Dyeing of Chemical Pulp with
Natural Dyes Sofia G. Papadaki*, Emmanuel G. Koukios
National Technical University of Athens
School of Chemical Engineering,Laboratory of Organic Chemistry and Technology
Bioresource Technology Unit
Multi-product/service biomass processing systems, consisting of sequences
including
Feedstock handling & storage
Pretreatment (physical, chemical, biological)
Fractionation to main and co-products
Product & co-product upgrading
Product & co-product marketing
Integrated material/energy/economic flows
Defining Biorefineries – some theory!
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Biorefineries are one of the pillars of sustainability.
Bioremediation of degraded land and poor crop production use
of agro-industrial wastes
Zero waste holistic use of renewable resources, green
chemistry principles
Profitability value added products, create employment, support
by national and European funds, etc.
Biorefineries and Sustainability
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Motivation
Nowadays, there is a worldwide resurgence of interest in natural dyes,
in the frame of the overall return to the natural resources.
This trend is based firstly on the fossil fuel depletion and secondly on
the increasing public awareness of the environmental and health
hazards related to chemical product.
Strict EU legislation Directives 2002/61/ΕU, 2004/92/ EU, EU
Regulataions Nob1907/2006, 1129/2011, 1333/2008.
Moreover, the natural dyes which are derived from wastes of
agricultural and forestry activity or the food and beverage industry,
such as vegetable and fruits peels or timber residues, and not edible
plants, such as weeds, show vital importance referring to
sustainability.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
The natural colorants could be classified in five groups:
◦ Polyphenolic compounds (flavonoids and tannins),
◦ Isoprenoids (carotenoids),
◦ Tetrapyrroles (phycobilins),
◦ Quinones and
◦ N-heterocyclic compounds.
Natural Dyes
All these compounds show an important multifunctionality as
long as they perform high antioxidant, anti-inflammatory, anti-
bacterial activity.
Fibrous products coloring
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
The process of coloring fibrous products is significantly
complicated, but it is based on the simple mechanism of binding
to the surface of the fiber or being trapped within them a
chromophore, chemical compound that brings color.
One characteristic property of natural dyes is their limited
resistance against leaching, which is the case of paper
recycling. For this reason, their application in paper industry
shows great importance.
The different drying, extraction and dyeing methods affect
drastically the dyeing capacity of various plants.
The scope of this work is the evaluation of dyestuff plant material
drying, extraction and pulp dyeing techniques effect on the
dyeing capacity of Eucalyptus globulus L. bark on chemical pulp.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Scope
Why chemical pulp?
The study of dyeability of chemical pulp is very important as it consists almost
the 70% of the worldwide produced pulp from wood annually, because of the
improved properties paper that produces. Moreover, studies have shown that the
absence of lignin in chemical pulp leads to the need of using larger amounts of
dye in order to obtain the required colour comparing with mechanical pulp.
Why Eucalyptus globulus L. bark?
The bark of E. globulus L. is a great source of natural dyes as it contains numerous
dyestaff components such as tannins and flavonoids, with most important the
eriodictyol, naringenin, quercetin, rhamnazin, rhamnatin and taxifolin.
Moreover, it is a forest and pulp and paper industry residue, which means zero
supply cost and zero environmental impact. Paper industries in Europe produce
annually ≈ 0,5 million tones of Eucalyptus bark indicating their potential to
compile with biorefinery concept.
Drying of dyestuff plant material
Dyestuff plant material treatment
Extraction of natural colorants
Chemical pulp preparation
Dyeing of chemical pulp
Handsheet formation
Color determination
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
EXPERIMENTAL PROCEDURE
Drying of Dyestuff Plant Material
9
Natural drying
The natural drying took place in a dark place at room temperature (25 oC)
and relative humidity (RH) 50% approximately, for one week.
Air drying
The air drying took place in a laboratory tunnel air dryer at different
levels of temperature (30, 50 and 70 ± 2 °C), relative humidity (50 and 95
% RH), constant air velocity (2 m/s) and atmospheric pressure for 24 h.
