Two kinds of disulfide-crosslinked polycaprolactam (DSPC) fibers with different disulfide (SS) contents (M
2 and M
4) were prepared from N-mercaptomethylated polycaprolactams and the set of them in various aqueous media was investigated.
When M
2 (sulfur content, 1.2%) was treated at 100% extension in cold water for 5 min, temporary set (measured after relaxation in the air) of 60% was obtained. The set did not increase significantly with prolonged setting treatment. When M
2 was kept at 100% extension in cold water, the initial rapid decay of the stress followed by levelling-off was observed. It is considered that the mechanism of set of M
2 in cold water is rearrangement of hydrogen-bonded network stabilizing the set structure. The temporarily set M
2 supercontracted when relaxed in boiling water, since the hydrogen-bonded network formed during setting was broken in boiling water. M
4 (sulfur content, 3.3%) was rubbery in water and could not be set by treatment with cold water.
When M
4 was treated in boiling water for 60 min, temporary set of 50% was obtained. Permanent set of 22% was retained when the set fiber was relaxed in boiling water for 60 min. A smaller permanent set of 9% was obtained by the treatment of M
2 in boiling water for 60 min. Both M
2 and M
4 contained a small amount of mercapto (SH) groups. M
2 modified with 2, 4-dinitrofluoro-benzene, which blocks SH, could not be set with boiling water. The controlling mechanism of set and its release in boiling water appears to be rearrangement of crosslinked structure via SH/SS interchange reaction.
When M
2 and M
4 were treated in aqueous ammonium thioglycolate at 25°C, large amounts of temporary sets were obtained. The stress relaxation and X-ray diffraction studies revealed that SS crosslinks were ruptured in a short time and DSPC fibers underwent orientation and crystallization. The set was lost when the fibers were relaxed in boiling water.
When M
4 was treated in 0.5% KCN at 50°C for 1hr, the highest amound of permanent set (67%) was obtained. It is considered that the set with KCN is due to the breakdown of SS crosslinks and subsequent formation of monosulfide crosslinks which are stable in boiling water.
M
4 pretreated with KCN solution could not be set with boiling water. This is another supporting evidence for SH/SS interchange mechanism to the setting in boiling water.
The mechanism of set of wool keratin fibers was discussed in relation to the above results.
抄録全体を表示