Extensional Flow Behavior of Methylcellulose Solutions Containing Fibrils

Area of Science:

• Rheology and Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Semidilute aqueous methylcellulose (MC) solutions are typically shear-thinning liquids at room temperature.
• The addition of salt can alter the self-assembly and rheological behavior of polymer solutions.

Purpose of the Study:

• To characterize the extensional properties of semidilute aqueous methylcellulose solutions.
• To investigate the impact of NaCl addition on MC solution rheology.
• To understand the role of self-assembled fibrils in modifying solution properties.

Main Methods:

• Utilized Capillary Breakup Extensional Rheometry (CaBER) for extensional property characterization.
• Tested both salt-free and 8 wt % NaCl solutions of methylcellulose at room temperature.
• Varied methylcellulose concentration to observe effects on rheological parameters.

Main Results:

• Salt-free MC solutions exhibited only power-law behavior.
• MC solutions with 8 wt % NaCl displayed both power-law and elastic regimes due to fibril formation.
• Extensional relaxation time increased from 0.04 s to 4 s, and apparent extensional viscosity rose from 40 Pa·s to 1300 Pa·s with increasing MC concentration in NaCl solutions.

Conclusions:

• The addition of NaCl induces methylcellulose self-assembly into fibrils, significantly altering extensional properties.
• Fibril formation enhances the elastic response and dramatically increases the extensional viscosity of MC solutions.
• These findings highlight the importance of solution composition on the rheological behavior of methylcellulose.