Processing and properties of PLA-HA nanocomposites: the effect of particle morphology and dispersants

The load bearing capacity of biodegradable polymeric medical devices remains limited; an improvement in mechanical properties is desirable to widen the range of applications. Incorporation of nanoparticles is explored to increase the mechanical properties of the base matrix whilst maintaining desirable polymeric processing routes. Various nanomaterials have been investigated for polylactic acid (PLA) reinforcement for orthopaedic applications; hydroxyapatite (HA), the main inorganic constituent of bone, is one of the most promising bioresorbable nanofillers. However, uncoated nanoparticles agglomerate easily during compounding; tailored coatings can offer new opportunities to improve dispersion. This study investigates the effectiveness of novel tailored dispersants on particle dispersion, rheological properties and on macroscopic mechanical properties, when coated onto HA nanoparticles (HANP). The dispersants consist of short-chain PLA with isosorbide head groups (isPLA), or neat dodecenylsuccinic anhydride (DDSA). HANP were synthesised via a hydrothermal counter-flow process with dispersant coatings added in-situ. Neat DDSA was purchased whilst isPLA was polymerised via a standard ring-opening route involving lactide, a tin catalyst and isosorbide initiator. Nanocomposites were compounded in a twin-screw recirculating extruder and assessed by TEM, rheology and mechanical measurements.