Effect of Allylation on Gelation Behavior of Aqueous Methylcellulose Solutions

Abstract

Methylcellulose (MC) is a water-soluble cellulose ether formed by the partial substitution of hydroxyl groups with methoxy moieties, called the degree of substitution (DS = 1.6-2.1) per anhydroglucose repeat unit (AGU). MC is a thermoreversible gel that phase separates and gels at ~60 °C and forms fibrils of diameter ~15 nm upon heating. In this project, the effect of allylation on the gelation behavior of MC solutions (Mw = 150 kg/mol) was studied. Allylated MCs were synthesized by reacting with various amounts of allyl bromide under room temperature and basic conditions. The amount of allyl groups substituted per AGU (mol allyl/mol AGU) was characterized through 1H-NMR spectroscopy. The gelation behavior of 2 wt% solutions of the allylated MCs was determined from the cloud point (Tcloud) and gel point (Tgel) temperatures using optical transmittance and rheology, respectively. Results show that Tcloud is similar to Tgel for all solutions and both decrease as mol allyl/mol AGU increases, indicating that allylation causes the early onset of phase separation, gelation and fibril formation due to an increase in the hydrophobicity of MC. Future work will include doing more trials, using other characterization techniques and grafting onto MC through thiol-ene click chemistry.