Kaolin in Technical Rubber

Kaolins (clays) find use in a variety of applications, either because of specific technical properties and/or because of their very favourable cost / performance ratio.

 

Fine kaolins have semi-reinforcing properties and may be used as either the primary filler in rubber or in order to partially replace or extend more highly reinforcing carbon blacks. Less fine (filler) kaolins confer lower levels of reinforcement and may be more readily used at higher volume loadings. In addition, the processing properties of filler clays are often more advantageous, since they are easier to disperse efficiently. If light coloured articles are to be produced, then kaolins such as Speswhite™ & Polwhite™ E or PoleStar™ 200R calcined clay can be used in brightly
coloured compounds.
All kaolin fillers share some common features because of the platelike shape of their particles, which results in some stiffening of the rubber compound. This gives much better extrusion and
calendering properties (exhibiting low die swell and good dimensional stability) than can be obtained from most other mineral fillers.

Washing Machine Seal

Formulationphr
Vistalon 3666175
Zinc oxide5
Stearic acid1
Titanium dioxide20
Speswhite™100
Polyvest 252
Sunpar 228025
Struktol WB2123
TMTD0.8
Tetrone A0.8
ZBDC2.0
Sulphur2.0
Properties
Tensile Strength (MPa)10.7
Modulus at 300% (MPa)2.8
Elongation at break (%)800
Tear Strength (N/mm)20
Hardness (° Shore A)45
Compression set at 70°C (%)24.4
Compression set at 100°C (%)31.3

Flooring Compound

Formulationphr
Vistalon 460860
Vistalon 250440
Zinc oxide5
Stearic acid2
Paraffin wax5
Polwhite™ E200
Sunpar 15030
Sulphur1.5
ZDC0.5
TMTD0.5
MBT1.5
Properties
Tensile Strength (MPa)5.8
Modulus at 300% (MPa)3.7
Elongation at break (%)440
Hardness (IRHD)73
Compression set at 70°C (%)79.3

In injection mouldings platy kaolins or talcs can cause anistropy while synthetic silicas or aluminium silicates give a high viscosity causing difficulties in mold filling. Calcined kaolin gives, as a consequence of its shape and size, little anistropy and low viscosity. Properties are also very good (but may be boosted by small amounts of synthetic silica) and a typical EPDM injection moulding for a spark plug cap is given below.

 


Spark Plug Cap

Formulationphr
Vistalon 7606100
Polyethylene Wax3
PoleStar™ 200R120
Precipitated Silica30
Plasticiser30
Polyethylene glycol3
ZMTI1
Sulphur0.2
Peroxide8
Curing characteristics
Minimum torque (lb/in)9.7
Maximum torque (lb/in)73.4
T2 (min)1.0
T90 (min)7.7
Mechanical Properties
Tensile Strength (Mpa)10.1
Elongation at Break (%)43.0
Modulus at 100%3.0
Hardness (Share A)64

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Dr. Flavio Catozzo

Dr. Flavio Catozzo

Product Spotlight

SUPREME TM

Supreme™ premium kaolin from IMERYS gives multiple benefits when used in decorative matt wall paints, functioning both as an opacifying extender and also as a rheology modifier.
For further information please click here