EFFECT OF HYDROXYAPATITE FILLER SIZE ON HIGH STRESS FATIGUE LIFE OF SELF-REINFORCED POLYLACTIC ACID COMPOSITES

Zaleha Mustafa; Kathleen Elizabeth Tanner; Siti Hajar Sheikh Md Fadzullah

Zaleha Mustafa Faculty of Industrial and Manufacturing Technology and Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.
Kathleen Elizabeth Tanner School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
Siti Hajar Sheikh Md Fadzullah Faculty of Mechanical Technology and Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.

Keywords: Fatigue testing, polylactic acid, hydroxyapatite, filler size, Weibull distribution, bone fixation

Abstract

In this study, the fatigue behaviour of self-reinforced polylactic acid (sr-PLA) biomaterials at high stress levels was investigated, and the influence of different filler sizes (2.99 μm and 20 nm) was evaluated using Weibull distribution analysis to assess their potential for bone fixation applications. The composite was produced by drawing PLA fibres in a PLA matrix containing hydroxyapatite (HA) particles of micrometre and
nanometre-sized particles to produce HA/PLA/PLA prepreg. The pre-impregnated sheets were then compression moulded and tested under quasi-static bending and flexural fatigue at an 80 % stress level, 2 Hz until failure. The addition of the filler enhances the bending properties of the composite. At the same time, the bending strength and modulus increase with a decrease in the filler size. Under the specific cyclic loading conditions tested, the initial data indicate that the Weibull median fatigue life of sr-PLA reduces with the presence of the fillers. However, the fatigue resistance of the HA-filled composite improved with a smaller filler size. The Weibull median fatigue life of HA/sr-PLA increases from 104,514 cycles to 254,884 cycles for μm-HA/PLA/PLA and nm-HA/PLA/PLA composites, respectively. The Weibull statistical model indicates that the scale parameters improve by 140 % when smaller filler particles (nm-HA) are used. During fatigue testing, the modulus of the composite decreased due to material damage. SEM analysis indicated that failure at the HA/matrix interface was a major contributing factor. Furthermore, fracture behaviour suggests that the materials are more susceptible to tensile stress, which may be attributed to limited bonding at the HA/matrix interface.