An Introductionto

Mineral Fillersfor Plastics

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FILLER

Filler = Something cheap to take up space?

Mineral “fillers” are actually most often used to improve one or more properties.

Effects of Mineral Fillers Depend On

Particle Shape

Particle Size

Volume Fraction in Matrix

Compatibility With/Adhesion To Matrix

Shape Sphere Cube NeedleAspect Ratio

1 1 5-20+

Shape Block Plate/Flake FiberAspect Ratio

2-4 20-200 20-200+

Basic Particle Shapes

Particle Size Distribution

Median Particle Size = Half the particles are larger, half are smaller

Size (top and bottom) Counts

Particle Size?

“Particle” Size = Median (or Average) = Equivalent Spherical Diameter (ESD)

Automated particle sizers match the behavior of a particle (regardless of shape) to that of an ideal sphere of specific diameter. Compare the “particle size” of dissimilar minerals with care.

ESD!!! = =

Aspect Ratio

Needle/Fiber Aspect Ratio:Ratio of mean length to mean diameter

Plate Aspect Ratio:Ratio of mean diameter of a circle of the same area as the face of the plate to the mean thickness of the plate

L

D

TD

For tensile and flexural stresses to be transferred from polymer matrix to anisometric filler, a certain critical aspect ratio must be exceeded. Once this critical ratio is exceeded, the efficiency of stress transfer increases with increasing aspect ratio.

Aspect Ratio

For the same volume fraction, increasing the aspect ratio increases a composite’s strength and stiffness.

Volume Fraction

Volume fraction: The volume occupied by the filler divided by the volume of the composite (Vf / Vc).

Fillers usually have their strongest influence on composite properties and cost when the volume fraction is sufficiently high to allow for the matrix to just coat all particles and fill inter-particle voids. For some properties this may be good, but for others, not so good.

Matrix Compatibility/Adhesion

Intimate contact with the matrix is essential to filler functionality.

Nonpolar organics (polypropylene, mineral oil) will better “wet” hydrophobic fillers (talc). Polar organics (nylon, polyurethane) will better wet hydrophilic fillers (mica, wollastonite).

Surface treatment/modification can optimize filler-matrix compatibility and adhesion.

Matrix Compatibility/Adhesion

Surface Treated: Filler + Process Aid

Surface treatments may not bond to the filler and do not bond to the matrix. They act like “wetting” agents to make the filler surface hydrophobic and more readily coated by the organic medium.

Matrix Compatibility/Adhesion

Surface Treatments:•Improve deagglomeration and dispersion.

•Reduce blend viscosity, allow higher filler loading.

Matrix Compatibility/Adhesion

Surface Modification: Filler + Coupling AgentModification is the durable attachment of coupling agent to the filler and to the surrounding matrix.

Filler-Coupler: Covalent bond

Matrix-Coupler: Chemical reaction or chain entanglement

Matrix Compatibility/Adhesion

Surface Modifiers:•Improve deagglomeration and dispersion.

•Reduce blend viscosity, allow higher filler loading.

•Improve impact, tensile, flexural and dielectric properties in polymers.

•Improved properties retention in polymers after environmental exposure.

Matrix Compatibility/Adhesion

Surface Modifiers:Silanes – Encapsulate filler particle in covalently bonded siloxane polymer; can condense more than one molecular layer.

Titanates – Individual molecules covalently bonded, no polymerization; monomolecular layer.

Both depend on the ability to form a bond via silanol (-Si-OH) on filler surface.

Matrix Compatibility/Adhesion

Silane Coupling:Excellent to Good – glass, synthetic silica, natural silica, wollastonite.

Good to Fair – mica, aluminatrihydrate, kaolin, talc, barite, titanium dioxide, iron oxides.

Slight to None – calcium carbonate, carbon black.

Matrix Compatibility/Adhesion

Silane- TreatedUntreated

Photomicrographs: Union Carbide Corporation

Mineral Filler Effects in PlasticsIncrease:

Stiffness (Tensile & Flex Modulus)Strength (Compressive, Flexural)

Thermal ConductivityAbrasion ResistanceWeather ResistanceDielectric StrengthSurface HardnessFluid ResistanceHeat ResistanceArc Resistance

OpacityDensity

Mineral Filler Effects in Plastics

Reduce:CreepGloss

FlammabilityTensile Strength*

Shrinkage ex MoldElongation at Break

Coefficient of Thermal Expansion*High aspect ratio fillers can increase tensile strength.

Mineral Filler Effects in PlasticsFiller Effect on Costs: Weight vs Volume

Density Cost Costlb./in.

3cents/lb. cents/in.

