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Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions

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Abstract

This work demonstrates for the first time the deconstruction of microfibrillated cellulose (MFC) into rod-like cellulose nanocrystals (CNCs) in concentrated low modulus sodium silicate solutions. To this aim, MFC suspensions at different concentrations were first treated in sodium hydroxide solutions and then amorphous silica powder was added. Optical microscopy and transmission electron microscopy observation showed how MFC was efficiently deconstructed into CNCs, evidencing the occurrence of a phase separation into an isotropic and mesogenic phase. The extracted CNCs were characterized by a remarkably higher length (600–1200 nm) in comparison with the plant-derived ones commonly reported in literature. FT-IR spectroscopy and 29Si MAS NMR confirmed that the Qn equilibrium of the suspended silicate species was affected, proportionally to the amount of MFC. It was also shown, that due to the excluded volume effect exerted by silicate anions, nematic or smectic ordering could be achieved for CNC concentrations far below the critical rod concentration predicted by the Doi-Edwards model.

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Abbreviations

WG :

Water glass (aqueous sodium silicate solution)

MFC :

Microfibrillated cellulose

Na-MFC :

MFC treated in 10 M NaOH solution

CNCs :

Cellulose nanocrystals

n :

SiO2/Na2O molar ratio, modulus

M sol :

Solid mass in the suspension obtained by weighting the solid residual (g)

M WG :

WG mass obtained by stoichiometric calculations (g)

M tot :

Suspension mass (g)

M MFC :

Mass MFC (wet) (g)

c s = 0.02:

Dry content of MFC

w s :

Solid weight fraction = \(\frac{M_{sol} }{M_{tot} }\)

w MFC :

MFC fibrils weight fraction = \(\frac{M_{MFC} \cdot c_{s} }{M_{WG} }\)

w CNC :

The weight fraction of CNCs (wCNC) on the suspension mass (Mtot) = \(\frac{M_{MFC} \cdot c_{s} }{M_{tot} }\)

ρ WG :

Density of a water glass suspension as a function of the solid content solution (g cm−3)

ρ CNC :

Density of CNCs (g cm−3)

MFC0 :

Pure water glass

MFC1 :

WG/MFC suspension with wMFC = 0.01

MFC2 :

WG/MFC suspension with wMFC = 0.02

\(Q_z^n\) :

Silicate consisting of z interconnected Qn units

w CNC = w MFC·w s :

CNCs weight fraction on the whole suspension mass

ϕ CNC :

Volume fraction of CNCs

ϕ WG :

Volume fraction of silicate anions

L CNC :

CNC’s length (m)

d CNC :

CNC’s diameter (m)

ν = ϕ CNC/(π/4)·d 2 CNC L CNC :

Number of rods per unit volume of solution

β :

Flow index

K :

Consistency index

\(\dot{\gamma }\) :

Shear rate (s−1)

η 0 :

Zero shear viscosity (Pa s)

η 0.01 :

Viscosity at shear rate = 0.01 s−1 (Pa s)

η s :

Viscosity of the suspending medium (Pa s)

σ y :

Yield stress (Pa)

G′, G″:

Storage and loss moduli (Pa s)

k B :

Boltzmann’s constant (J K−1)

T :

Temperature (K)

d* CNC :

Increased CNC’s diameter due to silicate adsorption (m)

d rod :

Diameter of a generic rod (Dogic and Frenkel) (m)

L rod :

Length of a generic rod (Dogic and Frenkel) (m)

d WG :

Diameter of a spherical silicate anion (m)

δ min :

Minimum interfibrillar distance (m)

s :

± number of brushes/4

D CNC :

Rotatory diffusivity of CNCs in diluted regime (m2 s−1)

\(D_{CNC}^{\prime }\) :

Rotatory diffusivity of CNCs in semidiluted regime (m2 s−1)

ω :

Frequency (Hz)

ω c :

Crossover frequency (Hz)

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Acknowledgments

This work was realised at CEITEC IPM—Central European Institute of Technology with research infrastructure supported by the project CZ.1.05/1.1.00/02.0068 financed from European Regional Development Fund. The support from the project Materials Research Centre at FCH BUT- Sustainability and Development REG LO1211 and the project LO1219 with financial support from the National Program for Sustainability I (Ministry of Education, Youth and Sports) is gratefully acknowledged. CIISB research infrastructure project LM2015043 funded by MEYS CR at the CF Biomolecular Interactions and Crystallization is also gratefully acknowledged. Finally, a special mention goes to Dr. Jiří Smilek, Dr. Alberto Viani, Dr. Jiri Holas and Prof. Giulio Malucelli for the support provided for the rheological tests, DIC microscopy, XRD analysis and data interpretation, respectively.

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Authors and Affiliations

  1. Institute of Physics of Materials AVČR, CEITEC IPM, Žižkova 22, 61662, Brno, Czechia

    Luca Bertolla & Ivo Dlouhý

  2. Materials Research Centre, Faculty of Chemistry, Brno University of Technology, Purkyňova 464/118, 61200, Brno, Czechia

    Eva Bartoničková

  3. CEITEC – Central European Institute of Technology, Masaryk University, Kamenice 5/4A, 62500, Brno, Czechia

    Jaromír Toušek & Jiří Nováček

  4. Institute of Theoretical and Applied Mechanics of the Czech Academy of Sciences, Centre of Excellence Telč, Batelovská 485, 58856, Telč, Czechia

    Petra Mácová

Authors
  1. Luca Bertolla
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  2. Ivo Dlouhý
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  3. Eva Bartoničková
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  4. Jaromír Toušek
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  6. Petra Mácová
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Correspondence to Luca Bertolla.

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Bertolla, L., Dlouhý, I., Bartoničková, E. et al. Deconstruction of microfibrillated cellulose into nanocrystalline cellulose rods and mesogenic phase formation in concentrated low-modulus sodium silicate solutions. Cellulose 26, 4325–4344 (2019). https://doi.org/10.1007/s10570-019-02364-6

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