The plasticisation of plastics using Deep Eutectic Solvents

Owing to the ease of manufacture, versatility of use and relatively low cost, plastics are used in a vast and expanding range of products, from paper clips to spaceships. Plastics are polymers with a range of additives to aid processing and modify the aesthetic, thermal and mechanical properties, depending on their applications. The application of ionic liquids and deep eutectic solvents as an alternative additive for polymers has gained some attention recently due to properties such as thermally stability. In this study deep eutectic solvents (DESs) were investigated in their application as potential additives for non-polar and polar polymers HDPE, PLA and PET. The mechanical and thermal properties including glass transition temperature, melting temperature, maximum tensile strength, and elongation at break were measured with and without DES additives. It is shown that with non-polar polymers (i.e. HDPE), the DESs reduce the intermolecular forces between the polymer chains creating more free volume in the polymer, allowing them to flow more easily and resulting in greater flexibility. The interaction of DESs with polar polymers (i.e. PLA), reduces the motility of the polymer chains and makes the materials more brittle. Plasticisers mainly improve the flexibility of polymers, which can be seen by changes in the glass transition temperature, Tg. This study shows only minor changes in Tg suggesting that the DESs acted as lubricants rather than plasticisers. This project also reveals how the ratio of DESs affected the properties of the plastic. The mechanical strength decreases with increasing DES content for both HDPE and PLA. It is also shown that DESs enable HDPE to be homogeneously mixed with starch reducing the overall cost of the plastic and making it more biodegradable.