Food-safe glycidyl-free chain extenders for polylactides

Abstract

Glycidyl-based chain extenders are broadly used as processing aids to enhance the physical properties of polyesters, but glycidyl-containing compounds have severe toxicity concerns. Reported herein are glycidyl-free chain extenders produced via the grafting of 9-(oxiran-2-yl)nonyl methacrylate (EAT) and 8-(3-octyloxiran-2-yl)octyl methacrylate (EAI) on biodegradable poly(ε-caprolactone) (PCL). EAI and EAT were grafted onto PCL via free radical grafting using melt extrusion to produce PCL-epoxy-grafted PCL-g-EAI and PCL-g-EAT. The obtained PCL-g-EAI and PCL-g-EAT were characterized by ¹H nuclear magnetic resonance (NMR) spectroscopy, intrinsic viscosity measurements, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and size exclusion chromatography (SEC). Using reactive melt extrusion, PCL-g-EAI and PCL-g-EAT were tested as potential chain extenders for poly(lactic acid) (PLA). PCL-g-EAI showed comparable or better mechanical properties than those of the commercial chain extender Joncryl ADR. A cytotoxicity assay has been conducted on PLA samples with the new chain extender and showed the absence of cytotoxicity in all samples. The outcomes reported in this paper offer new opportunities for the development of safer chain extenders.