Supplementary Material

Figure A: Evolution of span (x90,3 – x10,3) / x50,3 over process time during wet grinding of PBT

(stressing conditions: SE = 1.91 mJ, vtip = 6.3 m/s, dGM = 2.0 mm, feed concentration 18.5 wt-

%, process temperature 20 °C).

Figure B: SEM image of ground PBT obtained after about 5.5 hours of wet grinding

(stressing conditions: SE = 1.91 mJ, vtip = 6.3 m/s, dGM = 2.0 mm, feed concentration 18.5 wt-

%, solvent: ethanol, process temperature 20 °C).

Infrared spectroscopy

Infrared spectra of rounded PBT as well as PBT comminution products obtained for different

process times are given in Figure C. For all samples spectral features being typical for PBT

(Tomar and Maiti, 2009; Käppler et al., 2015) are found, i.e. the C=O vibrational band at

around 1715 cm-1, the CH2 bending mode at 1503 cm-1 and the CH2 wagging mode at

1530 cm-1 of the butylene units, the symmetric and asymmetric C-O-C stretching modes at

1206 cm-1 and 1103 cm-1, respectively, as well as modes due to the aromatic ring at 1409 cm-

1, 1504 cm-1 and 1018 cm-1, 873 cm-1 and 727 cm-1. The spectra of the wet comminuted PBT

powders are almost identical i.e. no pronounced changes in molecular structure during

grinding of PBT for process times of up to 345 minutes at the stressing conditions

summarized in section 3.1 occur. This indication corresponds well to the observations during

DSC characterization of the respective powders.

Only minor changes are observed for rounded PBT: compared to the ground material a

reduced intensity in the OH region (3700-3200 cm-1) is observed, which might be due the

removal of water from the material during rounding and subsequent solidification and (partial)

crystallization. The change in crystallinity observed by DSC could not be detected by IR

spectroscopy. It has been reported that amorphous PBT and the crystalline polymorphs may

be discriminated in the spectral region of the methylene rocking (900-1000 cm-1) and the

methylene bending vibration (1300-1550 cm-1). Stambaugh et al. (Stambaugh et al., 1979)

assigned the bands at 917 cm-1 and at 1456 cm-1 to the unstressed alpha-phase whereas

bands found at 935 cm-1 and 1388 cm-1 have components of both crystalline polymorphs.

Amorphous PBT shows bands at 938 cm-1 and 960 cm-1.

Figure C: IR spectra of wet comminuted PBT and rounded PBT powders in the wavenumber

region (a) 4000 cm-1 to 400 cm-1 and (b) 1700 cm-1 to 600 cm-1.

Figure D: DSC curves of PBT feed material, ground PBT and rounded PBT.

Literature

Käppler, A., Windrich, F., Löder, M., Malanin, M., Fischer, D., Labrenz, M., Eichhorn, K.-J.,

Voit, B., 2015. Identification of microplastics by FTIR and Raman microscopy: a novel silicon

filter substrate opens the important spectral range below 1300 cm−1 for FTIR transmission

measurements. Analytical and Bioanalytical Chemistry. 10.1007/s00216-015-8850-8.

Stambaugh, B., Lando, J.B., Koenig, J.L., 1979. Infrared studies of the reversible stress-

induced crystal-crystal phase transition of poly(tetramethylene terephthalate). J. Polym. Sci.

Polym. Phys. Ed. 17 (6), 1063–1071. 10.1002/pol.1979.180170614.

Tomar, N., Maiti, S.N., 2009. Thermal and crystallization properties of PBT/ABAS blends. J.

Appl. Polym. Sci 113 (3), 1657–1663. 10.1002/app.30172.