Impact of the structure of hydroxypropyl cellulose on its techno-functional properties

Hydroxypropyl cellulose (HPC) is a non-ionic cellulose ether in which some of the hydroxyl groups in the repeating glucose units have been hydroxypropylated. The resulting water-soluble polymer has many applications mainly in pharmaceutical and food industry. Due to the flexibility of its manufacturing process, HPC can be obtained in several grades characterized by different average molecular mass and different viscosity. However, it has already been reported that differences in functionality can occur between products of the same grade. Understanding the origin of these differences is a major challenge for both the food and pharmaceutical industries. This work compared different HPC samples of the same grade and related the functionality of the molecule to its structure in order to provide a new advances the structure-properties relationship. Interactions with water, interfacial properties, rheological behavior and cloud point have been measured with tensiometer, rheometer, and spectrophotometer respectively. Consistent differences have been observed between the investigated samples. Structural analysis was performed to tentatively correlate the structure, i.e. the degree of substitution (nuclear magnetic resonance) and the heterogeneity of distribution of substituents along the polymer chain (enzymatic hydrolysis) with the measured properties. The structure greatly affected the techno-functional properties of HPC. The results showed that the unexpected behavior of one sample could be due to the existence of a double population of polymers, varying by their degree of substitution, within this sample. These new elements bring a useful knowledge for any application using this polymer.