Page 326 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

5.6 CHAPTER 5

TABLE 5.4 Impact Styrene Stabilization: ASTM D-1925
Yellowness Index After 80°C Oven Aging
Hours Unstabilized 0.1 percent hindered phenol

0 2 2
250 35 2
500 5
750 10
1000 17

TABLE 5.5 Nylon 6 Stabilization: Hours
to 20 Percent Loss of Tensile Strength in
160°C Oven

Hindered Phenol, % Hours

0 5
0.2 60
0.4 115
0.6 170

free-radical degradation reaction. Two types of compounds are commonly used as nonrad-
ical peroxide-decomposers: aliphatic sulfides and organic phosphites.
5.1.1.2.1 Aliphatic Sulfides. The most popular one is dilauryl thio dipropionate
(DLTDP), nicknamed dillydip. For lower polarity and volatility, the lauryl groups are ex-
tended to stearyl (C ) (DSTDP).
18
5.1.1.2.2 Organic Phosphites. These are also often used. When they are used to sup-
plement the hindered phenol primary antioxidant, they are considered nonradical peroxide
decomposers. On the other hand, in many polymers, they may be used as the primary anti-
oxidant, presumably both to prevent the formation of peroxide and to decompose any per-
oxide that does form. The most popular is tris(nonylphenyl) phosphite, but many others
are also used.
5.1.1.3 Complexing Agents: Metal Deactivators. Transition metals (elements with
more than one valence state) catalyze oxidation reactions by complex redox (reduction-ac-
tivation) mechanisms,
.
.
RO:OH ↔ RO + OR
. ++ - +++
RO + M → RO + M
When traces of transition metal compounds are present in polymers, either as catalyst
residues (Ziegler-Natta, metallocene, single-site, polyesterification) or as impurities in fill-

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