Mechanical and tribological behaviour of PEEK reinforced with Sn-Zn-Bi alloy, short carbon fibres and graphene nanoplatelets

Abstract

A poliéteretercetona (PEEK) demonstrou um grande potencial como material de suporte contra componentes metálicos e cerâmicos em implantes ortopédicos. A vantagem do PEEK sobre os polímeros convencionais reside no facto de ter uma excelente estabilidade térmica, ser quimicamente resistente e possuir propriedades mecânicas e tribológicas superiores. Além disso, vários compósitos de PEEK foram investigados, que demonstraram melhores propriedades mecânicas e tribológicas do que os rolamentos de polímeros classicamente utilizados. Isto é importante porque o afrouxamento asséptico é a principal causa de falha do implante e ocorre devido ao desgaste dos componentes do implante. O objectivo deste estudo foi avaliar o efeito do reforço de PEEK com uma liga de brasagem suave composta por Sn-Zn-Bi e um reforço contendo SCF e GNP no seu desempenho tribológico. Quatro misturas compostas compostas de 67wt.% de PEEK e 33wt.% de reforços foram feitas por ligas mecânicas, onde o conteúdo total de GNP variou entre; 0 , 0,99, 2,31 e 4,95wt.%. e foram comparadas com PEEK puro e PEEK obtido comercialmente. Os testes mecânicos e tribológicos mostraram que a incorporação destes reforços na matriz de PEEK resultou num melhor desempenho mecânico e tribológico em comparação com o PEEK não preenchido. Além disso, a incorporação de diferentes conteúdos de GNP e particularmente 0,99wt.% resultou numa redução do desgaste de PEEK em três vezes. Concluiu-se que a redução do atrito e do desgaste dependia da concentração do PNB adicionado à matriz polimérica.

Polyetheretherketone (PEEK) has shown great potential as a bearing material against metallic and ceramic components in orthopaedic implants. The advantage of PEEK over conventional polymers such as polyethylene (PE) and ultra-high molecular weight polyethylene (UHMWPE) lies in the fact that it has excellent thermal stability, is chemically resistant in corrosive environments, and possesses superior mechanical properties. Furthermore, PEEK has presented advantages over metallic implants due to its lower stiffness (~3-4 GPa), which could help mitigate bone resorption. However, studies have demonstrated that pure PEEK has a low wear resistance when compared to these polymers, which is an undesirable property in joint implants. As a result, PEEK composites have been explored, which have demonstrated significantly improved mechanical and tribological properties, closer in range and comparable to conventionally used polymers. The aim of this study was to evaluate the effect of reinforcing PEEK with short carbon fibres (SCF) and graphene nanoplatelets (GNP) embedded in a soft Sn-based brazing alloy. Four composite mixtures composed of 67wt.% of PEEK and 33wt.% of varying concentrations of the reinforcements were made by mechanical alloying (MA). The reinforcement consisted of a fixed content of 89Sn-8Zn-3Bi wt.% and 3.3wt.% SCF whiskers with GNP being varied between; 0, 0.99, 2.31, and 4.95wt.%. The mechanical and tribological properties of these composites were compared with those of pure PEEK powder and commercially obtained PEEK. Mechanical and tribological tests showed that the incorporation of these reinforcements in the PEEK matrix resulted in enhanced mechanical and tribological performance compared to unfilled PEEK. Furthermore, the incorporation of different contents of GNP, particularly 0.99wt.% resulted in a reduction of wear of PEEK by three times. It was concluded that the reduction of friction and wear was dependent upon the concentration of GNP added to the polymer matrix.