• Top library match: Polylactic acid #746

• Low-wavenumber bands (690 and 753 cm⁻¹) cannot be confidently assigned to specific PLA vibrations with the available evidence; they may represent skeletal modes or minor impurities.
• The broad O–H absorption at 3501 cm⁻¹ could originate from absorbed atmospheric water; thus, its intensity may vary with sample handling.

Recommended next steps: Acquire a reference spectrum of pure PLA processed under the same conditions (e.g., ATR crystal, film thickness) to confirm the overall profile. Use DSC or TGA to verify the characteristic glass transition (~55–60 °C) and melting point (~150–160 °C) of PLA. If the O–H band at 3501 cm⁻¹ remains prominent after thorough drying, consider end-group analysis by NMR or titration to assess degree of hydrolysis or molecular weight.