Chemo-enzymatic pre-treatment of eucalyptus kraft pulp for phosphorylated nanocellulose production

Chemical, enzymatic and mechanical pretreatments are needed to disrupt cellulose fibre structure and mechanically process them to produce cellulose nanofibres (CNF). The combination of sequence of chemical and enzymatic pretreatment for CNF production had been poorly investigated, especially complementing them with cellulose functionalisation, such as phosphorylation. In this study CNF were obtained by a three-stage pre-treatment carried out on bleached eucalyptus kraft pulp (BEKP) as follows: a) cold caustic extraction with 15% NaOH (CCE15), b) enzymatic treatment with 50 U Trichoderma reesei endoglucanase (EG) and c) functionalisation by chemical phosphorylation (P) with urea and di-ammonium hydrogen phosphate. Pulps obtained from the different combinations were characterised for properties such as crystallinity, viscosity, S18 solubility, fibre morphology, FTIR, SEM and SEM–EDX to determine differences between samples and treatments. CNF of selected samples were prepared by homogenisation and characterisations were performed on drop cast films prepared from them. The main results showed that the opacity of the films varied between 14%–67%, the water vapour permeability varied between 163–322 g/m².day, the burst index was in the range of 2.0–3.3 kPa.m²/g, the tensile strength was between 6–120 MPa and the films made from phosphorylated CNF were air-impermeable. In conclusion, the combination of chemical-enzymatic pretreatments did not lead to a facilitation in CNF production compared to just performing phosphorylation or enzymatic treatment. Though, different CNF material properties can be obtained varying the pretreatments combination stages, which can be beneficial to implement if the goal is to produce CNF materials with special properties depending on the purpose.

Graphical Abstract