Designing green plasticizers: influence of molecular geometry on biodegradation and plasticization properties

The plasticizer di (2-ethylhexyl) phthalate (DEHP) and its metabolites are considered ubiquitous contaminants, which have a range of implications on the environment and human health. This work considered several alternative compounds with structural features similar to DEHP. This added to the understanding of why DEHP is so poorly biodegraded once it enters the environment. These alternative compounds were based on 2-ethylhexyl diesters of maleic acid (cis-isomer), fumaric acid (trans-isomer) and succinic acid (saturated analogue). The rates of biodegradation by the common soil bacterium Rhodococcus rhodocrous were shown to be dependent on the structure of the central unit derived from the diacid used to make the ester. The diacid components of DEHP and the maleate both had a cis orientation and they were the two that were slow to biodegrade. Plasticizing properties were also compared and, because the ester of the saturated succinic acid was degraded quickly and also had good plasticizing properties, it was concluded that the succinic esters of straight chain alcohols would make the best green plasticizers. The maleate ester had excellent plasticizing properties but this is mitigated by a significant resistance to biodegradation.