Page 371 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.51

5.9.2 Commercial Antistats
–
+
Quaternary ammonium soaps, R N X , have the most powerful antistatic action. Unfor-
4
tunately, they tend to decompose in high-temperature processing, so they are sometimes
post-applied as a 1 to 2 percent solution. They also encounter objections from the FDA.
Ethoxylated amines, RNH(CH CH O) H, approach quaternary ammonium soaps,
2
2
n
both in effectiveness and in problems.
Ethoxylated esters, RCO (CH CH ) OH, are the most widely used class. By balancing
2
2
2 n
the organic acid portion (R) against the polyoxyethylene portion, it is possible to control
polarity and therefore semicompatibility and rate of migration to the surface of the plastic,
thus making it self-renewable over the lifetime of the product. They adsorb water to the
surface, making it conductive and lubricating it to reduce friction. They are usually non-
toxic and stable enough for melt processing. Ethoxylated alcohols, RO(CH CH O) H, are
2
n
2
also used.
Glycerol mono- and di-esters perform fairly similarly to ethoxylated esters and are
used for this reason. Being derived from natural products, they are easily acceptable to
FDA.
Organic phosphate esters are also reported in similar use.
More recently, alkali sulfonates have been reported in PS and PVC.
5.9.3 Use in Commercial Plastics
LDPE typically uses 0.05 to 1.0 percent, HDPE 0.2 to 0.3, PP 0.5, and PS 2 to 4 percent.
Rigid PVC uses 1 to 2 percent, and plasticized PVC 2 to 5 percent.
5.9.4 Test Methods
5.9.4.1 Dust Attraction. Dust attraction is the oldest and crudest method. The techni-
cian rubs the plastic sample against his clothing, and then lowers it toward a dish of dust,
and notes the height at which the dust jumps up to the charged plastic. A more sophisti-
cated test uses a sooty flame to deposit soot on the plastic, and then measures the amount
of soot collected.
5.9.4.2 Surface Conductivity. Determining the surface conductivity of the plastic sam-
ple is a popular, simple measurement that is often assumed to correlate with antistatic be-
havior. Practical proof would be more reassuring.
5.9.4.3 Electrostatic Decay. A high static charge is applied to the sample electrically.
Then the rate of decay is measured instrumentally.
In all these methods, relative humidity is the most treacherous variable that must be
4
considered. This can produce a 10 range in electrical resistivity over the normal range of
ambient humidity.

5.9.5 Market Analysis
Ethoxylated fatty amines are 48 percent of the market, aliphatic sulfonates 25 percent,
fatty acid esters 16 percent, quaternary ammonium compounds 2 percent, others 9 percent.
For use in individual plastic materials, styrenics used 39 percent of the market, LDPE/
LLDPE 20 percent, HDPE 13 percent, PVC 12 percent, PP 11 percent, and others 5 per-
cent.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2006 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.