Composites between alumina and an ester-ether-ester bioresorbable copolymer

Composites between alumina and the bioresorbable poly(epsilon-caprolactone-oxyethylene-epsilon-caprolactone) block copolymer were obtained by reacting epsilon-caprolactone with preformed poly(ethylene glycol), in the presence of ceramic alumina powder, at 185 °C under vacuum. The mechanical properties, tested by compression and flexural strengths and Young’s modulus, show that the copolymer interacts poorly with the alumina grains. Both Scanning Electron and Atomic Force Microscopy show a scarce wettability between alumina and copolymer, as well as the aggregation of alumina micro-particles into clusters of big size. Both mechanical and morphological tests seem to indicate a stronger interaction between the alumina micro-particles than between the alumina surface and the reaction mixture during the polymerization, as well as a “compacting effect” by alumina on the forming copolymer. The FT-IR spectra of the composites show both copolymer and alumina absorption bands. The FT-IR analysis on the fractions of an extraction with chloroform indicates the presence of traces of poly(epsilon-caprolactone), stably bonded to alumina. The polymerization of epsilon-caprolactone with alumina alone in the same conditions gives poly(epsilon-caprolactone), mainly free and in minor part bonded to the alumina surface. Two polymerization mechanisms, simultaneously occurring, are proposed. The most relevant result of this work is the lack of chemical inertness of alumina towards epsilon-caprolactone, which leads to reconsider also the use of alumina as a biochemically inert material.