Sự
oxy hóa là nguyên nhân phổ biến gây hư hỏng cho vật liệu đàn hồi. Các yếu tố
như nhiệt độ, ánh sáng và hàm lượng kim loại trong cao su tăng nhanh quá trình
oxy hóa này. Nội dung này được trình bày cụ thể bên dưới.
…
EFFECTS
OF HEAT
As
noted, a small percent of oxygen, combined with an elastomer, can seriously
degrade the physical properties of that elastomer. Heat can greatly increase
the rate at which oxygen reacts with the polymer. The rate of reaction
approximately doubles for each 10oC increase in temperature. About a
50-fold increase in reaction rate occurs between room temperature and 70oC.
Another perspective would be that a change in physical properties, observed at
a service temperature of 150oC, would require about 8000 times
longer for the same change to occur at ambient temperature [9].
EFFECTS
OF LIGHT AND WEATHERING
UV
light promotes free radical oxidation at the rubber surface which produces a
film of oxidized rubber. Heat and humidity then accelerate the formation of a crazing
or alligatoring effect, and this oxidized layer can be rubbed off—giving a
chalking appearance.
EFFECTS
OF METALS
Heavy
metal (principally cobalt, copper, manganese, iron) ions are believed to
catalyze oxidative reactions in elastomers by influencing the breakdown of
peroxides in such a way as to accelerate further attack by oxygen. The first
corrective approach is to eliminate all sources of harmful metals. Compounds of
copper and manganese, such as stearates and oleates, which are directly soluble
in rubber, are particularly active, since they provide a direct source of heavy
metal ions. Even the less soluble forms such as the oxides can cause problems
by reacting with fatty acids used in compounding to produce more soluble forms.
Although
some antioxidants are active against catalyzed oxidation of rubber, in general,
the standard antioxidants do not give protection against the heavy metal ions.
Since the activity of the metal depends on its being in an ionic form, it is
possible to protect compounds by incorporating substances which react with
ionic metals to give stable coordination complexes.
…
Trích
đăng từ sách Handbook of Specialty
Elastomers, Robert C. Klingender,
CRC Press, 2008, trang 435 – 436
(vtp-vlab-caosuviet)
