A series of ten ionic liquids (ILs) was synthesised from the renewable resource mandelic acid. Low antimicrobial activity was demonstrated towards thirteen bacterial and twelve fungi strains, with a general trend of increasing bacterial toxicity in the order methyl ester < ethyl ester < butyl ester/amide. IL biodegradability was evaluated using the Closed Bottle Test (OECD 301D) and increased in the order of increasing alkyl chain length for the ester ILs (methyl < ethyl < butyl). Despite none of the ILs presenting as readily biodegradable, a series of biodegradation metabolites has been proposed. A series of twelve 1-methylimidazolium ester ILs was synthesised with bromide, bistriflimide (NTf2) and octyl sulfate (OctSO4) anions. Eight ILs suitable for plasticisation with poly(L-lactic acid) (PLLA) were melt extruded with PLLA at 10, 20 and 30 wt% IL. The tensile strength, Young’s modulus and elongation at break of the PLLA/IL films were measured. All four NTf2 ILs successfully plasticised PLLA (confirmed by depression of the Tg in DSC). Plasticisation was most successful at 20 wt% NTf2 IL, with the OctSO4 ILs demonstrating poor compatibility with PLLA. The effects of plasticisation were retained after 100 days for the NTf2 PLLA/IL films, with only minimal ageing observed. The dielectric properties of seven mandelic acid ILs and three 1-methylimidazolium ester ILs were measured using microwave dielectric spectroscopy. An insight into the polarity of the ILs was gained by using a cavity perturbation technique to obtain the IL dielectric constant, dielectric loss factor and loss tangent. The effect of the IL physical state on the dielectric properties was also investigated by taking measurements for three ILs above their melting points. These preliminary results allow the IL structures to be related to their dielectric properties, enabling the design of ILs with increased polarity.