34
Y. Qin et al.
when the water content of virgin PET reached a qualified value (<50 ppm) at 80 °C
(353.15 K) for 68 h, the recycled PET flakes still contained much more water inside
(>300 ppm). To achieve the required water content for the PET flakes, as well as to
shorten the drying time, a higher temperature of 140 °C (413.15 K) was needed. To
ensure the same thermal history before melt spinning, the drying procedure at 140 °C
for 48 h was employed for all five, as-received, materials.
Accordingly, an empirical Eq. (1) was proposed by Schubert to predict the water
content of PET materials at different drying temperature with different drying time:
H = H 0 · e
−t/τ
(1)
with
τ = A · e
B/T
(2)
where H 0 is the water content of as-received PET material (in ppm), and H refers
to the real water content after drying at temperature T in Kelvin scale with drying
time t (in hour); τ is a parameter dependent on the drying temperature; A and B
are constant, which are in relation to the properties and geometry of the measured
polymer materials. To predict the values of A and B, the data of rPET-A and rPET-B
obtained from two drying temperatures and the corresponding time were used, and
the results are shown in Table 4.
It should be noted that the values of A and B of both recycled PET flakes are
close to each other. To further verify the feasibility, the water content of three virgin
PET materials dried at 80 °C for 68 h were predicted by combining Eqs. (1) and
(2) with the average values listed in Table 4. Comparing with the actual measured
values in Table 3, the predicted values are acceptable considering the measurement
accuracy when the water content is below 50 ppm. Overall, the empirical equation
provides only a rough estimation which helps to design the drying temperature and
the drying time to remove the water content of the PET materials. The reliability of
this equation needs to be demonstrated by further experiments in detail, which is left
for future studies.
Table 4 Calculated A and B,
as well as the average values
of rPET-A and rPET-B
A (h)
B (K)
rPET-A
0.0561
2086.73
rPET-B
0.0787
1979.35
Average value
0.0674
2033.04
Y. Qin et al.
when the water content of virgin PET reached a qualified value (<50 ppm) at 80 °C
(353.15 K) for 68 h, the recycled PET flakes still contained much more water inside
(>300 ppm). To achieve the required water content for the PET flakes, as well as to
shorten the drying time, a higher temperature of 140 °C (413.15 K) was needed. To
ensure the same thermal history before melt spinning, the drying procedure at 140 °C
for 48 h was employed for all five, as-received, materials.
Accordingly, an empirical Eq. (1) was proposed by Schubert to predict the water
content of PET materials at different drying temperature with different drying time:
H = H 0 · e
−t/τ
(1)
with
τ = A · e
B/T
(2)
where H 0 is the water content of as-received PET material (in ppm), and H refers
to the real water content after drying at temperature T in Kelvin scale with drying
time t (in hour); τ is a parameter dependent on the drying temperature; A and B
are constant, which are in relation to the properties and geometry of the measured
polymer materials. To predict the values of A and B, the data of rPET-A and rPET-B
obtained from two drying temperatures and the corresponding time were used, and
the results are shown in Table 4.
It should be noted that the values of A and B of both recycled PET flakes are
close to each other. To further verify the feasibility, the water content of three virgin
PET materials dried at 80 °C for 68 h were predicted by combining Eqs. (1) and
(2) with the average values listed in Table 4. Comparing with the actual measured
values in Table 3, the predicted values are acceptable considering the measurement
accuracy when the water content is below 50 ppm. Overall, the empirical equation
provides only a rough estimation which helps to design the drying temperature and
the drying time to remove the water content of the PET materials. The reliability of
this equation needs to be demonstrated by further experiments in detail, which is left
for future studies.
Table 4 Calculated A and B,
as well as the average values
of rPET-A and rPET-B
A (h)
B (K)
rPET-A
0.0561
2086.73
rPET-B
0.0787
1979.35
Average value
0.0674
2033.04