Preparation and evaluation of acetylated mixture of citrate ester plasticizers for poly(vinyl chloride)

Tributyl citrate (TBC) and acetyl tributyl citrate (ATBC), as phthalate alternative plasticizers, show limited application due to low migration resistance, high volatilization rate and intense respiratory irritation. Meanwhile, the developed pure citrates, such as butyryl trihexyl citrate (BTHC) due to its high cost, and triisooctyl citrate (TOC) and acetyl triisooctyl citrate (ATOC) due to their low absorption property, are not attractive plasticizers to manufacture phthalate-free poly(vinyl chloride)s (PVCs). In this study, we developed an effective method to synthesize acetylated mixture of citrate esters (ATMC) composed of acetyl (dibutyl-monoisooctyl) citrate, acetyl (monobutyl-diisooctyl) citrate, and a small amount of ATBC and ATOC, as an alternative for phthalate plasticizers. ATMC combines the advantages of ATBC in being easily absorbed and ATOC in having good migration resistance. Characterization results showed that the dynamic viscosity, absorption property and plasticizing efficiency of ATMC11 (1:1 molar ratio of n-butyl alcohol to 2-ethylhexanol) were similar to those of di(2-ethylhexyl) phthalate (DEHP). The thermal volatilization and migration of ATMC11 were less than those of ATBC, and were comparable to those of DEHP, which could be attributed to the improved compatibility with PVC. The performance of ATMC11 was improved compared with that of the mixture of ATBC and ATOC. As an environmental bio-based plasticizer, ATMC11 was demonstrated as a biologically safe plasticizer by biological safety evaluation tests. Therefore, ATMC11 with excellent comprehensive performances and low cost can be candidate as an ideal phthalate alternative for soft PVC formulations.