3

PP homopolymer 0.0324 40 1.3Phlogopite mica

a0.1044 31.75 3.31

60% PP/40% mica 0.0448 36.7 1.64

PP homopolymer 0.0324 40 1.3Muscovite mica

b0.1044 4.5 0.47

60% PP/40% mica 0.0448 25.8 1.16

PP homopolymer 0.0324 40 1.3CaCO 3

c0.0972 8.54 0.83

60% PP/40% CaCO 3 0.0442 27.4 1.21

PVC homopolymer 0.0504 38 1.91CaCO 3

d0.0972 16 1.55

60% PVC/40% CaCO 3 0.0625 29.2 1.82

ahigh aspect ra tio, silane treated

blow aspect ratio, untreated

cdry ground, 3 m, uncoated

ddry ground, 1 m, coated

8%

36%

32%

23%

26%

11%

7%

5%

Cost? Cost per part = part volume X cost/unit wt X density

Primary Mineral Fillers In Plastics

Calcium Carbonate- dry-ground, wet-ground, stearate-coated, PCC.Kaolin- calcined, water-washed, delaminated, silane- modified.Talc- fine-ground high purity platy.

Mica- fine wet-ground and dry-ground, silane-modified.

Wollastonite- fine-ground, acicular, silane-modified.

Silica- fine-ground quartz and novaculite, precipitated and fumed synthetics, silane-modified.

Calcium Carbonate

 Ground calcium carbonate Dry-ground: nominal 200 to 325 mesh. Wet-ground: fine ground (FG; 3 to 12 m median, 44 m top), ultrafine ground (UFG; 0.7 to 2 m median, 10 m top). Wet-ground 75% solids slurry. Stearate-treated. 

Precipitated calcium carbonate Typically fine (0.7 m median) and ultrafine (0.07 m median), with and without stearate surface treatments.

Calcite CaCO3

Refractive Index: 1.66-1.74Specific Gravity: 2.71Mohs Hardness: 3-4

Calcium Carbonate

Scalenohedral Spherical

Prismatic AragoniticRhombohedral

Clustered Aragonitic

PCC

GCC/PCC

Photomicrographs: Minerals Technologies

KaolinKaolinite Al2Si2O5(OH)4

Refractive Index: 1.55-1.57 / calcined: 1.62Specific Gravity: 2.58 / partially calcined: 2.50 / fully calcined: 2.63Mohs Hardness: 2 / partially calcined: 4-6 / fully calcined: 6-8

Airfloat Dry-ground, air separated.  

Water-washed Water-slurried, often bleached and/or high-intensity magnetic separated, centrifuged or hydrocycloned for high purity specific particle size fractions; dewatered and dried, or concentrated to 70% solids slurry. 

Delaminated Coarse clay fraction from water-washing, attrition milled into thin, wide individual plates. 

Calcined Water-washed soft clay calcined to either partially or totally remove surface hydroxyl groups.

Kaolin

Platy

Airfloat Water-WashedDelaminated

Talc

Talc Mg3Si4O10(OH)2

Refractive Index: 1.59-1.60Specific Gravity: 2.75Mohs Hardness: 1

Platy Distinctly lamellar, soft talc, typically of >90% purity naturally or through beneficiation; type usually used for filler applications. 

Steatitic High purity, dense, very fine-grained talc that can be machined; usually used for ceramics applications.

Talc

Platy

Mica

Muscovite KAl2(AlSi3)O10(OH,F)2

Refractive Index:1.58-1.62Specific Gravity: 2.76-2.88Mohs Hardness: 2-2.5

Phlogopite KMg3(AlSi3)O10(OH,F)2

Refractive Index: 1.56-1.64 Specific Gravity: 2.78-2.85 Mohs Hardness: 2.5-3

Wet-ground Wet-milled to delaminate and grind; higher aspect ratio, sheen, and slip than dry-ground mica.  

Dry-ground Coarse-ground, >100 mesh, are hammer milled and screened or air separated; fine-ground, <100 mesh to <325 mesh, are air milled. 

Micronized Air milled to <20 or <10 m.

Mica

Platy

Wollastonite

Wollastonite CaSiO3

Refractive Index: 1.62-1.65Specific Gravity: 2.92Mohs Hardness: 4.5

Powder grades Milled wollastonite with low aspect ratio (3:1 to 5:1). Typically 200, 325, 400 and 1250 mesh.

Acicular grades Milled to very fine, needle-like particles. Typical aspect ratios in the range 12:1 to 20:1.

Wollastonite (Acicular)

Needle

SilicaQuartz SiO2

Refractive Index: 1.54Specific Gravity: 2.65Mohs Hardness: 7

Synthetic Silica SiO2

Refractive Index: 1.45Specific Gravity: 2-2.3Mohs Hardness: 5-6

Ground silica aka ground quartz, silica flour; <200 mesh ground high purity quartz, quartzite, sandstone, or silica sand. Typically >99% SiO2, high brightness, low moisture,

chemical inertness, relatively low surface area, low vehicle demand.  

