International Conference on:
“New Role for the World Sugar Economy in a Changed Political and
Economic Environment ”
Preparation and characterization of cation exchange resins
based on lignin grafting polyacrylamide and polyvinyl alcohol
Ahmed M. Abdelmawgood(a), Waleed K. El-Zawawy(b) and Ali A. Abdelhafez(c)
(a)
(b)
Quena Company for paper production, Quena, Egypt.
Cellulose and Paper Department, National Research Center, Dokki, Egypt.
(c)
Organic Chemistry, Asut University, Asut, Egypt.
Abstract:
Grafting of lignin, which is a by product resulting from pulping process, is
extremely interesting study. This is largely due to the free radical inhibiting
capability of the phenolic hydroxyl group present in the lignin which is capable
of forming quinonic structures stabilized by resonance over the whole lignin
molecule. Cation-exchangers were synthesized by graft polymerizaion of lignin
with polyvinyl alcohol and polyacryalamide using potassium persulfate as
initiator at different ratios, different reaction time and temperature. The different
grafting products were characterized by FT-IR spectroscopy. On the other hand,
swelling in water at different temperatures and times, swelling in water at
different pHs and in an aqueous solution of 0.9 wt % NaCl were also
investigated. Moreover, the thermal properties, thermal stability and mechanical
stability of the obtained cation exchange resins were also studied using
differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA),
respectively.
The ion-exchange capacity and the uptake of metal ions (mainly Cr 2+, Ni2+
and Cu2+) were detected by atomic absorption spectroscopy. The sorption of the
heavy metal ions Cu (II), Cr (II) and Ni (II) on a grafted polymer was found to
have affinity with metal ions in the following order: Cr (II) > Cu (II)> Ni (II).
Keywords: Lignin, graft polymerization, ion exchanges, thermal analysis,
atomic absorption.
Introduction:
Lignin is one of the most abundant organic polymers in the plant world
whose contents mainly depend upon the plant species. Lignin is found as a cell
wall component in all vascular plants and in the range 15-30% by weight. Lignin
is permanent glue, bonding cells together in the woody stems and thus giving the
stems their rigidity and impact resistance. Huge quantity of wood material is
utilized by pulp and paper industries. Many pulping processes such as soda
process, sulphite process and sulphate process are used for delignification. The
lignin thus removed from the wood is a major waste product of pulp and paper
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International Conference on:
“New Role for the World Sugar Economy in a Changed Political and
Economic Environment ”
industries. It is in the form of black liquor. The global production of lignin is
approximately 70 million tons per year [1]. Increasing and recurring production
and very less utilization of lignin create a disposal problem and has become a
matter of environmental concern. Lignin is considered as a source of different
functional groups for the polymer products. The most characteristic functional
groups present in lignin are methoxyl, hydroxyl, carboxyl, carbonyl and presence
of other double bonds conjugated with aromatic system [2]. Lignin can be used in
many applications, e.g. resin synthesis as novolak and resol phenol lignin
formaldehyde resin. Some lignin derivatives can be used as dispersants,
emulsifiers, adhesives and ion exchangers.
Studies concentrated on the free radical copolymerization of lignin with
unsaturated polymers are very limited, concentrating primarily on grafting of
lignin [3, 4]. Other monomers used as reactive diluents in unsaturated polyester
resins. Lignin was grafted with methyl methacrylate and vinyl acetate [5, 6],
styrene [7, 8], acrylonitrile [9], acrylic acid and acrylamide [10], and maleic
anhydride [11] among others [12]. However, the inhibiting capability of the
phenolic hydroxyl groups of lignin, coupled with resonance stabilization of
any quinonic structures formed [13], make lignin a rather inefficient grafting
target.
