacial thickness and Young's modulus, and the Johnson−Kendall−Robert (JKR) contact model was used to fit the force-deformation curves to verify the reliability of the AFM-QNM results. The interfacial thickness of these composites with double-layer structure was further verified by High Resolution Transmission Electron Microscope (HRTEM) directly. The BDS results indicate that apart from the bulklike α-relaxation, a slower αinf -relaxation by 1−2 orders of magnitude than bulklike α-relaxation was observed in these nanocomposites attributed to restricted segmental relaxation of interfacial NR chains by FS, and the relaxation times of these composites agree well with the results of interfacial thickness and Young's modulus. An in-depth analysis of the interfacial interaction mechanism of these FS/NR composites was given. This study helps us to deep understand the interface of nanofiber reinforced composites, and it provides guidance for the interfacial design of high performance rubber composites.

Dispersion and filler network structure of fibrillar silicates in elastomers

The dispersion and filler network of fibrillar silicate (FS) in elastomers were studied. The results showed that a good dispersion of FS in matrix during mechanical blending in unvulcanized composites contributed to a strong FS filler network, different from that of traditional reinforcing fillers. Meanwhile, the filler re-aggregation during vulcanization caused by the overlapping and intertwining of FS further strengthened the filler network. The factors including Mooney viscosity and molecular polarity of elastomer, type and amount of silane coupling agents used for filler modification, that may influence the filler network, were studied. Our study helps us to understand the mechanism for the formation of filler network of FS in elastomers and provides guidance for the preparation of high performance FS/elastomer composites.

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.

Mechanical Behavior and Fracture Toughness Evaluation of Multiphase Polymer Nanocomposites Using Impact and J-Integral via Locus Method

Fracture behaviors of fibrillar silicate clay (MMT) filled thermoplastic polyolefin (TPO) containing polypropylene (PP) blended with ethylene-propylene-diene monomer (EPDM) were systematically investigated using impact test method and J-integral by locus method. Drastic increase in impact strength is observed for all developed compositions and generally shows higher value for the selected phases containing dispersed nanoclay in PP matrix. A fracture mechanics approach has been adopted by mode I test, and the effects of specimen geometry have been investigated. Increase in interlaminar fracture energy value, Gc, and J-integral value, Jc, is marked as the crack propagated through the composite; that is, a rising “R-curve” is observed. Toughness measurements revealed that the fracture toughness increased with increasing clay content reaching maximum at 3 wt% of clay than pure PP. Moreover, enhancement of fracture toughness was more remarkable than that of stiffness. The fracture surfaces taken from different specimens were observed for exploring the fracture mechanisms using transmission electron microscopy (TEM) revealed a strong particle-matrix adhesion.

Plasticity/damage coupling in fibrillar silicate-reinforced polypropylene/ethylene–octene copolymer composite under strain-controlled loading

Mechanical properties and deformation mechanism of polypropylene (PP) filled with different weight percentage of ethylene–octene copolymer (EOC) and fibrillar silicate attapulgite (ATP) clay were investigated under uniaxial cyclic loading at constant crosshead speed to evaluate plasticity/damage coupling behavior. With increasing EOC and clay content, PP exhibited typical plastics response with marked stress drop at yield followed by steady state plastics region up to rupture. The addition of 3 wt% ATP clay to the PP/EOC blend shows enhanced impact strength up to four times compared to PP with decrease in yield strength by 24% implied synergistic toughening effect. Volume strain, which characterizes deformation damage, steadily increased over the whole plastics stage up to 5.2 for axial strain of 0.30 after a critical tensile strain of 0.05. The small energy value observed for large volume strain revealed matrix shear deformation as the controlling factor for energy dissipation without crazing. Fractography observation using scanning electron microscopy revealed formation of debonding and cavitations on the surface of PP matrix, contributing increase in the volume of all compositions.

Preparation of silver nanoparticle immobilized fibrillar silicate by poly(dopamine) surface functionalization

Surface modified fibrillar silicate (FS) was prepared by dopamine oxide polymerization and self‐assembly of poly(dopamine) (PDA) on the FS surface, presynthesized silver nanoparticles subsequently adhered to the PDA functionalized FS (FS‐PDA) surface by simply dipping FS‐PDA in silver nanoparticles solution, owing to the metal‐binding ability of catechol and nitrogen‐containing groups on the PDA coating on the surface of FS. The chemical composition of the modified FS surface was determined by X‐ray photoelectron spectroscopy. Surface morphological changes of the FS nanofibers were observed by transmission electron microscopy. The results indicated that the in situ spontaneous oxidative polymerization of dopamine on the FS surface and the immobilization of Ag nanoparticles on the surface of FS were successful. The FS‐PDA/Ag demonstrated a significant enhancement in antibacterial properties compared to the pristine FS by using Escherichia coli as model strain. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39859.

