Thermoplastic starch and glutaraldehyde modified thermoplastic starch foams prepared using supercritical carbon dioxide fluid as a blowing agent

Supercritical carbon dioxide (scCO 2 ) processed thermoplastic starch (scCO 2 a TPS), cellulose nanofiber (CNF) modified scCO 2 a TPS (scCO 2 a TPS 100 CNF 0.02 ) and glutaraldehyde (GA) modified scCO 2 a TPS 100 CNF 0.02 (scCO 2 a TPS 100 CNF 0.02 GA x ) foams were prepared for the first time using scCO 2 as a blowing agent during their foaming processes. The expansion ratio, cell density, moisture resistance, and compressive strength (σ c ) retention properties of each foam series were considerably improved with increasing scCO 2 pressure during the foaming processes. The expansion ratios and cell densities of each scCO 2 a TPS 100 CNF 0.02 GA x foam series were increased considerably to a maximum value, as the GA content approached an optimum value. The optimal scCO 2 11 TPS 100 CNF 0.02 GA 1.6 foam material exhibited a high expansion ratio and cell density at approximately 50 and approximately 8 × 10 8 cells/cm 3 , respectively. Compared with corresponding aged scCO 2 a TPS and scCO 2 a TPS 100 CNF 0.02 foam specimens, considerably better moisture resistance and σ c retention properties were observed for scCO 2 a TPS 100 CNF 0.02 GA x foam specimens, when they were modified with the corresponding optimum GA content. The moisture resistance and σ c retention for optimal prepared scCO 2 7 TPS 100 CNF 0.02 GA 0.4 , scCO 2 9 TPS 100 CNF 0.02 GA 0.8 and scCO 2 11 TPS 100 CNF 0.02 GA 1.6 foam materials improved further with increasing scCO 2 pressure. Possible reasons accounting for the highly expansion ratio, moisture resistance, and σ c retention properties for scCO 2 a TPS 100 CNF 0.02 GA x foams are presented.