Studies on Recycled Polyester
33
Table 2 The INVISTA’s information on virgin PET granules
IV a (dL/g)
Type
Application
vPET-1
0.64
Homo-polymer
Fibre-grade
vPET-2
0.81
Co-polymer
Bottle-grade
vPET-3
0.89
Homo-polymer
Fibre-grade
a Obtained by the conversion of solution viscosity into intrinsic viscosity, with an empirical relationship proposed by INVISTA, which is equivalent to ASTM method D-4603
Rearranged by authors from Ref. [12]
One should notice that in this study, the recycled PET flakes for fibre spinning
were originally from PET bottles, i.e., bottle-grade PET. Therefore, to provide a
good reference benchmark for the recycled PET flakes, three virgin PET granules,
composed of two fibre-grades and one bottle-grade, were selected (INVISTA Resins
& Fibers GmbH, Germany). The investigated virgin PET granules were deliberately
chosen according to the intrinsic viscosity (IV), which acted as the most important
factor to evaluate a polymer in fibre melt spinning and nonwovens industry. As
reported in the literature [1, 9, 18, 19, 21, 30–32], a varying range of IV from 0.52
to 1.05 dL/g has been used for PET fibre spinning. Thus, as summarized in Table 2,
three different IV, incremented from 0.64 to 0.89 dL/g, for the virgin PET granules
are determined. The virgin PET granules are shown in Fig. 1a as well.
2.2 Karl Fischer Titration
To prevent the PET molar mass from hydrolytic chain scission in the melt spinning
process, water content of PET materials must be less than 0.005 wt% (i.e., 50 ppm)
[33–36]. The water content after drying was determined using Karl Fischer titration (C30 Coulometric KF, Mettler-Toledo, Germany) with an oven temperature of
200 °C. As presented in Table 3, the as-received recycled PET flakes have nearly ten
times higher water content than that of virgin PET granules. The higher absorption of
the other contaminants in the recycled PET flakes is identified as the probable major
contributing factor for this phenomenon, such as PA (see Table 1). Consequently,
Table 3 The water content of different PET materials before and after drying, as well as the
predicted value of the virgin PET materials using Schubert Eq. (1)
Average water content (ppm)
rPET-A
rPET-B
vPET-1
vPET-2
vPET-3
Without drying
8807.2
7618.5
510.7
769.2
296.1
353.15 K for 68 h
328.1
317.0
14.6
17.5
9.8
Predicted value
–
–
21.1
31.7
12.2
413.15 K for 48 h
36.8
48.1
33
Table 2 The INVISTA’s information on virgin PET granules
IV a (dL/g)
Type
Application
vPET-1
0.64
Homo-polymer
Fibre-grade
vPET-2
0.81
Co-polymer
Bottle-grade
vPET-3
0.89
Homo-polymer
Fibre-grade
a Obtained by the conversion of solution viscosity into intrinsic viscosity, with an empirical relationship proposed by INVISTA, which is equivalent to ASTM method D-4603
Rearranged by authors from Ref. [12]
One should notice that in this study, the recycled PET flakes for fibre spinning
were originally from PET bottles, i.e., bottle-grade PET. Therefore, to provide a
good reference benchmark for the recycled PET flakes, three virgin PET granules,
composed of two fibre-grades and one bottle-grade, were selected (INVISTA Resins
& Fibers GmbH, Germany). The investigated virgin PET granules were deliberately
chosen according to the intrinsic viscosity (IV), which acted as the most important
factor to evaluate a polymer in fibre melt spinning and nonwovens industry. As
reported in the literature [1, 9, 18, 19, 21, 30–32], a varying range of IV from 0.52
to 1.05 dL/g has been used for PET fibre spinning. Thus, as summarized in Table 2,
three different IV, incremented from 0.64 to 0.89 dL/g, for the virgin PET granules
are determined. The virgin PET granules are shown in Fig. 1a as well.
2.2 Karl Fischer Titration
To prevent the PET molar mass from hydrolytic chain scission in the melt spinning
process, water content of PET materials must be less than 0.005 wt% (i.e., 50 ppm)
[33–36]. The water content after drying was determined using Karl Fischer titration (C30 Coulometric KF, Mettler-Toledo, Germany) with an oven temperature of
200 °C. As presented in Table 3, the as-received recycled PET flakes have nearly ten
times higher water content than that of virgin PET granules. The higher absorption of
the other contaminants in the recycled PET flakes is identified as the probable major
contributing factor for this phenomenon, such as PA (see Table 1). Consequently,
Table 3 The water content of different PET materials before and after drying, as well as the
predicted value of the virgin PET materials using Schubert Eq. (1)
Average water content (ppm)
rPET-A
rPET-B
vPET-1
vPET-2
vPET-3
Without drying
8807.2
7618.5
510.7
769.2
296.1
353.15 K for 68 h
328.1
317.0
14.6
17.5
9.8
Predicted value
–
–
21.1
31.7
12.2
413.15 K for 48 h
36.8
48.1