Interfacial enhancement of fibrillar silicates (FSs)/EPDM nanocomposites by surface modification of FS in supercritical CO2

Abstract In this work, surface modification of fibrillar silicate (FS) is conducted by using supercritical CO2(sc-CO2) technique. For comparison purpose, conventional modification method is also carried out. The results showed that physical adsorption of the modifier (KH570) on FS surface dominated by using conventional method, whereas chemical adsorption dominated by using sc-CO2 technique. In addition, a more uniform adsorption of the modifier on FS surface is successfully obtained by using sc-CO2 method. This is ascribed to the special gaseous and liquid characteristics of sc-CO2, which can facilitate the diffuse and the full contact of KH570 on the whole surface of FS. The modified FS are then melt blended with ethylene–propylene ethylidene norbornene terpolymer (EPDM) to prepare rubber composites with excellent high temperature performance and good ageing resistance. The results showed that a more uniform dispersion of FS in EPDM matrix and a stronger interfacial interaction between FS and EPDM are successfully achieved by surface modification of FS in sc-CO2, which lead to the obviously enhanced mechanical properties of the composites. Our work demonstrates a better surface modification technique for FS to largely improve the interfacial interaction between FS and EPDM and to obtain a high performance FS/EPDM elastomer composites for its wide application such as transmission belts of automobile.

Static and dynamic mechanical properties and fracture morphology of EPDM composites containing silicate nanofibers and short PA-66 microfibers

Ethylene propylene diene monomer rubber composites reinforced with micro- and nano-sized short fibers were made by mechanically blending of silanized fibrillar silicate (FS) nanofibers and polyamide 66 (PA-66) microfibers. A synergistic reinforcement on static and dynamic mechanical properties was revealed. When FS nanofibers and PA-66 microfibers were used together in an appropriate volume ratio, static and dynamic mechanical properties (such as tensile stress, mechanical anisotropy, compression modulus, dynamic storage modulus and tensile fatigue property) of the resulting composites were substantially improved. The co-reinforcement mechanism of nano- and micro-sized fibers was discussed in terms of composite fracture morphology. The synergetic reinforcement effect on the dynamic fatigue properties is attributed to the result of competitive factors including stress transfer, crack initiation and propagation, and matrix reinforcement, whereas the synergetic reinforcement effect on the static tensile properties is achieved due to the strong interfacial adhesion between FS nanofibers and rubber.

Structure and mechanical properties of nanodispersed fibrous silicate-reinforced ethylene-propylene-diene monomer nanocomposites

In this study, ethylene–propylene–diene monomer (EPDM)/fibrillar silicate (FS) nanocomposites were successfully prepared by mechanically blending EPDM with FS, which was modified by silane coupling agent KH570 containing methacryloxy group. The effects of silane content and modified FS on the dispersion of FS and mechanical properties of the composites were investigated. The impact of water in FS on mechanical properties of the composites was also evaluated. The results showed that modified FS could be dissociated into nanofibers dispersing evenly in the EPDM matrix by increasing substantially the loading of silane through the mechanical blending. The optimum loading level of silane coupling agent was up to 24 phr/100 phr FS. Silane KH570 could improve the dispersion of FS and strengthen nanofibers–rubber interfacial adhesion even at the loading of as high as 50 phr FS, making FS to exhibit excellent reinforcement to EPDM. Too much FS could not be completely dissociated into nanofibers, slowing down further improvement. The EPDM/FS composites exhibited the similar stress–strain behavior and obvious mechanical anisotropy with short microfiber-reinforced rubber composites. With the increase in silane coupling agent and modified FS, the number of nanofibers increased because of the exfoliation of FS microparticles; thus, the mechanical behaviors would become more obvious. It was suggested that the free water in FS should be removed before mechanically blending EPDM with FS because it obviously affected the tensile properties of the composites. Regardless of whether FS was dried or modified, the EPDM/FS composites changed little in tensile strength after soaked in hot water. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Mechanical properties and reinforcement mechanisms of hydrogenated acrylonitrile butadiene rubber composites containing fibrillar silicate nanofibers and short aramid microfibers

