Adjusting the lengths of
glass fibers and the relationship between fiber length and mechanical
properties for reinforced poly(ethylene terephthalate)
Nori Yoshihara*
Toyobo Research Center, Toyobo Co., Ltd.
Tel: 81-77-571-0083
Fax: 81-77-571-0084
e-mail: nori_yoshihara@kt.toyobo.co.jp
The effects
of fiber shape and compounding conditions on the distribution of glass fiber
length of reinforced poly(ethylene terephthalate) are studied. The
relationships between fiber length and mechanical properties are discussed. The
length of the fibers pulled out from the rupture cross section and the critical
fiber length are reported in different deformation modes.
Fibers of
finer diameter showed shorter average length and narrower distribution in the
compound. Bundle size showed little effect on the fiber length distribution at
the identical diameter. The weight average length, Lw, prepared by a
dry blending method is shorter than that by a melt blending method. A compound
with a Dulmage type screw has fewer short fibers than that with a full-flight
type screw. Therefore, the fiber length compounded with a mixing type screw,
such as Dulmage type, showed the sharp distribution. The flexural strength
depends more on the aspect ratio of fiber, Lw/D, than on Lw.
The Izod impact strength changed depending on Lw and on the content
of fibers longer than 0.25mm. The Lw values of fibers pulled out
from the rupture cross section were shorter in descending order for flexural,
tensile and notched impact test specimens. The maximum length of fibers, Lm,
leads to the approximate critical length, Lc, of the fiber fracture;
0.32mm for tensile, 0.50mm for flexural and 0.24mm for Izod impact. The value
of Lc for tensile was comparable to the theoretical one. As for flexural
fatigue under small strain at 23 ℃ or lower temperature, most of the glass fibers were
not pulled out, but were broken at the rupture cross section.