Method for preparing starch blends

A process for the production of starch blends in two twin-screw extruders arranged in series, where

• i) the starch, together with a plasticizer, passes through a wetting section of length 8D to 80D at temperatures below 85° C., with mixing, where D is defined as the screw diameter of the screw cylinder and the wetting section is defined as starting at that point on the extruder screw at which the starch and the entire or partial quantity of plasticizer encounter one another and ending at that point in the extruder at which the starch is gelatinized and is digested to give thermoplastic starch;
• ii) in a plastifying section of length 10D to 50D the extruder temperature is adjusted stepwise to above 130° C., where the starch is digested, destructured and thermoplastified, and is dispersed in the starch-immiscible polymer, and a water content below 5%, based on the starch blend, is established before the material leaves the extruder;
• where the starch-immiscible polymer is added in molten or granular form at any desired point in the extruder, and a mixture of all of the components present is consequently produced.

A starch blend consisting to an extent above 50%, of renewable feedstocks, comprising:

• i) 53 to 61% by weight of a polybutylene adipate-co-terephthalate (PBAT) and/or polybutylene sebacate-co-terephthalate (PBSeT), based on 1,4-butanediol from renewable sources;
• and
• ii) 39 to 47% by weight of a thermoplastified starch.