Crystalline polyglycolic acid, polyglycolic acid composition and production process thereof

A process for producing crystalline polyglycolic acid, wherein

• (a) a difference (Tm−Tc2) between the melting point Tm defined as a maximum point of an endothermic peak attributable to melting of a crystal detected in the course of heating at a heating rate of 10° C./min by means of a differential scanning colorimeter and the crystallization temperature Tc2 defined as a maximum point of an exothermic peak attributable to crystallization detected in the course of cooling from a molten state at a cooling rate of 10° C./min is not lower than 35° C., and
• (b) a difference (Tc1−Tg) between the crystallization temperature Tc1 defined as a maximum point of an exothermic peak attributable to crystallization detected in the course of heating an amorphous sheet at a heating rate of 10° C./min by means of a differential scanning calorimeter and the glass transition temperature Tg defined as a temperature at a second-order transition point on a calorimetric curve detected in said course is not lower than 40° C.,
• the process comprising applying heat history to crystalline polyglycolic acid at a temperature of not lower than (the melting point Tm of the crystalline polyglycolic acid+38° C.).

A polyglycolic acid composition comprising crystalline polyglycolic acid and a heat stabilizer, wherein the crystalline polyglycolic acid is crystalline polyglycolic acid, wherein

• (a) a difference (Tm−Tc2) between the melting point Tm defined as a maximum point of an endothermic peak attributable to melting of a crystal detected in the course of heating at a heating rate of 10° C./min by means of a differential scanning colorimeter and the crystallization temperature Tc2 defined as a maximum point of an exothermic peak attributable to crystallization detected in the course of cooling from a molten state at a cooling rate of 10° C./min is not lower than 35° C., and
• (b) a difference (Tc1−Tg) between the crystallization temperature Tc1 defined as a maximum point of an exothermic peak attributable to crystallization detected in the course of heating an amorphous sheet at a heating rate of 10° C./min by means of a differential scanning colorimeter and the glass transition temperature Tg defined as a temperature at a second-order transition point on a calorimetric curve detected in said course is not lower than 40° C., and wherein
• (c) a difference (T2−T1) between the temperature T2 at 3%-weight loss on heating of the polyglycolic acid composition and the temperature T1 at 3%-weight loss on heating of the polyglycolic acid is not lower than 5° C.

A polyglycolic acid composition comprising crystalline polyglycolic acid and a heat stabilizer, wherein a difference (T2−T1) between the temperature T2 at 3%-weight loss on heating of the polyglycolic acid composition and the temperature T1 at 3%-weight loss on heating of the crystalline polyglycolic acid is not lower than 5° C.

A process for producing a polyglycolic acid composition which comprises crystalline polyglycolic acid, wherein

• (i) a difference (Tm−Tc2) between the melting point Tm defined as a maximum point of an endothermic peak attributable to melting of a crystal detected in the course of heating at a heating rate of 10° C./min by means of a differential scanning colorimeter and the crystallization temperature Tc2 defined as a maximum point of an exothermic peak attributable to crystallization detected in the course of cooling from a molten state at a cooling rate of 10° C./min is not lower than 35° C., and wherein
• (ii) a difference (T2−T1) between the temperature T2 at 3%-weight loss on heating of the polyglycolic acid composition and the temperature T1 at 3%-weight loss on heating of the polyglycolic acid is not lower than 5° C.,
• the process comprising applying heat history to a polyglycolic acid composition containing crystalline polyglycolic acid and a heat stabilizer at a temperature of not lower than (the melting point Tm of the crystalline polyglycolic acid+38° C.).

A process for controlling the crystallinity of crystalline polyglycolic acid, comprising applying heat history to the crystalline polyglycolic acid for 1 to 100 minutes within a temperature range higher than the melting point Tm thereof, but not higher than (Tm+100° C.).