Solid state photocrosslinked starch based films: a new family of homogeneous modified starches

A new family of crosslinked starches were synthesised in the solid state by UV irradiation. The crosslinking treatment is novel because starch is treated in the solid state and no crosslinking agent is used. The original photosensitisers used were water soluble and members of the benzoic acid family. They were able to crosslink starch even at concentrations as low as 0.1%. The crosslinking kinetics were established by the determination of both the swelling degree and the gel fraction in order to characterise the network created. Crosslinking densities can be varied by altering the UV exposure time (1–10 min). Although the final crosslinking density is relatively low, it is still sufficient to render starch nearly insoluble in DMSO. The reactivity is discussed (i) as a function of the plasticisers content (water, glycerol, sorbitol), which can modify both the macromolecular mobility and the material density and (ii) as a function of the presence of a destructuring agent (NaOH) which favours starch accessibilites to the reactants. Mechanical properties were measured. Due to the relatively low crosslinking rate, only a slight increase is observed for crosslinked samples.