Studies on Recycled Polyester
59
for two processing temperatures. Then the graphs can be divided into four quadrants
using the reference points. Given the reference points, the measured value located
in quadrant I shows excellent performance and reliability of specimens; located in
quadrant II corresponds to a lower performance but remains an excellent reliability.
As interpreted in an analogous manner, the value located in the quadrant III means
a lower performance as well as a decreased reliability; located in the quadrant IV
means a desirable performance but poor reliability.
In Figs. 21 and 22, m F , m T and m ε over the corresponding characteristic force at
break F 0 , tenacity T 0 and elongation at break ε b,0 for rPET-B and vPET-1 fibres were
respectively plotted. It can be found that, taking two processing temperatures into
consideration, the maximal characteristic force at break F 0 , and the characteristic
elongation at break ε b,0 for both materials are achieved at 0.5 bar. Accordingly, the
main driving force for the performance of force at break and elongation at break
should be the take-up pressure, i.e., the draw ratio of fibres. That is, lower take-up
pressure leads to a higher force at break and higher elongation at break. Excluding
the influence of the diameter of fibres, the maximum of characteristic tenacity T 0
for rPET-B fibres can be obtained at 270 °C, 3.0 bar, while for vPET-1 fibres is at
280 °C, 3.0 bar. This phenomenon has been well analyzed from the perspective of
crystallinity and molecular chain orientation in Sect. 4.5.3.
The highest values of all the Weibull moduli m F , m T , m ε are revealed at 280 °C,
1.0 bar for rPET-B fibres, as seen in Fig. 21, however, at 280 °C, 0.5 bar for vPET1 fibres considering the error bar in Fig. 22. Therefore, the possible main driving
force (or forces) for the reliability of melt-spun PET fibres in this study could not
be identified clearly. The values of Weibull moduli m for each applied parameter are
also shown in the charts, which will guide the design on the processing parameters
of melt-spun PET fibre in the future.
To analyze the relationship between T 0 and ε b,0 , a power law equation was first
given by Schubert, Eq. (14):
T 0 = K (T ) · ε b,0
λ
(14)
where K (T ) is an adjustable parameter, which relies on the processing temperature
during the specific melt spinning process, and presumably also depends on the physical properties of the polymer materials, e.g., molar mass, branching structures, and
so forth. A higher value of K (T ) denotes a higher tenacity and a higher elongation at
break. λ is a material-dependent constant, which yields the same value for the same
material.
As presented in Fig. 23a, for the most desirable fibres from vPET-1, the constant
value of λ = −1.39 at both temperatures is obtained by the best fit. The K (T ) of
vPET-1 at 270 °C, K (270), and at 280 °C, K (280), are calculated respectively to
be 7331 and 9907, indicating that for vPET-1, 280 °C is a preferable processing
temperature for melt spinning. Both fitting lines in Fig. 23a are transferred to the
identical coordinate system in Fig. 23b, in order to provide a benchmark to evaluate
59
for two processing temperatures. Then the graphs can be divided into four quadrants
using the reference points. Given the reference points, the measured value located
in quadrant I shows excellent performance and reliability of specimens; located in
quadrant II corresponds to a lower performance but remains an excellent reliability.
As interpreted in an analogous manner, the value located in the quadrant III means
a lower performance as well as a decreased reliability; located in the quadrant IV
means a desirable performance but poor reliability.
In Figs. 21 and 22, m F , m T and m ε over the corresponding characteristic force at
break F 0 , tenacity T 0 and elongation at break ε b,0 for rPET-B and vPET-1 fibres were
respectively plotted. It can be found that, taking two processing temperatures into
consideration, the maximal characteristic force at break F 0 , and the characteristic
elongation at break ε b,0 for both materials are achieved at 0.5 bar. Accordingly, the
main driving force for the performance of force at break and elongation at break
should be the take-up pressure, i.e., the draw ratio of fibres. That is, lower take-up
pressure leads to a higher force at break and higher elongation at break. Excluding
the influence of the diameter of fibres, the maximum of characteristic tenacity T 0
for rPET-B fibres can be obtained at 270 °C, 3.0 bar, while for vPET-1 fibres is at
280 °C, 3.0 bar. This phenomenon has been well analyzed from the perspective of
crystallinity and molecular chain orientation in Sect. 4.5.3.
The highest values of all the Weibull moduli m F , m T , m ε are revealed at 280 °C,
1.0 bar for rPET-B fibres, as seen in Fig. 21, however, at 280 °C, 0.5 bar for vPET1 fibres considering the error bar in Fig. 22. Therefore, the possible main driving
force (or forces) for the reliability of melt-spun PET fibres in this study could not
be identified clearly. The values of Weibull moduli m for each applied parameter are
also shown in the charts, which will guide the design on the processing parameters
of melt-spun PET fibre in the future.
To analyze the relationship between T 0 and ε b,0 , a power law equation was first
given by Schubert, Eq. (14):
T 0 = K (T ) · ε b,0
λ
(14)
where K (T ) is an adjustable parameter, which relies on the processing temperature
during the specific melt spinning process, and presumably also depends on the physical properties of the polymer materials, e.g., molar mass, branching structures, and
so forth. A higher value of K (T ) denotes a higher tenacity and a higher elongation at
break. λ is a material-dependent constant, which yields the same value for the same
material.
As presented in Fig. 23a, for the most desirable fibres from vPET-1, the constant
value of λ = −1.39 at both temperatures is obtained by the best fit. The K (T ) of
vPET-1 at 270 °C, K (270), and at 280 °C, K (280), are calculated respectively to
be 7331 and 9907, indicating that for vPET-1, 280 °C is a preferable processing
temperature for melt spinning. Both fitting lines in Fig. 23a are transferred to the
identical coordinate system in Fig. 23b, in order to provide a benchmark to evaluate