Freeze drying
The plant materials were initially frozen at -30 oC for 48 h and freeze
dried for 24 h using a Lyovac Gt 2 laboratory freeze dryer. The freeze
drying was performed under high vacuum conditions (0.06 mbar).
The dried bark was ground in several sizes (Fritsch Cutting
Mill Pulverisette 15) and stored in dark and dry place.
Grain size classification took place, using the Fritsch
Vibratory Sieve Shaker Analysette 3 Spartan (measuring
range: 19.1 - 0.063 mm, sieving time: 10 min, middle
amplitude).
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Dyestuff Plant Material Treatment
For the production of the natural dyes, conventional, ultrasound and
microwave assisted aquatic extraction took place.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Extraction of natural colorants
In both cases, specific amounts of the ground bark were extracted with 125 ml of
deionized water. In each experiment the determination of the specific amounts of
extracted plant material resulting from the Φ/Χ ratio, which derives from the oven dry
weight of the extracted plant material divided by the oven dry weight of the pulp dyed
with the plant extract. The final extract obtained after filtration of the insoluble residues
through a copper filter fabric.
Method Temperature (oC)
Time (min)
Conventional Extraction 40, 80 15, 30, 60
Ultrasound Assisted Extraction 250 W and 20 kHz
25, 40, 80 5, 10, 15
Microwave Assisted Extraction 200 W and 400 W
40, 80 5, 10 ,15
Chemical pulp preparation
Chemical pulp originated from spruce softwood was used.
The supplied chemical pulp was torn into small pieces by
hand and added into deionized water (2 % w/w mixture
consistency).Then, vigorous mixing of the resulting
mixture took place for 6 h using a mechanical mixer at
2000 rpm. After filtration, the produced pulp had
moisture content of 92% w/w and was stored in an
airtight plastic pot at 4 oC.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
All the produced extracts were used for the dyeing of chemical pulp.
Conventional and ultrasound assisted process took place.
In all cases, the dyeing was realized using a liquor ratio of 55:1 ml/g.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Dyeing of Chemical Pulp
Method Temperature (oC)
Time (min)
Conventional Dyeing 25, 40, 80 15, 30, 60
Ultrasound Assisted Dyeing 250 W and 20 kHz
25, 40, 80 5, 10, 15
Microwave Assisted Dyeing 200 W and 400 W
40, 80 5, 10,15
Isotropic handsheet derived from dyed and undyed pulp were formatted
according to SCAN-C-26:76 and SCAN-C-M5:76 methods using the
Lorentzen and Wettre standard equipment (sheet former model SCA, sheet
press and rapid dryer). The handsheets were stored in a dark and dry place for
at least 24 hrs before their color determination.
The CIE L*a*b* system was applied for the color determination of the
produced sheets by using a Dr. Lange colorimeter.
The final dyeing result derived from the total color difference ΔE*ab between
each dyed sheet and a reference sample (undyed sheet). The total color
difference is given from the following equation:
where ΔL*= L*sample - L
*reference, Δa*= a*
sample - a*
reference and Δb*= b*sample - b
*reference
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Handsheet formation and color measurement
RESULTS General assumptions
Severe extraction and dyeing conditions (Te = Td = 80 oC and te = td = 60 min) give
tense dyeing result.
The “limiting saturation value”, describes the fact that beyond this limit any increase
of the Φ/Χ ratio is unable to cause any further colour change, as the pulp fibers
cannot absorb any more dye.
Even in mild conditions the limiting saturation value for E. globulus L. bark is around
Φ/Χ = 1.4. Therefore, the experiments for optimization of grain size, extraction
and dyeing method occurred with extracts produced at Φ/Χ ratio of 0.4 and 0.6
units, respectively. By avoiding the saturation limit, every colour change would be
significant.
