Studies on Recycled Polyester
37
2.5 Morphological Study and Diameter Evaluation
To evaluate the fibre surface roughness, the PET fibres generated at 270 °C and 0.5 bar
were representatively selected to be performed the scanning electron microscopy
observation (SEM, AURIGA, Carl Zeiss Microscopy, Germany). Furthermore, the
overall morphology and diameters of the investigated PET fibres were analyzed by
another optical microscope (VHX-J250 Keyence, Japan).
2.6 Single Fibre Tensile Test
The mechanical properties in the materials characterizations are of great significance
to evaluate the applications of the products. In this work, the tenacity and elongation
at break of drawn PET fibres were investigated using a single fibre tensile tester
(Vibrodyn 400, Lenzing Instruments, Austria). The continuous melt-spun PET fibres
were cut into specimens with a length of about 50 mm for the tensile test. For each
group of fibres produced under one combined processing condition (one material, one
processing temperature, and one take-up pressure), at least 20–30 specimens were
prepared and used to obtain the average value and standard deviation. Before the
tensile test, the specimen between the rubberized clamps was carefully straightened
with a tiny initial force of 0.2 cN (1 cN = 0.01 N).
2.7 Hot Shrinkage
Due to the low crystallinity of PET material, the orientation of molecular chains is
mainly located in the amorphous zone. Therefore, the hot shrinkage measurement
was considered as the most suitable method to quantify the orientation. The hot
shrinkage ratio (S R) after thermal treatment, defined as the variation of percentage
in the length of the fibres can be obtained as presented in Eq. (8):
S R = (L 0 − L 1 )/L 0 × 100%
(8)
where L 0 and L 1 are the lengths of initial PET fibre and the corresponding value
after thermal treatment, respectively. The loose PET fibres were treated in an oven
with a temperature of 90 °C for 60 min. The temperature of 90 °C was employed,
which is located in the range from the glass transition temperature T g to the onset
recrystallization temperature T c,onset of all the studied PET fibres (see the DSC data
in Table 9). Thus, the shrinking effect due to recrystallization on the fibre length
can be avoided. For PET fibres produced under each processing condition, at least
ten specimens were investigated by taking pictures before and after the thermal
treatment. The initial length and the length after thermal treatment were analyzed
37
2.5 Morphological Study and Diameter Evaluation
To evaluate the fibre surface roughness, the PET fibres generated at 270 °C and 0.5 bar
were representatively selected to be performed the scanning electron microscopy
observation (SEM, AURIGA, Carl Zeiss Microscopy, Germany). Furthermore, the
overall morphology and diameters of the investigated PET fibres were analyzed by
another optical microscope (VHX-J250 Keyence, Japan).
2.6 Single Fibre Tensile Test
The mechanical properties in the materials characterizations are of great significance
to evaluate the applications of the products. In this work, the tenacity and elongation
at break of drawn PET fibres were investigated using a single fibre tensile tester
(Vibrodyn 400, Lenzing Instruments, Austria). The continuous melt-spun PET fibres
were cut into specimens with a length of about 50 mm for the tensile test. For each
group of fibres produced under one combined processing condition (one material, one
processing temperature, and one take-up pressure), at least 20–30 specimens were
prepared and used to obtain the average value and standard deviation. Before the
tensile test, the specimen between the rubberized clamps was carefully straightened
with a tiny initial force of 0.2 cN (1 cN = 0.01 N).
2.7 Hot Shrinkage
Due to the low crystallinity of PET material, the orientation of molecular chains is
mainly located in the amorphous zone. Therefore, the hot shrinkage measurement
was considered as the most suitable method to quantify the orientation. The hot
shrinkage ratio (S R) after thermal treatment, defined as the variation of percentage
in the length of the fibres can be obtained as presented in Eq. (8):
S R = (L 0 − L 1 )/L 0 × 100%
(8)
where L 0 and L 1 are the lengths of initial PET fibre and the corresponding value
after thermal treatment, respectively. The loose PET fibres were treated in an oven
with a temperature of 90 °C for 60 min. The temperature of 90 °C was employed,
which is located in the range from the glass transition temperature T g to the onset
recrystallization temperature T c,onset of all the studied PET fibres (see the DSC data
in Table 9). Thus, the shrinking effect due to recrystallization on the fibre length
can be avoided. For PET fibres produced under each processing condition, at least
ten specimens were investigated by taking pictures before and after the thermal
treatment. The initial length and the length after thermal treatment were analyzed