Israel González Tovar LEPAMAP Group

University of Girona (Spain)

Content The improvement of paper’s strength through refining

Cellulose nanofibres (definition, sources and production)

Addition of CNF into papermaking suspensions

Experiments

Results Conclusions

Mechanical refining (beating) is the main method to improve paper’s strength

Refined fibres present better properties than normal fibres, however…

What are cellulose nanofibres (CNF)?

Source: Isogai 2010

Why CNF in papermaking?

˃ Compatibility ˃ Large specific surface area (great bonding capacity) ˃ High strength and stiffness ˃ Transparency

How do we release the microfibrils? Chemical pre-treatment (TEMPO-mediated oxidation)

EXPERIMENTS:

How do we release the microfibrils? Enzymatic pre-treatment

EXPERIMENTS:

EXPERIMENTS:

TEMPO-mediated oxidation

(bleached euc pulp)

TEMPO-CNF (surface

application)

Enz-CNF bulk application

(1.5, 3 and 4.5%)

Enzymatic treatment

(bleached euc pulp)

Mechanical and physical

characterization

Solution A (0.45wt% CNF)

Solution B (0.45 wt% CNF+2.5wt%

starch size press)

Density, porosity, opacity, breaking length, scott bond, burst index

Catiotic demand, surface area, yield, transmittance, diametre

Sample

Cationic

demand

(µeq·g/g)

Surface

area

(m2/g)

Diametre

(nm)

Yield

(%)

Transmittance

(800nm, %)

Degree

of polym.

Enzymatic CNF

(4 h contact time, 240 g/ton) 258 105.2 23.8 34.0 38.9 307

TEMPO-oxidized CNF

(15 mmol HClO, alkaline pH) 1988 323 8.3 >95 84.7 197

Bulk application: non-chemical CNF have lesser impact on pulp’s drainability

Surface application: shorter fibres penetrate better into the paper’s structure

RESULTS

High carboxylic content

Lower polymerization degree

Shorter nanofibres

TEMPO-oxidized CNF are better for surface application because:

RESULTS

CNF-reinforced papers show improved strength

RESULTS

Achieved without mechanical refining!!!, preserving fibre’s original length and properties.

Increase of 273%!!!!

RESULTS

Bulk (cm3/g)

Opacity (%)

Gurley Porosity (s)

1,91 88,6 1,1 1,81 88,2 2,1

1,76 87,6 3,0 1,70 87,0 3,8

Effect of enzymatic CNF on physical properties added in masse to bleached kraft hardwood pulp

CNF content Thickness (μm)

0 145,52 1,5 138,64 3 133,88

4,5 129,34

ºSR

15 21

24 29

RESULTS

Papers become denser after CNF addition (more compact structure)

RESULTS

CNF-reinforced papers present also improved internal cohesion

RESULTS

Costs of CNF production: a pending task

Type of CNF Pretreatment Nanofibrillation Process at 2wt% fiber Total

Cost (€/kg CNF) Treatment Conditions Chemicals

(€/kg CNF) Energy

(€/kg CNF)

Enzymes (€/kg CNF)

Energy consumption

(kW·h/kg)

Energy cost* (€/kg CNF)

Enzymatic hydrolysis

T=50ºC, pH=5, 240g/t, 4h and

5wt% fiber 0,01** 0,07 0,48 19,1 1,53 2,09

TEMPO oxidation 15 mmols 303,06** 0,03 0,00 19,1 1,53 304,62

RESULTS

CNF are an interesting alternative over mechanical beating.

CNF improve mechanical and physical properties of paper by

increasing the amount of hydrogen bonds between fibres.

CNF can be applied as bulk additives or as coatings.

Addition of CNF as bulk and surface additive increase paper’s strength in 273%.

TEMPO-oxidized CNF have high fabrication costs in comparison to enzymatic CNF.

CONCLUSIONS

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