Fractography evolution in accelerated aging of UHMWPE after gamma irradiation in air

• Published in: Biomaterials Vol. 25; no. 1; pp. 9 - 21
• Main Authors: Medel, F., Gómez-Barrena, E., Garcı́a-Alvarez, F., Rı́os, R., Gracia-Villa, L., Puértolas, J.A.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 2004
• Subjects: Accelerated aging; Air; Biocompatible Materials - chemistry; Biocompatible Materials - radiation effects; Degradation; Dose-Response Relationship, Radiation; Elasticity; Fractography; Fracture mechanisms; Gamma Rays; Hot Temperature; Materials Testing - methods; Molecular Conformation; Polyethylene; Polyethylenes - analysis; Polyethylenes - chemistry; Polyethylenes - radiation effects; Sterilization; Surface Properties; Tensile Strength; Time Factors; UHMWPE; White band; Degradation; Fracture mechanisms; Polyethylene; UHMWPE; Accelerated aging; White band; Fractography
• ISSN: 0142-9612; 1878-5905
• DOI: 10.1016/S0142-9612(03)00464-2

We studied the fracture surface evolution of ultra high molecular weight polyethylene (UHMWPE) specimens, manufactured from GUR 1050 compression moulded sheets, after gamma sterilisation in air followed by different aging times after thermal treatment at 120°C. Degradation profiles were obtained by FTIR and DSC measurements after 0, 7, 14, 24 and 36 h aging. We observed by SEM the morphology patterns at these aging times, in surface fractographies after uniaxial tensile test of standardised samples. The results pointed out clear differences between short and long aging times. At shorter times, 7 h, the behaviour was similar to non-degraded UHMWPE, exhibiting ductile behaviour. At longer times, 24–36 h, this thermal protocol provided a highly degraded zone in the subsurface, similar to the white band found after gamma irradiation in air followed by natural aging, although closer to the surface, at 150–200 μm. The microstructure of this oxidation zone, similarly found in gamma irradiated samples shelf-aged for 6–7 years, although with different distribution of microvoids, was formed by fibrils, associated with embrittlement of the oxidised UHMWPE. In addition, the evolution of the oxidation index, the enthalpy content, the mechanical parameters, and the depth of the oxidation front deduced from the fractographies versus aging time showed that a changing behaviour in the degradation rate appeared at intermediate aging times.