In the frames of this study, not only the final dyeing result but also the low cost and
environmental impact were taken under consideration during the selection of the
most efficient extraction and dyeing conditions. Therefore, conditions such as short
residence time and low temperature were preferred.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
0
5
10
15
20
25
30
35
40
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 2,2
ΔΕ
*
Φ/Χ (g/g)
TE = 80 oC, tE = 60min
TB = 80 oC, tB= 60min VB/X = 55:1 ml/g
Grain size effect on total color difference (ΔE*ab )
In this figure, the effect of
grain size on the ΔE*ab is
presented at severe
conventional extraction and
dyeing conditions.
The optimum grain size
ranges from 1.4 to 1.0 mm.
The decrease of ΔE*ab as the
grain size increases is
significant.
The ΔE*ab could be
tripled by using the
optimum grain size.
From this point all the
experiments occurred at the
optimum grain size.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Effect of extraction methods on total color difference in various conditions
(ΔE*ab ).
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
0
5
10
15
20
25
30
35
80 o
C, 6
0 m
in
80 o
C, 3
0 m
in
80 o
C, 1
5 m
in
40 o
C, 6
0 m
in
40 o
C, 3
0 m
in
40 o
C, 1
5 m
in
80 o
C, 5
min
80 o
C, 10 m
in
80 o
C, 1
5 m
in
40 o
C, 5
min
40 o
C, 1
0 m
in
40 o
C, 1
5 m
in
25 o
C, 5
min
25 o
C, 1
0 m
in
25 o
C, 1
5 m
in
80 o
C, 5
min
80 o
C, 1
0 m
in
80 o
C, 1
5 m
in
40 o
C, 5
min
40 o
C, 1
0 m
in
40 o
C, 1
5 m
in
ΔΕ*a
b
Extraction conditions (Te, te)
Microwave Assisted
Extraction
Conventional
Extraction
Ultrasound Assisted
Extraction
Td=25oC
td= 30min
Φ/Χ = 0.6
Eucalyptus globulus L. bark
L* a* b* h
(degrees)
C ΔΕ*
Conventional
Extraction
79,0 8,2 13,2 58,15 15,54 22,5
Ultrasound Assisted
Extraction
74,1 7,57 10,81 55,00 13,20 23,62
Microwave Assisted
Extraction
73,47 8,11 11,67 55,20 14,21 28,32
Effect of dyeing methods on total color difference in various conditions
(ΔE*ab ).
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Eucalyptus globulus L. bark
L* a* b* h
(degrees)
C ΔΕ* ΔΕ* Φ/Χ=2,2
Conventional
Dyeing 79,0 8,2 13,2 58,2 15,5 22,5 28,6
Ultrasound
Assisted Dyeing 78,3 7,2 11,9 58,8 13,9 20,4 30,1
Microwave
Assisted Dyeing 75,9 8,2 15,7 62,4 17,7 28,1 36,5
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
Effect of drying methods and condition on dyeing capacity of Eucalyptus globulus
L. bark
Dyestuff plant
material Method a b k0 k R2 SSE
Eucalyptus
globulus L.
Air drying 2.5 -0.4 3.3E-07 - 0.9403 2.7 E-02
Freeze
drying - - - 1.4 E-02 0.9997 1.02E-05
A first order kinetic model describing the moisture transfer during drying is considered:
-dX/dt = k (X – Xe)
where X is the material moisture content (dry basis) during drying (kg water /kg dry solids), Xe, is
the equilibrium st moisture content of dehydrated material (kg water /kg dry solids), k is the
drying rate (min-1),and t is the time of drying (min).
Assuming that the hot air flow in the case of air drying and the layer thickness are stable, the drying
rate is related only to the air temperature (T) and humidity (Y) as it is described:
The fitness was checked with coefficients of determination (R2) and the sum of square errors
(SSE). Air drying
Color stability against ageing.
Relatively mild
conditions of conventional
extraction and dyeing were
selected in order to study
the colour stability.
