Table 1: Vibrational Combination Bands of Polylactic Acid (PLA).

Calculated position (cm-1) Observed position (cm-1) Assignment
4725 4770 νasCH3 + νC = O (1780)
4725 4725 νasCH3 + νC = O (1740)
4635 νsCH3 + νC = O
4420 4438 νasCH3 + δasCH3
4351 4372 νasCH3 + δasCH3
4330 4307 νsCH3 + δasCH3
4330 νasCH3 + δ(CH) wagging
4260 4255 νsCH3 + δsCH3
4240 νsCH3 + δ(CH) wagging
4233 4217 νasCH3 + (νCOC + δCH)
4180 4175 νasCH3 + (νCOC + ρ asCH3)
νCH3 + δCH
4143 4135 νsCH3 + (νCOC + δCH)
4098 4086 νasCH3 + ρasCH3
4090 νsCH3 + (νCOC + ρasCH3)
4065 4051 νasCH2 + νCOC