Prediction of the lifetime of nitrile-butadiene rubber by FT-IR.
A quantitative measurement method with FT-IR was proposed for a thermal degradation analysis of nitrile-butadiene rubber (NBR). An NBR film was prepared as a model sample on a barium fluoride (BaF2) crystal plate, which was subjected to a heat treatment. The absorbances of various functional groups were measured directly by FT-IR after thermal degradation at high temperatures. By measuring the absorbances, it was possible to readily determine quantitatively each of the functional groups after the degradation of NBR. By assuming that the NBR lifetime was the point at which the absorbance of a carbon-carbon double bond reaches 45% of that prior to thermal treatment, a method for predicting the lifetime of NBR heated below 150 degrees C was proposed, by using an Arrhenius plot of the heating time versus heating temperature.
Study on the deterioration of an epoxy-type adhesive containing nitrile rubber.
高温高湿環境下でニトリルゴム(NBR)/エポキシ樹脂系接着剤の加速寿命試験を行い,接着剤の劣化について検討した。その結果,接着剤のガラス転移温度(Tg)の低下や透過型電子顕微鏡(TEM)観察下におけるNBRへのオスミウム酸の染色能の低下が認められ,接着剤の劣化はミクロ相分離構造を形成しているNBRの劣化に起因することが判明した。NBRの劣化としては主に酸化反応による炭素-炭素二重結合部の切断であるが,そのほかにニトリル基やNBR中に変性されたアクリル酸とエポキシ基との反応でできたエステル基の減少も確認された。また,NBR中の酸化防止剤が接着剤の硬化を目的とする加熱処理過程で気化してしまうことにより,この劣化は更に加速されていることが分かった。
Early Cretaceous Feathers from Victoria
Unusually well preserved fossil feathers from Lower Cretaceous (VaIanginian-Aptian) claystones at Koonwarra, Victoria, are the oldest (c. 110-125 million years) bird remains yet found in the southern hemisphere, They are among the oldest bird remains known in the world, being antedated only by the toothed Archaeopteryx from the late Jurassic of Bavaria, and being more or less the same age as Gallornis from the Lower Cretaceous of France. The Victorian fossil feathers are evidence for essentially worldwide distribution of birds soon after the beginning of the Cretaceous, if not before. The feathers could conceivably have come from toothed birds.