Method for analyzing content of D-lactic repeating units in polylactic acid

A method for analyzing the content of D-lactic acid repeating units (D content) in a polylactic acid, comprising the steps of:

• 1) Obtaining quantitative data of tacticity from an NMR spectrum of a polylactic acid;
• 2) Obtaining the arrangement of a hypothetical polylactic acid with three parameters:
• a L-lactide ratio parameter, a meso-lactide ratio parameter and a racemization parameter;
• 3) Obtaining tacticity data of the hypothetical polylactic acid of step 2;
• 4) Obtaining a standard deviation of the quantitative data of tacticity of step 1 and the quantitative data of tacticity of the hypothetical polylactic acid of step 3;
• 5) Repeating steps 2 to 4 to obtain the L-lactide ratio parameter, meso-lactide ratio parameter and racemization parameter in which the standard deviation of step 3-4 has been minimized;
• and
• 6) Obtaining the D content in the polylactic acid from the L-lactide ratio parameter, meso-lactide ratio parameter and racemization parameter obtained in step 5.