Effects of Fillers on Polymer Properties

Several equations claim to predict the properties of filled plastics, especially Young s modulus. The subject has been extensively studied. In practice the effects of a given amount of a given filler on polymer properties will depend on the filler s physical and mechanical properties, its chemical composition, particle shape and size, size distribution, specific surface area, siuface chemistry, interparticle spacing and extent of agglomeration. 

Fillers with high aspect ratios (length diameter ratio) are better at reinforcing a polymer than chimky particles with a roughly spherical shape. High aspect ratio fillers will normally produce a significant increase in modulus, heat distortion temperature and creep resistance. 

Particle shape is often expressed in terms of whether the particles are roughly spherical, platelike or needle-like. Particles tend to come in three varieties elongated, spherical, and plate like. Wollastonite particles are elongated almost to the shape of fibres, with a high aspect ratio that enables them to reinforce the polymer, improving its mechanical properties and replacing more expensive glass. 

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. 

High aspect ratio fillers include wollastonite and talc, and mica, a lamellar or plate-like filler, also has a modest reinforcing effect. 

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