Page 337 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.17

5.1.5.6 Tributyl Tin Oxides. These (Fig. 5.4–VI) have been useful in vinyls, polyure-
thanes, and marine paints. Use is decreasing because of worry about toxicity.
5.1.5.7 Copper Powder. At high loading (70 percent), copper powder has been recom-
mended for control of fouling in marine paints.
5.1.5.8 Alkyl Amines. Alkyl amines have been grafted onto polymer surfaces in recent
research to make them bactericidal.
5.1.5.9 Use in Commercial Plastics. The major use is in plasticized PVC to protect the
ester plasticizers. Other wide uses are in polyester urethanes and in oil paints. Typical
products include shower curtains, wall and floor coverings, carpet underlay, marine uphol-
stery, awnings, refrigerator gasketing, weatherstripping, swimming pool liners, water
beds, and hospital sheeting.

5.2 FILLERS AND REINFORCEMENTS

When large amounts of solid materials are finely dispersed in a polymer matrix, we call
these materials fillers or reinforcements. In terms of total tonnage, these are the leading
type of additives in plastics. Some of their effects are quite general. Many of their specific
effects are so different that it is best to study them in four distinct classes.
1. Extender fillers
2. Reinforcing fillers
3. Reinforcing fibers
4. Specialty, or “functional” fillers

5.2.1 General Effects
Most fillers and fibers are inorganic materials of high density, polarity, modulus, melting
point, refractive index, and solvent resistance, so incorporating them into organic poly-
mers produces major changes in properties.
5.2.1.1 Packing. Many of these properties are proportional to the volume fraction of
fillers or fibers added. Maximum packing fraction can be calculated geometrically and
confirmed experimentally. For spherical particles, maximum packing fraction can go as
high as 85 percent. For conventional fibers, it can go as high as 91 percent. Man-made fi-
bers with rectangular or hexagonal cross sections are easy to make and theoretically can be
packed neatly to approach 100 percent!
5.2.1.2 Processability. Dispersion of polar fillers and fibers in the molten polymer re-
quires special care to produce interfacial wetting and shear mixing to produce dispersion.
Fillers and fibers rubbing against screws and channels produce frictional heating, and they
add thermal conductivity; both effects can speed the processing cycle. They do increase
viscosity considerably, which makes processing more difficult, and they are so hard that
abrasion of process equipment requires more frequent replacement.
5.2.1.3 Mathematical Modeling. Mathematical modeling can attempt to predict and ra-
tionalize effects on properties but requires so many assumptions that it leaves quite a gap
between theory and practice.

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