Cellulose activation

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Cellulose activation

Stina Grönqvist (VTT), Thad Maloney (Aalto),

Taina Kamppuri (TUT), Marianna Vehviläinen (TUT),

Terhi K. Hakala (VTT), Tiina Liitiä (VTT),

Tuomas Hänninen (VTT), Anna Suurnäkki (VTT)

Finnish Bioeconomy Cluster FIBIC Oy

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Cellulose activation

What and how:

Opening of pores and altering of fibril aggregates and highly ordered regions in cellulose fibres by:

Mechanical treatments

Degrading treatments

Swelling treatments

Why:

To enhance the accessibility and reactivity of cellulose to chemicals (solvents and reagents)

Dependent on the structure and morphology of the cellulose fibres and solvent or reagent used

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Motivation

Currently, the strategic target for the European forest industry is to find new viable applications for wood fibres.

The industrial interest is focused on novel added-value products based on regenerated fibres.

This is mainly due to the promising market trends especially in the textile industry combined with the environmental considerations related to currently used fibre raw materials, e.g. cotton.

Current regenerated fibres produced by e.g. viscose and Lyocell processes involve the use of harsh and toxic chemicals.

Fubio cellulose aims to develop novel sustainable, both non-aqueous and aqueous based solvent systems for dissolving pulps

Finnish Bioeconomy Cluster FIBIC Oy 29.8.2013

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Dissolution Dissolving grade pulp

Pre-treatment: mech. + enz. treatments

Regenerated fibres

Clothes

Hygiene products,

wipes

FuBio Cellulose

From cellulose to textiles

The process development of novel sustainable solvent systems for cellulose is connected with the opening up of the fibre structure

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Dissolving grade pulps


Produced either by sulphite or prehydrolysis kraft process a high cellulose content and only traces of hemicelluloses and lignin

Dissolving grade pulps used for: production of cellulose derivatives regenerated cellulose

Requirements: good accesibility and reactivity of cellulose

Challenges:

The removal of the non-cellulosic compounds in pulping and bleaching cause, the cellulose fibrils to aggregate and form tight structures in drying

decreased fibre reactivity the lost conformability and swelling capacity cannot be recovered by rewetting the fibres

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Cellulose fibres


Egal Mlle Magali (2006): Structure and properties of cellulose/NaOH aqueous solutions, gels and regenerated objects. Ecole Doctorale 364: Sciences Fondamentales et Appliquées, Ecole des mines de Paris, France, p.30.

Simplifying :

Wood is a complex natural composite built up of fibres that are glued together by lignin

fibres consist of fibrils that are held together by lignin and hemicellulose.

fibrils are built up of bundles of microfibrils

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Schematics

of cellulose

microfibril

behavior during

different

processing

steps


Pönni et al (2013): Accessibility of cellulose: Structural changes and their reversibility in aqueous media, Carbohydrate Polymers. Volume 93, Issue 2 2013 424 - 429

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Mechanical treatment

Enzyme treatment

Dope Fibres

State-of-the-art Biocelsol process

Scale: 500 g Mechanical shredding by Baker Perkins, 5 h, 20 % Enzyme treatment: commercial enzyme, pH 5, 3h, 5 %

Pulp

Disintegrated pulp Mechanically treated pulp (5h)

No major changes in the

visual appearance of fibres due to 5 h mechanical shredding by the Baker Perkins machine

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What does the state-of-the-art treatment do?


Mech. treatment

Baker Perkins

(0- 5h)

Enzymatic

(2 dosages) vrs. acid hydrolysis

Dissolution of samples in NaOH/ZnO

Pulp

Analyses: dissolved sugars, pulp viscosity, molar mass distribution, pore size

distribution, WRV, solubility

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Enzyme aided modification of cellulose


Kvarnlöf 1997: Activation of dissolving pulps prior to viscose preparation. Dissertation. Karlstad University.

