Quantification of residual monomer in polylactide by gas chromatographic internal standard method

An analytical method has been developed to quantitatively determine the residual lactide monomer in polylactide (PLA) using an internal standard method of gas chromatography (GC). The experimental results showed that diphenyl ether (DPE) was an appropriate internal standard for quantitative analysis of residual lactide in PLA. PLA and DPE were dissolved in dichloromethane and precipitated in hexane . At the same time, the residual lactide in PLA and DPE as an internal standard were extracted to hexane from the polymer solution . The resulting solution could be directly injected into a GC system. Therefore, the residual lactide was determined quantitatively using an internal standard method of GC. This method is practical for measuring the residual lactide content in PLA. When the lactide content is 5.0%, the relative standard deviation ( RSD ) of the measurements is 1.7%, while RSD is 6.9% at the low level of 0.4%, which indicates that the method is sufficiently precise.