FOAMABLE RESIN COMPOSITION HAVING BIODEGRADABILITY

PROBLEM TO BE SOLVED: To obtain a resin composition having a very stable melt viscosity by mixing a polylactic acid having a specified L isomer/D isomer ratio with a polyisocyanate compound and a polyhydric alcohol or polybasic carboxylic acid in a specified ratio and reacting the resulting mixture. SOLUTION: A polylactic acid having an L isomer/D isomer ratio of 95/5 to 60/40 or 40/60 to 5/95 is mixed with 0.6-3 wt.%, based on the polylactic acid, polyisocyanate compound having an isocyanato content >=2.0 equivalents/ mol and a polyhydric alcohol selected from among glycerol, erythritol, and pentaerythritol or a polybasic carboxylic acid selected from trimellitic acid and pyromellitic acid and used in such an amount satisfying the relationships. In the relationships, E is the number (equivalents/g) of the terminal carboxyl groups of the polylactic acid; the members of a set of x, n, and M1 and the members of a set of W, N, and Mc are the amounts (wt.%), functionalities (equivalents/mol), and molecular weights (g) of the isocyanate compound and the polyhydric alcohol or the polybasic carboxylic acid, respectively.