Talc particles

Talc particles sprinkled on the surface may become virtually immobile if the surface is even slightly contaminated, indicating that the surface elements become stagnant and are setting up a considerable resistance to the clearing of the surface by eddies of liquid approaching obliquely (D9). 

Exposure of women to cosmetic talcum powder, has been related to the observed presence of the characteristic phyUosilicate talc particles in normal and in malignant ovary tissue (Henderson etal., 1979). The experimental demonstration in rats of migration of talc particles from the vagina to the ovary, illustrates the potential route of entry into the body (Henderson etal., 1986). 

The second complicating factor is interfacial turbulence (1, 12), very similar to the surface turbulence discussed above. It is readily seen when a solution of 4% acetone dissolved in toluene is quietly placed in contact with water talc particles sprinkled on to the plane oil surface fall to the interface, where they undergo rapid, jerky movements. This effect is related to changes in interfacial tension during mass transfer, and depends quantitatively on the distribution coefficient of the solute (here acetone) between the oil and the water, on the concentration of the solute, and on the variation of the interfacial tension with this concentration. Such spontaneous interfacial turbulence can increase the mass-transfer rate by 10 times 38). 

This continual replacement of liquid is readily visible with talc particles sprinkled on to the interface though stationary on the average (if the stirrers in phases 1 and 2 are contra-rotated at appropriate relative speeds), they make occasional sudden, apparently random, local movements, which indicate that considerable replacement of the interface is occurring by liquid impelled into the interface from the bulk. Spontaneous interfacial turbulence, associated with such processes as the transfer of acetone from solvent to water, may further increase the rate of transfer by a factor of two or three times (44, 48, 51). Other systems (48), such as benzoic acid transferring (in either direction) between water and toluene, give transfer rates only about 50% of those calculated by Eq. (26), suggesting either that this equation is not valid or that there is an interfacial resistance. This point is discussed in detail below. 

The quantity Cr correlates the effects of monolayers, both spread and adsorbed, on K, as in Fig. 11. As one may show quantitatively with talc particles, the eddy velocity at the interface is greatly reduced by the mono-layer. The latter restrains fresh liquid from being swept along the surface, i.e., there is less clearing of the old surface. If now All is the surface pressure resisting the eddy due to its partly clearing an area (Fig. 12) in... 

Figure 7 shows the effect of filler particle shape on the viscosity of filled polypropylene melts, containing glass beads and talc particles, of similar density, loading and particle size distribution. The greater viscosity of the talc-filled composition was attributed to increased contact and surface interaction between these irregularly shaped particles. 

Talc particles of different lamellarity and specific surface area have been incorporated into polyethylene vinyl acetate (EVA) copolymer/magnesium hydroxide (MH) composite system.63 The fire retardancy of this system has been studied and compared with formulations containing only EVA and MH and formulations containing EVA, MH, and organomodified montmorillonites (oMMT). It was observed that talc with higher lamellar index showed fire behavior similar to that of EVA/MH/ oMMT system with some intumescence. 

Polymers filled with platy talc exhibit higher stiffness, tensile strength, and creep resistance than do polymers filled with standard particulate fillers. These properties are maintained at both ambient and elevated temperatures. Surface treatments for talc particles include magnesium and zinc stearates, silanes, and titanates. 

Tablets of medication intended for oral use contain inert filler materials such as talc (magnesium silicate), corn starch, cotton fibers, and other refractile and nonrefractile substances. Long-term drug abusers are known to prepare a suspension of medication for injection by dissolving the crushed tablet of cocaine, heroin, methylphenidate, or other narcotic in water. They then boil the solution and filter it through a crude cigarette or cotton filter before injecting the solution intravenously, subcutaneously, or intramuscularly. The talc particles eventually embolize to the retinal circulation and produce a characteristic form of retinopathy.

The extent of talc particles observed in the posterior pole appears to correlate with the duration of drug abuse and with the cumulative number of tablets injected. Often, the drug abuser injects from 10 to 40 tablets daily, and some abusers inject as many as 100 tablets daily for several years. Talc retinopathy is usually not found in drug abusers who have injected less than 9,000 tablets, but it is consistently found in most patients who have injected more than 12,000 tablets. 

As the talc, cornstarch, and other insoluble tablet fillers embolize to the lungs, they become trapped within the pulmonary tissues and eventually cause pulmonary hypertension. This leads to the development of collateral vessels that allow part of the venous retmn to bypass the lungs and enter the left side of the heart, where the particles are further embolized to the eye and other organs of the body. The presence of talc particles in the eye indicates that substantial foreign body damage has occurred in the lungs. 

The talc particles are more numerous in the perimacular region than in other areas of the retina, probably because of the rich blood supply and greater blood flow in that area. The particles lodge in the walls of the precapillary arterioles and capillaries, producing focal occlusion of these vessels in the retina and choroid. The occlusions are caused primarily by the cellular reaction to the emboli. 

