No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Structural modification of sepiolite (natural magnesium silicate) by thermal treatment: Effect on the properties of polyurethane adhesives
Abstract
A sepiolite silicate was heat-treated at 550 and 1000°C to modify its structure, and was used as a filler in a solvent-based polyurethane (PU) adhesive. The treated sepiolites were characterized by X-ray diffraction and infra-red spectroscopy, and it was observed that the water was irreversibly removed from the structure and pores of the sepiolite, changing the structure. The increase of temperature produced a collapse of the sepiolite structure. The rheological, mechanical, thermal and adhesion properties of the filled PU adhesives were measured. In general, the addition of treated sepiolite to PU adhesives resulted in a loss of adhesive properties with respect to the blank (PU adhesive with untreated sepiolite). The loss in properties was more noticeable as the treatment temperature increased. Thus the PU adhesives containing treated sepiolite had reduced rheological properties (lower viscosity, lower storage and loss moduli, and they did not provide thixotropy and pseudoplasticity to the solutions) with respect to the PU adhesive filled with untreated sepiolite. On the other hand, the addition of treated sepiolite decreased the mechanical and thermal mechanical properties of PU films. The T-peel strength of roughened and roughened + chlorinated (with 1 wt% trichloroisocyanuric acid in 2-butanone) styrene-butadiene rubber/PU adhesive joints was improved if the PU adhesive contained untreated sepiolite, but it decreased if the sepiolite was heat-treated. Interactions between the untreated sepiolite, the solvent and the polyurethane were responsible for the improved properties of PU adhesives. These interactions disappeared when the sepiolite was heat-treated, because of the destruction of the structure of the sepiolite and the removal of surface silanol groups.
... The thermal behavior of natural sepiolite has been studied in detail in the literature [28,[36][37][38][39][40][41][42]. First, superficially adsorbed and zeolitic water molecules are lost at temperatures of up to 170 • C, while, in the temperature range from 300 to 350 • C, half of the coordination water molecules are removed, and the structure folds, entrapping the second half of the coordination water in the collapsed channels. ...
... A slight response to humidity from about 18% RH was observed in the S1FeSUB and S1FeXS samples because of the presence of Fe 2 O 3 , as can be seen in the XRD patterns as well as the XPS and FTIR spectra. Fired sepiolite becomes hydrophobic because of the loss of the four water molecules coordinated to magnesium ions, as well as structure folding [28,[36][37][38][39][40][41][42]. However, the presence of iron or tungsten ions restores its hydrophilicity [2,28]. ...
... A slight response to humidity from about 18% RH was observed in the S1FeSUB and S1FeXS samples because of the presence of Fe2O3, as can be seen in the XRD patterns as well as the XPS and FTIR spectra. Fired sepiolite becomes hydrophobic because of the loss of the four water molecules coordinated to magnesium ions, as well as structure folding [28,[36][37][38][39][40][41][42]. However, the presence of iron or tungsten ions restores its hydrophilicity [2,28]. ...
Nowadays, humidity sensors are attracting a great deal of attention, and there are many studies focusing on enhancing their performances. Nevertheless, their fabrication through facile methods at reasonable cost is a significant factor. In this article, a new magnesium silicate nanopowder was successfully synthesized using a simple and low-cost sol–gel method. Subsequently, modified sepiolite was achieved by the substitution of iron ions in the synthesized nanopowders. The specimens were then characterized by X-ray diffraction, field emission–scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric–differential thermal analysis, infrared spectroscopy, and nitrogen adsorption. Furthermore, humidity sensors were manufactured by screen printing the prepared powders on alumina substrates with interdigitated Pt electrodes. The results showed that the fabricated sensors with modified sepiolite exhibited interesting characteristics for humidity detection.
... Theoretically, it has been found that liquid water will turn into steam at temperatures above 100 • C, and its volume will theoretically increase by about 1000 times [27]. In addition, in the range of 100-300 • C, the adsorbed water in the pores will change from a liquid phase to a gas phase, but the crystalline structure will not be destroyed [28,29]. Accordingly, if sepiolite is placed in a pressure vessel filled with high-temperature steam, its pore volume will increase significantly. ...
As a common method for preparing micron powder in industrial operations, the mechanical extrusion method simply pursues the particle size without considering the microstructure characteristics of sepiolite, which leads to problems such as bundles of sepiolite not being effectively dispersed, and thus the disruption of fibers is inevitably caused. In this work, a new micronization method for disaggregating these bundles while preserving the original structural integrity of the fibers is proposed based on steam pressure changes. The effects of steam pressure changes on the particle size distribution, microstructure, and properties of treated sepiolite are studied using X-ray fluorescence spectrometer (XRF), X-ray diffractometer (XRD), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), and a specific surface area and aperture analyzer (BET). The experimental results show that the particle size of sepiolite powder depends greatly on steam pressure, and sepiolite powder with mass ratio of 91.6% and a particle size D97 of 21.27 μm is obtained at a steam pressure of 0.6 MPa. Compared to the sepiolite after mechanical extrusion, the sepiolite treated with steam pressure changes can maintain the integrity of its crystalline structure. The specific surface area of sepiolite enhanced from 80.15 m² g⁻¹ to 141.63 m² g⁻¹ as the steam pressure increased from 0.1 to 0.6 MPa, which is about 1.6 times that of the sample treated with mechanical extrusion.
... This has brought to an adequate surface area to be able to interact with the rubber and diminish filler-filler distance. Surface area is an important factor in the composite structure, the larger the surface area of the filler, higher possibility of contact takes place 25,26 , giving efficient stress-transfer from one another The decrease in tensile strength with sepiolite content above 15 phr is simply contributed to the agglomeration of filler or so-called filler-filler interaction 20 . When high amount of sepiolite was added, the sepiolite itself tend to interact themselves due to the strong physical adsorption among them. ...
The use of mineral fillers in rubber industry has been increasingly focused. Sepiolite is considered as one of the mineral fillers that exploits unique characteristics. This is due to its unique needle-like fibrous and a tunnel-like micro-pore channel structures. Therefore, adding this filler in natural rubber (NR) matrix would bring tremendous advantage. The study was carried out in the form of curing characteristics, tensile properties and morphology together with the dynamic properties. Filling sepiolite to NR has brought to a noticeable enhancement of curing characteristics, tensile properties and morphology. This is contributed to the distinctive structure of sepiolite itself, it provides a better dispersion to the NR. Surface roughness of the composites is visibly found which is responsible for the mechanical properties. Further verification was also monitored through the dynamic properties of the composites. The obtained profiles are in good agreement to the tensile properties and morphological characteristics observed.
... In all cases, a fundamental aspect to achieve these effects is obtaining an excellent dispersion of the sepiolite inside the polymer (Alan and Iş çi, 2014;Torr o-Palau et al., 1997), being sometimes necessary a chemical modification of the surface of the sepiolite, which improves the compatibility between the sepiolite and the polymer and allows achieving a better dispersion (Chen et al., 2011). ...
