The application of alkaline hydrolysis to study the change in the fine stru
cture of bicomponent polyester fibers as their surface is removed progressi
vely was explored. The samples were prepared with a poly(butylene terephtha
late) (PBT) sheath and a poly(ethylene terephthalate) (PET) core. The reage
nt used to hydrolyze the PET was 1M NaOH in 75/25 methanol to water since i
t appeared to react topochemically with the fiber. The solution reacted mor
e rapidly with PET than with PET. Thus, when necessary to retard the weight
loss of the bicomponent fibers, after a 2-h hydrolysis with this reagent t
o remove PET, it was replaced with aqueous 1M NaOH solution containing 0.1%
cetrimmonium bromide. Unlike homofil PET or PET fibers, where alkaline att
ack appeared to be confined to the surface and left the residue relatively
smooth, the bicomponent fiber was attacked unevenly, and penetration to the
PET core occurred before all the PET at the surface was removed. Neverthel
ess, most of the reaction was confined initially to the PET sheath. The ten
acity and extension at break of the PET-PET fiber passed through a maximum
as hydrolysis progressed. The fall in tenacity at high weight losses is asc
ribed to increasing surface defects in the fiber surface. After removal of
the PET by the hydrolysis, the birefringence of the residue became progress
ively higher. The synergistic effect of the PET sheath on the properties of
the PET core and the possible causes of the nonuniform hydrolysis at the P
ET surface are discussed. An equation is proposed that includes an interact
ion parameter, which can be utilized to determine which property is affecte
d most by the hydrolysis of a bicomponent fiber. In this instance, it appea
rs from the parameters that the order is strength > extension at break appr
oximate to birefringence. (C) 1999 John Wiley & Sons, Inc.