Page 331 - Handbook of Plastics Technologies

PLASTICS ADDITIVES

PLASTICS ADDITIVES 5.11

5.1.3.6 Market Volume. The total market for PVC heat stabilizers may be about 100
million pounds in the United States and 1 billion pounds worldwide, half for organotin and
half for metal soap-epoxidized fatty ester-organic phosphite systems.

5.1.4 Ultraviolet Light Stabilizers
Five percent of the sunlight that penetrates the ozone layer and reaches the Earth is high-
energy short-wavelength ultraviolet (UV) radiation, 290 to 400 nm. When polymers are
used out of doors, absorption of this UV energy raises the electrons of primary covalent
bonds from their low, stable energy level up to higher unstable energy levels that lead to
degradation (Tables 5.9 and 5.1). Polymer structures that can absorb UV include benzene
rings, C=C, C=O, OH, ROOH (Table 5.10), and especially conjugated groups of such
structures. Even polymers that do not contain such groups may still degrade, and the
blame is then placed on impurities or complex-formation. UV degradation can lead to
cleavage to lower molecular weight or cross-linking to higher molecular weight, unsatura-
tion, photooxidation, and photohydrolysis, all of which result in weathering deterioration.

TABLE 5.9 UV Wavelengths and Energy Levels

UV wavelength, nm Energy level, kcal

259 111
272 105
290 100
300 95
320 90
340 84
350 81
400 71

TABLE 5.10 UV Absorption by
Functional Groups in Polymers

Benzene rings <350 nm
C=C <250 nm
C=O <360 nm
O-H <320 nm
ROOH <300 nm

There are a number of ways to protect plastic products for use outdoors, as described be-
low.

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