Nanocomposite hydrophilic flexible polyurethane foams were prepared by in situ polymerization using an organomodified sepiolite as filler. The sepiolite affinity by nitrates dissolved in water was increased by treating them with quaternary ammonium salts (S-QAS), leading to remarkable nitrates maximum adsorption capacity (qmax = 23.30 mg/g). The Langmuir model well described the adsorption process of the nitrates by the modified sepiolite, and more remarkably, the sepiolite suffers no decrease of their nitrates removal capacity after being imbibed in the flexible polyurethane foam. The proper selection of the polyurethane chemistry allows significant contact between the polluted-water and the sepiolite, even when enclosed inside the cell walls. Accordingly, the as-prepared hydrophilic polyurethane/sepiolite foams provided a facile removal of nitrates-pollution from water, even actual nitrates-polluted water with a competitive adsorption environment, without the need to control or modify the pH and temperature of the polluted water neither to add further filtration steps to collect the active particles from the water.
... The first small weight loss below 100 °C is attributed to the loss of free water and the second weight loss between 173.05-333.2 and 333.2-493.2 °C is attributed to the loss of constitution water paralleled with transformation to crystalline nature, so the released energy is due to this transformation [31,32] . The resulted weight loss in different prepared fertilizer was 14.01 wt% in Z, 10.04 wt% in NZ, and 17.38 wt% in ZP , 18.8 wt% in NZP. ...
A field experiment was carried out at Baloza Research Station of the Desert Research Center, North Sinai, Egypt, to study the effect of applying 50, 75 and 100% of the recommended rates of nano-zeolite phosphorus (20.9% P2O5), zeolite phosphorus (8% P2O5), and the ordinary superphosphate fertilizer (15.5% P2O5) to yield components, nutrients content, uptake by straw, seeds of peanut crop (Giza 6 cultivar), and the level of available nutrients in the sandy soil. Zeolite and nano porous-zeolite measuring a dimension of 730.8 and 90.2 nm, respectively, were used in this study. Application of nano-zeolite phosphorus resulted in the highest values of yield components including 1.89, 3.48, 1.46-ton fed⁻¹ and 53.2 % for pod, straw, seeds crop and oil content, respectively. This study came to the conclusion that the well-organized use of fertilizers can be enhanced through using nano sources, so the pollution hazard can be reduced.
... The first small weight loss below 100 °C is attributed to the loss of free water and the second weight loss between 173.05-333.2 and 333.2-493.2 °C is attributed to the loss of constitution water paralleled with transformation to crystalline nature, so the released energy is due to this transformation [31,32] . The resulted weight loss in different prepared fertilizer was 14.01 wt% in Z, 10.04 wt% in NZ, and 17.38 wt% in ZP, 18.8 wt% in NZP. ...
... They are commonly used as viscosity modifiers, with the B20 grade designed for intermediate polarity systems and B40 for high polarity systems. The sepiolite nanoparticles have high aspect ratios (particle lengths range from 500 to 1500 nm and diameters from 20 to 40 nm - [28]) and are characterised by porous channels (3.6 Å x 10.6 Å), which are oriented along the particle's length, and can absorb water and some organic monomers [29]. ...
Rod-like sepiolite organoclays are incorporated into a simple, first-generation commercial bismaleimide (BMI) to improve the inherent brittleness of the cured polymer; montmorillonite clay is used as a baseline comparison. Both solution and solid state blending methods are evaluated to determine which offer the best method of dispersion. Increased Pangel B40 (sepiolite) loading leads to finer particle sizes and a narrower size distribution indicating that the nanoclay assists the grinding and particle size refinement. The cured nanocomposites containing sepiolite nanoclays offer superior storage modulus to the montmorillonite. Introduction of Pangel B40 achieves around a 15–42% increase in plane-strain fracture toughness (depending on loading) and modest increases (+2%) in char yield when compared with the unmodified BMI.
... However, C30B-CPN maintained a higher breaking extension value even at higher clay-concentrations and it was still comparable with the breaking extension of pristine PU film. Generally, with incorporation organoclay in PU matrix, the tensile strength and stiffness of CPN increase up to a certain concentration with a sacrifice in elasticity (Torro-Palau et al., 1997). Interestingly, in this case, the breaking extension increased along with strength and Young's modulus of CPN with increasing clay-loading up to 3 wt%, which was a consequence of the change in interfacial interactions between PU and modified silicates. ...
Organo-modified montmorillonite (Mt) and bentonite reinforced clay/polyurethane nanocomposite (CPN) films were produced by master-batch based melt-mixing route, followed by compression molding. A novel route for preparation of master-batch by solution mixing was explored by using sonication and high-speed stirring. It was found that master-batch prepared by solvent mixing route resulted in good dispersion of clay-platelets in master-batch and finally in CPN. The concentration of both organoclays was varied from 1 to 5 wt% in final CPN, which were prepared by melt-mixing of master-batch and neat polyurethane (PU) in a twin-screw extruder.
The presence of hydroxyl group in the clay-modifier of Mt, attributed to nearly exfoliated structure up to 3 wt% due to improved interaction by hydrogen bonding with ether groups or urethane linkages. Whereas, organo-modified bentonite showed partially intercalated and flocculated morphology, due to the absence of any polar group in the clay-modifier. As a consequence, Mt/PU nanocomposites showed much better mechanical and gas barrier properties in comparison to bentonite/PU nanocomposites. Moreover, a significant reduction in helium gas permeability and improvement in mechanical (tensile and tear) properties were observed for CPN produced with both organoclays in comparison to neat PU. At lower volume fraction of organoclays, a good correlation was obtained between gas permeability values determined experimentally and predicted by two different mathematical models.
... Sepiolite is a natural hydrated magnesium silicate of the same family of clays as attapulgite and differs structurally from bentonites (montmorillonites). Differences arise from the existence of discontinuities and inversions in the silica sheet that give rise structural channels filled with water molecules and running along the axis of the particle (Ruiz et al. 1996;Torró-Palau et al. 1997). The presence of these inversions gives sepiolite characteristic needle-like morphology instead of plate-like montmorillonite. ...
This paper investigates the sorption characteristics and mechanisms of pyrene onto two types of natural sepiolite-brown (B-Sep) and white (W-Sep). The effects of relevant properties such as clay content, surface area, pore diameter and volume, divalent cations, and organic carbon content were investigated by single component batch adsorption systems. The results suggest that pyrene has high affinity for both sepiolite and its sorption behavior could be mainly affected by exchangeable strongly hydrated cations such as Ca2+ and H2O in the zeolite-like channels and by open channel defects (OCD) structures but no so much by the large number of Si-OH groups located on the sepiolite’s basal surfaces. Mesoporosity rather than surface area largely controls the sorption capacity and intensity of both sepiolites. This is shown by the increase in pore volume that exhibited the greatest increase in BET surface area. Particle size and morphological changes of both sepiolites following pyrene adsorption determined by FE-SEM showed that the sepiolite fibers are much longer than their widths, which are only several laths (several nanometers). This is a result of growth, mostly along the c-axis, at the expense of the diffusion of pyrene molecules through aqueous solution. As a consequence, a significant fibrous morphology is produced following the adsorption of pyrene by both sepiolites.