AbstractShort‐fiber‐reinforced rubber composites (SFRCs) with hydrogenated acrylonitrile butadiene rubber (HNBR) as the matrix and fibrillar silicate (FS) nanofibers and short aramid microfibers (DCAFs) as the fillers were developed, and their tensile properties, compression moduli, and mechanical anisotropies were investigated. The results indicated that the properties of the HNBR/DCAF/FS composites were determined by the loadings of the FS nanofibers and DCAF microfibers. A small amount of the microfibers combined with an appropriate amount of the nanofibers resulted in synergetic reinforcement and imparted to the SFRCs significantly improved mechanical properties without substantially compromising the rubbery characteristics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Mild and Selective Oxidation of Alcohols Using Oxone® as An Oxidant Catalyzed by Palygorskite in Water

Palygorskite, a natural, environmentally friendly and inexpensive fibrillar silicate clay mineral, was applied as a catalyst in the oxidation of alcohols in aqueous media. The oxidation transformation effectively proceeded in the presence of an environmentally benign oxidant Oxone ® . Benzyl alcohols, benzhydrols, cyclic and aliphatic alcohols could be oxidized to their corresponding acids or ketones in moderate to high yield and good selectivity at 50 °C or 70 °C in 21 hours.

Bis-GMA/TEGDMA dental composites reinforced with nano-scaled single crystals of fibrillar silicate

Presently, dental composites have been widely adopted by the profession as the restorative material of choice; as compared to dental amalgams, the composites possess better esthetic property, have less safety concern, and have shown reasonably satisfactory clinic results. Dental composites consist of resin matrices and inorganic fillers. The monomer of 2,20-bis-[4-(methacryloxypropoxy)-phenyl]propane (Bis-GMA) has been used as an important dental base monomer since it was invented in the 1960s [1, 2]; for example, Bis-GMA is the base monomer in the Z100 Restorative Dental Composite produced by the 3M Corporate. Bis-GMA is a very viscous, honey-like liquid. To improve handling qualities, a diluent monomer of tri(ethylene glycol) dimethacrylate (TEGDMA) is added to thin the resin. In the Bis-GMA/TEGDMA dental resin systems, Bis-GMA functions to limit the polymerization-induced volumetric shrinkage and to enhance the resin reactivity, whereas TEGDMA provides for the increased vinyl double bond conversion [3, 4]. Albeit dental resins have been reinforced with inorganic fillers of glass/ceramic powders containing surface-silanized particles, relatively low strength and durability of the composites have limited their uses [5–8]: dental composites have flexural strengths typically ranging from 80 to 120 MPa, which can fulfill the requirement of filling tooth cavities but cannot survive large stress-bearing restorations such as crowns and bridges; furthermore, the strength of dental composites decreases substantially after being used for a period of time. The average service lifetime of dental composites is considerably shorter than that of dental amalgams [9, 10]. Investigations of the failures revealed that, among numerous issues, the inorganic filler was a major contributor [11, 12]. Many inorganic filler particles currently used for dental composites are spherical or irregular in shape. Such filler particles at occlusal surfaces are susceptible to dislodgement from the resin matrix during wear with food boluses. This would cause the reinforcement effect to be lost. Chopped glass fibers and/or high strength whiskers with diameters of 5–50 lm and aspect ratios larger than 10 have also been investigated to reinforce dental resins [13–16], and the resulting composites showed higher mechanical properties. Several reinforcement mechanisms including ‘‘Bridging,’’ ‘‘Pull-out,’’ and ‘‘Load Transfer’’ were proposed for understanding the fiber/whisker reinforcement [17, 18]; in particular, ‘‘Bridging’’ is a powerful reinforcement mechanism. If a micro-crack is initiated in a resin matrix under contact wear and/or other stresses, the fillers remain intact across the crack planes supporting the applied load. Crack-opening is resisted by the bridging fillers; thus the resin matrix is reinforced. Requirements for fillers to achieve effective ‘‘Bridging’’ reinforcement include high strength and large aspect ratio values; tooth enamel rods are an example of elongated fillers, and crystalline platelets in dental glass/ceramics are another example [19]. Nonetheless, the dental composites reinforced with fibers/whiskers generally possess mechanical properties that still need further improvements; this is L. Zhang Y. Gao Q. Chen H. Fong (&) Department of Chemistry, South Dakota School of Mines and Technology, 501 East St. Joseph Street, Rapid City, SD 57701, USA e-mail: Hao.Fong@sdsmt.edu

