Metal-oxide-coated thermoplastic microparticles having biodegradability

Core-shell particles (A), comprising:

• a core (B) comprising a thermoplastic polyester (C) with a melting range of lower than 160° C.;
• a shell (D) comprising partially water-wettable particles (E) of metal oxide, wherein the partially water-wettable particles (E) have a methanol value of less than 30;
• and
• where the metal content of the core-shell particles (A) is at least 2.5% by weight.

A process for producing core-shell particles (A), comprising the steps of:

• providing a core (B) comprising a thermoplastic polyester (C) with a melting range of lower than 160° C.;
• providing a shell (D) comprising partially water-wettable particles (E) of metal oxide, wherein the partially water-wettable particles (E) have a methanol value of less than 30;
• wherein the metal content of the core-shell particles (A) is at least 2.5% by weight;
• wherein in a first step, the thermoplastic polyester (C) is heated to above its melting range, and accordingly becomes free-flowing, and emulsified with the partially water-wettable particles (E) in water, forming a particle-stabilized oil-in-water emulsion (G) having a discontinuous phase comprising molten polyester (C) and a continuous water-containing phase;
• wherein in a second step, the particle-stabilized oil-in-water emulsion (G) is cooled to below the melting range of the polyester (C), wherein the molten, particle-stabilized polyester droplets (C) solidify and the partially water-wettable particles (E) become attached to the surface of the polyester particles (C), forming the core-shell particles (A).