... The characteristic bands of Fe-O-Fe bonds were present in the FTIR spectrum of Sep/ Fe 2 O 3 , which reflected the formation of α-Fe 2 O 3 . However, the silicate backbone was comparatively stable in hydrothermal condition, because the characteristic bands of Si-O-Si groups in the range of 1200 cm −1 to 1000 cm −1 almost show no change after hydrothermal reaction [41,42]. This confirmed that the silica framework of Sep was still present in the hybrid pigment as an important component. ...
A series of clay/Fe2O3 red hybrid pigments with vivid color, good stability and low cost were synthesized via a facile one-step reaction of Fe3+ solution with sepiolite (Sep) or halloysite (HNTs). Sep or HNTs play a key role to promote the in-situ transformation of Fe3+ into red hybrid pigments, because only black product was formed from Fe3+ in the absence of them. The addition of Sep and HNTs avoids the usage of any chemical precipitants, which is greatly superior to the traditional process. The a⁎ coordinate values of the sepiolite/Fe2O3 (Sep/Fe2O3) and halloysite/Fe2O3 (HNTs/Fe2O3) hybrid pigments are 25.1 and 34.4, respectively, which indicate they have well red color performance. The positive influence of Sep or HNTs on the crystallization process and dispersion of Fe2O3 particles is responsible for the good red color. In addition, the hybrid pigments exhibit excellent stability to resist external attacks such as light, acid, alkaline, organic solvents and high temperature, and can be facilely spray-coated onto various substrates, e.g., glass, wood plate, ceramic plate, stone plate, and polyester plate, etc.. Therefore, they are potential to be used as promising low-cost environment-friendly colorants in many fields such as ceramic, painting, coating, and printing.
... The thermal behavior of sepiolite has been extensively studied in the literature too [12][13][14][15][16][17]: in the first step, water superficially adsorbed and zeolitic water are removed up to 170°C (eq. 2), while, between 300° and 350°C, a half of the coordination water molecules is removed and the structure folds (eq. ...
Different metal ions (W4+, Co2+, Cu2+, Gd3+, La3+, Mn2+, Nd3+, Sm3+, Sr2+, Y3+ and Zn2+) were precipitated onto sepiolite (an inorganic clay) under basic conditions. Thermogravimetric-Differential Thermal Analysis (TG-DTA) combined with X-Ray Diffraction (XRD), nitrogen adsorption (BET technique) and Field Emission Scanning Electron Microscopy (FESEM) were used to study both the distribution and structure of precipitated metal ions species onto sepiolite. Humidity sensors were prepared in the form of pellets, where powders were uniaxially pressed and thermally treated at 550°C for 1 h then, gold electrodes were screen-printed. Among the studied metals, tungsten showed a significant response towards humidity at room temperature from 40% RH.
... The thermal behavior of sepiolite has been extensively studied in literature (Nagata et al., 1974;Serna et al., 1975;Torró-Palau et al., 1997;Fig. 3. XRD patterns corresponding to the different metal ions doped-sepiolite (*: sepiolite, JCPDS card 13-0595; §: anhydrous sepiolite (Valentín et al., 2007 Valentín et al., 2007;Kok, 2013): in the first step, water superficially adsorbed and zeolitic water are removed up to 170°C (Eq. ...
After precipitation under basic conditions and subsequent thermal treatment, different oxide/hydroxide nanoparticles (based on W4+, Co2+, Cu2+, Gd3+, La3+, Mn2+, Nd3+, Sm3+, Sr2+, Y3+ and Zn2+) were formed onto sepiolite grains. Thermogravimetric-Differential Thermal Analysis (TG-DTA) combined with X-ray diffraction (XRD), nitrogen adsorption at -196°C, Field Emission-Scanning Electron Microscopy (FE-SEM), Diffuse Reflectance UV-visible (DR-UV-vis) spectroscopy and Infra-Red (IR) spectroscopy were used to study the particle size distribution, the morphology and the composition of the modified sepiolites.Humidity sensors were prepared in the form of pellets, where powders were uniaxially pressed and thermally treated at 550. °C for 1 h then, gold electrodes were screen-printed. Among the different studied compositions, tungsten-doped sepiolite exhibited a significant response towards relative humidity (RH) at room temperature starting from 40% RH.
... The band at 1451 cm -1 is attributed to the dolomite impurity [24]. The band at 1211 cm -1 is due to Si–O–Si bond [43]. The bands corresponding to the in plane Si–O–Si vibrations are observed at 1023, 982, and 473 cm -1 [44]. ...
Thermal and structural properties of three clays (sepiolite and two kaolinites) from Turkey were studied by thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR), and surface area measurement techniques The adsorption of sulfur dioxide (SO2) gas by these clays was also investigated. SO2 adsorption values of K1, K2, and S clay samples were measured at 20 °C and pressures up to 106 kPa. Sepiolite sample (S) primarily consists of pure sepiolite, only dolomite present as accompanying mineral. Both kaolinite samples, K1 and K2, mainly contain kaolinite as the major clay mineral and quartz as impurity. In K2 sample, muscovite phase is also present. Simultaneous TG–DTA curves of all clay samples were obtained at three different heating rates 10, 15, and 20 °C min−1 over the temperature range 30–1200 °C. It was found that the retention value of SO2 by S clay (2.744 mmol/g) was higher than those of K1 (0.144 mmol/g) and K2 (0.164 mmol/g) samples.
... Marcilla et al. [21] believed that sepiolite acted as catalyst during the thermal decomposition of polymers under inert atmosphere. Sepiolite by thermal treatment using as filler in a solvent-based polyurethane adhesive had been reported [22], but the study of thermal properties of sepiolite/polyurethane elastomer nanocomposite has been challenging. ...
The effects of sepiolite modified with γ-aminopropyltriethoxylsilane (KH550-Sp) on thermal properties of polyurethane (PU) nanocomposites were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and tensile test. The DSC results showed that the glass transition temperature of hard segments in PU/KH550-Sp nanocomposite increased with the increase of KH550-Sp, because sepiolite restricted the formation of hydrogen bonding within hard segments of polyurethane. TG results revealed that the thermal stability of PU was improved by KH550-Sp, and the onset decomposition temperature for PU nanocomposites with a KH550-Sp content of 3 wt% was about 20 °C higher than that for pure PU. The tensile properties of pure PU and nanocomposites before and after ageing 120 °C for 72 h were determined, and it was observed that the percentage loss in tensile strength decreased with the addition of KH550-Sp because of an oxidation barrier of KH550-Sp confirmed by ATR-FTIR.
... The strong and broad peak at 1081.1 cm À1 is associated with the stretching mode of siloxane (Si-O-Si), while the peak at 793.3 cm À1 is also because of the vibration of O-H [21]. The Si-O coordination bands at 1213 and 1014 cm À1 represent the stretching of Si-O in the Si-O-Si groups of the tetrahedral sheet [22], and two peaks at 714.2 and 620.4 cm À1 represent the bending vibration of Mg 3 OH of adsorbent sample. The band at 473.1 cm À1 is due to Si-O-Al (octahedral) and Si-O-Si bending vibrations, respectively, for composite adsorbent [23]. ...
