Synthesis and evaluation of novel sustainable aliphatic plasticizers into different polymer systems.

Plasticizers are essential to the polymer industry to (i) facilitate the processing and (ii) modify the mechanical and thermal performance of polymer materials. The need to reduce the environmental impact and toxicity of plasticizers means that viable alternatives to phthalates must be found. This has become a major current challenge. Bacterial polymers such as polyhydroxyalkanoates (PHA) like poly(hydroxy-octanoate) (PHO) appear to be promising precursors for meeting these expectations. Bacterially synthesized from sustainable resources such as plastic waste or biomass, PHOs possess ester functions and alkyl side chains that are relevant for plasticizing some rigid polymers such as PVC or thermoplastic polyurethanes (TPU). In this preliminary and conceptual study, oligomers of PHO with terminal hydroxyl functions (PHO-diol) were successfully synthesized by transesterification from PHO. The addition of alkyl chain ends was achieved by reaction with hexyl mono-isocyanate, to produce PHO-hexyl. These 2 compounds were tested for their plasticizing properties. Rigid PVC and TPU matrices were selected to evaluate the different additives (PHO-diol, PHO-hexyl and two conventional reference phthalates) at different concentrations. Polymer glass transition temperatures (Tg) were significantly reduced with all plasticizers. Plasticizing effects similar to those of phthalates were obtained with PHO-hexyl, both on the thermal and mechanical properties, compared to PHO-diol wich shows less plasticizing effects. The processability of a very rigid and brittle bio-based TPU was greatly improved with the addition of just 15 % of PHO-hexyl as plasticizer into the TPU matrix, as well as with the commercial phthalates. It is opening up a wide range of applications for this previously hardly exploitable sustainable betulin-based TPU. PHO-hexyl is thus emerging as a very promising example of a sustainable plasticizer and a potentially credible alternative to phthalates. This new plasticizer makes it possible to obtain high-performance materials that are more respectful of the environment.