Aim: To drop the pulp viscosity to a level where dissolution of cellulose in selected solvent system is possible

Due to the compact structure of cellulose the accessibility to chemicals and enzymes is restricted mechanical treatment needed

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Dyes:

Yellow; larger particles and higher affinity to cellulose

Blue; smaller in size, stains all sites that are too small for the yellow dye

More yellow -> more open structure

Shredding time min

micropore volume

g/g

total pore volume

g/g

Accessible surface area

m2/g

0 0.42 0.53 9

30 0.43 0.75 28

60 0.44 0.78 29

150 0.47 0.82 30

300 0.48 0.91 37

Simons staining Solute exclusion approach

Effect of shredding with Baker Perkins on fiber

structure

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Effects of shredding on the following

enzymatic hydrolysis step


• Shredding (0-300 min) as indicated in the figure • Enzyme treatment: 2h, 50°C, pH 5

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Porosity development by hydrolysis


Shredding time min

micropore volume

g/g

total pore volume

g/g


m2/g

Disintegrated pulp 0.42 0.53 9

Shredded 5 hours 0.48 0.91 37

Shredded 5h + 2h E (0.25 mg/g)

0.61 1.05 38

Shredded 5h + 2h E (1 mg/g) 0.61 1.17 48

Treatment micropore volume

g/g

total pore volume

g/g


m2/g

Disintegrated pulp 0.42 0.53 9

Acid hydrolysis (viscosity ~250 ml/g) 0.36 0.43 6

Enzymatic hydrolysis (viscosity ~250 ml/g) 0.62 0.86 21

No

mec

ha

nic

al

tr

eatm

ent

Acid vrs. enzymatic hydrolysis

Effect of enzyme dosage

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Effect of pre-treatments on solubility

29.8.2013

300 min

60 min

30 min

150 min

Pulps shredded by Baker Perkins and then treated enzymatically (1 mg/g) for 2h.

Cellulose content in the solutions was 5.5 wt%.

Shredding time

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Development of novel sustainable aqueous

based dissolution systems


The mechanical treatment should: Modify accessibility of cellulose for enzymatic (and/or chemical modification) Be techno-economically feasible

The enzymatic treatment should:

Drop pulp viscosity, without formation of low molecular weight material, low polydispercity of Mw-distribution

As a result of the combined mechanical and enzymatic treatments:

Cellulose should be soluble in selected system (here in NaOH/ZnO) and result in a clear solution without undissolved particles

The properties of the regenerated fibres should be on targeted level


Enzyme treatment

Dope Fibres Pulp

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Screening of new enzymes

accepted discarded discarded discarded

Shredding Enzymatic treatment

Pulp Dissolution

into NaOH/ZnO

Microscopy images

Falling ball viscosity and

alfa

If soluble

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Screening of potential mechanical treatments

Testing of various mechanical equipment

Equipment selected based on expected capability to cause internal (and moderate external) fibrillation

Conditions for the mechanical treatment selected based on prior to art knowledge


Sprout Waldron disc refiner, Pearl mill PFI mill

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Screening of various ways to combine the

mechanical and enzymatic processing steps

Pulp than can be dissolved in selected

solvent and results in regenerated fibres with

target properties


Pulp

Enzymatic treatment


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Conclusions

The process development of novel sustainable solvent systems for cellulose is connected with the opening up of the fibre structure

Apparently, it is necessary to break internal bonds within the fibre wall so that fibres swell and pores expand.

In the studied system:

Opening of the fibre matrix due to mechanical treatment seems to proceed in steps, it seems that after a certain amount of stress some structures are broken down or collapsed, resulting in further opening of the matrix.

The surface area available to an enzyme increased from 9 to 37 m2/g in 5 hours of shedding and was further increased substantially by the action of the enzyme.

There seems to be limited amount of accessible sites with adequate pore size available in the pulp for enzyme catalysis

Increased porosity results in better solubility of the cellulose.

The work carried out to develop novel sustainable aqueous based dissolution systems for dissolving pulps has resulted in very promising results.


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Acknowledgements

The work has been partially funded by the Finnish Bioeconomy Cluster (FIBIC) through the Future Biorefinery (FuBio) programme.

The technical assistance of Maija Järventausta, Leena Nolvi, Mariitta Svanberg and Nina Vihersola is gratefully acknowledged.


Business

Cellulose activation