CALCIUM-BINDING BY CELLULOSE AND LIGNIN

Binding of calcium ions by 0.20% suspensions of purified fibers, micro crystalline cellulose (MCC), alpha-cellulose (CEL), acid-swollen cellu lose (ASC), alkali lignin and kraft pine lignin were investigated. Mor e endogenous calcium was released under acidic conditions (pH < 6) and more exogenous Ca2+ was bound at higher pH levels for all fibers. Fro m Scatchard analysis, MCC and CEL had little affinity for exogenous Ca 2+, ASC had one type of nonspecific binding site, and both lignins had two types of specific binding sites. MCC and CEL tended to bind more Ca2+ after enzymatic digestion, whereas ASC and both lignins tended to bind less Ca2+.