Green Synthesis Of Bio-Based Benzoxazines And Epoxies From Thymol-Citronellal For Low-Toxicity Thermosets
摘要
As an alternative to petroleum based raw materials, bio-based bisphenol (TC) was derived from thymol (T) and citronellal (C) emphasizing two principles of green chemistry by employing safer solvents and auxiliaries for synthesis and utilization of renewable feedstocks are justified. The novelty of this work lies in demonstrating the dual utility of this renewable bisphenol (TC) for the first time in the synthesis of two commercially significant thermosets polybenzoxazines and epoxy resins establishing a sustainable possible replacement for conventional petrochemical monomers. Benzoxazines (TC-fa, TC-la and TC-sa) were synthesized using TC with three different primary amines viz. furfurylamine (fa), laurylamine (la) and stearylamine (sa) separately. Also, TC was epoxidized to obtain bio-based epoxy (TC-E). The molecular structure of the targeted benzoxazines and epoxy were confirmed by spectral analysis. TC-fa showed lowest temperature of 205 °C to undergo polymerization. Whereas, poly(TC-sa) was found to possess highest water contact angle of 144o with a corrosion inhibition efficiency of 98.8% which was further supported by DFT studies. On comparing the antimicrobial activity and cytotoxic effects of TC with benzoxazines, TC exhibited greater bacteriostatic property with 30 and 20 mm inhibition zone against E.coli and S.aureus. Also, TC coated cotton fabric exhibited 99.9% bacterial growth inhibition efficiency. Mild toxicity with IC50 value of 138.81 µg/mL was exhibited by TC when compared to benzoxazine. The epoxidized bisphenol (TC-E) was cured with different curing agents and found the suitable catalyst to cure the epoxy resins at a least temperature of 141 °C. Thermally cured epoxy material was subjected to flexural test which revealed a maximum flexural stress of 0.77 MPa and a modulus of 40.20 MPa.