BACKGROUNDSubcritical water treatment is considered an environment-friendly method to liquefy biomass to prepare valuable chemicals. Several researchers have studied the solid obtained after autohydrolysis treatment for use as reinforcement in biocomposities and was the base pulp and paper technologies. The novelty of this present research is the use of solid in the manufacture of starch foams. RESULTSSubcritical water was used to extract hemicellulosic carbohydrate from walnut shells at temperatures from 160 to 260 degrees C for 15min and at 200 degrees C for various treatment times. The maximum yield was obtained at 200 degrees C for 15min. The residue of the walnut shells obtained at the maximum carbohydrates extraction 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. CONCLUSIONIt was considered that the prepared biodegradable foam was a promising material to take the place of plastic products in the future. (c) 2014 Society of Chemical Industry