Synthesis and Characterization of Green Poly(lactic Acid)-Based Biomaterial

Introduction

Biodegradable and Bioabsorbable polymers have been identified as alternative materials for biomedical applications. The development of biomaterials for application in medicine is one of the great challenges of research in biomaterial science. Aliphatic polyester represent an important family of biodegradable polymer. Poly (lactic acid) is one of them which is produced from agriculture resource via combined fermentation and polymerization processes, and has attracted attention recently due to its biodegradability, biocompatibility and widespread use in the biomedical field. Main interest was dedicated towards applications in tissue engineering and drug delivery 1-4. The main approach of this work is to employ direct polycondensation method to synthesize green PLA by using stannous octoates to catalyze lactic acid with focus on the influence of the polymerization conditions (solvent, pressure, catalyst and temperatures) on the final polymer’s products. The advantage of this method is that the lactic acid is directly included as the monomer in compare with the ring-opening polymerization needs high purity of lactide made by lactic acid cyclic dimer as the monomer and high-purity of monomer is not required, consequently. Thus, the final product under polycondensation process has considerable potential to apply in biomedical applications. The PLA were characterizations by different techniques, such as; Fourier Transfer Infrared Spectroscopy (FTIR), H1 NMR spectroscopy, Gas Permeation Chromatography and Different Scanning Calorimetry.

Materials and Methods

The first part of the polycondensation was conducted in a 1000 mL reaction vessel with a five neck head sealed with a flange. This was equipped with an overhead stirring shaft driven by a motor, a reflux condenser, and a nitrogen gas inlet. At the end of each polymerization reaction, polylactic acid polymers were dissolved in chloroform and precipitated in ethanol. PLA matrices at different operating conditions and parameters were synthesized in the present work. The lactic acid was synthesized under vacuum via direct melt/solution polycondensation of the samples contains catalyst and solvent were taken periodically to investigate itself polycondensation. The first stage of the polymerization was started when the first water distilled off for 5 h, then released cooling system with gradually increased temperature to set at 180 oC, small quantity (0.5 w/w %) of catalyst was added to the polymerization. These polymerizations were achieved 4 times under different conditions to evaluate and tailored molecular weights of the PLA synthesised. Further procedure of this polymerization is shown in section 2.1, and total of four different samples were synthesized and classified under the Table 2.1. The final product was dissolved in chloroform and then precipitated in ethyl alcohol to eliminate a side reaction. Table 2.1

Results

The result showed that the molecular weight (Mwt) of PLA in the absent of solvent and catalyst increased with increasing polymerization time to reached 24,828 Da at 72 h with abroad of polydispersity PDI (3.9). Highest Mwt of 29,736 Da was obtained at polymerization temperature and time of 180 oC and 24 hours, respectively with toluene as a solvent. This led to a highest inherent viscosity of 0.52 dl/g. FTIR spectra demonstrated disappearance of the main characteristic peak of hydroxyl group in lactic acid at 3482 cm-1 with increasing intensity of carbonyl group. PLA synthesized with toluene and catalyst (Sn(Oct)2) exhibited higher thermal transition properties of, glass transition, crystallinity and melting temperatures of 47 oC, 118 oC and 171.10 oC, respectively. The results in Table 3.1 are considerable potential for biomaterials applications. Table 3.1

Discussion and Conclusion

The chemical structure of the PLA synthesized was investigated and confirmed by FTIR and 1H-NMR. Several parameters were tested including the effect of solvent and catalyst on the polymerization, in addition to polymerization temperature and time in the absent of solvent and catalyst, these resulted can me attributed to the facts that particularly intermolecular transesterification to monomer and oligomer esters resulting in the formation of the monomer and oligomeric lactides of low molecular weight. Another important reason is that the oxidative, random main-chain scission, which can be relatively sensitive to thermal degradation 5-8. In summary, synthesis of the PLA polymer was examined under various polymerizations conditions. Optimal conditions were found to be 180 oC with using (Sn(Oct)2) as the catalyst and toluene as the solvent. Highest Mwt obtained 29,736 g/gmole with relative good thermal stability.

Acknowledgements

Authors would like to acknowledge financial support from Agriculture and Agri-Food Canada, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Faculty of Engineering and Architectural Science at Ryerson University in Toronto, Canada.

References

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