Method for preparing thermoplastic starch by in-situ reactive extrusion plasticization process and method for preparing starch/polymer blend by in-situ reactive extrusion plasticization and compatibilization process

A method for preparing a starch/polymer blend by an in-situ reactive extrusion plasticization and compatibilization process, the method comprising:

• a) mixing formaldehyde and urea for reaction to produce a hydroxymethylurea solution;
• b) uniformly mixing the hydroxymethylurea solution and starch followed by drying to produce a hydroxymethylurea-plasticized starch, wherein the hydroxymethylurea solution adheres to a surface of starch granules or enter into the starch granules to break interchain and intrachain hydrogen bonds of the starch;
• c) uniformly mixing the hydroxymethylurea-plasticized starch, a polymer, a chain extender and an inorganic filler to obtain a reaction mixture;
• and
• d) subjecting the reaction mixture to extrusion and granulation in a screw extruder to produce the starch/polymer blend, wherein during the extrusion, the hydroxymethylurea of the hydroxymethylurea-plasticized starch undergoes an in-situ reaction on the surface of the starch granules and inside the starch granules to form urea-formaldehyde, and an active group on a macro-molecular chain of the urea-formaldehyde is capable of interacting with an active functional group on a macro-molecular chain of the starch or the polymer;
• wherein the reaction mixture is prepared from A parts by weight of the polymer, B parts by weight of the starch, C parts by weight of the hydroxymethylurea solution, 0.5-1 part by weight of the chain extender and 5-10 parts by weight of the inorganic filler, wherein 60≤A<100, 0<B≤40 and 0<C≤15.