Sepiolite fibers

FIGURE 12 TEM image of the cross section of a sepiolite fiber (A) and structural model of this silicate (B), showing the tunnels and channels available for interaction with organic species. (Adapted from Refs. 244 and 224.)... 

CTA" -sepiolite and the rapid hydrolysis-polycondensation reaction gives rise to a silica network in which sepiolite fibers become entrapped [74],... 

Substitution and variations in the tetrahedral sites change the manner of side linkages for the ribbons, effecting the octahedral cation and water associations. In addition, different ribbon widths can lead to different numbers of octahedral cations. Variation in the width of chains and substitution of cations and water are easily accomplished, which means that accurate and consistent chemical and crystal structural data on these minerals are difficult or, at best, approximate. However, the minerals do form fibers with a consistent fiber axis repeat of about 0.512 nm (Preisinger, 1959 Rautureau et al., 1972). Sepiolite and palygorskite represent the widest possible structural and chemical diversity among fibrous silicate minerals. 

The fibrous structure of sepiolite is composed of talc-like ribbons with two sheets of tetrahedral silica units linked by oxygen atoms to a central octahedral sheet of magnesium. It has needle-shaped particles with chaimels oriented along the fibers which can absorb liquids. Sepiolite has three kinds of water hygroscopic water, crystallization water, and constitution water. The ciystallization water is removed at 500°C and constitution water is removed at 850°C at which point physical properties change brought about by ciystal folding of sepiolite. ... 

Typical fillers calcium carbonate, talc, glass fiber, glass beads, glass flakes, silica flour, wollastonite, mica, sepiolite, magnesium hydroxide, carbon black, clay, metal powders (aluminum, iron, nickel), steel fiber, si-licium carbide, phenolic microspheres, wood fiber and flour, antimony trioxide, hydrotalcite, zinc borate, bismuth carbonate, red phosphorus, potassium-magnesium aluminosilicate, fly ash, hydromagnesite-huntite... 

Typical fillers calcium carbonate, calcium sulfate, silica, organic fibers, graphite, mica, bentonites, sand, aluminum hydroxide, sepiolite, rubber particles... 

Clay constitutes the most abundant and ubiquitous component of the main types of marine sediments deposited from outer shelf to deep sea environments. The clay minerals are conventionally comprised of the <2 pm fraction, are sheet- or fiber-shaped, and adsorb various proportions of water. This determines a high buoyancy and the ability for clay to be widely dispersed by marine currents, despite its propensity for forming aggregates and floes. Clay minerals in the marine environments are dominated by illite, smectite, and kaolinite, three families whose chemical composition and crystalline status are highly variable. The marine clay associations may include various amounts and types of other species, namely chlorite and random mixed layers, but also ver-miculite, palygorskite, sepiolite, talc, pyrophyllite, etc. The clay mineralogy of marine sediments is therefore very diverse according to depositional environments, from both qualitative and quantitative points of view. 

Polymer Nanocomposites The morphology and dispersion state of a filler-like sepiolite (lamella and fiber type) were determined using STEM [66]. 

This chapter reviews the use of the sepiolite/palygorskite group of clays as a nanofiller for polymer nanocomposites. Sepiolite and palygorskite are characterized by a needle-like or fiber-like shape. This peculiar shape offers unique advantages in terms of mechanical reinforcement while, at the same time, it allows to study the effect of the nanofiller s shape on the final composite properties. The importance of the nanofiller shape for the composite properties is analyzed in Section 12.2, introducing the rationale of the whole chapter. After a general description of needle-like nanoclays in Section 12.3, the chapter develops into a main part (Section 12.4), reviewing the preparation methods and physical properties of polyolefin/needle-like clay nanocomposites. 

Reinforcement of PP by 5 vol% of fiber-like and platelet-like filler in the case of (a) unidirectional alignment and (b) random orientation of the filler. The dashed vertical line shows the average sepiolite aspect ratio. Arrows show the smallest aspect ratio necessary to reach theoretical reinforcement (rule of mixtures—horizontal solid line) [11]. 

Acosta, J. L., Morales, E., Ojeda, M. C., and Linares, A. 1986. Effect of addition of sepiolite on the mechanical properties of glass-fiber reinforced polypropylene. Angewandte Makromolekulare Chemie 138 103-110. 

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