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Hi all,

We having been having problems with intermittent voids over the past year while making a polypropylene part for our customer. These voids will appear over the course of a few weeks in the thick wall section of the part, then will disappear completely for another few weeks, only to reappear again. There seems to be some correlation between the raw material we use and when the defects occur. We buy the specific grade of raw material from one manufacturer, but it appears that they have two different manufacturing sites for this specific grade of PP material. When we use material from site 1 we seem to have problems, but when we use material from site 2 the problem seems to go away. We have tried to process the problem out of the part but as it is a validated process there is only so much that we can do at this current moment.
Unfortunately it doesn't seem as it's going to be as easy as asking for material from site 2 only, the material manufacturer is very resistant to the idea that there could be differences between the two sites, and will take some convincing otherwise.
See the two pictures attached and let me know what you think. One is raw material granules from site 1 (pellets with one big void/bubble inside), the other from site 2 (pellets with smaller multiple bubbles inside). I would have expected them to look more similar than they actually are.

Thanks in advance,
DM1977