HIPS Material ESCR result VS Sun flower oil & oleic Acid

Hai All,
Good Morning.

Regarding on ESCR test for HIPS material, i have some question about 100% virgin material and Mix with 30% regrain.

1. 100% Virgin HIPS VS Sun flower oil/Oleic Acid --> Result OK, no cracking on inner liner
2. MIx with 30% regrain VS Sun flower oil/Oleic Acid --> some area of inner liner was cracking.

Between 100% virgin and 30% mixing with regrain, is there any different about rubber particle size ?
If you have experienced about this topic,let me know, and let to discuss.

Thank you,

Warm Regards,

Aria