สำนักราชบัณฑิตยสภา

229 Suda Kiatkamjornwong et al วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ IR spectroscopy and AFM of the sheets The untreated sheet and treated sheets were subjected to IR spectroscopy (FT-IR Spectrometer, Nicolet iS 10, Thermo Fischer Scientific, U.S.A.) for changes in functional groups. The surface roughness was obtained using atomic force microscopy (NanoScope-IV, Veeco, USA), operated in a tapping mode and presented in terms of Ra distance and root mean square roughness as follows: (Z x,y _ Z average ) 2 (3) N 2 Σ N x,y=1 RMS xy = Printing The water-based pigmented inkjet inks (cyan, magenta, yellow and black) were mea- sured for their surface tension with an Interfacial Tensiometer (Kruss 6, KRÜSS GmbH, Hamburg, Germany). The sheets were printed by an ink-jet printer (Stylus T13, Seiko Epson Corporation, China) with a conventional set of water-based pigmented ink (Inkman, Thailand). The continuous tone reproduction chart in the QEA Test Chart was extracted by Illustra- tor software for printing the plastic sheets with the inkjet inks in the print at the highest printing quality and without color management. Duplication of each experiment was done. Comparison of the printing qualities between the untreated and treated plastic sheets was performed. Results and discussion Based on the structure of PLA as shown in Figure 1, the IR spectra of the PLA pellets and the PLA sheet, identical peaks are found as follows: the medium peaks at 2997 and 2941 cm -1 for C-H stretch, the strong peak at 1741 cm -1 for the carbonyl ester (-C=O) stretch, the medium peak at 1446 cm -1 for C-H bending, at 1381 and 1357 cm -1 medium peaks for the _ C-H scissoring, two strong peaks at 1180 and 1080 cm -1 for O _ C=O ester stretch and two medium peaks of C-H bending at 869 and 754 cm -1 . All the exposed PLA films by 30 W RF oxygen plasma for 30 s, 10, 15, 20, 25, 30, and 40 min did not give any degraded products because the IR spectra are identical. Where Z average is the average Z value within the examined area, Z x,y is the local Z value, and N indicates the number of points within the area [11].