Solár R., Mamoň M., Hudec J., Reinprecht L.

Effect of biotic and a-biotic pre-treatments of hornbeam wood on its properties important

from viewpoint of kraft and organosolv pulping.

Solár R., Mamoň M., Hudec J., Reinprecht L.

Faculty of Wood Sciences and Technology. Technical University of Zvolen,

T.G. Masaryka 24, 96053 Zvolen, Slovakia.

Introduction

Production of chemical pulps is an expensive matter connected with high consumption of energies, chemicals and water, and the product contains residual lignin requesting tedious bleaching steps.

From the above reasons an extensive research concerning also pre-treatment of wood by white-rot fungi has been carried out in the last decades. The achieved results, however were not always positive - alkaline pulping.

For fungal pre-treatment is characteristic so called „bio-pulping” effect, based on the release in the structure and partial delignification of wood.

Introduction

Similar effect on the structure, chemical composition and physical properties of wood might have also alkaline/oxidative sequences of chemical pre-treatment.

Advantage of a-biotic agents might be in more uniform effect, shorter time of action and un-necessity of chips sterilisation.

Aim

The estimation of some physical and chemical changes of hornbeam wood pre-treated by white-rot fungi and chemical agents, as well, related to kraft and organosolv pulping and the pulps properties.

Material, selection of specimens

The hornbeam wood test specimens of dimensions 2.5x2.5x1 cm were made from two sections taken from middle part of the tree trunk in age of 90 years.

Shorter dimension of each specimen was parallel, and the longer ones perpendicular to grain. From the specimens a comparable series, each comprising 8 specimens, were prepared.

Pre-treatments

For 30-day bio-degradations of hornbeam wood, the following white-rot fungi were used:

Trametes versicolor - erosive fungus

Phanerochaete chrysosporium - erosive fungus Ceriporiopsis subvermispora - lignin-selective strain.

Chemical pre-treatments were as follows:

- 48 h alkaline (2.5 % NaOH) step followed by 48 h oxidation with 7.5

% H2O2 (with, or without dicyandiamide activator),

- 48 h alkaline (2.5 % NaOH) step followed by 48 h oxidation with 8 and 4 % per-acetic acid, as well. Pre-treatments were carried out

at the ambient temperature (22-23 oC).

Pre-treatments

Bio-mimetic pre-treatment:

Bio-mimetic system, similar to low-molecular complexes generated by

lignin-selective fungi, has been used as a control of delignification

efficacy of the applied biotic and a-biotic agents.

Composition: 4-aminopyridine/TBH peroxide/Cu2+ complex

proposed by Messner et al. (2003); molar ratios were increased for 50 %. Hydromodul was 1:16, and delignification at 50 oC lasted 72 h.

Measurements and analyses

Weight loss Facial swelling after 48 h dipping in H2O or pre-treatment Coefficients of axial permeability Kinetics of facial swelling in water Extract (ethanol/toluene) Lignin determination (ASTM 13 m) Cellulose determination (Kürschner-Hoffer) Bleaching - activated H2O2 at 33 and 62 oC (1 + 1h) DP - from intrinsic viscosity of bleached pulps in FETNA soln.

Pulping

Kraft pulping:

sulfidity of liquor 21.5 %; active alkali 16.0 %, time to reach the pulping temperature of 170 oC - 75 min, pulping at the temperature – 60 min; hydromodul 1:4.1 .

Organosolv pulping: liquor - 0.03 M (COOH)2 in ethanol/water 1:1 v/v, time to reach the pulping temperature of 160 oC - 75 min, pulping at the temperature 60 min; hydromodul 1:5.2 .

Note: pulping in small scale autoclaves without stirring, dimensions of chips cut from the specimens were 3x3x10mm (longer dimension parallel to grain), their moisture content before pulping - 6.4 %.

Results and discussion

All pre-treatments resulted in the weight loss of hornbeam wood, changes in physical properties and in its altered chemical composition, as well (Figs. 1-5, Tabs. 1 and 2).