The adsorption of U(VI) from aqueous solutions onto composite adsorbent (Gumalgin Cromatic) has been studied using a batch adsorber. The parameters that affect the U(VI) sorption, such as contact time, solution pH, initial U(VI) concentration, and temperature, have been investigated and optimized conditions determined. The adsorption patterns of metal ions on composite adsorbent followed the Langmuir, Freundlich and Dubinin-Radushkevich isotherms. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Langmuir model and that the sorption is physical in nature (the sorption energy Eads = 14.45 kJ/mol). Thermodynamic parameters (ΔH°ads = –129.55 kJ/mol, ΔS°ads = 357 J/mol K, ΔG°ads (298.15 K) = –23.11 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process. The results suggested that the composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.
... Studies of sepiolite nanocomposites have revealed that the polymer matrixes mainly include epoxy resin [18,19], poly(lactic acid) [20], poly(-caprolactone) [20], Nylon-6 [21], polypropylene [22,23], polyaniline [24], polyethylene [9], styrene butadiene rubber [25], and so on. Sepiolite by thermal treatment using as filler in a solvent-based polyurethane adhesive has been reported [26]. However, the study of segmented polyurethane elastomer as a polymer matrix of sepiolite nanocomposite has been challenging. ...
The polyurethane (PU) nanocomposites were prepared using organomodified sepiolite (organo-Sp) by in situ polymerization method. The clay was modified with three different organic modifiers such as γ-aminopropyltriethoxylsilane (KH550), hexadecyltrimethylammonium bromide (CTAB) and lauric acid (LA). The morphology and the dispersion of organo-Sp in polyurethane were characterized by scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy. The influence of organo-Sp on the tensile properties, water resistance and swelling rate of polyurethane composites was studied. The results showed the properties and structure of polyurethane nanocomposites were related to the kind of organic modifier.Research highlights▶ KH550 was the best among the three organic modifiers by comparing tensile properties, water resistance and swelling rate. ▶ FTIR revealed the strong interaction between KH550-Sp and the PU matrix. ▶ TEM revealed the compatibility of KH550-Sp and PU was improved. ▶ SEM confirmed the good dispersion of KH550-Sp in PU matrix.
... Many studies concerning the use of modified materials for the adsorption of metal ions have been fullfilled. For example, [28] investigated the surface modification of sepiolite with quaternary amines; [29] FTIR and zeta potential measurements of sepiolite treated with some organosilanes; [30] the structural modification of sepiolite (natural magnesium silicate) by thermal treatment; [31] the effect of particle size on surface modification of silica nanoparticles by using silane coupling agents and their dispersion stability in methylethylketone; [32] the synthesis and characterization of epoxy resin modified with nano-SiO 2 and γ-glycidoxypropyltrimethoxy silane; [33] the effects of surface modification of fumed silica on interfacial structures and mechanical properties of poly(vinyl chloride) composites; [34] the grafting of trialkoxysilane on the surface of nanoparticles by conventional wet alcoholic and supercritical carbon dioxide deposition methods; [35] FT-IR spectroscopic investigation of adsorption of 3-aminopyridine on sepiolite and montmorillonite from Anatolia; [36] the determination of vanadium, manganese, silver and lead by graphite furnace atomic absorption spectrometry after preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane. But no studies about modification by [3-(2-aminoethylamino)propyl]trimethoxysilane compound of sepiolite have been found. ...
Surface modification of clays has become increasingly important due to the practical applications of clays such as fillers and adsorbents. The surface modification of sepiolite with [3-(2-aminoethylamino)propyl]trimethoxysilane has been employed. The modified sepiolite surface was investigated by FTIR, XRD and DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and methoxy groups of [3-(2-aminoethylamino)propyl]trimethoxysilane. The changes on electrokinetic properties of modified sepiolite particles were studied by measuring the zeta potential of particle as a function of metal concentration and equilibrium pH of solution. It was found that the zeta potential of the clay particles was always negative independent of the metal concentration in solution. This study also provides some evidence for the adsorption of metal ions on modified sepiolite. The adsorption of metal ions onto modified sepiolite has varied with the type of metal cations. The available basic nitrogen centers covalently bonded to the sepiolite skeleton were studied for Co(II), Cu(II), Mn(II), Zn(II), Fe(III) and Cd(II) adsorption from aqueous solutions. It was found that the amount of metal ion adsorbed onto modified sepiolite increases with increase in solution equilibrium pH and temperature, whereas it generally decreases with the ionic strength. The experimental data were correlated reasonably well by the Langmuir adsorption isotherm and the isotherm parameters (qm and K) were calculated. The ability to adsorb the cations gave a capacity order of Zn(II) > Cu(II) ~ Co(II) > Fe(III) > Mn(II) > Cd(II) with affinities of 2.167×10−4, 1.870×10−4, 1.865×10−4, 1.193×10−4, 0.979×10−4 and 0.445×10−4 mol g−1, respectively.
Sustainable hydrogen production can be achieved efficiently by steam reforming of bio-ethanol. The use of low-cost and abundant minerals as catalyst supports can further improve the sustainability of the process....
Sepiolite (Si 12 Mg 8 O 30 (OH,F) 4 ].(H 2 O) 4 Á8H 2 O) is a valuable filler with an enormous capacity to be used in thermoplastic composites, substituting costly reinforcing fillers, such as graphene and CNTs. Sepiolite strengthened polymers nanocomposite materials have encouraged the field of research and ventures because of their strengthening ability and bio-compatibility in polymer composites. Sepiolite shows remarkable characteristics over various fillers due to its higher specific surface area and channel type structure. Numerous investigations were performed to decide different properties of Sepiolite strengthened polymer composites in various applications, for example , tensile strength, flexural strength, impact strength, stiffness, thermal, flammability, thermo-mechanical, and morphological. This review paper focuses on the mechanical and thermal properties of sepiolite strengthened polymer nanocomposites. Generally, it can be determined that the properties of sepiolite loaded thermoplastic polymer composites mainly depend on filler content, matrix, bond interaction, shape, size of sepiolite particles. Further assessment and development are required to expand its utilization in several applications. These comprise the utilization of nano-size sepiolite made synthetically as functionalized filler in thermoplastics. Ó 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
Nanocrystalline magnesium silicate with high surface area has been synthesized by precipitation method using ammonium hydroxide and different surfactants. The results show that the anionic surfactant has a significant effect on the synthesis of nanocrystals. The method makes efficient use of stabilizing surfactant and the nanocrystals show higher sorption efficiency and chemical stability. Transmission electron microscopy (TEM) shows a nanostructure consisting of different shapes according to different surfactants. According to the results of distribution coefficient on different nanoparticles which applied in the polluted water in Egypt founded that, the selectivity order Fe³⁺ > Al³⁺ > Mn²⁺ >Zn²⁺> Pb²⁺.
