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Role of higher aromatic content in modulating properties of cardanol based benzoxazines
Shukla S.,
Published in Elsevier Ltd
Volume: 99
Pages: 684 - 694
Mono-benzoxazine monomers based polybenzoxazines suffer from a lower crosslink density and char yield that especially is further diluted by the presence of longer alkylene chain in cardanol (C). In order to improve the crosslink density, char yield and to understand the role of higher aromatic content vs functionality, a series of cardanol-based benzoxazine monomers were synthesised. The amine condensed with cardanol and paraformaldehyde were aniline (a), 4-triphenylmethylaniline (ta), and tetra-aminophenyl methane (tapm) via solventless methodology. The C-a and C-ta are mono-benzoxazines while C-tapm is a tetra-benzoxazine monomer. The monomers were structurally characterised using FT-IR, 1H and 13C NMR spectroscopy and mass spectrometry. The ring opening polymerisation temperature (ROP) of monomers and thermal stability of resins was determined using DSC and TGA while mechanical properties were determined using rheometry. The curing kinetic study using FT-IR and DSC showed C-ta has intermediate curing behaviour between the C-a and C-tapm. The Ea for curing reaction C-a, C-ta and C-tapm was found to be 143, 126 and 70 kJ/mol. The lowest Ea for curing reaction of C-tapm (tetra-benzoxazine) is due to its highest functionality but C-ta (mono-benzoxazine) has lower Ea than C-a which can be accounted to the presence of more reactive sites provided by the additional aromatic rings in the former. It was found that the incorporation of higher aromatic ring in benzoxazine monomers is another route in enhancing the crosslink density besides higher functionality to modulate their properties. © 2016 Elsevier Ltd
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Published in Elsevier Ltd
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