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Study of gelation behavior of methylcellulose Jieyi Zhang
Faculty Adviser: T. P. Lodge Department of Chemistry, University of Minnesota
Background
References
Objectives
Acknowledgements
Future Directions
Conclusion
Cloud Point Results
Rheology Results
1. Kobayashi. Kazuto, Huang. Ching-I, Lodge. Timothy P.
Thermoreversible Gelation of Aqueous Methylcellulose
Solutions. Macromolecules (1999) 32, 7070-7077.
2. Chevillard. C., Axelos. M.A.V. Phase separation of
aqueous solution of methylcellulose. Colloid &Polymer
Science (1997) 275, 6.
Solution Preparation:
Set up a hot plate with a temperature monitor and heat a
large beaker of deionized water to 75-80 °C.
Have another beaker of deionized water of room temperature
and an ice bath larger than the flask ready.
Measure the desired amount of polymer, and keep it in a petri
dish.
Put a stir bar in a clean round –bottomed flask and zero the
balance with the flask on top.
Measure approximately 50g of hot deionized water into the
flask.
Mount the flask onto a stand and place a stir plate under, add
the MC polymer when the hot water is cooled to 70°C. Stir for
10 minutes.
Put the flask back on the balance and slowly add room
temperature deionized water to give 100g of solution.
Put the stopper on top of the flask to avoid evaporation, and
mount the flask back on the stand and still for another 10
minutes.
Place the flask in ice bath and stir for another 10minuites.
Have the solution rest overnight to clear up bubbles.
Degas the solution under vacuum before use.
Experiment
Methylcellulose (MC) is a hydrophobic polymer
derived from substitution reaction of cellulose that
replaces the hydroxyl group by methoxide group.
It undergoes thermo-reversible gelation at around
20-50 °C which allows it to function as a
thickener, emulsifier, and binder.1 Although
several thermoresponsive polymers include
poly(N-isopropylacrylamide), cellulose derivatives
and poly(vinyl ether)s have been studied
previously, but how the phase separation and
gelation are related remain poorly understood.2
Delete me & place your
LOGO in this area.
Testing sample preparation:
for cloud point and rheology testing,
Use Parafilm to seal the tip of the syringe.
Carefully pour solution into syringe.
Take off the Parafilm and push the end to get rid of the
bubble.
Slowly inject the solution into a clean vial and seal the tip with
Parafilm
Cloud point measurement:
Prepare a vial with deionized water.
Prepare another vial that contains methylcellulose solution;
place a temperature meter inside the vial to measure the
temperature of the solution.
Warm up the laser for 10 minutes.
When taking cloud points below room temperature, add a few
drops of liquid nitrogen to bring the temperature down.
Allow the solution to spend at least 15 minutes before taking
a reading.
Measurements should be taken with 1°C increment for all
solutions except for low concentration solutions at low
temperature, which measurement could be taken with 2°C
increment.
Rheometer measurement:
Initialize the rheometer with couette geometry and inject the
testing solution.
Program the rheometer with identical heating rate as that in
the cloud point measurement and start the test.
From the cloud point experiment, it was
observed that the normalized transmittance
was a good measurement of the clouding
behavior, and depict the phase separation
phenomena well. The rheological experiment
with identical heating rate allowed accurate
measurement of gelation behavior of a
heating rate sensitive material. The results
from cloud point and rheometer
measurements of commercially available
thermo reversible methylcellulose solutions
suggest that there is correlation between
them as it is shown in the cloud point and gel
point vs. concentration plot. 86% normalized
transmittance was defined to be the cloud
point in this experiment because it matches
the gel point very well. One of the most likely
possible reasons for the small deviation
observed in gel points and cloud points for
larger concentrations is air bubbles in higher
concentration solutions are difficult to get rid
of.
Methylcellulose of the other molecular weight
should be further tested to examine the
correlation between phase separation and
gelation. In addition, the reason why the cloud
point defined at 86% transmittance matches the
gel point data well should be further
investigated.
The gel point of the solution was first estimated using
temperature ramp. For example, the following graph is a plot
of temperature ramp result of the tested methylcellulose
solution at 1.99wt%.
A more precise gel point was obtained from programing a
test with the same heating rate as that in the cloud point
measurement. The following is a sample graph of tan(𝛿) vs.
temperature of the tested methylcellulose solution with
concentration of 1.99wt% .
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The goal of the project was to probe the
relationship between phase separation and
gelation behavior of methylcellulose solutions.
Cloud point was measured to Phase
separation behavior was
The phase separation behavior of methylcellulose solution was
monitored with laser and laser power meter, and the gelation
behavior was monitored with AR-G2 rheometer.
Mw Mn Mw/Mn DS C*
156±6kg/mol 12.3±0.1kg/mol Mw/Mn=12.65±.1
4
1.8 0.29%wt
The properties of the MC polymer tested is listed below:
The cloud point and gel point at various
concentrations were plotted in the following graph:
This project was supported by the Undergraduate
Research Opportunities Program of University of
Minnesota and could not have been completed without the
help and guidance of John McAllister and Professor Tim
Lodge.