Fully Renewable, Effective, and Highly Biodegradable Plasticizer: Di- n-heptyl Succinate

Abstract

The ubiquitous environmental presence of industrial plasticizers such as di(2-ethylhexyl) phthalate (DEHP) and the known health and environmental impact has created a need to develop truly green plasticizers that (i) are nontoxic, (ii) rapidly biodegrade, and (iii) are produced from renewable feedstocks across their whole life cycle including synthesis. For example, linear succinate diesters have been shown to provide similar or better plasticizing properties compared to DEHP, excellent biodegradation kinetics, and no toxicity concerns. However, the feedstocks used to synthesize said succinates were petroleum-based. In this case study, di-n-heptyl succinate (DHPS) was fully synthesized from the commercially available, renewable feedstocks succinic acid and n-heptanol. In addition, the synthetic route was improved upon by switching to a solventless process utilizing only nitrogen gas to remove water from the esterification reaction, thereby eliminating the need for a workup. The plasticizer effectiveness of DHPS in poly(vinyl chloride) (PVC) demonstrated similar or better plasticizing properties (glass transition temperature and tensile and rheological properties) than DEHP, and comparably to previously tested succinate diesters in terms of plasticizer effectiveness. Biodegradation experiments with the common soil bacterium Rhodococcus rhodochrous revealed rapid biodegradation kinetics in the time frame of 2 weeks, without the buildup of stable metabolites. Taken together, the results indicate that DHPS is a fully renewably sourced, biodegradable, low-risk, effective, and thus green plasticizer for PVC.