Enhancement of the mechanical properties of polylactides by solid-state extrusion. II. Poly(L-lactide), poly(L/D-lactide), and poly(L/DL-lactide)

Abstract

Polylactides with various degrees of chain regularity-crystalline poly(L-lactide); amorphous poly(L/D-lactide), and amorphous poly(L/DL-lactide)-were processed into high-strength, high-modulus resorable rods using solid-state extrusion through a conical die. The rods with a highly fibrillated structure had flexural strengths at a yield of up to 215 MPa and flexural modulus of up to 13.7 GPa. The initially amorphous poly(L/DL-lactide) developed approximately 25% of crystallinity after solid-state extrusion. Poly(L/D-lactide) remained amorphous independently of the treatment procedure applied. The shear strengths, flexural strengths, and flexural moduli of the solid-state extruded rods increased with increasing draw ratio. For the semicrystalline materials, solid-state extrusion enhanced the crystallinity. The achievable draw ratios during solid-state extrusion, and in consequence the final mechanical properties, were lower for poly(L/D-lactide) and poly(L/DL-lactide) than for poly(L-lactide).

Initial mechanical properties of phosphate-glass fibre-reinforced rods for use as resorbable intramedullary nails

“…In this study, the strength of the PLA rods increased to *125 MPa, whilst the modulus remained at *3.8 GPa. The increase seen for flexural strength was likely due to chain orientation as a result of the forging process [26][27][28]. The SEM micrographs in Fig 6 d and e show some evidence for chain orientation from the cross section of the PLA rod in comparison with the plate.…”

“…Thus, reinforcement is required to produce a device with mechanical properties matching that of cortical bone [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] GPa for Young's modulus and 90-140 MPa for flexural strength] [14,15]. Various methods have been explored to enhance the mechanical properties of polymers, such as self-reinforcement [16][17][18][19][20], particulate reinforcement [Hydroxyapatite (HA), Calcium phosphate (CaP)] [21][22][23][24][25] and drawing [26][27][28]. Another recent approach for reinforcing biodegradable polymer matrices has been to use resorbable phosphate based glass fibres (PGF) [14,15,[29][30][31][32].…”

Improvement of Flexural Strengths of Poly(L-lactic acid) by Solid-State Extrusion

“…This is a remarkably small decrease compared with the other studies [5,6] in which billets used for solid-state extrusion were prepared by the melt extrusion process. Ferguson et al [5] improved the mechanical properties of various polylactides by the solid-state extrusion technique up to the maximum flexural strength and modulus of 215 MPa and 13.7 GPa, respectively. In their study, M -v of PLLA decreased from 415 000 for the raw material to 200 000 for the melt-extruded sample.…”

“…[2,5,6] Examples of equatorial WAXS diffractograms of the billet and solid-state extruded rods are shown in Figure 1. WAXS diffraction pattern of the billet having a crystallinity of 30% shows small diffraction peak around 16 8, while those of solid-state extruded rods exhibit high crystallinity with orthorhombic crystal structure.…”

“…[1] Various methods have been utilized in order to improve the mechanical properties of biodegradable polymeric materials such as orientrusion, [2] self-reinforcing method, [3] and solid-state extrusion technique. [4 -6] These methods mostly involve the transformation of spherulitic to fibrillar structures [2,5,6] leading to a high degree of chain orientation. In addition, these methods were designed to fabricate materials having not only enhanced mechanical properties but also large cross-sectional areas Full Paper: Solid-state extrusion technique was employed for the improvement of flexural strengths of poly(l-lactic acid) (PLLA) that is currently used as materials for various internal fixation devices.…”