Renewable thermoplastic starch/sugar alcohol blends and their oxygen barrier application

Abstract

Fully renewable oxygen barrier thermoplastic starch (TPS)/sugar alcohol blown films were innovatively prepared by blending proper loadings of Erythritol (ET), Sorbitol (ST), and Lactitol (LT) and supercritical carbon dioxide (scCO2) assistance. The oxygen transmission rate (OTR) values of the properly prepared scCO2TPSxETy, scCO2TPSxSTy, and scCO2TPSxLTy films reduced to 4.3, 6.6, and 12.5 cm3/m2∙day∙atm, which are about 5–28 times smaller than those of the conventional TPS films reported in the literature. The free‐volume‐cavity characteristics (FVCC) and OTR detected for TPSxETy (or scCO2TPSxETy), TPSxSTy (or scCO2TPSxSTy), and TPSxLTy (or scCO2TPSxLTy) films diminished to a minimum, as their ET, ST and LT loadings came near an optimal value. Slightly smaller OTR and FVCC values were detected for scCO2TPSxETy, scCO2TPSxSTy, and scCO2TPSxLTy films than those of corresponding TPSxETy, TPSxSTy, and TPSxLTy films prepared without scCO2‐assistance. The smallest OTR and FVCC detected for the properly prepared TPSxETy (or scCO2TPSxETy), TPSxSTy (or scCO2TPSxSTy), and TPSxLTy (or scCO2TPSxLTy) films diminished with decreasing sugar alcohol's molecular weight. An essential result is that the OTR of the properly prepared scCO2TPSxETy film was merely 4.3 cm3/m2∙day∙atm, which is small enough to meet the demand of high oxygen barrier packaging application. Dynamic molecular relaxations detected for these films disclosed that ET, ST, and LT were compatible with TPS, as their loads were ≤ the optimum value. The distinctly reduced OTR and FVCC for these properly prepared films are partially attributed to the reinforced molecular interactions between sugar alcohol and TPS's hydroxyl groups when they were prepared with scCO2‐assistance, optimal sugar alcohol loading, and/or smaller sugar alcohol's molecular weight.Highlights High oxygen barrier thermoplastic starch/sugar alcohol blown films were prepared. The lowest oxygen transmission rate of the renewable film was 4.3 cm3/m2∙day∙atm. This oxygen transmission rate is qualified for high oxygen barrier application. Boosted oxygen barrier property was ascribed to the reduced free volume values.