Effect of processing conditions on mechanical properties of poly (D, L-lactide) and MDI chain-extending poly (D, L-lactide) /hydroxyapatite composite

Background: Polylactic acid (PLA) is very degradable in the processing conditions and at the processing temperature so its mechanical properties reduce greatly. Objective: To investigate the effects of processing conditions on the mechanical properties of poly (D, L-lactide) (PDLLA), methylenediphenyl diisocyanate (MDI) chain-extending PDLLA (PDLLA/MDI) and MDI chain-extending PDLLA/hydroxyapatite (HA) composites (PDLLA/HA/MDI). Design: A grouping and control study was designed. Setting and Methods: The experiment was carried out in the College of Materials, South China University of Technology. Using methylenediphenyl diisocyanate (MDI) as chain-extender to prepare MDI chain extending PDL-LA (PDLLA/MDI) and MDI chain-extending PDLLA/HA composites (PDLLA/HA/MDI composites) and utilizing self-designed moulding and extruding equipment to process these biodegradable materials. Main Outcome Measure: Effects of processing condictions on PDLLA, PDLLA/MDI and PDLLA/HA/MDI. Results: At the optimal processing conditions of molding temperature 165 °C, extruding temperature 100 °C and mould chamber length 10 mm, bending strength of PDLLA and PDLLA/HA composites is 35.1 MPa and 31.2 MPa, respectively and their bending modulus is 2 413.6 MPa and 1 735.0 MPa, respectively. At the optimal processing conditions of molding temperature 100 °C, extruding temperature 100 °C and mould chamber length 10 mm, bending strength of PDLLA/MD and PDLLA/HA/MDI composites is 51.3 MPa and 55.4 MPa, respectively and their bending modulus is 1 830.9 MPa and 2068.5 MPa, respectively. Conclusion: The processing conditions affected obviously mechanical properties of PDLLA, PDLLA/MDI and PDLLA/HA/MDI composites and MDI chain-extending enhanced significantly mechanical properties of these materials.