Polyacids as bonding agents in hydroxyapatite polyester-ether (Polyactive 30/70) composites.

A previously developed method to improve the interface between hydroxyapatite (HA) and a polyester-ether (Polyactive 70/30) by using polyacrylic acid or poly(ethylene-co-maleic acid) has been applied to HA/Polyactive 30/70 composites noting that polyactive 30/70 contains less polyethylene glycol (PEG) segments and a higher concentration of rigid poly(butylene terephthalate) (PBT) segments. The mobility of the PEG segments is significantly affected by the existence of a high concentration of rigid PBT segments. Our experimental results show that this method is indeed suitable for making HA/Polyactive 30/70 composites. The hydrogen bond/dipole interaction forming ability of the PEG segment is not affected by the existence of relatively large amounts of PBT segments. By using these coupling agents, the mechanical properties of the composite can be significantly improved both in dry and wet states. A fractographical study of the fracture surfaces revealed that the surface modified HA particles maintain better contact at fracture. It also showed that larger HA particles may initiate cracks and that such particles may be responsible for a decrease in the tensile strength of the composites.