Influence of cationic polyacrylamide molecular weight on the retention of mixed talc and ground calcium carbonate fillers of different particle sizes

This study investigated the relationship between cationic polyacrylamide (C-PAM) molecular weight and inorganic filler particle size in paper retention, using the Wet End Process Simulator to replicate industrial sheet forming under vacuum dewatering and vibration. Stocks containing larger-particle talc exhibited greater flocculation and poorer formation than those with smaller-particle ground calcium carbonate (GCC), with formation further deteriorating as C-PAM molecular weight increased from 6 to 8 × 10 6 . The reduced specific surface area of talc limited polymer adsorption, leaving excess C-PAM to promote fiber flocculation. This result demonstrates that the number of polymer electrolytes can be either insufficient or excessive depending on the available adsorption surface area, and that the retention of small-sized fillers with a large specific surface area requires low-molecular-weight C-PAM, which has shorter chain lengths but is present in greater numbers. In mixed-filler systems (talc:GCC = 50:50), higher proportions of 8 × 10 6 C-PAM increased talc retention, while higher proportions of 6 × 10 6 C-PAM enhanced GCC retention. Results indicate that high-molecular weight C-PAM is more effective for large suspended solids, whereas lower-molecular weight C-PAM better retains smaller fillers under limited polymer dosage. These findings provide practical guidelines for selecting retention aid molecular weight based on filler particle size in papermaking.