Ion exchange materials consist of functional groups bound to different
polymeric frameworks available in various physical forms including hydrogels,
resins, fibers, membranes and fabrics having widely differing chemical and
physical properties. The majority of these forms have synthetic polymer
structures i.e. such as polyethylene (PE), polystyrene (PS) and polyvinyl fluoride
(PVF) while some of them are obtained from modified natural polymer sources
including chitosan, starch, and cellulose. The aim of this study is to prepare
cationic exchange resins based on lignin grafting polyacrylamide and polyvinyl
alcohol.
Experimental
The raw material used in this work was Kraft bagasse black liquor
delivered from Quena Company for paper production, Egypt. Precipitation of
lignin from kraft black liquor was carried out using 20 % sulfuric acid, after
precipitation, lignin was filtered, washed with distelled water until neutrality and
then air dried.
FT-IR spectra were recorded on solid samples in potassium bromide (KBr)
pellets by means of an FT-IR Thermo-Nicolet Model 670 Instrument (Thermo
Electron, Madison, WI).
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International Conference on:
“New Role for the World Sugar Economy in a Changed Political and
Economic Environment ”
Grafting of lignin
Lignin will be dissolved in solvent of NaOH or used as a powder to be grafted
with the PVA and PAM at different ratios and under different reaction time and
temperature (table 1).
Absorption of Different Metal Ions
For the determination of the affinity of graft lignin cation exchanger for the
absorption of metal ions, 0.2 gm of the dried lignin gel was stirred for 30 min. in
solution (25 ml) containing 20 ppm of different metal ions. The suspension was
then filtered and the remaining element ions in the filtrate were estimated using
Atomic absorption .The elements investigated were Cr, Cu, and Ni.
Results and discussion
FTIR analysis
The infrared spectra obtained for the precipitated lignin and grafted lignin
samples are presented in Figure 1. The samples presented a broad band attributed
to OH stretching (3400-3460 cm-1), and peaks corresponding to C-H stretching of
methyl and methylene group (2840-3000 cm-1) and methyl group of methoxyl
(2690-2880 cm-1). The most characteristic vibrations of lignins correspond to
those of aromatic rings at approximately 1600 cm-1, 1500 cm-1 and 1420 cm-1.
After grafting with PVA, these bands were present in the spectra but with
different intensities due to grafting.
Figure 1. FT-IR of lignin and Lignin-PVA.
Cation-exchange resins
A series of cation-exchange resins was prepared from lignin from bagasse
black liquor by graft polymerization lignin with polyvinyl alcohol and
polyacryalamide using potassium persulfate as initiator at different ratios,
different reaction time and temperature. All the prepared samples are tabulated in
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International Conference on:
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Economic Environment ”
table 1.
Table 1. All prepared samples codes and conditions
Sodium binding capacity
Sodium binding capacity gives an indication of the efficiency of the
produced cation exchanger toward metal ions absorption. Figure 2 shows the
sodium binding capacity of all gel samples (grafted lignin).
Figure 2. Sodium binding capacity of grafted lignin samples (A, B, C, D, E and F).
Metal ion absorption
The absorption ability of grafted lignin for metal ions was investigated.
Table 2 shows the metal uptake (Cr, Cu, and Ni) from their mixture in solution
containing 20 ppm of metal. It can be seen from the table that the picking-up
tendency of the prepared ion exchangers depend on the ion. Cr and Cu have the
highest binding efficiency, while Ni ion is picked up the least. This can probably
be attributed to both steric and electronic effects. The ion exchange affinity is
also related to the charge and the hydrated radius of the metal ion. In addition, the
binding ability of the different metal ions to the ion exchanger is affected by the
semi hard acid.
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International Conference on:
“New Role for the World Sugar Economy in a Changed Political and
Economic Environment ”
Table 2. Metal ion uptake by cation exchangers produced from grafted lignin.
Metals
A
B
C
D
E
F
Cr
11.425
5.814
12.240
5.286
13.836
6.827
Ni
2.946
1.633
6.746
3.493
4.535
4.010
Cu
7.487
5.517
6.195
7.382
7.682
5.010
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