Durability of crosslinked polyethylene in human-contact applications: Stabilisation challenges

Highly crosslinked polyethylene polymers (XLPE) are used in many human-contact applications that require assurance on aspects of durability, longevity and safety. The work described in this paper focuses on applications in the medical field and in the construction industry. These are related to the use of XL-UHMWPE for articulating surfaces in orthopaedic implants particularly in total hip and knee replacements, and the use of XL-HDPE for potable water pipes. Safety, performance and durability of the end-use products are mandatory for their approval and use in such applications. However, it has long been recognised that the stabilisation of such highly crosslinked polymers by commercial antioxidants (AO) faces many challenges including the possible interference of the AOs with the crosslinking step, as well as the issues of safety associated with AO leaching and migration of into the human-environment. Here, the effect of AOs on the long-term oxidative stability of the end-use polymer artefacts in these applications is examined and compared with that obtained with some new alternative stabilisation systems. Results show that, in both applications, it was possible to achieve superior levels of retention of the AO in the polymer and long-term thermal stabilising (LTTS) performance (ageing) with minimum interference with the crosslinking process, thereby addressing issues of stabilisation, health and safety of polymers used in direct contact with the human environment

Photo-stabilization of biopolymers-based nanocomposites with UV-modified layered silicates

Eco-friendly in-situ stabilised biopolymer nanocomposites based on polyamide 11 (PA11) and polylactic acid (PLA) were prepared by melt mixing in the presence of a modified organo-montmorillonite clay containing a chemically-bound hindered amine UV-stabilising function, [(UV)OM-MMt]. Characterisation of the newly synthesised organo-modifier containing the reactive hindered amine (HAS) UV-stabilising function [(UV)OM] has confirmed a successful synthesis. The (UV)OM was then introduced into NaMMt through ion exchange reaction to prepare the UV stabiliser-bound organo-modified-MMt, [(UV)OM-MMt]. The in-situ stabilised PA11- and PLA- nanocomposites (PA11-(UV)OM-MMt and PLA-(UV)OM-MMt) were characterised and their photoxidative stabilities (under accelerated weathering conditions) were compared with their nanocomposite analogues containing either the organo-modified MMt (OM-MMt) alone (i.e. without UV-stabiliser) or the OM-MMT containing conventionally added commercial hindered amine HAS-UV-stabiliser (Cyasorb® UV-3853). It was found that both of the newly prepared in-situ stabilised PA11- and PLA- nanocomposites gave good clay dispersion and have demonstrated a much higher, especially in PLA-nanocomposites, photo-oxidative stability compared to the corresponding nanocomposites but in the absence, or the presence, of the conventionally added HAS-UV-stabiliser

Degradation of Polymer Clay-Nanocomposites: a Novel Approach to Enhancing Service Life Performance

A new strategy was adopted to achieve effewctive stabilisation of clay-polyamide nanocomposite

What happens to the vitamin E in a vitamin-stabilised HXLPE?

Today many of the second-generation highly cross-linked polyethylenes (HXLPE) use vitamin E (chemical name: α-tocopherol) as antioxidant to further enhance the longevity of the implant. There are two main technologies how to add the vitamin E to the polyethylene: by infusion or by blending. Depending on the manufacturing and sterilisation process and the chosen level of cross-linking, the vitamin E will thus be subjected to different amounts of high energy irradiation