This information is taken from: Blow Molding Handbook, Rosato, Rosato, DiMattia (2003)

“It has always been a necessary “evil” that at the end of a production run the plasticator has to be cleared of all its plastics in the barrel/screw to eliminate barrel/screw corrosion or contamination; this is also required when a change of material occurs.

According to these authors, the following table (briefing from its original) show us what to do:

Guidelines for Plastic Changes
Material in MachineMaterial Changing toMix with rapid purge and soakTemperature bridging materialFollow with
ABSPPABS——–PP
ABSSANSAN——–SAN
ABSPolysulfoneABSPEPolysulfone
ABSPCABSPEPC
ABSPBTABSPEPBT
AcetalPCAcetalPEPC
PEPPPE——–PP
PEPEPE——–PE
PPABSABS——–ABS
PVCAny MaterialLLDPE or HDPE——–New Material
PVCPVCLLDPE or HDPE——–PVC
PPSPVCPPSPEPE