Khalid, Munira (2023) Polylactic acid / polyhydroxyalkanoate /eggshell based hydroxyapatite biocomposites for bone tissue applications. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

Orthopedic issues related to bone repair and regeneration are common and difficult. Biodegradable polymer composites containing hydroxyapatite can solve this issue by mimicking the composition and structure of genuine mineralized bone tissue. Eggshell waste precursor was chemically precipitated to generate HAP powder. Melt-blended polylactic acid (PLA) and polyhydroxyalkanoate(PHA) were optimized using the statistical design of the experiment, the Taguchi technique. PLA/PHA/HAP biocomposite was made by melting and injection moulding. HAP powder, PLA/PHA melt blend, and PLA/PHA/HAP samples were characterized by X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX), Melt flow index (MFI), Universal testing machine (UTM), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and Scanning electron microscopy (SEM). From XRD and FTIR results, the optimal eggshell CaCO3 conversion calcination temperature was 900°C. EDX reported Ca/P ratio of 1.64 for HAP synthesized by chemical precipitation. Uncalcined HAP was found to have the Ca/P closest to the original HAP value of 1.67. PLA and PHA were melt blended to improve their mechanical properties as well as to reduce the cost, as PHA is a very expensive polymer. The PLA and PHA MFIs were 6.3 and 13.2 g/10 minutes. As PHA content rose, melt blend MFI rose. According to UTM analysis, 75PLA/25PHA improves tensile strength by 84%, impact strength by 80%, and elongation by 30%. According to TGA, PHA starts degrading at 295°C and PLA at 363°C. PLA improves PLA/PHA melt blend stability. Taguchi method optimized PLA/PHA melt mixing at 190°C, 60 rpm, and 6 minutes. 2% Maleic anhydride, as a compatibilizer, improved interfacial adhesion. The PLA/PHA/HAP biocomposite results showed that 10% uncalcined HAP loading to optimum blend exhibited superior mechanical properties. Greater loading of HAP decreases composites’ tensile strength due to poor interfacial adhesion and agglomeration of HAP particles. The biocompatibility of biocomposite was tested using simulated body fluid. SEM showed the growth of apatite layers on biocomposite surfaces, making them viable for bone implants

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