how impurities (hemicelluloses, ink and lignin) affect the functionalization of cellulose fibres
DESCRIPTION
Cellulosic fibres offer sustainable reinforcement for polymer-based biocomposites (e.g. WPC), but usually require some chemical modification to achieve good compatibility. Since cellulose reactivity largely depends on pulp characteristics, especially on purity of the samples, the reaction rate of four different pulp samples, namely bleached softwood kraft (b-SKP), virgin thermo-mechanical (TMP), recycled TMP and acetosolv weat straw, has been compared. Functionalization of cellulose fibres has been carried out through a set of oxidation reactions expected to benefit fibrillation and thus reinforcing ability.TRANSCRIPT
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HOW IMPURITIES (HEMICELLULOSES, INK AND LIGNIN)
AFFECT THE FUNCTIONALIZATION OF CELLULOSE FIBRESA. Salvador1, J. Hidalgo1, M. Azpeitia1, P. Orsolini2, P. Tingaut2, T. Zimmermann2 and A. Tejado1
1Tecnalia Research & Innovation, Sustainable Construction Div., Spain
2EMPA, Swiss Federal Laboratories for Materials Science and Technology, Switzerland
CELLULOSE SAMPLES
Objective Cellulosic fibres offer sustainable reinforcement for polymer-based biocomposites (e.g. WPC), but usually require some chemical modification to
achieve good compatibility. Since cellulose reactivity largely depends on pulp characteristics, especially on purity of the samples, the reaction rate of four different pulp
samples, namely bleached softwood kraft (b-SKP), virgin thermo-mechanical (TMP), recycled TMP and acetosolv weat straw, has been compared. Functionalization of
cellulose fibres has been carried out through a set of oxidation reactions expected to benefit fibrillation and thus reinforcing ability.
Conclusions The impurities present on recycled newspapers (mainly ink and inorganic fillers) delay the reactivity of cellulose fibres, apparently by hampering
the diffusion of reactants into the fibre wall and buffering the reaction medium at alkaline pH. Virgin TMP, with no buffering effect, shows a rapid pH evolution and fast
reaction related to the damaged fibres and extensive presence of fines. On the other hand, the hemicelluloses present on wheat straw pulp participate of the reaction
and increase the overall rate due to their ready accessibility. Furthermore, the short and thin-walled WS fibres also collaborate to accelerate the reaction by allowing a
rapid diffusion of reactants into the fibre wall, contrary to the thick-walled non-damaged softwood kraft pulp. Regarding the reaction yield, measured here as total [H+]
generated, hemicelluloses (WS) do contribute to increase the total amount, while lignin (TMP) and impurities (Recycled) reduce the extent of the reaction. This work
also states that the pH range for maximum reaction rate is not significantly affected by the presence of the impurities.
La Compagnie Industrielle de la Matière Végétal, FR (Bouchra Benjelloun) and ECOPulp Oy, FI (Ari Hentonnen),
valuable partners of the INNOBITE consortium, and Smurfit Kappa Nervion, ES (Javier Pérez) are greatfully acknowledged for providing the pulp
samples for this study. Esther Strub and Anja Huch (EMPA, CH) are greatfully acknowledged for the SEM imaging.
Cell-A Cell-B Cell-C Cell-D
b-SKP TMP Recycled WS
Bleached
Softwood Kraft
Virgin Thermo
Mechanical
Recycled
TMP
Acetosolv
Wheat Straw
1000 µm 1000 µm
FUNCTIONALIZATION
Chemistry A well-known and highly efficient
reaction (carboxylation of dialdehyde cellulose)[1]
was used to compare the behaviour of the different
pulps under equal conditions.
Fibrillation (SEM of Cell-A)
Kinetics Oxidation reactions were initially
monitored through pH evolution. Proton (H+)
generation rate and yield were determined.
Effects on fibres The presence of negatively charged groups induces
fibrillation and disintegration of fibres.
Fib
res
be
fore
tre
atm
en
t(S
EM
)
Sample pH for Rmax pH for R>80%
Cell-A 4.2 4.2 - 4.5
Cell-B 4.3 4.2 - 4.5
Cell-C 3.9 3.8 - 4.5
Cell-D 4.2 4.1 - 4.3
Disintegration (Optical Micrographs of Cell-A)
Reaction rate (R) vs pH
Reaction yield vs time1000 µm 1000 µm
IMPURITIES
Highly pure High lignin % ≈30% ink + inorganics High hemicellulose %
FIBRES
Non-damaged Damaged with lots of fines Highly damaged Short and thin-walled
COMPOSITION (%)
(C: Cellulose, H: Hemicellulose, L: Lignin, O: Other impurities)
99.5 58.7 36.2 58.2
0.5 14.3 25.8 40.3
0 26 8.4 1.3
0 1 29.6 0.2
References[1] Tejado et al. 2012
Cellulose 19(3):831-842; Yan
et al. (2012) Langmuir
28:7834-7842; Tejado et al.
(2011) Prov. Patent Appl.
USPTO 61/450,222.
100 µm
200 µm
100 µm1000 µm
Acknowledgements
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10
0 1 2 3 4 5
Time (h)
15 20
Diffusion of reactants into the fibre wall
pH
pH vs time