Find a civil or mechanical consulting engineering company that designs clean rooms in your country and build it. Make it at least a class 1000 clean room (In the United States and Canada, Federal Standard 209E (FED-STD-209E) was used until the end of November 2001 to define the requirements for clean rooms. On November 29, 2001, these standards were superseded by the publication of ISO specification 14644-1.) with a cleaning station out front if you are getting your XLPE in polyethylene bag lined cardboard boxes.
Make sure your plastic conveying system is also class 1000 and that the inside surface of the lines is perfectly clean along with all the enclosed and dust free surge bins and extruder hoppers.