화학공학소재연구정보센터
Polymer Engineering and Science, Vol.43, No.2, 297-305, 2003
Influence of chemical composition on the rheological behavior of condensation reaction resins
In this paper, the chemorheological and dynamic mechanical behavior of melamine-formaldehyde (MF) resins of four different formaldehyde/melamine (F/M) molar ratios (1.25, 1.5 1.75 and 2.00) are investigated. MF resins polymerize via a polycondensation reaction involving formation of up to 10 wt% of H2O on cure. This typically results in rapid and extensive foaming of the resin when it is cured under atmospheric pressure. Experimental adaptation for the foaming behavior of MF resins is used to gather rheological information concerning the curing kinetics and the mechanical response of neat MF resins of different molar ratios. Likewise, the procedures developed allow curing of the resins under atmospheric pressure, hence allowing volatile evacuation as occurs during venting procedures (commonly used during compression molding of MF molding compounds) or as a result of absorption by hydrophilic fillers or substrates. The results show that increased moisture content in the B-stage leads to faster reaction rates and greater foaming. Gelation and vitrification times are identified for each molar ratio, and are found to increase with decreasing molar ratio. The dynamic mechanical behavior of carefully molded neat MF samples of different molar ratios is studied using DMTA. T-g is found to be 200degreesC for the resin with the lowest formaldehyde content (F/M = 1.25), and around 230degreesC for the other resins. The storage shear modulus above T-g is studied, and the results show that the crosslink density increases with increasing molar ratio.