Polyolefin based plastics are extensively used for packaging applications and as such they tend to have a short service life but they have a long environmental persistence. One strategy to accelerate the mechanical degradation of polyolefin plastics in the environment is to blend them with carbohydrate based polymers. Unfortunately polyolefins are hydrophobic whereas carbohydrates tend to be hydrophilic so the two do not blend without chemical modification of the carbohydrate. In this study high density polyethylene, HDPE and thermoplastic starch, TPS are used as the polymers with deep eutectic solvents, DESs as the modifiers. Both TPS and DESs are biodegradable and the DESs are water miscible and biocompatible ensuring that the composite plastic contains a biodegradable flaw which should enable mechanical and chemical degradation. It is shown that DESs enable facile mixing of the two polymers. The composite has a strength similar to TPS but a ductility greater than either of the two components. The glass transition temperature of the composite plastic shows that they are homogeneously mixed and data suggests that the DESs act as lubricants rather than plasticisers.