Micro vs nano: influence of filler size on the rheological and mechanical properties of highly-filled PLA/HAp and PCL/HAp composites
Bartłomiej Kryszak, Aleksandra Ujčić, Veronika Gajdošová, Miroslav Šlouf, Konrad Szustakiewicz
Abstract
ABSTRACT This work aims to elucidate the influence of filler particle size on the rheological behaviour, as well as the micro- and macromechanical properties, of polymer-ceramic composites. For this investigation, two widely used biodegradable polymers, polylactide and polycaprolactone, were selected as the polymer matrices. Hydroxyapatite powders with average particle sizes of 10 μm and 60 nm were used as fillers. A series of composites were prepared using twin-screw extrusion and injection moulding techniques, with micro- and nanoparticle hydroxyapatite concentrations of 20 wt% and 40 wt% for polylactide and 20 wt% for polycaprolactone. The produced materials were subjected to comprehensive analysis, including morphological evaluation (scanning electron microscopy), thermal characterisation (differential scanning calorimetry, thermogravimetric analysis), rheological testing and mechanical property assessment at both micro (micro indentation) and macro (tensile, impact strength) scales. The research was guided by three main objectives: to carry out a comparative analysis of composites with different polymer matrices, to evaluate the effect of the filler on the properties of the given polymer matrix and, finally, to investigate the effect of the filler particle size on the overall performance of the composites. In general, polylactide-based materials exhibited brittleness and strong polymer-filler interactions, whereas polycaprolactone-based materials were ductile and showed weak polymer-filler interactions. Overall, the incorporation of hydroxyapatite resulted in a proportional increase in Young’s modulus, with values increasing from 2.4 to 4.3 MPa for polylactide and from 0.25 to 0.59 MPa for polycaprolactone. The use of nanometric filler resulted in more desirable mechanical properties and improved polymer melt stability compared to composites containing micrometric filler. The research makes a valuable contribution to the design and production of composite materials for biomedical applications.