Study of gelation behavior of methylcellulose D

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.