Micro- and Nanofibrillated Cellulose from Annual Plant-Sourced Fibers: Comparison between Enzymatic Hydrolysis and Mechanical Refining

Abstract

The current trends in micro-/nanofibers offer a new and unmissable chance for the recovery of cellulose from non-woody crops. This work assesses a technically feasible approach for the production of micro- and nanofibrillated cellulose (MNFC) from jute, sisal and hemp, involving refining and enzymatic hydrolysis as pretreatments. Regarding the latter, only slight enhancements of nanofibrillation, transparency and specific surface area were recorded when increasing the dose of endoglucanases from 80 to 240 mg/kg. This supports the idea that highly ordered cellulose structures near the fiber wall are resistant to hydrolysis and hinder the diffusion of glucanases. Mechanical MNFC displayed the highest aspect ratio, up to 228 for hemp. Increasing the number of homogenization cycles increased the apparent viscosity in most cases, up to 0.14 Pa·s at 100 s^-1 (1 wt.% consistency). A shear-thinning behavior, more marked for MNFC from jute and sisal, was evidenced in all cases. We conclude that, since both the raw material and the pretreatment play a major role, the unique characteristics of non-woody MNFC, either mechanical or enzymatically pretreated (low dose), make it worth considering for large-scale processes.

Keywords: enzymatic hydrolysis; hemp; jute; mechanical pretreatments; nanocellulose; nanofibers; non-wood cellulose; sisal.

Figure 1

General experimental layout.

Figure 2

Chemical composition of the pulps from jute (a), sisal (b), and hemp (c).

Figure 3

Effect of mechanical and enzymatic pretreatments on fiber length, expressed as the length-weighted mean.

Figure 4

Yield of nanofibrillation and transmittance at 600 nm for jute, sisal and hemp MNCF after extensive PFI refining and different numbers of HPH cycles.

Figure 5

Yield of nanofibrillation (a) and transmittance at 600 nm (b) for jute, sisal and hemp MNCF whose pretreatment consistent of an endoglucanase-mediated hydrolysis at different dosages. The horizontal axis indicates the HPH sequence: cycles at 300 bar, at 600 bar and at 900 bar.

Figure 6

Evolution of the apparent viscosity at 100 s⁻¹ of suspensions of MNFC from jute (a), sisal (b) and hemp (c). Numbers in italics represent the slope of a trend line.