Colour measurements
took place on dyed
handsheets four days and
six months after their
dyeing.
The dyeing result of E.
globulus L. bark on chemical
pulp show significant
stability against ageing.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
CONCLUSIONS
The presented results prove that the E. globulus L. bark can be used sufficiently as a source of natural colourants for the chemical pulp.
The grain size affect drastically the dyeing capacity of the bark and the optimum grain size was determined in the range of 1.4 and 1.0 mm.
The low dyeing temperature and short extraction residence time that were achieved show great industrial interest because of their low cost and environmental impact.
The dyed handsheets showed great colour stability in ageing, a fact that presents the E. globulus L. bark as a promising dyestuff material with application mainly in packaging products.
Referring to the ultrasound and microwave assisted processes
In both cases of extraction and dyeing, strongest dyeing result was achieved in shorter time and lower temperature in comparison with the conventional ones.
“The limiting saturation value” was achieved in lower Φ/Χ ratios.
Air drying in low temperature and high RH was indicated as the optimum drying method for the dyestuff plant material.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
SUGGESTIONS FOR FURTHER STUDY
The study of the dyeing capacity of the remain liquor after
the dyeing process, in order to save water, energy and raw
materials.
The alternative exploitation of the remain plant material
as absorbent, fertilizer or biofuel.
The use of mordants in order to achieve stronger and
more stable dyeing results.
28/7/2014 FIBRA 2nd Summer School, 26-31 July 2014, Lisbon
PRESENTATION OF THE BTU/NTUA GROUP
BIORESOURCE TECHNOLOGY UNIT
National Technical University of Athens (NTUA), Athens, Greece (1917-)
School of Chemical Engineering (1917-)
Division IV: Process & Product Development (1983-)
◦ BTU was established in the mid-80’s
PRESENTATION OF BTU/NTUA
BTU Vision The emergence of a new generation of
technologies for the large-scale conversion of renewable raw materials of biological origin to various industrial and energy market outlets
◦ Research, development, demonstration and diffusion as “levers” for technological change
PRESENTATION OF BTU/NTUA
BTU Strategy & Approach
Systemic: Identifying critical questions for in-depth investigation within well-defined frames
◦ Integrated energy and material systems
Interdisciplinary: Combining various relevant scientific and technical elements
◦ Engineering; chemical; biological; socio-economic
Networking: National, European, International
PRESENTATION OF BTU/NTUA
BTU Research Areas
Evaluating the Resource Basis
◦ Studies of bioresource potential; physico-chemical characteristisation of crops and residues
New Resource/End-use Interfaces
◦ Biorefining; Physico-chemical fractionation and pretreatment of lignocellulosic asnd other biological raw materials
PRESENTATION OF BTU/NTUA
BTU Research Areas (cont’d)
Utilisation of Non-wood Fibre Sources
◦ New feedstocks for cellulose and fibre industries; environment friendly conversion processes
Bioethanol/BioH2: Steps to Solar Future
◦ Fermentation of lignocellulosics and other unconventional substrates; new bioconversion routes; sustainable biosystems
PRESENTATION OF BTU/NTUA
BTU Research Areas (cont’d)
Bio-Heat and Bio-Electricity Options
◦ Thermochemical densification; pre-pyrolytic treatment; upgrading lignocellulosic and other unconventional feedstocks
Integrating Local/Regional Applications
◦ Local-level bioenergy studies; technology diffusion; policy & decision-making support tools and models
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SUPER: Sustainability policy and
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Acknowledgements
The research has been supported by the Senator Committee of Basic Research, Program “PEVE 2009”, R.C. No
65/1784 of the National Technical University of Athens. The authors wish to thank the Athenian Paper Mills - Softex
for the donation of the spruce softwood chemical pulp.
THANK YOU FOR YOUR
ATTENTION
Contact Info:
Dr. Sofia Papadaki
Bioresource Technology Unit, NTUA
Tel. +302107723149; +306976291715