Sample C (at%) O (at%) N (at%) C-C,C-H (%) C-O, C-OH (%) C=O,O-C-O (%) O-C=O (%)         285.0 eV 286.5 eV 287.8 eV 289.2 eV Untreated 95.0 5.0 0 93.3 5.7 0.1 0.9 PP 5x 84.2 15.7 0.13 81.5 10.4 4.0 4.1 PP 20x 82.9 15.4 1.76 84.6 7.9 3.3 4.3

Table 1: Atomic concentration obtained from XPS spectra and relative concentration of functional groups obtained from high-resolution C 1s spectra for untreated and plasma treated PP 5x and PP 20x tube.