Preparation and characterization of γ‐irradiated crosslinked silicone rubber/organoattapulgite composites

AbstractSilicone rubber (SR)/organoattapulgite (OAT) composites were prepared with γ‐irradiation crosslinking at a dose range varied from 30 to 300 kGy. Natural fibrillar silicate attapulgite (AT) was modified by silane coupling agent, and the obtained OAT was used as reinforcing fillers in SR. The effect of irradiation doses on the degree of crosslinking of SR/OAT composites was determined by solvent swelling method. It was found that the molecular weight between crosslinks (Mc) reduced with the increase in irradiation doses. Moreover, the addition of OAT to SR matrix promoted an increase in the crosslinking density of the composites because of the presence of the active crosslinking sites of OAT. The mechanical properties of the SR/OAT composites including tensile strength, elongation at break, and Shore A hardness subjected to various irradiation doses were studied. The experimental results showed that the tensile strength, elongation at break, and Shore A hardness were all improved significantly in the presence of OAT, which indicated that OAT was an alternative reinforcing filler of SR. In addition, the effect of various irradiation doses on the mechanical properties of SR and SR/OAT composites was also investigated. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Interface and mechanical properties of peroxide cured silicate nanofiber/rubber composites

AbstractFour representative rubber matrices with varying molecular polarity, such as SBR, NBR, EPDM, and CNBR, were reinforced by mechanical blending with γ‐(methacryloxy)proxyltrimethoxy silane (KH570) silanized natural fibrillar silicate (FS)/unmodified FS when dicumyl peroxide was used as a curing agent. The effects of the loading amount of silane coupling agent KH570 and the type of rubber matrix on the dispersion of FS as well as the FS‐rubber interfacial bonding were investigated. The mechanical properties of various rubber composites filled with unmodified FS and silanized FS individually were compared. As indicated by SEM and TEM, unmodified FS showed better dispersion in polar CNBR than in nonpolar SBR, whereas the improvement of the dispersion is more for SBR after the silanization of FS, constructing a stronger filler network. Compared with unmodified FS/rubber composites, silanized FS/rubber composites exhibited a higher interphase crosslinking network as well as a lower loss factor, indicating the improvement of the FS‐rubber interfacial bonding. The more the loading amount of KH570 was, the more the FS‐SBR bonding was improved. Similarly, the improvement of the FS‐rubber bonding was more evident in nonpolar SBR and EPDM after FS was silanized, causing the more increase in mechanical properties, relative to polar NBR and CNBR. In strong molecular polar rubber such as CNBR and NBR, the strong interfacial bonding was achieved even if FS was not silanized with KH570, so that the composites filled with unmodified FS also possessed good mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Structure and Mechanical Properties of PP/EPDM/Attapulgite Ternary Blends

Polypropylene(PP)/ethylene-propylene-diene copolymer (EPDM)/fibrillar silicate attapulgite (AT) ternary blends were first prepared via the two-step melt blending process, by which the AT was blended with EPDM prior to compound with PP. Structure and mechanical properties of the blends were investigated. According to the analysis of TEM and DMA test, it was concluded that as for PP/EPDM/AT ternary blends, the typical “sea-island” morphology was observed, and the morphology of encapsulated structure like sandbag was formed in PP matrix besides neat EPDM dispersion domain, where EPDM encapsulated fibrillar silicate AT. The most-odds diameter (Dm), the number-average diameter (Dn) and the weight-average diameter (Dw) of dispersed particles decreased with increasing EPDM. PP/EPDM/AT ternary blends showed higher yield strength and dynamic modulus than the corresponding PP/EPDM binary systems due to the reinforcement of AT. PP/EPDM/AT ternary blend (100/20/5) possessed the balanced yield strength (21.9 MPa) and impact strength (47.7 kJ·m−2), relative to 23.0 MPa and 9.4 kJ·m−2 of PP. The micromechanical deformation process-mainly debonding of dispersed particles and shear yielding was mainly responsible for impact resistance of the ternary blends.

