Chemistry Reference
In-Depth Information
9.6 LUBRICANTS
Lubricants are sometimes added to polymer formulations. Lubricants mini-
mize frictional forces between moving surfaces. They can be used to improve
processability or to improve dispersion of other additives such as pigments
or fillers. They can be external lubricants to provide lubrication between the
polymer surface and metallic processing equipment such as molds used in
injection molding. The external lubricant can be applied to the mold surface as
a spray or it can be added to the polymer formulation where it migrates to the
polymer surface. Commonly these are paraffin waxes (oligomeric polyethy-
lene), fatty acids such as stearic acid, fatty acid salts such as sodium stearate,
or fatty acid amides, such as stearamide. One issue with external lubricants
is that they migrate to the surface; that is, they plate out on the surface. Inter-
nal lubricants typically have greater solubility in the polymer. They promote
movement of polymer chains in the bulk polymer. Like plasticizers they can
lower the heat properties of the formulation, but unlike plasticizers, they are
typically used in low levels to minimize the effect on upper use temperature
of the molded article and on modulus. Esters of fatty acids such as glycidyl
ester or butyl stearate are used. Another example is fatty acid amides such as
ethylene bis-stearamide.
O
R
O
O
O
N
O
R
′
C
17
H
35
O
C
17
H
35
H
C
17
H
35
R
″
O
O
O
Butyl stearate
O
Glycidyl ester
Ethylene bis-stearamide
9.7 FLAME RETARDANTS
Flame retardants are additives used to retard the ignition and burning of plas-
tics. By the use of flame retardants, plastic formulations can meet the various
fire safety standards needed. One agency that provides fire resistance certifi-
cations is Underwriters Laboratory Inc. These certifications are often in the
form of a UL rating. There are various UL tests and ratings. The goal is to
make the test relevant to the application. One common way of rating plastics
is the UL 94 vertical burn test. A flame is applied for 10 seconds to a plastic
specimen and the removed until the flaming stops. The flame is then reapplied
for another 10 seconds and removed. Depending on how long the specimen
burns and whether there are flaming plastic drips, a rating is assigned.
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