Method to start-up a process to make expandable vinyl aromatic polymers

A method for production of expandable vinyl aromatic polymer pellets comprising:

• during start-up of the production of the expandable vinyl aromatic polymer pellets:
• introducing a vinyl aromatic polymer, an expandable agent, and optionally additives to a pelletizer (L) comprising a first die plate having a plurality of holes of large diameter and a first cutting means;
• and
• producing pellets in the pelletizer (L) until a polymer flow rate is in an operating range of a pelletizer (S);
• when the polymer flow rate is in the operating range of the pelletizer (S), switching the introduction of the vinyl aromatic polymer, the expandable agent, and optionally the additives from the pelletizer (L) to the pelletizer (S), and operating the pelletizer (S) at conditions effective to produce the expandable vinyl aromatic polymer pellets, wherein the pelletizer (S) comprises a second die plate having a plurality of holes of small diameter and a second cutting means;
• recovering the expandable vinyl aromatic polymer pellets from the pelletizer (S);
• recovering the pellets from the pelletizer (L);
• and
• recycling the pellets produced by the pelletizer (L), wherein the recycling of the pellets produced by the pelletizer (L) comprises:
• introducing the pellets produced by the pelletizer (L) to a side extruder;
• and
• mixing the pellets produced by the pelletizer (L) with the vinyl aromatic polymer, the expandable agent, and optionally the additives prior to introducing the vinyl aromatic polymer, the expandable agent, and optionally the additives into the pelletizer (S).