Results - weight loss

Fig. 1 Weight loss of hornbeam wood due to biotic and a-biotic pre-treatments (%)

0

2

4

6

8

10

12

14

16

18

Pre-treatment

We

igh

t lo

ss (

%)

Results - facial swelling

Fig. 2 Final value of facial swelling of sound and pre-treated hornbeam wood specimens (%)

0

5

10

15

20

25

Pre-treatment

Facia

l s

welli

ng (

%) Sound w ood

Pre-treated

Results - kinetics of facial swelling

Fig. 3 Kinetic plots and relative rate constants of facial swelling of hornbeam wood pre-treated by white-rot fungi; 0 - sound wood, 1 – T. versicolor, 2 – P. chrysosporium, 3 – C. subvermispora

0

2

4

6

8

10

12

14

16

0 30 60 90 120 150 180 210 240 270 300 330 360

Time [s]

Fac

ial

swel

ling

% 3 k=450*10-3 [%.s-1]

1 k=1272*10-3 [%.s-1]

2 k=1487*10-3 [%.s-1]

0 k=4*10-3 [%.s-1]

Results - kinetics of facial swelling

Fig. 4 Kinetic plots and rate constants of facial swelling of hornbeam wood pre-treated with white-rot fungi; 0 – sound wood, 4 - NaOH/ H2O2, 5 – NaOH/H2O2 + activator, 6 – NaOH/8 % per-acetic acid, 7 - NaOH/4 % per-acetic acid, 8 – bio-mimetic system

0

2

4

6

8

10

12

14

16

0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600

Time [s]

Fa

cia

l sw

elli

ng

[%

]

6

k=10.8*10-3 [%.s -1]

4

k=8.3*10-3 [%.s -1]

5

k=8.2*10-3 [%.s -1]

0

k=4.1*10-3 [%.s -1]

7

k=6.0*10-3 [%.s -1]

8

k=16.6*10-3 [%.s -

1]

Results - kinetics of facial swelling

As it follows from Fig. 3, fungal pre-treatments increased extremely the rate of hornbeam wood facial swelling in its first-fast phase (more than for two orders).

The effect of chemical pre-treatments (Fig. 4) was much weaker, and caused only 1.5 to 2 multiple increase in the relative rate constant of facial swelling, in comparison with sound wood.

The difference in the rate of swelling of bio –, and chemically pre-treated wood is possibly in higher porosity of the bio-degraded material, and in extreme shrinkage (for 30 and 20 %, respectively) of chemically degraded wood.

Results - kinetics of facial swelling

Extreme shrinkage of chemically pre-treated wood in the drying hints at formation of high number of hydrogen bonds among the wood components in its former - deeply relaxed ultrastructure.

Numerous cohesive bonds in the structure of dry chemically pre-treated wood possibly slow down the rate of wood/polar liquid interactions, reflected outward in the facial swelling.

Results - axial permeability

Fig.5 Drop in the coefficient of axial permeability of pre-treated hornbeam wood at moisture content above FSP (%)

05

1015

202530

3540

4550

Pre-treatment

Dro

p in p

erm

eabili

ty (

%)

Results - axial permeability

As it follows from Fig. 5, all pre-treatments significantly reduced the

axial permeability of wood. The most „effective” in this respect

was the lignin- selective fungus C. subv. and bio-mimetic system.

Explanation of this phenomenon follows from different swelling mode of the vessels in sound and by white-rot fungi pre-treated hornbeam wood (Fig. 6).

Results - cross-sections of the lumina

A[%

]

Sound wood

-15

-10

-5

0

5

10

15

1 2 3

Biodegraded wood

1 2 3

±1.96*Std. Err.

±1.00*Std. Err.

Mean

Fig. 6 Confidence intervals for means of changes in the vessels lumina cross-sections ( A) in wetting; 1-ethanol/water mixture, 2-sulphate liquor, 3-NSSC liquor (hornbeam wood, 30-day degr. by P. chrysosporium, weight loss - 16.2 %, (MANOVA, Duncan test)

Results - swelling mode

Comparison of mean areas of cross-sections of the lumina in the vessels showed, that the swelling of their cell walls in

sound wood enlarged the lumina cross-sections, thus increasing

its permeability.

Swelling of the cell walls in the vessels of bio-degraded wood

proceeds in both directions „inside and outside” the lumina, and reduces its axial permeability.

Results - chemical alterations

Pre-treatment Lignin Cellulose Trametes versicolor 21.36 13.43

Phanerochaete chrysosporium 36.26 5.15 Ceriporiopsis subvermispora 50.39 2.71

2.5 % NaOH/H2O2 5.23 - 6.47 2.5 % NaOH/H2O2 + activator 7.34 - 8.75

2.5 % NaOH/8 % per-acetic acid 34.71 - 8.48 2.5 % NaOH/4 % per-acetic acid 14.13 - 9.02

Bio-mimetic system 6.17 - 0.17

Tab. 1 Amounts of lignin and cellulose removed from hornbeam wood in the course of pre-treatments (%)

Results - chemical alterations

All biotic pre-treatments resulted in deep delignification of a substrate. Most effective in this respect was the lignin-selective fungus C. subvermispora, that removed approximately 50 % of lignin at the cost of only 2.7 % of cellulose.