This work investigated the sensitivity towards humidity, NO2 and H2 of ZnO modified sepiolite (Si12Mg8O30(OH)4.(H2O)4⋅8H2O). To this aim, sepiolite powder was first modified by leaching magnesium ions in HCl then, by precipitating under basic conditions nano-sized Zn-based compounds and subsequent thermal treatment. The powders were characterized by X-ray diffraction (XRD), specific surface area measurements, thermogravimetric and differential thermal analysis and field emission scanning electron microscopy, as well as, high resolution transmission electron microscopy. The XRD patterns showed that all leached heat treated samples at 550 °C for 1 h were made of anhydrous sepiolite and of ZnO. Sensors were then obtained by screen printing these materials onto commercial alumina substrates with Pt electrodes. All the investigated compositions were capable of detecting NO2 down to ppm level and 20 ppm H2, at an optimal working temperature of 300 °C. These detection limits are in line with the current best results reported in literature.
This chapter constitutes one of the very few reviews in the existing literature on shoe bonding, and it gives an updated overview of the upper to sole bonding by means of adhesives. The surface preparation of rubber soles and both the formulations of polyurethane and polychloroprene adhesives are described in more detail. The preparation of adhesive joints and adhesion tests are also revised. Finally, the most recent development and technology in shoe bonding is described.
UV-curable polyurethane acrylate (PUA) is currently used as an encapsulant for undersea sonar devices, and new, desirable polymeric materials should have lower swelling ratios when in contact with seawater and paraffin oil, along with better mechanical strength, when compared to PUA after impregnation. We blended PUA with boron nitride (BN) to fabricate these desirable composites for sonar encapsulants. PUA-coated BN was prepared and was found to have better interfacial adhesion between the PUA matrix and the BN filler. The surface-modified filler showed enhanced dispersibility and affinity due to the surface treatment with functional groups that affected the surface free energy and the structural similarity of the doped crystallized diisocyanate molecule in the matrix. Studies of these composites showed that the swelling ratios decreased with increasing BN PUA content. The tensile strength of the BN-PUA/PUA composite in either seawater or paraffin was higher than that of the BN/PUA composite as the immersion time increased. We conclude that these composites are promising materials for use as sonar encapsulants and can significantly improve both mechanical strength and long term stability.
Novel poly(ether-imide) and sepiolite nanocomposites were synthesized based on a unique diamine monomer with the aim of improving physical and mechanical properties of final polyimide films. The diamine was polycondensed with 4,4′-(hexafluoroisopropylidene) diphthalic anhydride to produce related poly(ether amic acid) prepolymer. Pure poly(ether-imide) and nanocomposite films were prepared via thermal imidization process of poly(ether amic acid). Coexistence of ether, pyridine, and phenylene functional groups in the diamine chemical structure resulted in flexible polyimide films with significant thermal, physical, and mechanical properties. Thermal stability, glass-transition temperature, dimensional stability, and tensile properties of polymer and nanocomposites were studied and compared. Morphology of nanocomposites was also investigated using scanning and transmission electron microscopic methods to study the distribution and dispersion behavior of sepiolite nanofibers in the polyimide matrix. By introduction of sepiolite nanoparticles, overall improvement of properties was observed in respect to pure polyimides. Copyright © 2015 John Wiley & Sons, Ltd.
Inorganic nanofibers are characterized by small size effect, quantum size effect and surface effect. Inorganic nanofibers and polymer form polymer and inorganic nanocomposites, which has become an active research area and showed good development and application prospects. As a typical type of inorganic fibrous minerals, sepiolite group mineral fibrous materials can not maximize nano-effect due to small particle size, high specific surface area, high surface energy and easy reunion of inorganic nanofibers. Based on the above reasons, this paper systematically summarizes the processing technologies of sepiolite group mineral fibrous materials, and proposes the suitable processing technology of batch production of sepiolite group mineral fibrous materials at low cost based on the analysis.
We added modified sepiolite to a polypropylene (PP)/ammoniumpolyphosphate (APP)/di-pentaerythritol (DPER) composite to study the effect of sepiolite on the retarding behavior of the intumescent flame retardant (IFR) PP flame. The flame retarding behavior of the PP/IFR composite was tested using the limiting oxygen index (LOI) and cone calorimeter tests (CONE). The results show that sepiolite increases the LOI value of the PP/IFR and it is more effective than other nano-fillers such as layered double hydroxides (LDH) and organic montmorillonite (OMMT). The sepiolite decreases the heat release rate (HRR) and the total heat release (THR) of the PP/IFR composite. The flame- retardant mechanism of the PP/IFR/sepiolite system is also discussed in terms of catalytic charring after analysis by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). For the binary APP/DPER mixture, sepiolite reduces the mass loss rate and increases the amount of residue at high temperature under nitrogen and air atmospheres. This has been considered to be strongly associated with the interaction between sepiolite and APP. FTIR and XPS results show that the P—O—Si bond forms at high temperature for binary mixtures of APP/sepiolite. With the addition of sepiolite to the PP/IFR, the char residue burnt is dense and homogeneous, which is important for the flame retardant performance.
Fumed silicas of different specific surface area (90-380 m/g) were added to a thermoplastic polyurethane (PU) solution. After solvent removal, solid fumed silica-PU composites were obtained. The viscoelastic properties of PU were improved by adding fumed silica and only a solid-like behavior in PU-fumed silica composites was obtained. The increase in the specific surface area of the fumed silica up to 200 m / g increased the moduli of the composites. Fumed silica-PU interactions were responsible for the improved rheological properties of the composites. The activation energies for viscous flow of the composites were 14-16 kcal/mol and increased as the specific surface area of fumed silica increased. The glass transition temperature (obtained from DMTA and DSC experiments) and the crystallization rate of fumed silica-PU composites decreased compared with PU and also decreased with increasing surface area of the fumed silica. The contact angle values were similar in all the composites and the strength of PVC/fumed silica-PU composite joints was not affected by the specific surface area of the fumed silica.
—Both fumed silica and sepiolite have been used as a filler of polyurethane (PU) adhesives. Although effective, the small particle size and the relative high cost of fumed silica are limitations in some applications. Sepiolite is cheaper than fumed silica, but its relatively large particle size facilitates its settling from the adhesive solutions. In this study, the usefulness of using sepiolite + fumed silica mixtures as a filler in solvent-based PU adhesives is demonstrated. The rheological and adhesion properties of the PU adhesive solutions and the rheological and mechanical properties of the PU films (without solvent) were studied. SEM micrographs of PU films showed the morphology and compatibility of the fillers with the PU matrix. The use of sepiolite + fumed silica mixtures inhibited the settlement of the filler from the PU adhesive solutions, increased both the storage and the loss moduli, and improved the rheological and mechanical properties of the PU. On the other hand, the green (immediate) T-peel strengths of roughened styrene-butadiene rubber/PU adhesive joints and plasticized PVC/PU adhesive joints were greatly improved in filled PU adhesives. The effects produced by using fumed silica alone or sepiolite + fumed silica mixtures were very similar, although in general, somewhat more marked in fumed silica-filled PU.
