Hydrolytic and thermal stability of urea-formaldehyde resins based on tannin and betaine bio-fillers

In this work, betaine (trimethyl glycine) and tannin (complex biomolecules of polyphenolic nature) were used as bio-fillers. Urea-formaldehyde (UF) resin with a molar ratio of formaldehyde versus urea (FA/U) of 0.8 was synthesized in situ with tannin and betaine as bio-fillers, to obtain UF resin with reduced free FA content and increased hydrolytic and thermal stability by the principles of sustainability. The samples TUF (with tannin) and BUF (with betaine) were characterized by using X-ray diffraction analysis (XRD), non-isothermal thermogravimetric analysis (TGA), and differential thermal analysis (DTA), supported by data from Fourier Transform Infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The percentage of free FA in modified BUF resin is 0.1%, while the percentage of free FA in tannin-modified resin is 0.8%. The hydrolytic stability of the modified UF resins was determined by measuring the concentration of liberated FA in the modified UF resins, after acid hydrolysis. The modified BUF resin is hydrolytically more stable because the content of released FA is 3.6% compared to the modified TUF resin, where it was 7.4%. Based on the value for T_5%, the more thermally stable resin is the modified TUF resin (T_5% = 123.1°C), while the value of the T_5% for the BUF resin is 83.1°C. This work showed how UF bio-composite with reduced free FA content and increased hydrolytic and thermal stability can be obtained using tannin and betaine as bio-fillers.