Carboxylated nanocellulose foams as superabsorbents

Abstract

Hypothesis: Carboxylated nanocellulose fibres formed into foam structures can demonstrate superabsorption capacity. Their performance can be engineered by changing process variables.

Experiments: TEMPO-oxidised cellulose nanofibres of varying concentration and surface charge are produced from hardwood kraft pulp. Foams were prepared through a 2-step freezing and lyophilisation process. The absorption capacity of water and saline solution (0.9 wt%) were measured as a function of time and related to the foam structure.

Findings: The absorption capacity of nanocellulose foams can be manipulated from initial gel properties and processing conditions. Pore structure and distribution of nanocellulose foams are dictated by fibre content and charge density and freezing rate. The best performing foams are at 0.3-0.5 wt%, with a carboxylate concentration of 1.2 mmol/g and frozen at -86 °C before freeze-drying, which can absorb 120 g H₂O/g fibre. Fibre surface charge influences the absorption capacity of the foams by dictating the amount of participating carboxylate groups. Absorption capacity in saline (60 g/g) is lower than in deionised water (120 g/g); but is only slightly lower than that of a commercial polyacrylic acid (PAA) SAPs (80 g/g). Nanocellulose foams are attractive renewable alternatives for superabsorbent applications, contributing to a reduction of plastic microspheres.

Keywords: Foam; Nanocellulose; Structure; Superabsorbent; TEMPO-mediated oxidation.