Carboxymethylated Pulp as Starting Point to PrepareHydroxypropylmethyl Cellulose withEnhanced Gel Rheological Properties in an Aqueous Medium

Hydroxypropyl methylcellulosein an aqueous solution upon heating tendsto undergo thermalgelation, where thepolymer chains form a network and precipitatefrom solution. This occurs at a temperature known asthermal gelationpoint. Polymer precipitationcauses a significant drop in the shear viscosity. This could be a disadvantage in a hot environment or in applications were heat is applied. In this work, a hydroxypropylmethyl cellulose (HPMC)was formed that undergoes thermal gelationwith no polymer precipitationand with enhanced rheological properties. The target HPMC was prepared from wood pulp withalow content of carboxymethyl groups. The produced hydroxypropyl methylcellulose(CMHPMC)derivativeshowed uniquephysical properties that are not achievable with typical hydroxypropyl methylcellulose.The thermal gelation temperature of an aqueous solution of CMHPMC wasincreasedfrom 55 °C for commercial HPMC to 85 °C forCMHPMC. Asubstitution level of carboxymethylationthat led to an HPMC witha thermal gelation and with no precipitationwas determined to bea 0.15of carboxyl groupsper anhydroglucose repeat unit.In addition, the carboxymethylatedpulp showed an enhanced reactivity towards etherification reactions