Redispersible bacterial nanocellulose powders

E. ROSSI; SALVAY, A.G.; M.I. ERREA; M.L. FORESTI

CABA

Congreso; CIBIQ2023 II Iberoamerican Congress of Chemical Engineering - Global Symposium on Nanocelluloses; 2023

CIBIQ

The obtention of powdered products through dehydration of cellulose nanofibrils suspensions is known to promotetheir irreversible aggregation and loss of nanometric size and distinctive properties. This phenomenon, known ashornification, occurs due to the formation of hydrogen bonds between the cellulose nanofibrils during the dryingprocess. Because of the technological and commercial need of reducing the water content of nanocellulosesuspensions, in recent years various alternatives have been proposed to avoid hornification and produce redispersiblepowders, most of them by the addition of capping agents.In this context, the inclusion of a polyhydroxylated additive such as sorbitol (S) during the drying process of bacterialnanocellulose (BNC) is herein proposed, with the hypothesis that it would have a disruptive function of the interchainhydrogen bridges by establishing interactions with cellulose hydroxyl groups. Different BNC:S mass ratios (i.e. 1:1, 1:3and 1:5), drying methods (freeze- and oven-drying) and redispersion techniques (high-speed homogenization withUltra-Turrax (UT) and mechanical stirring (MS)) were studied. The redispersibility of BNC was analyzed usingsedimentation assays, rheological measurements, and Congo Red specific surface area (SSA) determination of theredispersed powder suspensions. The suitability of the complete removal of sorbitol from redispersed samples wasalso studied.The results indicated that in all cases freeze-dried samples showed better redispersibility than oven-dried ones.Besides, irrespectively of the mass ratio used, the addition of sorbitol prior to freeze-drying led to redispersed BNCsuspensions that resembled the never-dried ones (ND) (Fig 1a). The benefits derived from sorbitol addition were evenmore noticeable for oven-dried powders (Fig 1a). Contrary to freeze-dried samples, oven-dried samples withoutsorbitol addition did not redisperse at all (Fig 1b). On the other hand, additivated powders could be thoroughlyredispersed in water showing SSA values similar to those of ND samples (Fig 1c). About rheological studies,suspensions resulting from the redispersion of dried non-aditivated BNC powders showed significantly lower viscositythan never-dried BNC suspensions, which is consistent with the irreversible aggregation of the nanofibers during thedrying process. On the other hand, and in agreement with SSA and sedimentation results, sorbitol addition beforedrying (BNC:S 1:3) allowed for recovering the viscosity values typical of ND BNC suspensions.All these results, together with the possibility of easily removing sorbitol by proper filtration, suggest that its addition asa capping agent could be a promising strategy to produce redispersible BNC powders.