Dissolution behavior of abietic acid in water from the matrices of cellulose nanofibers

Solid dispersion materials of abietic acid (ABA) in mechanically fibrillated cellulose nanofiber (CNF), TEMPO-oxidized cellulose nanofiber (TOCNF), and partially deacetylated chitin nanofiber (ChNF) without or with aluminum sulfate (Alum) were prepared using a conventional solvent-evaporation method. ABA was retained in basically an amorphous form in the solid dispersion materials. The interactions between ABA and the nanofibers (NFs) were different between anionic NFs (CNF and TOCNF) and cationic NF (ChNF)-containing solid dispersion materials. The ABA dissolved in water from CNF- and ChNF-containing solid dispersion materials increased with an increase in shaking time and leveled off, whereas the amount released from TOCNF-containing solid dispersion materials increased rapidly, reached a maximum at the initial stage and then decreased gradually. The different behaviors might be presumed to depend on the narrowness of the NF fiber width rather than the ionic nature of the NFs. Alum basically inhibited ABA dissolution from CNF-containing solid materials, whereas it promoted ABA dissolution from TOCNF and ChNF-containing solid materials unless Alum addition was excessive. The former might correspond to a decrease of dissolved colloidal substances by Alum in acidic papermaking systems.