Cellulose nanofibrils prepared by twin-screw extrusion: Effect of the fiber pretreatment on the fibrillation efficiency

Abstract

Twin-screw extrusion (TSE) is a rather recent method to produce cellulose nanofibrils (CNFs) at a high solid content under continuous feeding. Here, never-dried commercial eucalyptus pulp was used as starting material to produce CNFs by TSE after a chemical pretreatment to introduce carboxylic groups via TEMPO-mediated oxidation and carboxymethylation. Five samples with acarboxyl content ranging from 800 to 1300 µmol.g-1 were produced to explore how the carboxyl content affects the aptitude of cellulose fibers to be broken down to nanoscale. The properties of the resulting CNFs in terms of nanosized fraction, morphology and rheological properties were investigated. A critical carboxyl content of 700 µmol.g-1was a prerequisite for the successful conversion of cellulose fibers into a CNF gel by TSE, regardless the pretreatment method. The degree of swelling of the fibers was put forward to account for this critical parameter.

Review on Nonconventional Fibrillation Methods of Producing Cellulose Nanofibrils and Their Applications

“…The authors found that no significant fibrillation could be achieved when employing traditional NaOH-treated pulp fibers even after an oxidative pretreatment, a finding potentially attributable to the limited shearing capacity of the mini-TSE. To fibrillate commercially produced never-dried pulp, the authors explored more extensive TEMPO oxidation and carboxymethylation pretreatments . The pH level of TEMPO oxidation was deliberately raised to 10 to achieve a carboxyl content as high as 1350 μmol/g.…”

“…To fibrillate commercially produced never-dried pulp, the authors explored more extensive TEMPO oxidation and carboxymethylation pretreatments. 44 The pH level of TEMPO oxidation was deliberately raised to 10 to achieve a carboxyl content as high as 1350 μmol/g. By fibrillating pulp fibers modified with either TEMPO oxidation or carboxymethylation at a carboxyl content of 800 μmol/g, a 50 wt % fraction of nanoscale material was achieved.…”

“…The method was developed for use with pulp fibers with diameters on the tens of microns. Researchers have however employed centrifugation to measure the WRV of micro- or nanofibrils via the reduction of easy-to-remove bulk water, leaving water bound to fibril surfaces and in their pores. , Similarly, the Canadian Standard Freeness (CSF) measures the water drainage rate from fibers and is often correlated to a degree of fibrillation, as the CSF value is related to the surface area and swelling behavior of fibers and fibrils. Like the WRV, CSF is primarily used for larger fibers, and its efficacy with micro- and nanomaterials is problematic, as the drainage rate is reduced to near-zero as the fibril size decreases …”

“…Many researchers have invested significant effort in the development of pretreatments that potentially reduce the energy consumption for CNF production and ensure consistency of the products’ composition and properties . Additionally, pretreatments have been shown to reduce the likelihood of clogging during the disintegration process . Different strategies have been developed for the pretreatment of lignocellulosic feedstocks for CNF production.…”

“…47 Additionally, pretreatments have been shown to reduce the likelihood of clogging during the disintegration process. 44 Different strategies have been developed for the pretreatment of lignocellulosic feedstocks for CNF production. Such strategies include chemical, 48−51 physical, 52,53 mechanical, 54,55 and enzymatic treatments, 56,57 in addition to combinations thereof.…”