Rare synonym for 防腐剤 (ぼうふざい). Used in some technical or older contexts, but 防腐剤 is overwhelmingly more common.
See also: 防腐剤
This document uses the notation 制腐剤, but normally it is written as 防腐剤.
Compound of 制 (せい, 'control') + 腐 (ふ, 'decay') + 剤 (ざい, 'agent'). The derivation is transparent, but the term itself is rare.