Palygorskite fibers

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. 

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. 

Palygorscite Palygorskite Palygorskite, calcined. SeeAttapulgite PAMAM. See Polyamidoamine PAN carbon fiber. See Carbon fiber Parachlorobenzotrifluoride. See p-Chlorobenzotrifluoride Parachlorometacresol. See p-Chloro-m-cresol Parachlorometaxylenol. See Chloroxylenol Paracymene Paracymol. See p-Cymene Paradichlorobenzene Paradichlorobenzol. See p-Dichbrobenzene Paradioxybenzene. See Hydroquinone... 

TEM images of palygorskite (a) typical bundle of fibers with fine smectite flakes and (b) "bird s-nest" aggregate of fibers with entrapped grains of calcite and apatite. (Reproduced from Giiven, N. et ah. Clays Clay Miner., 40, 457,1992. With permission from The Clay Minerals Society.)... 

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. 

Palygorskite and sepiolite are porous microcrystalline solids that have high adsorptive capacity, from which derives multiple industrial applications. Their peculiar crystal structure consists of talclike ribbons parallel to the fiber axis, alter-... 

---