A rheological investigation of sol–gel transition of hydroxypropyl cellulose with nonionic surfactant sorbitan monopalmitate: Modulation of gel strength by UV irradiation

Abstract

Abstract The interaction of hydrophobically modified biocompatible polymer hydroxypropyl cellulose (HPC) with nonionic surfactant sorbitan monopalmitate (Span 40) in aqueous solutions have been studied using rheology. The associated physicochemical properties of the HPC+ Span 40 mixed system such as cac, psp and cmc were studied as a function of Span 40 concentration. Steady shear rheological experiments indicate that the HPC as well as HPC+ Span 40 systems possesses two distinct regions in the rheogram Newtonian followed by Pseudoplastic behavior, and behave as plastic systems with the value of m parameter in the empirical Cross model equation η 0 − η α / η − η α = 1 / 1 + C ( γ ) m varying between 0.725–0.675 and 2.24–1.58 in the first and second shear thinning regions. Dynamic rheological results suggest that the microstructural changes that occur during thermo reversible gelation of aqueous solutions of HPC and HPC+ Span 40 systems follow a two step mechanism i.e., gelation followed by precipitation. The thermal stability of the HPC hydrogel decreases as the concentration of Span 40 increases. Moreover, increase in the UV radiation dose on 10% HPC increases its gel strength probably due to the formation of active radicals in the polymer which on further reaction results in formation of highly cross linked gel of high viscoelasticity. However, this phenomena was not observed in 10% HPC solution after addition of Span 40.