Background: Subcritical water treatment was considered an environmental friendly method to liquefy biomass to prepare valuable chemicals. However, fewer researches had considered taking use of the residue after subcritical water treatment. Therefore, the residue obtained after treatment was used to prepare biodegradable foam in this study.
Results: Subcritical water was used to extract carbohydrate from walnut shells at temperatures from 160 to 260 oC for 15 min and at 200 oC for various treatment times. The maximum yield was obtained at 200 oC for 15 min. The residue of the walnut shells obtained at the maximum carbohydrates yield was used to prepare a biodegradable foam by compounding with corn starch using a technique similar to compression molding. It was found that replacing 20% of the corn starch by the residue had no deleterious effects on the density and morphology, as indicated by scanning electron microscopy. The prepared foams had a dense outer skin and a less dense interior with large, mostly open cells. The flexural strains were similar to that of foamed polystyrene and the flexural modulus and flexural stresses were larger.
Conclusion: It was considered that the prepared biodegradable foam was a promising material to take place of plastic products in the further.