Fumed silicas of different surface areas (90–380m2/g) and primary particle size (20–7nm, respectively) have been added to solvent-based thermoplastic polyurethane (PU) adhesives. Addition of silica increased the viscosity, imparted pseudoplasticity, and thixotropy or rheopexy to PU adhesive solutions. Rheological data of adhesive solutions fitted well the Casson model. Fumed silicas with intermediate surface areas (130–200m2/g) provided the best rheological performance to PU adhesive solutions. The increase of time after preparation of PU adhesive solutions produced an increase in viscosity, more marked pseudoplasticity and enhanced thixotropy (rheopexy was not exhibited). The reduced rheological properties of PU solutions containing Aerosil 380 have been ascribed to the relatively large size of the clusters produced by aggregation of small primary fumed silica particles, which under the experimental conditions used in this study were not fully dispersed in the PU solution. Contact angles obtained by placing adhesive drops on rubber substrates increased when the adhesive contains silica, the trend obtained was similar to that exhibited by the flow curves. This may indicate that a relationship between wettability and rheology of PU adhesive solutions may exists. Green (immediate) strength of roughened R1 rubber/PU adhesive joints was improved, if the adhesive contained fumed silica and did not vary with the surface area of the fumed silica, but the strength for (roughened+chlorinated) R2 rubber/PU adhesive joints was similar if the adhesive contained or not fumed silica, and independently of the surface area.
Raw and thermally treated sepiolites from the Mantoudi area, Euboea, Greece, were investigated by means of X-ray diffraction
(XRD) in combination with thermo-gravimetric analysis (TG/DTG) and differential thermal analysis (DTA), as well as Fourier
transform (FTIR) spectroscopy, in order to study the collapse of the sepiolite structure with increasing temperature. The
main mineral constituent (>95%) is a well crystallized sepiolite. Quartz and dolomite occur in minor amounts. Calcination
of the samples was carried out up to 350, 720 and 820°C, for 2 h, and ‘sepiolite dihydrite’, ‘sepiolite anhydrite’ and ‘enstatite’
were formed, respectively, as magnesium co-ordinated water and octahedrically co-ordinated hydroxyl groups, are removed and
the dehydroxylated phase recrystallize to enstatite (MgSiO3). These structural and textural changes play an important role to the properties and uses of the studied sepiolites.
This paper deals with understanding the surface behaviors of calcined clay and the organic/inorganic system. The surface properties like the adsorption thermodynamic parameters and the dispersive component of the surface energy were determined by the adsorption of n-alkanes on the solids that were the subject of interest, i.e. calcined sepiolite and polystyrene coated calcined sepiolite. Inverse gas chromatography (IGC) was used for this purpose. The dispersive component of the surface energy of system lies between the members of system. Additionally Diffuse Reflectance Infrared Fourier Transform (DRIFT) technique was used to record the functional groups of solids. Copyright © 2010 John Wiley & Sons, Ltd.
—Different amounts (5-20 wt% with respect to the solids content in the adhesive) of a hydrated magnesium/aluminum silicate (attapulgite) were added to solvent-based polyurethane (PU) adhesive formulations. The rheological, thermal, mechanical, surface, and adhesion properties of the filled PU adhesives obtained were measured. The addition of attapulgite provided an increase in viscosity, imparted thixotropy and pseudoplasticity to the PU adhesive solution, and produced an increase in storage and loss moduli. Increase in the amount of attapulgite enhanced these effects. Some interactions (not well defined in this paper) between the attapulgite, the polyurethane, and/or the solvent seemed to be responsible for the improved properties of the filled PU adhesives. Furthermore, the addition of attapulgite increased the mechanical properties, decreased the glass transition temperature, affected the crystallization rate and melting process, and modified the surface properties of the PU adhesive films (without solvent). On the other hand, the immediate (green) T-peel strength of roughened or (roughened + chlorinated with 1 wt% trichloroisocyanuric acid solutions in 2-butanone) styrene-butadiene rubber (SBR)/PU adhesive joints was greatly improved if the adhesive contained attapulgite. However, similar T-peel strength values in fully cured adhesive joints (measured 72 h after bond formation) were found irrespective of whether the PU adhesives contained attapulgite or not.
Laboratory-prepared magnesium silicate (MgSi-I) was modified with HNO3, H3PO4 and NaOH to give MgSi-II, -III and -IV, respectively. The modified products were examined in respect to structure, thermal stability and ion exchange properties. The investigations indicated that MgSi-I has strong tendency to react with alkaline and acid media, especially with the phosphate group. The sorption performance of the materials for Cu2+, Cd2+, Ni2+ and Fe3+ transition metal ions was studied as a function of pH. The modified materials offer excellent potential for heavy metals removal compared to the unmodified one. Magnesium silicate that treated with HNO3 (MgSi-II) revealed the higher silica content, thermal stability and sorption efficiency relative to the other series. Besides, it retains 62.8% of its ion exchange capacity after heating up to 400°C.
The dynamic behaviour during the crosslinking of an epoxy polymer near the gel point was monitored using rheological multiple frequency experiments. The influence of a needle-shaped inorganic nanofiller, sepiolite, either non-modified or organically surface modified during the cure process in the presence of an aliphatic and an aromatic hardener was investigated. The validity of various criteria for determining the gel point was examined for the crosslinking of these filled thermosets. The WinterChambon criterion at the gel point is obeyed by the unfilled and by the non-modified sepiolite-filled epoxy matrix with either of the two hardeners. However, physical gels are formed in the presence of the organically modified sepiolite and the WinterChambon criterion is not valid. For all the systems investigated, the nanofiller reduces the time to reach gelation. Critical relaxation exponents and gel strength have been determined indicating a more elastic and stronger gel in the presence of the aliphatic hardener. (c) 2012 Society of Chemical Industry
Modification of sepiolite clay has been performed using triethoxy-3-(2-imidazolin-1-yl)propylsilane in the presence of toluene solution. The modified material was characterized by FTIR spectroscopy, XRD, and simultaneous DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and the silane group of the triethoxy-3-(2-imidazolin-1-yl)propylsilane by releasing the ethoxy groups to the solvent. Thermal decomposition of natural and modified sepiolites was carried out with a thermogravimetric analyzer. In TG and DTA analysis, during gradual heating in an oxidizing atmosphere, the modified sepiolite was oxidized, giving rise to significant exothermic peaks. The exothermic peak in the temperature range of 200−650 °C depended on the modifier loading and provided evidence of bond formation on the sepiolite surface. For natural sepiolite, a mass loss of 20.43% was observed up to 900 °C, whereas this value increased to 31.90% for modified sepiolite under oxygen atmosphere. Electrokinetic properties of the modified-sepiolite suspensions were also examined as a function of the initial electrolyte concentration and equilibrium pH using a Zeta Meter 3.0 instrument. To determine the adsorption capacity of modified sepiolite for metal ions, the experiments were examined as a function of pH, ionic strength, and temperature. The adsorption capacity of modified sepiolite increased with increasing pH and temperature, but ionic strength was found to have no significant effect. The experimental data were analyzed using the Langmuir and Freundlich adsorption models. Satisfactory agreement between the metal uptake capacities by the modified sepiolite was expressed in terms of the correlation coefficient (R2). The Langmuir model represented the sorption process better than the Freundlich model, with R2 values ranging from 0.9603 to 0.9977.
