Formation of cellulose-starch gels using various cellulose sources

Cellulose, the most abundant natural polymer, is biocompatible and environmentally friendly. Diverse sources of cellulose exist, such as wood-pulp fibers or bacterial cellulose, which, after oxidation using the TEMPO-oxidation process, form nanofibrils dispersible in water and present shear-thinning properties. Starch is also an abundant natural polymer, and is frequently a waste product from food processing. In this project, in collaboration with universities (Exeter, Bath, Norwich) and industrial partners, we aim to study interpenetrating cellulose-starch hydrogels, with possible applications in personal care or agrochemicals. Two sources of cellulose were studied: anionic cellulose (AC) nanofibrils obtained from wood-pulp (manufactured by Croda) and oxidized bacterial cellulose (BC) from Acetobacterxylinum culture. At 1wt%, partially oxidized cellulose nanofibril suspensions present a weak gel behavior, with shear-thinning properties. Starch, either corn or potato starch, can also form shear-thinning gels at high weight fraction (>5wt%). We have prepared starch-cellulose mixtures, with a fixed weight fraction of cellulose (1wt% of AC or BC) and different starch weight fractions (1, 5, 10,15 wt%). Samples have been studied via rheology measurements, small-angle X-ray scattering, light scattering and electron microscopy. For both cellulose sources, at low weight fractions of starch, the rheological properties are completely dominated by those of the cellulose fibrils. At higher starch concentration, samples behave as strong shear-thinning gels, with enhancements of viscosities, elastic and loss moduli, but with noticeable differences in viscosity values and loss factor upon strain for the two types of cellulose, related to the structural differences of the nanofibrils