Browsing by Author "Bukhari, Syed Attaullah Shah"

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    Microwaves assisted Poly-L-Lactide synthesis using covalently immobilized candida antarctica lipase B onto Nanopolystyrene
    (Universiti Teknologi Malaysia, 2015) Bukhari, Syed Attaullah Shah
    Microwave-assisted enzymatic synthesis of polymer and biomaterials is an emerging technology due to a number of advantages including rapid uniform heating, shortened reaction time and energy saving with the least impact on environment. Perfect immobilization is the prerequisite for the application of enzyme in polymerization while L-lactide free of metals contaminant reduces the racemization and earlier degradation of poly-l-lactide acid (PLLA). In microwave-assisted enzymatic ring-opening polymerization (eROP), simultaneous cooling promotes the molar mass, yield and avoids the degradation of polymer. In this work, optically pure L-lactide was prepared from the aqueous L-lactic acid with no metal catalyst in a single step by using microwave heating. Nanobiocatalytic system was developed by covalently immobilizing Candida antarctica lipase B (CalB) onto 1-fluoro-2-nitro-4-azido benzene activated nanopolystyrene beads. Nanopolystyrene was fabricated through nanoprecipitation. Nanobiocatalytic system was employed in a ring opening polymerization of L-lactide in toluene and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM][PF6]) 200 watt (W) of microwave input. In microwave-assisted eROP of L-lactide, the effects of enzyme concentration, dielectric heating time, different solvents (toluene, ionic liquid) and simultaneous cooling were explored. The combination of techniques including immobilized yield, enzyme activity, enzyme stability, specific rotation power, field emission scanning electron microscopy (FESEM), proton nuclear magnetic resonance (1HNMR), Fourier transform infrared spectrometer (FTIR), differential scanning calorimetry (DSC) and viscometery were used to characterize the obtained products. Results confirmed 98 % of optically pure L-lactide was achieved in microwave-assisted backbiting reaction of L-lactic acid oligomers. Morphology results corroborated that most of nanopolystyrene beads were in the range of 100-200 nm that enabled 218 µg/mg of immobilized yield. Enzyme activity of immobilized-CalB was improved to 4.42× 103 mU p-nitrophenol/min. The reaction time of eROP was reduced significantly to 8 h due to the synergistic effects of dielectric heating and immobilized-CalB. The maximum 99 % L-lactide conversion was achieved by 8 % (w/w) concentration of immobilized-CalB in ionic liquid and toluene due to the covalent immobilization of CalB and specific heating affects of microwaves. In summary, 52.76 % crystalline PLLA was achieved in eROP. PLLA with maximum viscosity molecular weight of 59,756 g/mol was obtained by the application of simultaneous cooling. Thus, the novel one-step synthesis of optically pure L-lactide using microwave irradiation and nanobiocatalytic system was developed and used in combination in the PLLA synthesis