自己強化ポリ乳酸スクリューの強度に及ぼす延伸前成形手法の影響

抄録

Poly(lactic acid) (PLA) has attracted much attention as typical bioabsorbable materials. In this study, the effect of higher order structure before drawing on mechanical properties of PLA screws were investigated. PLA screws were prepared through a series of routes including compression-molding or casting, extrusion and forging. Crystallinity and orientation function as the higher order structures, and shear strength as mechanical properties were measured. As a result, the shear strengths of the screws of casted billets were higher than that of the screws of compression-molded billets. The orientation function of casted billet was higher than that of the compression-molded billets for low extrusion ratio. The orientation function of screws from extruded billets showed opposite tendency to that of billets before extruding. On the other hand, crystallinity of screw was constant irrespective of the extrusion ratio and molding method. Those results suggested that shear strength of screw mainly depend on molecular orientation. Crystallinity of rod which molded by casting and extruded in extrusion ratio 1 was about 37 % while that of compression-molded rod was about 20 %. And, orientation function of casted billet decreased from 0.5 to 0.35 by extrusion in extrusion ratio 1.3 while that of compression-molded billet increased from 0.1 to 0.6. These results might be due to a difference in crystal size induced during cooling in the molding of billets.