Improvement of thermal stability and mechanical properties of medical polyester composites by plasma surface modification of the bioactive glass particles

Abstract

Poly(l-lactide) (PLLA), poly(ε-caprolactone) (PCL) and poly(l-lactide/ε-caprolactone) (PLCL) are medical (co)polyesters that are conventionally manufactured by thermoplastic processing techniques, such as injection molding or extrusion. However, the addition of bioglass particles causes a degradation reaction of the matrix at high temperatures and could limit the fabrication of composite systems by the above mentioned processes. In this work, a surface modification of bioactive glass particles by plasma polymerization of acrlylic acid is proposed as a strategy for the improvement of thermal stability of bioglass filled composite systems. The developed poly(acrylic acid) layer on the surface of bioglass particles, hinders the degradation reaction between the Si–O− groups present in the surface of the particles and the CO groups of the polymer's backbone. As an illustration, the onset degradation temperature (Tonset) of PLLA, PCL and PLCL increased respectively from 185.0, 240.1 and 192.2 for bioglass (BG) filled composites to 240.4, 299.5 and 245.7 °C for their modified bioglass (mBG) filled counterparts. Finally, neat PLLA and composites having 15 vol.% of BG and mBG were melt-compounded and subsequently hot pressed to obtain tensile test samples. Non-modified bioglass filled PLLA film was too brittle and difficult to handle due to the sharp reduction of molecular weight during thermoplastic processing. On the contrary, modified bioglass filled PLLA presented a slight increase in Young's modulus with respect to unfilled PLLA but a decrease in both tensile strength and elongation at break.