Reactions between melamine formaldehyde resin and cellulose: Influence of pH

Nuclear magnetic resonance of 13C in the liquid state and dynamic mechanical analysis were performed on composite materials obtained from a sample of ashless filter paper immersed in aqueous solutions of a melamine formaldehyde resin with a high NH ratio. The resin aqueous solution was studied at pH 6, 7, and 9. After a cure performed at 85°C we showed that acid conditions improved the mechanical properties of the composite because of self-condensation reactions of the amino resin while for the other pH values the mechanical properties of the cellulose were not changed because mainly hydrolysis reactions occurred. For a cure performed at 140°C and under acid conditions the degree of crosslinking of the resin increased while for the other pH mainly cocondensation reactions appeared. Finally, from the study of moisture sorption measurements performed on a composite material elaborated at pH 7 and for different relative humidity values we showed that mainly the Langmuir absorption mode was modified by the presence of the resin. This last result allowed us to propose a complete scenario of the events that appeared during the formation of the composite material.