Fabrication and evaluation of Bis-GMA/TEGDMA dental resins/composites containing nano fibrillar silicate

Objective To investigate the reinforcement of Bis-GMA/TEGDMA dental resins (without conventional glass filler) and composites (with conventional glass filler) with various mass fractions of nano fibrillar silicate (FS). Methods Three dispersion methods were studied to separate the silanized FS as nano-scaled single crystals and uniformly distribute them into dental matrices. The photo-curing behaviors of the Bis-GMA/TEGDMA/FS resins were monitored in situ by RT-NIR to study the photopolymerization rate and the vinyl double bond conversion. Mechanical properties (flexural strength, elastic modulus and work-of-fracture) of the nano FS reinforced resins/composites were tested, and analysis of variance (ANOVA) was used for the statistical analysis of the acquired data. The morphology of nano FS and the representative fracture surfaces of its reinforced resins/composites were examined by SEM/TEM. Results Impregnation of small mass fractions (1% and 2.5%) of nano FS into Bis-GMA/TEGDMA (50/50 mass ratio) dental resins/composites improved the mechanical properties substantially. Larger mass fraction of impregnation (7.5%), however, did not further improve the mechanical properties (one way ANOVA, P > 0.05) and may even reduce the mechanical properties. The high degree of separation and uniform distribution of nano FS into dental resins/composites was a challenge. Impregnation of nano FS into dental resins/composites could result in two opposite effects: a reinforcing effect due to the highly separated and uniformly distributed nano FS single crystals, or a weakening effect due to the formation of FS agglomerates/particles. Significance Uniform distribution of highly separated nano FS single crystals into dental resins/composites could significantly improve the mechanical properties of the resins/composites.

Bis-GMA/TEGDMA dental composites reinforced with electrospun nylon 6 nanocomposite nanofibers containing highly aligned fibrillar silicate single crystals

The objective of this research was to study the reinforcement of electrospun nylon 6/fibrillar silicate nanocomposite nanofibers on Bis-GMA/TEGDMA dental composites. The hypothesis was that the uniform distribution of nano-scaled and highly aligned fibrillar silicate single crystals into electrospun nylon 6 nanofibers would improve the mechanical properties of the resulting nanocomposite nanofibers, and would lead to the effective reinforcement of dental composites. The nylon 6/fibrillar silicate nanocomposite nanofibers were crystalline, structurally oriented and had an average diameter of approximately 250 nm. To relatively well distribute nanofibers in dental composites, the nanofiber containing composite powders with a particle structure similar to that in interpenetration networks were prepared first, and then used to make the dental composites. The results indicated that small mass fractions (1% and 2%) of nanofiber impregnation improved the mechanical properties substantially, while larger mass factions (4% and 8%) of nanofiber impregnation resulted in less desired mechanical properties.

Overall properties of fibrillar silicate/styrene–butadiene rubber nanocomposites

AbstractThe mechanical properties, heat aging resistance, dynamic properties, and abrasion resistance of fibrillar silicate (FS)/styrene butadiene rubber (SBR) nanocomposites are discussed in detail. Compared with white carbon black (WCB)/SBR composites, FS/SBR composites exhibit higher tensile stress at definite strain, higher tear strength, and lower elongation at break but poor abrasion resistance and tensile strength. Surprisingly, FS/SBR compounds have better flow properties. This is because by rubber melt blending modified FS can be separated into numerous nanosized fibrils under mechanical shear. Moreover, the composites show visible anisotropy due to the orientation of nanofibrils. There is potential for FS to be used to some extent as a reinforcing agent for rubber instead of short microfibers or white carbon black. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2725–2731, 2006

The Anisotropy of Fibrillar Silicate/Rubber Nanocomposites

AbstractSummary: Fibrillar silicate (FS)/rubber nanocomposites were successfully prepared by directly mixing modified FS with rubber matrix. It is found that FS could be separated into nano‐fibrils with diameters less than 100 nm by the shear forces during mixing. The stress‐strain characteristics of these composites are similar to those for short micro‐fiber/rubber composites (SFRC). Nevertheless, these FS/rubber composites have some outstanding advantages over the conventional SFRC, even though the reinforcing effect of FS is restricted due to its small shape aspect ratio. More importantly, the differences in mechanical properties of the composites in the two different directions show that SBR/FS and NBR/FS composites both exhibit obvious anisotropy, which strongly depends on the preparation process, FS concentration, and rubber matrix. These factors were thoroughly investigated in this paper, and it can be concluded that the anisotropy of the composites was due to the orientation of nano‐fibrils. magnified image