Talc particle size

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.]...

In thick, high-volume PO applications such as extruded pipe, standard (20-pm) talcs provide effective stiffness. But finer talc grades may allow reduced resin use by allowing thinner parts with equivalent beam stiffness. Reduced talc particle sizes (near 1 pm), for instance, can create a better balance of properties in thinner parts to help justify increased filler cost that results from the use of very fine talcs. Lower talc loadings may also be possible the newest high-aspect-ratio talcs are said to create the same mechanical properties at 3%-7% loadings in PP than in PP compounds loaded with 20% standard talc. Cases 8.1 and 8.2 cover applications in which different talcs supply these different functional needs [7-10]. 

Effects of talc and impact modifier in TPO. Data show influence of talc particle size (at 15% talc loading) and impact-modifier content in homopolymer-PP TPO. Finer talc sizes increase impact resistance and flexural modulus higher impact-modifier loading increases impact while reducing modulus. 

Sch Schone, J., Kotter, L, Grellmann, W. Properties of polypropylene talc compounds with different talc particle size. J. of Plastics Technology 2 (2012) 230-251. 

EFFECT ON IMPACT STRENGTH 8.3.1 Effect of Talc Particle Size... 

Talc producers most commonly use screens for particle size analysis of coarser products (+325 mesh (ca 44 -lm)) and the Micromeritics (Georgia)... 

Mineral fillers are used for light-colored compounds. Talc has a small particle size and is a semireinforcing filler. It reduces air permeabihty and has htde effect on cure systems. Calcined clay is used for halobutyl stoppers in pharmaceutical appHcations. Nonreinforcing fillers, such as calcium carbonate and titanium dioxide, have large particle sizes and are added to reduce cost and viscosity. Hydrated siUcas give dry, stiff compounds, and their acidity reduces cure rate hence, their content should be minimized. 

The extraction time has been observed to vary linearly with polymer density and decreases with smaller particle size [78,79]. The extraction time varies considerably for different solvents and additives. Small particle sizes are often essential to complete the extraction in reasonable times, and the solvents must be carefully selected to swell the polymer to dissolve the additives quantitatively. By powdering PP to 50 mesh size, 98 % extraction of BHT can be achieved by shaking at room temperature for 30 min with carbon disulfide. With isooctane the same recovery requires 125 min Santonox is extractable quantitatively with iso-octane only after 2000mm. The choice of solvent significantly influences the duration of the extraction. For example talc filled PP can be extracted in 72 h with chloroform, but needs only 24 h with THF [80]. pH plays a role in extracting weakly acidic and basic organic solutes, but is rarely addressed explicitly as a parameter. 

The great importance of minerals in prebiotic chemical reactions is undisputed. Interactions between mineral surfaces and organic molecules, and their influence on self-organisation processes, have been the subject of much study. New results from Szostak and co-workers show that the formation of vesicles is not limited to one type of mineral, but can involve various types of surfaces. Different minerals were studied in order to find out how particle size, particle shape, composition and charge can influence vesicle formation. Thus, for example, montmorillonite (Na and K10), kaolinite, talc, aluminium silicates, quartz, perlite, pyrite, hydrotalcite and Teflon particles were studied. Vesicle formation was catalysed best by aluminium solicate, followed by hydrotalcite, kaolinite and talcum (Hanczyc et al., 2007). 

Many inert pigments (often known as fillers) are incorporated into paper in addition to the cellulosic fibres. They may be added to improve certain optical properties—in particular opacity and brightness—or simply as a cheap replacement for costly fibre. The two most common pigments are kaolin (china clay) and chalk (limestone), but talc and speciality pigments such as titanium dioxide are also used. The particle size for general purpose fillers is normally expressed as an equivalent spherical diameter (esd) and this is determined from sedimentation data. Values for the common paper-... 

The rubber compound usually requires an inert inoiganic filler and small particle size carbon particle for reinforcement. The rubber polymers vary in inherent tensile strength from very high in the case of natural mbber to almost nonexistent for some synthetic polymers, eg, SBR. The fillers most commonly used for mbber compounds include carbon black, day, calcium carbonate, silica, talc (qv), and several other inorganic fillers. 

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. 

Fig. 7. The effect of filler particle shape on the viscosity of polypropylene (PP) at 200 °C (A) neat PP ( ) PP containing 40% by weight glass beads (O) PP containing 40% by weight talc. (Filler size distributions similar, at 44 pm or less) [17]...

Shear yield behaviour of polymer melts containing plate-like filler particles is also prevalent and is clearly shown in Fig. 8 for talc-filled polystyrene. In this system an estimate was made of shear yield values, which were found to increase with increasing particle loading and decreasing particle size. These results are compared with reported yield values for other particulate-filled polymers in Table 2. It is evident that shear yield values also depend on the particle type and thermoplastic matrix used. 

---