Results of a survey of asbestos fibers in consumer cosmetic talc powders from Italian and international markets using electron microscopy, electron diffraction, and energy dispersive x-ray analysis showed that asbestos was detected in 6 of 14 talc samples from the European Pharmacopeia (Paoletti et al. 1984). Chrysotile was identified in 3 samples, 2 samples contained tremolite asbestos and anthophyllite asbestos, and 1 sample contained chrysotile and tremolite asbestos. The authors noted that, in all talc powders analyzed, fibrous talc particles frequently were present that were morphologically similar to amphibole asbestos fibers. Counting fibers as particles with aspect ratio >3 1 and width < 3 m, the percentages of particles that were asbestos fibers ranged from <0.03% to 0.13% for 4 samples, and were 18% to 22% for the other 2 samples. Paoletti et al. (1984) noted that the European Pharmacopeia, at that time, had not established analytical quality control of asbestos contamination. 

A heroin addicted patient, who had been foUowed up for 6 months for increasing dyspnea due to chronic cor pulmonale, was admitted to an intensive care unit. She died shortly after. Postmortem lung biopsies showed talc particles within alveolar walls and alveolar macrophages, as well as alterations in blood vessels (26). 

These concerns are based on some epidemiological studies whose results were barely significant statistically and of questionable biological importance. (Their results lacked dose-response relationships, and were inconsistent and ambiguous. Further whether inanimate talc particles can translocate from the perineum to the ovaries, a precondition if they were to cause ovarian cancer, remains unresolved.)... 

Talc filled thermoplastic materials were studied in rheometers of different geometries (elongational, capillary, parallel plate). Geometry of the testing method and the flow paths had an important influence on the orientation of talc particles. In addition to flow decrease, an increased concentration of filler had a pronounced effect on both flow and orientation. The cross-sectional distribution of particles de-... 

Talc is always an attractive subject of such studies due to its platelet structure. In thermoforming and compression molding processes of three resins (PP, HDPE, and PPS), each containing 20% talc, the talc particles were always parallel to the specimen surface, regardless of the resin used. Crystallites grew in a direction normal to the surface of talc particles and thus were perpendicular to the specimen surface. But in the case of unfilled HDPE, crystallites grew parallel to the specimen surface. There was no difference in crystallite growth direction in the case of polypropylene with and without talc. 

Applications. Numerous uses of x-ray analysis were reported for filled systems. They include orientation of talc particles in extruded thennoplastics, particle size deteimination in nanocomposites, crystallinity of talc nucleated PP, crystallinity of polymerization filled PE, diffraction pattern of filled PVA, structure of nanocomposites based on montmorillonite, degree of filler mixing, structural characteristics of fillers, structure of carbon black filled rubber, the effect of apatite concentration on the structure of wood pulp, and graphite as template. " This list shows the versatility of the method in applications to filled systems. 

Figure 18.3 shows that orientation of talc particles increases slightly with increased filler volume. The negative orientation function parameter indicates that particles are oriented parallel to the mold surface as might be expected Irom the application of an unidirectional force perpendicular to the surface of the mold. A study compared compression molding with two forms of extrusion and compression molding produced a higher orientation of particles than did the extrusion processes. 

Figure 18.9. The effect of talc particle size on extruder output. [Adapted, by permission, from Ishibashi J, Kobayashi A, Yoshikawa T, Shinozaki K, Antec 96. Vol. I. Conference Proceedings, Indianapolis, 5th-10th May 1996,386-90.]...

The process of formation of the crystalline state is controlled by the kinetics of nucleation and this may arise in a number of ways. Primary nucleation in a quiescent state must be associated with foreign bodies such as deliberately added nucleating agents, such as fine talc particles, or residual impurities such as heterogeneous catalyst particles followed by spherulite growth. The plot of extent of crystallinity, (p, as a function of time is sigmoidal in nature and follows an Avrami equation of the form... 

The effect of the adsorbed surfactant-polymer complex on the rheology of the air-aqueous solution interface is easily detected by the talc particle test (Regis-mond, 1997). A small quantity of calcined talc powder is sprinkled on the surface of the aqueous solution in a 10-cm Petri dish. A gentle current of air is directed tangentially to the talc particles for 1-2 s and then removed. The observed movement is noted in the following categories fluid (F), viscous (V), gel (G) (= almost no flow), solid (S) (= no flow), and viscoelastic (VE) (= net movement, with some recovery upon removal of air current). 

The most remarkable effect of talc on plastics is the increase of stiffness. In general, the flexural modulus of a polyolefin increases by 150-200% with every 20% of talc added. The more platy the talc particles, the greater the effect. 

On the contrary, finer talc particles increased flexural modulus of wood-flour (27.5% w/w) - filled nonoriented polypropylene (27.5% w/w) from 430,000-... 

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