1. Synthesis of Lignosulfonate Hydrogels
cross-linked with PEGDGE
Maika Bui, Xiaoxu Teng, Junna Xin, Jinwen Zhang
Composite Materials and Engineering Center
Northwest Advanced Renewables Alliance, Summer Undergraduate Research Experience
Introduction
Hydrogels are network based polymers noted for their ability to retain large amounts of water. Industries take advantage of their hydrophilic property to enhance its products; these include drug delivery services, soil
rehabilitation, biosorption, etc. Lignosulfonate is a copious lignin-derived byproduct from the pulping process of paper production. Because of the economical and sustainable advantages of using biomass over fossil-fuels,
industries are looking towards replacing synthetics with bio-based materials. In this study, sodium lignosulfonate is cross-linked with poly (ethylene glycol) diglycidyl ether (PEGDGE) to form hydrogels. Reaction (PEGDGE mass,
lignosulfonate mass, temperature) and application (time, pH) conditions are manipulated to optimize maximum swelling capacity.
O
OCH3
HO
NaO3S
OH
O
O O
O
n+
85℃
+NaOH
O
O
O
OH
O
HO
Scheme 1. Reaction scheme for crosslinking sodium lignosulfonate
(SLS) with PEGDGE to synthesize sodium lignosulfonate hydrogel (SLSH)
50 100 150 200 250 300 350 400 450 500
50
60
70
80
90
100
Temperature (
0
C)
Weightloss(%)
Sodium lignosulfonate
Hydrogel with lignosulfonate
4000 3500 3000 2500 2000 1500 1000 500
Wave length (cm
-1
)
Sodium lignosulfonate
Hyldrogel with sodium lignosulfonate
Fig. 1 Thermogravimetric analysis (TGA) of sodium lignosulfonate
(SLS) and lignosulfonate hydrogel (SLSH) (5 mg, heating rate
10℃/min, temp. room-500 ℃)
Fig.2 FT-IR spectra of sodium lignosulfonate (SLS) and
lignosulfonate hydrogel (SLSH) (scanned scanned 32 times in the
range for 4000 to 500 cm-1)
Reaction Conditions Application Conditions
0 10 20 30 40 50 60
0
10
20
30
40
Swellingcapacity(g/gxerogel)
Time (min)
20
0
C
40
0
C
60
0
C
2 4 6 8 10 12
20
25
30
35
40
45
50
Maximumswellingratio/100(%)
pH value
3 g SLS
3.5 g SLS
4 g SLS
70 75 80 85 90
20
25
30
35
40
45
50
Maximum swelling ratio/100
Yield
Temperature (
0
C)
Maximumswellingratio/100(%)
84
85
86
87
88
89
Yield(%)
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
20
25
30
35
40
45
50
Maximum swelling ratio/100
Yield
Mass of PEGDGE (g)
Maximumswellingratio/100(%)
82
84
86
88
90
Yield(%)
3.0 3.5 4.0 4.5 5.0
20
25
30
35
40
45
50
Maximum of swelling ratio/100
Yield
Mass of sodiun lignosulfonate (g)
Maximumofswellingratio/100(%)
78
80
82
84
86
88
Yield(%)
Fig. 3 Different reaction temperature to
swelling ratio and yield of SLS hydrogels (4g
SLS,1.2g PEGDGE, 10 ml water, 0.5g NaOH,
temp. 70-90◦C in increments of 5)
Fig. 4 Different amounts of cross linker to
swelling ratio and yield of SLS hydrogels (4g
SLS, 85◦C, 10 ml water, 0.5g NaOH, PEGDGE
1.0g-2g in increments of .2)
Fig. 5 Different amounts of sodium
lignosulfonate to swelling ratio and yield of SLS
hydrogels (1.2g PEGDGE, 85◦C, 10 ml water, 0.5g
NaOH,SLS 3.0-5g in increments of 0.5)
Fig. 6 Relationship between swelling time
and swelling capacity (4g SLS,1.2g PEGDGE,
10 ml water, 0.5g NaOH, 85◦C, media pH 3-
11 in increments of 2)
Fig. 7 Variation of the maximum swelling
ratio with pH value for different usage of
sodium lignosulfonate (4g SLS,1.2g PEGDGE,
10 ml water, 0.5g NaOH, room temperature)
Conclusion
Future Directions
• Investigate various methods of modifying lignosulfonate hydrogels to
increase swelling capacity
• Optimize swelling capacity conditions for lignin amine hydrogels
Acknowledgements
This work, as part of the Northwest Advanced Renewables Alliance
(NARA), was funded by the Agriculture and Food Research Initiative
Competitive Grant no. 2011-68005-30416 from the USDA National
Institute of Food and Agriculture.
References
1. Xuliang Liu, Mingsong Zhou, Suya Wang, Hongming Lou, Dongjie
Yang,Xueqing Qiu. Synthesis, structure, and dispersion property of a
novel lignin-based polyoxyethylene ether from Kraft lignin and
poly(ethylene glycol) [J]. ACS Sustain. Chem. Eng., 2(2014):1902-1909]
To optimize the swelling capacity of SLSH, preparation requires 4g SLS and 1.2g PEGDGE synthesized at 85◦C. With 4g SLS, the hydrogel swelling capacity was 39g water/g xerogel; addition of SLS exhibited a decrease in
swelling capacity. With 1.2g PEGDGE, the hydrogel swelling capacity was 37g water/g xerogel; addition of PEGDGE exhibited a decrease in swelling capacity. Within 2 minutes, the SLSH reached its maximum swelling capacity.
Experimental Methods
1. Hydrogel Preparation: A water bath with a thin layer of oil was set to heat at various temperatures. 10 ml of deionized water was poured into a screw-top glass vial along with a stir bar. The vial was placed into the water-oil
bath. Different amounts of sodium lignosulfonate (code no. 700317) was slowly added to the vial with the while stirring at 900 rpm. The vial is capped and left to stir for 2 hours. After two hours, sodium hydroxide and
PEGDGE was added to the mixture. The stir bar was removed and capped vial was removed from the water-oil bath. After the hydrogel formed, it is removed from the vial and washed multiple times with cold water, hot
water, and ethanol until the liquid runs clear. Products were freeze dried into xerogel and then ground into a fine powder.
2. Swelling Capacity Tests: Approximately 0.20 g of each ground freeze dried hydrogel sample is placed into the bottom of a teabag. The samples were submerged in their respective water baths and left for two hours. After
two hours, the teabags are blotted with paper towels and a spatula is used to scoop out the swollen hydrogels for mass measurement. For tests run in respect to time, The samples were submerged into room temperature
water baths. At each designated time interval, the teabags are taken out, blotted, and then weighed.
Results and Discussion
As the temperature condition increases,
the swelling ratio increases as well.
The swelling capacity of the SLSH
increases as the amount increases to
1.2g PEGDGE; it decreases thereafter.
The swelling capacity of the SLSH
increases as the amount increases to
4g SLS; it decreases thereafter.
As the pH of the media increases, the
swelling ratio of the SLSH increases.
SLS and SLSH show similar trends in weight loss. In comparison to SLS,
SLSH exhibited greater loss in weight in respect to temperature
because of its moisture content.
There are bands at 1114 and 951 cm-1, which is attributed to C-O-C
vibrations. This is evident that crosslinking PEGDGE and SLS was
successful.
SLSH reaches equilibrium within 2
minutes in room temperature media.
Yield % = (mpost swelling－mprior swelling)/mpost swelling×100 Swelling ratio (%) = (mswollen－mdry )/mswollen ) X100 Time Swelling ratio (%) = (mtime－mdry )/mtime ) X100
◦C