Vật
liệu đàn hồi PU nổi bật với tính chất cơ lý kéo, xé, mài mòn tốt, còn kháng tốt
với nhiều loại dung môi. Tuy nhiên, vật liệu PU rất dễ bị thủy phân trong môi
trường nước. Phần tài liệu sau đây sẽ giới thiệu chung về tính kháng hóa chất của
vật liệu PU.
…
In
certain fluids the polyurethanes, like other rubbers, swell but when removed
and allowed to dry out they return to their original dimensions. This is not
always so with other elastomers or plastics since they may contain plasticizers
which can be leached out by the fluid, resulting in permanent shrinkage. The
effect of organic materials on polyurethanes is dependent upon the chemical
groups present in these materials.
Alcohols,
acids, and ketones and esters tend to cause swelling and degradation,
particularly at high temperatures. Aliphatic hydrocarbons and esters are
generally inert, but aromatic hydrocarbons are more active and promote swelling
at room temperature and gradual breakdown at higher temperatures. Up to service
temperatures of about 50°C polyurethane elastomers in contact with these
organic fluids, or their greases, can be considered as some of the most
resistant materials available when the combined effects of oil or grease and
weathering are encountered.
Chlorinated
solvents cause swelling and sometimes degradation. The tensile and tear
strengths are reduced to about 25% of their initial values after 6 months'
immersion in chloroform at room temperature. Methylene chloride causes even
more rapid breakdown, whilst carbon tetrachloride and trichloroethylene are
relatively inert, although swelling does occur.
Rapid
breakdown also occurs upon immersion in 12% sodium hypochlorite and 30%
hydrogen peroxide. In 10% hydrogen peroxide, however, the effect is much
reduced.
The
resistance of polyurethane elastomers to immersion in water has been identified
as relatively poor and is directly applicable to immersion in dilute solutions
of inorganic materials in water. Provided the inorganic substance has no
catalytic effect the solution can be expected to behave as pure water. However,
acidic or alkaline media accelerate hydrolytic attack and therefore solutions
of salts of weak acids or bases are likely to degrade polyurethanes faster than
water. As a generalization, it can be stated that, provided the pH of a
solution lies between the values of 5·5 and 8, the action of the solution can
be considered similar to the action of water. At higher acidities or higher
alkalinities it is advisable to test the effect of the particular solution. As
would be expected, strong acids and bases attack polyurethanes rapidly.
…
Trích
đăng từ sách Polyurethane Elastomers, C. Hepburn, Elsevier Science
Publisher, 1992, trang 382 – 387
(vtp-vlab-caosuviet)
