Effect of super critical carbon dioxide and alkali treatment on oxygen barrier properties of thermoplastic starch/poly(vinyl alcohol) films.

Sustainable oxygen barrier thermoplastic starch (TPS)/polyvinyl alcohol (PVA) blown films were successfully prepared by blending proper PVA loads during NaOH-treating and supercritical carbon dioxide (scCO₂) assisted processing. The NaOH-treated TPS or scCO₂TPS films showed smaller free-volume-cavity characteristics (FVCC) and oxygen transmission rate (OTR) than those of TPS (or scCO₂TPS) prepared without proper alkali-treatment. Smaller OTR and FVCC values were detected for NaOH-treated scCO₂TPS films than those of NaOH-treated TPS films prepared without scCO₂-assistance. All OTR and FVCC values detected for proper alkali-treated scCO₂TPS_yPVA_z films diminished distinctly to a smallest value, when their PVA loads came near a solubility limit value of 27.5 wt%. An essential result is that the OTR of the optimal NaOH-treated scCO₂TPS_yPVA_z film is merely 3.1 cm³/m² day atm, which meets the requirement of high oxygen barrier plastics. Dynamic molecular relaxations and WAXD patterns detected for proper NaOH-treated scCO₂TPS_yPVA_z films disclosed that PVA was compatible with TPS, as PVA loads were ≤ the solubility limit value. The distinctly reduced OTR and FVCC detected for optimal NaOH-treated scCO₂TPS_yPVA_z films are partially attributed to the reinforced molecular interactions between hydroxyl groups of TPS and PVA, as they were blended with proper PVA loads during their alkali-treating and scCO₂-aid processing. [ABSTRACT FROM AUTHOR]