Improvement on the Mechanical Performance and Resistance Towards Hydrolysis of Poly(glycolic acid) via Solid-state Drawing

【摘要】 Poly（glycolic acid） is a biocompatible as well as biocomposable polymer with superior mechanical and barrier properties and,consequently, has found important applications in both medical and packaging fields. However, the high hydrolysis rate in a high humidity environment restricts its application. In this work, a solid-state drawing process after melt extrusion is applied in order to produce fibrous PGA with enhanced mechanical properties and a much better resistance towards hydrolysis. The crystal structure of PGA gradually transformed from spherulites into oriented fibrous crystals in the stretching direction upon solid-state drawing. Meanwhile, both the length of microfibril and the size of lamellae increased initially with the drawing ratio（DR）, while the chain-folded lamellae transformed into extended-chain fibrils at high（er）DR. The oriented structures lead to an overall improvement of the mechanical properties of PGA, e.g., the tensile strength increased from 62.0±1.4MPa to 910±54 MPa and the elongation at break increased from around 7% to 50%. Meanwhile, the heat capacity of totally mobile amorphous PGA(ΔC_p⁰=0.64 J·g^-1·℃^-1) was reported for the first time, which was used to analyze the content of mobile amorphous fraction(X_MAF) and rigid amorphous fraction（XRAF）. Both the oriented chain-folded lamellae crystals and the tightly arranged RAF are beneficial to prevent water molecules from penetrating the matrix, thus improving the resistance towards hydrolysis. As a consequence, the fibrous PGA with a DR of 5showed a tensile strength retention rate of 17.3% higher in comparison with the undrawn sample after 7-days accelerated hydrolysis. Therefore,this work provides a feasible method to improve the mechanical and resistance towards hydrolysis performance of PGA, which may broaden its application and prolong the shelf-life of PGA products.更多还原

【Abstract】 Poly（glycolic acid） is a biocompatible as well as biocomposable polymer with superior mechanical and barrier properties and,consequently, has found important applications in both medical and packaging fields. However, the high hydrolysis rate in a high humidity environment restricts its application. In this work, a solid-state drawing process after melt extrusion is applied in order to produce fibrous PGA with enhanced mechanical properties and a much better resistance towards hydrolysis. The crystal structure of PGA gradually transformed from spherulites into oriented fibrous crystals in the stretching direction upon solid-state drawing. Meanwhile, both the length of microfibril and the size of lamellae increased initially with the drawing ratio（DR）, while the chain-folded lamellae transformed into extended-chain fibrils at high（er）DR. The oriented structures lead to an overall improvement of the mechanical properties of PGA, e.g., the tensile strength increased from 62.0±1.4MPa to 910±54 MPa and the elongation at break increased from around 7% to 50%. Meanwhile, the heat capacity of totally mobile amorphous PGA(ΔC_p⁰=0.64 J·g^-1·℃^-1) was reported for the first time, which was used to analyze the content of mobile amorphous fraction(X_MAF) and rigid amorphous fraction（XRAF）. Both the oriented chain-folded lamellae crystals and the tightly arranged RAF are beneficial to prevent water molecules from penetrating the matrix, thus improving the resistance towards hydrolysis. As a consequence, the fibrous PGA with a DR of 5showed a tensile strength retention rate of 17.3% higher in comparison with the undrawn sample after 7-days accelerated hydrolysis. Therefore,this work provides a feasible method to improve the mechanical and resistance towards hydrolysis performance of PGA, which may broaden its application and prolong the shelf-life of PGA products.更多还原