Film Recovery Constraints on Optical and Gravimetric Assessment of Pulsed Gas–Solid Cleaning of Model Plastic Films

Cleaning-induced mass changes depend on which films enter the post-cleaning weighing. This study quantifies that dependence using 84 model film runs in an established pulsed gas–solid apparatus and a laboratory stirred water reference. The count-matched weighing criterion retained 26 runs (31.0%): 24.0% of dry cleaning runs and 88.9% of stirred water reference runs. Ten of 21 groups had no eligible gravimetric observation. In one incomplete recovery run, assigning the mean initial clean film mass to the unweighed piece gave a scenario contribution of 19.5 percentage points of the unrestricted gravimetric index, illustrating potential bias without correcting the observation. Optical normalization denominators ranged from 68.0 to 76.2 percentage points; separately selected films introduced a conditional sampling uncertainty component of 0.33–0.99 percentage points in optical recovery. At 120 s, the nominal 5 g polyethylene (PE) configuration had 15.2 percentage point lower mean optical recovery than the 3 g configuration despite similar film count recovery. Reporting recovery-dependent coverage alongside each endpoint keeps laboratory comparisons tied to the film populations actually measured.