Accelerated in vitro degradation properties of polylactic acid/phosphate glass fibre composites Reda M. Felfel 1,2 • Kazi M. Zakir Hossain 1 • Andrew J. Parsons 1 • Chris D. Rudd 1 • Ifty Ahmed 1 Received: 31 October 2014 / Accepted: 4 March 2015 Ó Springer Science+Business Media New York 2015 Abstract Degradation properties were studied for poly- lactic acid (PLA) and phosphate glass fibre (40P 2 O 5 – 24MgO–16CaO–16Na 2 O–4Fe 2 O 3 , denoted as P40) rein- forced unidirectional (UD) and randomly mat (RM) PLA composites using phosphate buffer saline (PBS) media over a range of temperatures from 21 to 85 °C. Glass transition and melting temperatures for PLA decreased from 61.3 and 167.4 to 52.7 and 151.6 °C, respectively, and crystallinity increased from 9.2 to 58.3 % during 3 days of degradation period in PBS media at 85 °C. Appearance of sharp crys- talline peaks after degradation at higher temperatures which was confirmed via X-ray diffraction analysis was also indicative of increase in crystallinity. However, flex- ural strength decreased by approximately 20 % (for PLA) and by around 50 % (P40 RM and P40 UD composites) of the initial strength after degradation in PBS at 37 °C. No significant changes in mechanical properties were observed before and after degradation of composites at 21 °C for 56 days. Monomodal molecular weight distribution for the PLA before and after degradation in PBS at 37 °C was replaced by bimodal after degradation at higher tem- peratures. Arrhenius equation applied for the change in molecular weight of the polymer and composite samples and the obtained degradation activation energies were 85.4, 78.7 and 74.1 kJ mol -1 for PLA within PLA alone, P40 RM and P40 UD composites, respectively. Time prediction was applied to correlate short-term degradation (at elevated temperatures) to the long-term effects (at 37 °C) using both ‘tipping point’ and molecular weight as co-ordinates. Introduction The degradation behaviour of bioresorbable polymers and composites plays a crucial role in the choice of material for bone fixation applications. Many factors affect the degrada- tion rate of the polymers such as chemical structure, crys- tallinity, molecular weight and molecular weight distribution, temperature, and pH. The effect of temperature is particularly remarkable to access the accelerated degradation properties [1–4]. The influence of temperature on the degradation pro- cess is not only useful in understanding the resorption be- haviour of the devices in vivo, but also it is important for developing a model to predict the life time of the device using an accelerated degradation method. Some polymers take more than 3 years for complete degradation, such as poly-L- lactic acid (PLLA) [5], which depends on the environment as well as the molecular weight of polymer. This has prompted the use of different methods in order to shorten the time of degradation studies, but it is difficult to guarantee that the results will remain valid at body temperature (37 °C) [2]. However, with appropriate precautions, degradation studies conducted at higher temperatures can be of great value and result in saving time and research funds [6]. Temperature has a crucial effect on the degradation of ab- sorbable polymers. Firstly, the rate of hydrolysis increases with degradation temperature, potentially making possible a corre- lation between short-term effects at high temperature and long- term effects at physiological temperature. Secondly, body temperature varies between the human and certain animals such as rabbits and pigs that are used as in vivo models [2]. & Reda M. Felfel reda.felfel@nottingham.ac.uk; rmfelfel@mans.edu.eg 1 Division of Materials, Mechanics and Structures, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK 2 Physics Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt 123 J Mater Sci DOI 10.1007/s10853-015-8946-8