Molecular and functional modification of hydroxypropylmethylcellulose by high-intensity ultrasound

The application of high-intensity ultrasound (HIUS) to modify biopolymers is increasingly been studied. Because of cavitation, HIUS can modify the structure of some proteins and polysaccharides. The objective of this study was to evaluate the effect of high-intensity ultrasound on the particle size of hydroxypropylmethylcellulose (HPMC) with different molecular weights by dynamic light scattering and to assess the impact on some relevant functional properties. Solutions of different commercial HPMC of the same type and degree Of Substitution, but differing in molecular weight were prepared at 0.01-7 %wt concentration and submitted to HIUS. The size distributions and Z(average) (Zav) of particles, before the treatment, immediately after HIUS treatment and up to 3 days after treatment, were measured by dynamic laser light scattering as well as the cloud point, gelation temperature, thermal transitions (the last by differential scanning calorimetry), apparent viscosity and water mobility by NMR. Ultrasound treatment of HPMC induced the formation of concentration-dependent transient clusters. The performance of HPMC on 10:90 oil-in-water emulsions was not modified by ultrasound as well as the gelation parameters characterizing the gel regime (gelation temperature, thermal transitions by DSC). However, the Cloud point decreased by 8-9 degrees C. Changes in viscosity and water mobility were observed for high molecular weight HPMC revealing structural modifications that were not apparent for the low molecular weight HPMC. (C) 2008 Elsevier Ltd. All rights reserved.