The influence of adding small amounts of calcium carbonate or sepiolite fillers on the adhesion properties of UV surface-treated ethylene vinyl acetate copolymer (EVA) was studied. In this paper, it has been demonstrated that the addition of 3-7 wt% filler enhanced the extent of the surface modifications (wettability, surface chemistry, roughness) and increased the adhesion of EVA. These effects were more marked when 7 wt% sepiolite filler was added to EVA, likely due to its higher aspect ratio.
Infrared transmission and emission spectroscopy were used to analyze the difference in structure and thermal behavior of two Chinese palygorskites. The position of the main bands identified in the infrared spectra of the palygorskites studied is similar for these two Chinese samples, but there are some differences in their intensity, which is significant. This discrepancy is attributed to the existence of impurities and the geological environments in different regions. The infrared emission spectra clearly show the structural changes and dehydroxylation of the palygorskites when the temperature is raised. The dehydration of the palygorskites is followed by the loss of intensity of the OH stretching vibration bands in the region of 3600-3200 cm(-1). Dehydroxylation is followed by the decrease in intensity in the bands between 3700 and 3550 cm(-1). Dehydration of pure palygorskite was completed by 600°C. Partial loss of coordinated water was observed at 400°C. Infrared emission spectroscopy is an effective method to determine the stability of the mineral.
In this work adsorption of uranium on natural, heat and acid treated sepiolite was studied. For acid treatment HCl and H(2)SO(4) were used separately. Heat and acid treatment caused some changes in sepiolite such as surface area, micropore volume (cm(3)/g) and average pore diameter (A). Different amounts of Mg ions were extracted from the lattice depending on the type of acid. After acid treatment with HCl, the amount of Mg left in the sepiolite changed a little. During H(2)SO(4) treatment the sepiolite structure was progressively transformed into amorphous silica. These heat and acid treatments changed adsorption capacity and mechanism of uranium on sepiolite. Data obtained from the adsorption experiments were applied to Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. Using these isotherms different adsorption capacities were found for natural and treated sepiolite samples. The capacity values were 3.58x10(-3), 3.14x10(-3), 2.78x10(-3) and 1.55x10(-3)mol/g for HCl treated, heat treated, natural and H(2)SO(4) treated sepiolite samples, respectively. In order to evaluate the adsorption mechanism adsorption energies were calculated by the D-R isotherm. According to the adsorption energy values uranium fixed to the natural and heat treated sepiolite surface with ion exchange (12.75 and 12.12 kJ/mol, respectively). Simple physical attractions were the driving force for adsorption on HCl and H(2)SO(4) treated ones (6.62 and 6.87 kJ/mol, respectively).
Rheology of sepiolite-based epoxy suspensions as well as morphology and dynamic mechanical properties of the corresponding nanocomposites are discussed in this paper. The influence of the type of sepiolite used, i.e. non-modified, aminosilane and glycidylsilane surface modified, and of the process developed to prepare the epoxy suspensions were investigated. Except for low amount of filler, a shear thinning behavior was observed in the others sepiolite-based epoxy suspensions. The interactions developed between the sepiolite and the epoxy matrix are responsible for the magnitude of the shear thinning effect and are related to the morphology of the nanocomposites. The best dispersion of sepiolite was achieved using either an emulsion process or a glycidyl functionalized sepiolite.
Nematic liquid crystals were obtained in sterically stabilized suspensions of rodlike particles of sepiolite clay, with an average length up to 900 nm and aspect ratio up to 40. In agreement with computer simulations for hard spherocylinders, the isotropic-nematic transition shifted to lower volume fractions with increasing aspect ratio. However, the coexistence gap was broadened noticeably due to particle polydispersity. The sepiolite crystal structure includes channels filled with zeolitic water, which can be replaced by indigo dye molecules. The indigo molecules are constrained inside the zeolitic channels to be aligned along the long axes of the rods. As a result, the colloidal nematic phase showed a marked dichroism, with an order parameter up to 0.5 for magnetically aligned samples, similar to typical values for dye-doped thermotropic liquid crystals.
Flip chip assembly directly on organic boards offers
miniaturization of package size and reduced in interconnection
distances, resulting in a high performance and cost-competitive
packaging method. This paper describes the investigation of alternative
low cost flip-chip mounting processes using electroless Ni/Au bumps and
anisotropic conductive adhesives/films as an interconnection material on
organic boards such as FR-4. As bumps for flip chip, electroless Ni/Au
plating was performed and characterized for plating speed, surface
roughness, and elemental analysis as a function of plating condition.
High plating rate and surface planarity of the electroless Ni were
considered as requirements for ACA flip chip bumps. In order to obtain
high plating rate and low surface roughness, plating conditions were
determined by controlling complexing agents in electroless Ni solution.
Annealing effects on Ni bump characteristics showed that the formation
of crystalline Ni with Ni3P precipitation above 300°C
causes an increase in hardness and intrinsic stress, resulting in
reliability limitation. As an interconnect material, modified ACFs
composed of Ni conductive fillers for electrical conductor and
nonconductive inorganic fillers for modification of film properties such
as CTE and tensile strength were formulated for improved electrical and
mechanical properties of ACF interconnection. The thermal cycle life of
ACAs flip chip on organic boards was usually limited by the CTE mismatch
between chip and board. However, flip chip assembly on FR-4 boards using
modified ACAs almost doubled the thermal cycle life
Fibrous sepiolite crystals derive much of their commercial value from their molecular size channels and grooves. The crystals fold upon drying and these channels and grooves are lost. A model for the folding and unfolding of the crystals is presented. Extensive i.r., X-ray and thermogravi- metric evidence shows that folding occurs when approximately half of the water of hydration, which is coordinated to the edge magnesium atoms inside of the channels, is removed. This occurs near 175~ under vacuum and near 300~ in air. When the crystals fold, all remaining water molecules enter a new environment, that of the hexagonal holes of the neighboring silica surface. A true anhydride is produced at about 500~ under vacuum when the final water is lost, but this final dehydration produces no important structural change. Rehydration of the anhydride to the normal hydrated sepiolite does not occur at room temperatures in 100% r.h. However, above, 60~ rehydration does occur. not after the high temperature treatment. Nagata et al. (1974) consider that the folded stage produced at half dehydration will rehydrate, but the true anhy- dride does not rehydrate even under hydrothermal conditions, Our study is designed to clarify the conditions un- der which sepiolite folds and unfolds and the involve- ment of the water of coordination in the folding. In- terpretation of TGA-DTGA. X-ray powder diffrac- tion patterns and, especially, careful study of the major changes observable in the i.r. spectra of the struc- tural OH during the dehydration and folding process will be used to explain a folding model.
The structure and properties of sepiolite are reviewed. Surface properties, such as porosity and sorption are detailed, as well as dehydration and thermal behaviour. Industrial applications of sepiolite are based on: a) Sor-btive properties; b) rheological properties; c) catalytic properties; The Theological behaviour of sepiolite suspensions, as expressed by viscosity, is shown to be related to following factors; type of medium (aqueous or organic), type and concentration of electrolyte, pH, shear-stress and pregelification. With appropriate pretreatments, sepiolite is shown to be useful in following applications: Absorbents, environmental deodorants, catalyst carriers, polyesters, asphalt coatings; paints, pharmaceutical uses, decolorizing agents, filter aids, anticaking agents, phytosanitary carriers, cigarette filters, plastisols, rubber, animal nutrition, detergents, cosmetics, agriculture (soil conditioning, fluid carriers for pregerminated seeds, seed coating; fertilizer suspensions) grease thickeners, NCR paper, drilling fluids.
