36
Y. Qin et al.
Q = v 0 · π · (D 0 /2)
2
= v E · π · (D/2)
2
= v F · π · (D F /2)
2
(4)
v F = v 0 · (D 0 /D F )
2
(5)
D R = v F /v E = D
2
/D
2
F
(6)
where Q is the throughput in the extrusion process, v 0 is the extrusion speed of the
piston and D 0 is the diameter of the piston, which are the same as defined in Eq. (3).
v E denotes the speed of extruded filaments when they leave from the die; D F denotes
the diameter of drawn PET fibres which are collected by a perforated plate below
the aspirator for further analysis. As calculated, the range of take-up speed v F in
this study is varying from ca. 60 to 3500 m/min, which is different from each PET
material at the same take-up pressure due to the different elongational viscosities.
The draw ratio D R of all the drawn fibres varies from ca. 20 to 1000 with the take-up
pressure increasing from 0.5 to 3.0 bar.
2.4 Differential Scanning Calorimetry
The melting behaviour and crystallization properties of all the investigated PET
grades, as well as the representative PET fibres, were examined using a differential
scanning calorimetry (DSC, TA Q2000, TA Instruments, USA) in a nitrogen atmosphere. For the PET raw materials, the specimens with the weight of ca. 6 mg were
heated up to 300 °C with a rate of 10 °C/min. Afterwards, the specimens were kept
for 3 min at 300 °C before cooled down to 25 °C with the same rate. The same cycle
(heating up and cooling down) was repeated again, aiming at erasing the thermal
history of PET material when processing. For the PET fibres, the first heating scan
was used to obtain the glass transition temperature T g , melting temperature T m , and
crystallinity X c influenced by different processing parameters. The crystallinity X c
was calculated by the following equation [39]:
X c = (H m − H c )//H
0
m
(7)
where the H m denotes the enthalpy of fusion for the specimen at the melting point,
H c denotes the enthalpy of recrystallization, and H
0
m denotes the enthalpy of
fusion for a 100% crystalline polymer at the equilibrium melting point, which is
reported as 135.8 J/g for PET [40].
Y. Qin et al.
Q = v 0 · π · (D 0 /2)
2
= v E · π · (D/2)
2
= v F · π · (D F /2)
2
(4)
v F = v 0 · (D 0 /D F )
2
(5)
D R = v F /v E = D
2
/D
2
F
(6)
where Q is the throughput in the extrusion process, v 0 is the extrusion speed of the
piston and D 0 is the diameter of the piston, which are the same as defined in Eq. (3).
v E denotes the speed of extruded filaments when they leave from the die; D F denotes
the diameter of drawn PET fibres which are collected by a perforated plate below
the aspirator for further analysis. As calculated, the range of take-up speed v F in
this study is varying from ca. 60 to 3500 m/min, which is different from each PET
material at the same take-up pressure due to the different elongational viscosities.
The draw ratio D R of all the drawn fibres varies from ca. 20 to 1000 with the take-up
pressure increasing from 0.5 to 3.0 bar.
2.4 Differential Scanning Calorimetry
The melting behaviour and crystallization properties of all the investigated PET
grades, as well as the representative PET fibres, were examined using a differential
scanning calorimetry (DSC, TA Q2000, TA Instruments, USA) in a nitrogen atmosphere. For the PET raw materials, the specimens with the weight of ca. 6 mg were
heated up to 300 °C with a rate of 10 °C/min. Afterwards, the specimens were kept
for 3 min at 300 °C before cooled down to 25 °C with the same rate. The same cycle
(heating up and cooling down) was repeated again, aiming at erasing the thermal
history of PET material when processing. For the PET fibres, the first heating scan
was used to obtain the glass transition temperature T g , melting temperature T m , and
crystallinity X c influenced by different processing parameters. The crystallinity X c
was calculated by the following equation [39]:
X c = (H m − H c )//H
0
m
(7)
where the H m denotes the enthalpy of fusion for the specimen at the melting point,
H c denotes the enthalpy of recrystallization, and H
0
m denotes the enthalpy of
fusion for a 100% crystalline polymer at the equilibrium melting point, which is
reported as 135.8 J/g for PET [40].