| Summary: | 碩士 === 國立臺灣科技大學 === 化學工程系 === 96 === This thesis was motivated by the practical need to develop a scalable and cost-effective separation method to recover hyaluronic acid (HA), a commercially valuable medical biopolymer, from bacterial culture broth. This challenge can potentially be addressed by taking advantage of the polyanionic character of HA. Through the electrostatic interaction with cationic matrix, HA is expected to be recovered. In this thesis quaternary ammonium modified cellulose fibers were used to recover HA directly from the Bacillus subtilis culture.
At the first stage of the studies, two variant of cellulose fibers were prepared by grafting different type of the antibacterial quaternary ammonium compound (QAC). Silane (3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride) and choline based ionic liquid analogue (sodium hydroxide and 2–chloroethyltrimethylammonium chloride based deep eutectic solvent) were used to quaternize the cellulose fibers surface. Results from elementary analysis, grafting ratio determination by weight measurement and Fourier transform infrared spectroscopy demonstrated that either silane or choline has been successfully grafted onto the surface of cellulose fibers after the chemical modification.
Prior to the adsorption studies, the antibacterial assessments were performed. It was shown that both silane modified cellulose fibers (SMC) and choline modified cellulose fibers (CMC) have antibacterial activity against E. coli and B. subtilis, with the former had better activity due to the presence of long alkyl chain on the quaternary ammonium groups of SMC. The antibacterial activity for E. coli is higher than that for B. subtilis due to the difference in cell wall structures. The feasibility of the antibacterial cellulose fibers on HA adsorption was then explored. Adsorption of HA onto the modified cellulose fibers was carried out at different pHs (3–8) and temperatures (277, 291, 310 K). Adsorption isotherms followed the Langmuir isotherm model and the adsorption was thermodynamically favorable. The maximum adsorption capacity for SMC and CMC was found to be 183.67 mg/g (at pH 4, 310 K) and 351.32 mg/g (at pH 7, 277 K), respectively. The adsorbed HA on SMC could be effectively desorbed as much as 90.11% by 1 N NaCl at pH 7 while changing the pH to 3 was effective to desorb 36.50% of HA from CMC. The adsorption capacity of SMC decreased to 49% after 3 cycles, whereas the capacity of CMC decreased to 89%.
Finally, the capability of the modified cellulose fibers on the recovery of HA directly from B. subtilis culture was demonstrated. SMC was used in this process rather than CMC due to its high desorption efficiency. The antibacterial effect of SMC caused by its strong hydrophobic character also good for HA recovery. One gram of SMC was able to adsorb 14.94 mg of HA directly from the B. subtilis culture. The adsorption capacity of SMC used in this recovery process was much less than in the equilibrium adsorption studies due to the competition adsorption occurred in the culture broth.
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