Process for making new biofragmentable materials: Comparative study of thephysical properties of wheat starch and cellulose acetate blends and thoseof wheat starch and starch acetate blends

Bio-fragmentable starch blends were obtained by extrusion, using either whe at starch and cellulose acetate dry blends, in which the degree of substitu tion (DS) of cellulose acetate was close to 2.3, or wheat starch and starch acetate dry blends in which the DS of starch acetate was around 1.5. After preparation, the dry blends were stored for one week at 20 degrees C and 6 5% relative humidity (RH) before being injection moulded to produce standar dised samples for tensile tests. Tensile strength tests (ISO/R527) and Char py shock tests (ISO/R179) were carried out on the injection moulded samples after having been stored under the same conditions of temperature and RH. The dimensional stability of the samples was estimated by measuring the vol umetric shrinkage after storage. The hydrophobic behaviour of the blends wa s evaluated by measuring the development of the contact angle of a drop of water placed on the samples. This study showed that starch was not compatib le with 2.3 DS cellulose acetate. The samples prepared with starch and 2.3 DS cellulose acetate blends had a thin surface layer composed of cellulose diacetate. This layer increased the hydrophobic property of the samples. On the other hand, starch seemed to be compatible with 1.5 DS starch acetat e, The samples prepared with starch and 1.5 DS starch acetate blends were g lobally homogeneous and did not exhibit any surface layer, but the blends w ere less hydrophobic than the previous ones.