EFFECTIVE LOW TEMPERATURE CURE CARDANOL BASED MONO-FUNCTIONAL BENZOXAZINES: A COMPARISON

Abstract

An attempt 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 1H NMR spectroscopic studies. Among the different benzoxazines studied, the p-aminophenol based benzoxazine possesses the lowest curing (191°C) temperature (C-a 282°C > C-pt 262°C > C-fa 258°C > C-aa 251°C > C-na 227°C > C-ap 191°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° > poly(C-pt) 117° > poly(C-na) 124° > poly(C-aa) 124° > poly(C-ap) 131° > poly(C-fa) 134°. 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.