In the present work, the changed properties of isotactic polypropylene caused by adding untreated sepiolite and n-decylaldehyde treated sepiolite were analyzed by studying the isothermal crystallization processes and the dynamic properties of the resulting composites. Variations in the surface activity of the n-decylaldehyde treated sepiolite leads to significant changes in the measured properties compared to those observed in the composites containing untreated sepiolite. This allows the assumption that the structure of the interface filler/polymer is modified as a function of filler activity.Die durch Modifizierung von isotaktischem Polypropylen durch Zugabe von unbehandeltem und mit n-Decylaldehyd behandeltem Sepiolith geänderten Eigenschaften werden durch Untersuchung der isothermen Kristallisationsprozesse und der dynamischen Eigenschaften der erhaltenen Proben ermittelt. Die Variation der Oberflächenaktivität des behandelten Sepioliths führt zu auffälligen Eigenschaftsänderungen im Vergleich zu Proben, die unbehandelten Sepiolith enthalten. Dies führt zur Annahme, daß die Struktur der Grenzfläche Füllstoff/Polymeres in Abhängigkeit von der Füllstoffaktivität modifiziert wird.
Five polycaprolactone polyurethane adhesives of similar chemical nature but different viscosities were used to bond ultrasonically cleaned, unchlorinated and chlorinated, styrene-butadiene rubber adherends. The peel strengths of the joints were influenced by the adhesive viscosity. Contact angle measurements using several liquids (water, ethane diol, glycerol, 1-bromonaphthalnene and tricresyl phosphate) and the adhesives did not display the same trend as that noted in the peel strength experiments. Therefore, the changes in peel strength could not be ascribed to thermodynamic factors only, since there was also a reaction between the chlorine in the surface modified adherends and the polyurethane. On the other hand, it has been shown that an increase in polar and a decrease in non-polar groups of the polyurethane adhesives is produced for those adhesives having a viscosity less than 2 Pa s.
L'interface charge-polymére des matériaux polymères á composants multiples joue un rôle fondamental pour toutes leurs propriétés. Le présent travail met en évidence l'importance qu'ont pour les propriétés des composites à base de polypropyléne et de sépiolite aussi bien l'adhésion interfaciale que la formation de structures ordonnées autour des particules. Les essais réalisés lors de cette étude prouvent que quand il y a variation des propriétés superficielles de la sépiolite sous l'effet de l'organophilisation à travers ses groupes silanols, son comportement thermique et dynamique varie.
The i.r. spectra of the water present in sepiolite allowed us to identify on the hydrated sample two kinds of water molecules: (a) water molecules which have their two hydroxyl groups involved in hydrogen bonds, they give i.r. absorption in 3370 cm−1 range and at 1655 cm−1, (b) water molecules which have only one hydroxyl group involved in a hydrogen bond. The last kind of water molecules has the Cs symmetry and gives two stretching bands: one at 3570 cm−1 which corresponds to OH groups involved in weak hydrogen bonds and another at lower frequency which corresponds to OH groups involved in stronger hydrogen bonds.
Bound water of sepiolite dehydrates in two steps in the temperature range of 250-650~ as shown in the TG-curve. These steps are described here as steps II and III. At step II, half of the bound water is removed; other half at step III. From step II to IlL discontinuous changes are confirmed in such properties as activation energy of dehydration, a-dimension, axial ratio, and intensities and spacings of X-ray powder reflections. A structural state at step II may be recognized as a distinct phase in the dehydration process.
Resumen
Se estudia el efecto de la deshidratación sobre la superficie especifica y distribución del tamaño de poro en sepiolita y palygorskita. Se emplean las técnicas de A.T.D., A.T.G., adsorción-desorción de nitrógeno y microscopía electrónica.
La eliminación del agua higroscópico-zeolitica incrementa en los dos minerales la superficie especifica y la proporción de microporos accesibles a las moléculas de nitrógeno.
Con la pérdida del agua de cristalización disminuye, en ambos minerales, la superficie especifica y la proporción de los citados microporos, desapareciendo los de anchura inferior a 7 Å en las próximidades de la eliminación completa de esta clase de agua.
La eliminación del agua de constitución origina neuvos descensos de la superficie especifica en la sepiolita de acuerdo con las alteraciones sufridas, puestas de manifesto en al análisis térmico; más acusadas que en la palygorskita.
Different amounts (5-30 wt% with respect to the polyurethane content in the adhesive) of a new filler, a partially defibrillated natural hydrated magnesium silicate (sepiolite), were added to solvent-based polyurethane (PU) adhesive formulations. The rheological, mechanical, surface, and adhesion properties of the PU adhesives obtained were measured. Increase in the amount of sepiolite added to PU adhesives led to an increase in viscosity and imparted thixotropy and pseudoplasticity to the adhesive solution. However, the addition of sepiolite produced an increase in storage and loss moduli and a decrease in the mechanical properties but did not affect the surface properties of the PU adhesive films. On the other hand, the immediate (measured 30 s after joint formation) T-peel strength of roughened or (roughened + chlorinated with 1 wt% trichloroisocyanuric acid solutions in 2-butanone) styrene-butadiene rubber/PU adhesive joints was greatly improved if the adhesive was filled with up to 10 wt% sepiolite. The T-peel strength measured 72 h after bond formation was similar for the joints prepared with PU adhesives without and with up to 10 wt% sepiolite. The joint strength decreased if the amount of sepiolite in the PU adhesive was 20-30 wt%, due to the poor mechanical properties and too high moduli of the adhesives. Some interactions between the sepiolite, the polyurethane, and/or the solvent seemed to be responsible for the improved properties of filled PU adhesives. These interactions were responsible for the increased storage and loss moduli and the displacement of Tg of the PU adhesive films to higher temperature when it contained sepiolite. Furthermore, the addition of a high amount of sepiolite changed the rheological behaviour of the PU to a solid, giving rigidity to the structure, which is responsible for the reduced adhesion in roughened rubber joints produced with polyurethanes containing 20-30 wt% sepiolite.
The optimization of a composite based on polyethylene blend matrices with unmodified and titanate coupling agent-modified sepiolite has been studied. The analysis of the tensile, flexural, and impact behavior shows that the tensile and flexural properties, mainly the moduli, improve with increasing content of both filler and high-density polyethylene (HDPE) in the composite. The surface-modified sepiolite has a behavior similar to the unmodified one and no improvement of the mechanical properties is noticeable. In order to explain these effects a morphological study on fracture surfaces of the composites was performed using scanning election microscopy.
Silicates Industriales
- Chambers
Revista de Plásticos Modernos
- Arroyo
Revista de Plásticos Modernos
- González-Hernández
Adición de resinas de hidrocarburos a adhesivos de policloropreno
- Fernández-Gómez