Abstract: A double structure bag includes an inner bag including a second food storage opening, wherein the inner bag includes a first and second bent portions located in an area adjacent to the second food storage opening, and wherein the first bent portion includes first openings at both side, and the second bent portion includes second openings at both side; an outer bag in which the inner bag is stored, having a first food storage opening, wherein the outer bag includes a tunnel, which having third openings at its both ends; and two elongated zipping members, each of which placed in one of the first and second bent portions, respectively, wherein both ends of each elongated zipping member are placed outside the outer bag by passing through the tunnel and by coming out from the third openings, respectively, whereby the second food storage opening is closed by pulling the elongated zipping members from the side to side, and wherein the elongated zipping members are tied together after area where the first food storag

Abstract: A process for producing polylactic acid includes the steps of polycondensing lactic acid to a lactic acid prepolymer having a weight-average molecular weight of 10,000-50,000 in a batch-type polymerization reactor, and polycondensing the lactic acid prepolymer to lactic acid polymer having a weight-average molecular weight of at least 100,000 by means of a screw-type extruder.