Bioplastics, which will see rising demand in the next years, have to be compounded by using a twin screw extruder like conventional plastics. By using a twin-screw extruder, the molecular weight of the bioplastic polyhydroxybutyrate (PHB) can be degraded under control. In a second step, the short-chain PHB and a soft phase can be compounded to a larger block copolymer by means of reactive extrusion. The processing step takes place in a process- and material-efficient manner without catalysts, solvents and purification processes. The development of the block copolymer improves the ductile properties of the material without changing the thermal or chemical characteristics.