US Patent 7223815 Polylactic acid composition containing modifier

A modifier for a polylactic acid comprising a block polymer (C) having a polymer block (A) satisfying relationship (1):7.80≦σ/ρ<8.54wherein σ represents a solubility parameter value of a polymer block; and ρ represents a density value of a polymer block,and a polymer block (B) satisfying relationship (2):8.54≦σ/ρ<9.20wherein σ and ρ have the same meanings as described above,wherein each of the aforementioned polymer block (A) and the aforementioned polymer block (B) is independently a polymer block selected from the group consisting of a polyester block, a polyether block, and a polyhydroxycarboxylic acid block, and said block polymer (C) has a glass transition temperature of 0° C. or lower, can enhance impact resistance, flexibility, and tensile strain, while biodegradability of the polylactic acids and thermal resistance are maintained, and in addition, is free from bleed-out from the moldings formed from a polylactic acid composition.