Novaculite Platy microcrystalline quartz, low moisture, >99% SiO2, brightness generally less than other ground

silicas, but lower binder demand and abrasivity, wider range of particle size grades (as small as 2 m avg)

Ground Silica

Low Aspect Ratio, Irregular Shape

Novaculite (Silica)

Platy

Other Mineral Fillers In Plastics

Barite- dry-ground natural, precipitated as blanc fixe

Diatomite- calcined fine dry-ground

Feldspar, Nepheline Syenite- fine dry-ground

Pyrophyllite- fine dry-ground

Barite BaSO4

Refractive Index: 1.64-1.65Specific Gravity: 4.5Mohs Hardness: 3-3.5

Barite

Filler grade High brightness, high purity, usually <325 mesh or finer; typically >95% BaSO4, <0.1% Fe2O3, <0.5%

moisture. 

Blanc fixe Precipitated barium sulfate for higher brightness and purity and finer particle sizes than available with barite.

Barite

Blocky

Photomicrograph: Huber Engineered Materials, part of J.M. Huber Corporation

Diatomite

Diatomite SiO2

Refractive Index: 1.401.43 / calcined 1.431.47Specific Gravity: 2.02.1 / calcined 2.12.3Mohs Hardness: 4.55 / calcined 5.56

Flux-calcined Calcined at ~1200oC with a sodium carbonate or sodium chloride flux; milled, screened, and air classified; fine fraction (<325 mesh) is white filler grade; maximum void volume, can exceed 90%, and consequent high absorptivity.

Straight-calcined Calcined between 870o and 1100oC in a rotary kiln; milled, screened, and air classified. Pink color from iron oxidation usually precludes filler use.

Natural diatomite Gently crushed and milled ore; screened or air classified; fine fraction (<325 mesh) for some filler uses.

Diatomite

Weird

Diatomite is the microscopic skeletons of diatoms, unicellular algae found in both fresh and sea water.

FeldsparOrthoclase KAlSi3O8

Refractive Index: 1.52-1.54Specific Gravity: 2.57Mohs Hardness: 6 

Microcline KAlSi3O8

Refractive Index: 1.52-1.54Specific Gravity: 2.54-2.57Mohs Hardness: 6

Albite NaAlSi3O8

Refractive Index: 1.53-1.54Specific Gravity: 2.62Mohs Hardness: 6 

Anorthite CaAl2Si2O8

Refractive Index: 1.58-1.59Specific Gravity: 2.76Mohs Hardness: 6

Filler grade – principally albite (soda spar) with a mixture of other feldspar minerals; usually produced by flotation and magnetic separation followed by milling; finest grades are air classified

Feldspar

Low Aspect Ratio, Irregular Shape

Nepheline SyeniteNepheline (Na,K)AlSiO4

Refractive Index: 1.53-1.55Specific Gravity: 2.57Mohs Hardness: 5.5-6 

Microcline KAlSi3O8

Refractive Index: 1.52-1.54Specific Gravity: 2.54-2.57Mohs Hardness: 6

Albite NaAlSi3O8

Refractive Index: 1.53-1.54Specific Gravity: 2.62Mohs Hardness: 6

Nepheline syenite is a rock composed of soda and potash feldspars and nepheline.

Filler grade Filler grades are finely ground (325 mesh to 1250 mesh) and have high brightness (>93) and low vehicle demand.

Nepheline Syenite

Low Aspect Ratio, Irregular Shape

PyrophyllitePyrophyllite Al2Si4O10(OH)2

Refractive Index: 1.59-1.60Specific Gravity: 2.8Mohs Hardness: 1.5

In US: natural blends with sheet silicates, diaspore, andalusite and quartz; quartz makes them unsuitable for many filler applications.

Filler grade Airfloat, 200-325 mesh.

Refractory grade Low in alkalis (<1%), i.e., a low mica content; fluxes (Fe2O3, FeO, TiO2) <1%.

Ceramic grade High alkali (i.e. higher mica) for lower melting point/faster firing; low coloring oxides for white ware.

Agricultural grade Carrier for active ingredients in pesticide dusts, selection based on fineness and bulking values.

Pyrophyllite

Platy

R.T. Vanderbilt Company, Inc. offers a wide range of mineral fillers: wollastonite, talc, industrial talc, kaolin and pyrophyllite.

For more information, contact us at:Headquarters:R.T. Vanderbilt Company, Inc.30 Winfield Street, P.O. Box 5150,Norwalk, CT 06856-5150(203) 853-1400 Fax: (203) 853-1452Web Site: www.rtvanderbilt.come-mail: plastics@rtvanderbilt.comWest Coast Office:6280 Manchester Boulevard, Suite 204,Buena Park, CA 90621(714) 670-8084 Fax: (714) 739-1488e-mail : laoffice@rtvanderbilt.comCanadian Office:1 Eva Road, Suite 419,Etobicoke, Ontario, M9C 4Z5, Canada(416) 626-6027 Fax: (416) 626-6139 e-mail : dhook@rtvanderbilt.com 

European Office:32 Rue du Vieil Abreuvoir, 2eme etage78100 Saint Germain en Laye, France011-33-1-390-41342 FAX: 011-33-1-39041345e-mail : jbenton@rtvanderbilt.com