Kaolin aspect ratios

Typical concentration range generally >40 wt% calcium carbonate, calcinated kaolin, talc - 20-40 wt% carbon fiber 5-30% (depending on aspect ratio) " titanium dioxide - 1 wt% (occasionally concentrations of 10 wt% are found in thin sections) " ferromagnetic powder - up to 90 wt% " stainless steel fiber - 2-3 wt% " nickel fibers for magnetic properties -10-30% starch in biodegradable products - 4-8 wt% ... 

There are basically only three types of platelet-type fillers which can be considered for use in thin barrier films. These are aluminum flake, mica and talc (Table II). Other types of platelets, such as glass, stainless steel or brass flakes and certain aluminum silicate minerals, such as kaolin clay, are either too large in particle size or have too low an aspect ratio to be useful. With these three... 

Hydrous kaolins are naturally occurring minerals found as hexagonal plates of varying crystalline uniformity. The plates are often associated with one another as stacks or booklets (Fig. 6.1). These particles have low aspect ratios and typically exhibit small surface area. Aspect ratio is defined by the ratio of the plate diameter to the plate thickness. 

European kaolin fiUer 78-82 1.5-2.5 Broad 6-10 Plates relatively high aspect ratio... 

Engineered European kaolin 82-84 1.5-2.0 Somewhat steeper 10-12 Plates high aspect ratio... 

North American kaolin filler 80-85 0.3-1.5 Broad 15-20 Blocky stacks of plates, low aspect ratio... 

Talc and hydrous kaolins are naturally platy by nature, and degree of platiness can be enhanced by the delamination process. Oftentimes, these products are differentiated by aspect ratio which is defined as the ratio of plate diameter to plate thickness. Key benefits of shape-engineered platy particles include reduced sheet permeability along with improved smoothness and printability. 

For example, coarse kaolins of high aspect ratio are considered excellent choices for supercalendered grades based on ease of retention and improved print quality in the final sheet. As shown in Fig. 6.12, replacement of only 25% of the PCC with platy kaolins can significantly impact sheet permeability. In this example, five... 

Modification of mechanical properties High aspect ratio glass fibers, mica, nanoclays, carbon nanotubes, carbon/graphite fibers, and aramid/synlhetic/natural fibers Low aspect ratio talc, CaC03, kaolin, wood fiour, wollastonite, and glass spheres Control of permeability Reduced permeability impermeable plate-like fillers mica, talc, nanoclays, glass flakes Enhanced permeability stress concentrators for inducing porosity CaCOj and dispersed polymers... 

Kaolin, being plate-like filler with a relatively low aspect ratio [6,7,12,13], may impart certain mechanical property improvements in thermoplastics. Similar to other plate-... 

Low Aspect Ratio Mechanical Property Modifiers with detailed description of talc, kaolin, wollastonite, wood flour, and calcium carbonate. Chapters 12-16. 

Talc, mica and kaolin particles are plate-like, so aspect ratio in this case means the ratio of one of the two larger dimensions to the smallest one. Several common fillers have chunky particles, with all three dimensions similar (e.g., calcium carbonate), so their reinforcing ability is lower than that of wollastonite. 

Kaolin is a hydrated aluminium silicate of variable composition, derived from clay minerals. The main constituent is kaolinite, with the formula Al2O3.2SiO2.2H2O, usually accompanied by a variable amount of feldspar, quartz, mica or similar minerals. The structure consists of hexagonal sheets, with an aspect ratio of 10. Purification is required before use. 

Keywords filler, aspect ratio, particle shape, calcium carbonate, talc, platelets, reinforcement, glass fiber, kaolin, particle size, particle size distribution, chemical composition, adhesion, interface, aggregation, specific surface area, flow-induced orientation, hardness, surface free energy, surface tension, surface treatment, mechanical properties, thermal properties. 

The aspect ratio of the final flake products depends upon the origin of the mica and the processing method. Large flake pegmatite mica and wet milled mica can have aspect ratios in excess of 100. By contrast, processed mica flakes from schist and kaolin deposits tend to have aspect ratios in the area of 30 to 60. 

Powdered fillers, also called low-aspect ratio fillers, are mainly of inorganic origin. Patents mention many inorganic powdered fillers [52-54]. They function as inactive fillers and also as reinforcing agents for many plastics, such as polyolefins, polycarbonates, polyformaldehyde, polyamides, PVC, epoxies, and polyesters [55,56]. Most often recommended are feldspar, woUastonite, mullite, asbestos, silicon, silicates, cristobalite, a series of metals, Al, Zn, Pb, Mn, Ba, Ti, Fe, Co, Ni, etc., and their oxides, carbonates, and basic mineral compounds such as spodumene, montmorillonite, kaolin, bentonite, etc. Powdered fillers are added in large quantities, 40-90% by weight of composite. 

As a secondary processing after the water suspension, a delamination process cleaves or splits the kaolin into very thin platelets. Delamination can be achieved by abrasion using beads as the grinding medium or extrusion of a kaolin water paste [93 ]. Aspect ratios for delaminated grades are as great as 200 to 1 for large platelets [95]. 

Fibrous reinforcements, such as glass and asbestos, and acicular reinforcements, such as wollastonite, also tend to orient parallel to the flow direction. Since they all have lower thermal expansions than plastics, use of these minerals tend to promote warping, especially in crystalline polymers. Fillers such as mica, talc and kaolin, also orient in the flow direction, but their platy, more two-dimensional shape does not contribute to warping. High aspect ratio mica, because of its extreme platiness, is used to counteract the natural warping tendency of highly crystalline thermoplastic polyesters. 

Mineral fillers are naturally occurring or synthetic nonblack, nonmetallic solid-surface particles. Such fillers have assorted shapes, from nodular to platy to aci-cular. When describing filler shape, the term aspect ratio is employed to describe the relationship of one dimension to another. Mineral fillers for PVC have historically included calcium carbonate (ground and precipitated), alumina trihydrate (ATH), barytes, talc, mica, kaolin, feldspar and nepheline syenite, and wollastonite. 

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