From abiotic agents the most effective was the sequence comprising

2.5 % NaOH/8 % per-acetic acid with 35 % of lignin removed from

wood.

All alkaline/oxidation sequences of pre-treatments were accompanied by an increase in the content of cellulose - possibly due to sorption of xylane in alkaline environment.

Results - kraft and organosolv pulp

Fig. 7 Yield of kraft and organosolv pulps based on the weight of pre-treated wood (%)

0

10

20

30

40

50

60

70

80

90

Pre-treatment

Yie

ld (%

)

Kraft

Organosolv

Results - pulps, residual lignin and DP

Tab. 2 Content of residual lignin in the unbleached pulps and their DP after hydrogen peroxide bleaching

Kraft Organosolv Pre-treatment / pulp Lignin (%) DP Lignin (%) DP

Sound wood 3.70 918 8.10 753 T. versicolor 7.51 741 5.87 460

P. chrysosporium 6.34 856 5.76 483 C. subvermispora 5.02 840 5.10 465

NaOH/H2O2 0.43 726 12.02 - NaOH/H2O2 + activator 0.41 855 12.64 - NaOH/per-ac. acid, 8 % 0.44 685 0.80 451 NaOH/per-ac. acid, 4 % 0.47 883 2.11 488

Results - selectivity of delignification

Fig. 8 Effect of pre-treatments on the selctivity of kraft pulping of hornbeam wood, given as residual lignin to pulp yield ratio

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0,18

Pre-treatment

Lign

in to

pul

p ra

tio

Kraft

Organosolv

Results - selectivity of delignification

Negligible content of residual lignin in the kraft pulps from chemically pre-treated hornbeam wood (Tab. 2), and the corresponding low lignin to pulp ratios ( Fig. 8) point out at the extremely increased selectivity of kraft delignification in this case.

Pre-treatments of hornbeam wood by white-rot fungi influenced the contents of residual lignin in the kraft pulps negatively, and reduced the selectivity of kraft process for 30 %.

On the other hand, the fungal pre-treatments and those based on the application of NaOH/per-acetic acid improved the selectivity of acid catalysed organosolv pulping.

Conclussions

From the obtained experimental data the following conclusions may be derived:

All pre-treatments resulted in the wood weight loss almost equal to 11 %, exception were those with the use of P. chrysosporium and NaOH/8 % per-acetic acid, causing approx. 16 % weight loss of the tested specimens.

Extreme values of facial swelling of wood pre-treated by a-biotic agents hint at deeply relaxed ultra-structure of wood - resulting from cleavage of physical and chemical bonds in the lignin-carbo- hydrate matrix.

Conclussions

Both biotic and a-biotic pre-treatments increased the rate of facial swelling of hornbeam wood- expressing outward the rate of wood/water surface interactions.

All pre-treatments resulted in marked drop in axial permeability of hornbeam wood, especially deep reduction caused fungus C. subvermispora and bio-mimetic system.

White-rot fungi efficiently delignified the pre-treated material, and the amount of lignin removed varied within 21 – 50 %, however at the cost of deep loss of cellulose.

Conclussions

Chemical agents were less effective in delignification with only 7 to

35 % of removed lignin from wood, but did not cause any loss of

cellulose.

Activated hydrogen peroxide markedly increased the hornbeam wood delignification, however as compared to pure hydrogen peroxide pre- treatment, it had no influence on the residual lignin in the pulp.

Comparison of residual lignin in the pulps confirmed highly positive influence of a-biotic pre-treatments on the selectivity of kraft and organosolv pulping.

Conclussions

Deep biotic or a-biotic delignification of wood prior to pulping does not inevitably guarantee a deep reduction in the content of residual lignin in the unbleached pulp!

Conclussions - illustr. of the last aitem

Fig. 9 Lignin contents in the compared wood samples and corresponding unbleached kraft pulps (%)

0

2

4

6

8

10

12

14

16

18

20

Soundw ood

T. vers. P. chrys. C. subv. H2O2 H2O2+act.

8%perac.

4%perac.Pre-treatment

Lig

nin

(%

)

Lignin in w ood

Lignin in pulp

End

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