Effective Low Temperature Cure Cardanol Based Mono-Functional Benzoxazines: A Comparison

Anattempt has been made in the present work to assess the thermal and hydrophobic behavior of sustainable and renewable bio-based cardanol benzoxazines synthesized by reacting different aryl amines with varied functionalities (viz., aniline (a), p-toludine (pt), p-fluoroaniline (fa), p-aminophenol (ap), p-acetylaniline (aa), p-nitroaniline (na)) with cardanol (C) in presence of formaldehyde at an appropriate conditions. The varied molecular nature of benzoxazines obtained was characterized for their molecular structure, curing behavior, thermal stability and hydrophobic behaviour by analytical techniques. The structural elucidation of benzoxazines was carried out by FTIR and H-1 NMR spectroscopic studies. Among the different benzoxazines studied, the p-aminophenol based benzoxazine possesses the lowest curing (191 degrees C) temperature (C-a 282 degrees C > C-pt 262 degrees C > C-fa 258 degrees C > C-aa 251 degrees C > C-na 227 degrees C > C-ap 191 degrees C). The thermal stability of different cardanol based polybenzoxazines was studied by TGA technique. Among the different samples of cardanol benzoxazine systems studied, the benzoxazines viz., poly(C-fa) and poly(C-ap) possess the higher thermal stability and higher char yield than those of other polybenzoxazines (viz., poly(C-a) > poly(C-pt) > poly(C-na) > poly(C-aa) > poly(C-ap) > poly(C-fa)). The limiting oxygen index (LOI) value of polybenzoxazines has been calculated from char yield of polybenzoxazines. Poly(C-ap) and poly(C-fa) show the LOI value greater than 26, which as certain their good flame retardant behaviour. The values of water contact angle obtained for cardanol based benzoxazines are in the following order, poly(C-a) 112 degrees > poly(C-pt) 117 degrees > poly(C-na) 124 degrees > poly(C-aa) 124 degrees > poly(C-ap) 131 degrees > poly(C-fa) 134 degrees. Cardanol based benzoxazines derived from varying nature of amines groups influence the both thermal and hydrophobic behavior according to their chemically interactive and molecular geometry.